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Yao Y, Li H, Wang M, Li P, Lam M, Iza M, Speck JS, DenBaars SP, Nakamura S. High external quantum efficiency (6.8%) UV-A LEDs on AlN templates with quantum barrier optimization. Opt Express 2023; 31:28649-28657. [PMID: 37710681 DOI: 10.1364/oe.491622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Accepted: 07/07/2023] [Indexed: 09/16/2023]
Abstract
AlGaN-based UV-A LEDs have wide applications in medical treatment and chemical sensing; however, their efficiencies are still far behind visible LEDs or even shorter wavelengths UV-C counterparts because of the large lattice mismatch between the low-Al-content active region and the AlN substrate. In this report, we investigated the composition and thickness of the quantum barrier in the active region in terms of LED performance. Due to the improved strain management and better carrier confinement, efficient UV-A LEDs (320 nm - 330 nm) with EQEs up to 6.8% were demonstrated, among the highest efficiencies at this wavelength range.
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Li P, Li H, Yao Y, Qwah KS, Iza M, Speck JS, Nakamura S, DenBaars SP. Hybrid tunnel junction enabled independent junction control of cascaded InGaN blue/green micro-light-emitting diodes. Opt Express 2023; 31:7572-7578. [PMID: 36859886 DOI: 10.1364/oe.480393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Accepted: 01/05/2023] [Indexed: 06/18/2023]
Abstract
We demonstrate vertical integration of nitride-based blue/green micro-light-emitting diodes (µLEDs) stacks with independent junctions control using hybrid tunnel junction (TJ). The hybrid TJ was gown by metal organic chemical vapor deposition (p + GaN) and molecular-beam epitaxy (n + GaN). Uniform blue, green and blue/green emission can be generated from different junction diodes. The peak external quantum efficiency (EQE) of the TJ blue µLEDs and green µLEDs with indium tin oxide contact is 30% and 12%, respectively. The carrier transportation between different junction diodes was discussed. This work suggests a promising approach for vertical µLEDs integration to enhance the output power of single LEDs chip and monolithic µLEDs with different emission colors with independent junction control.
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Sauty M, Lopes NMS, Banon JP, Lassailly Y, Martinelli L, Alhassan A, Chow YC, Nakamura S, Speck JS, Weisbuch C, Peretti J. Localization Effect in Photoelectron Transport Induced by Alloy Disorder in Nitride Semiconductor Compounds. Phys Rev Lett 2022; 129:216602. [PMID: 36461952 DOI: 10.1103/physrevlett.129.216602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Accepted: 10/19/2022] [Indexed: 06/17/2023]
Abstract
Near-band-gap photoemission spectroscopy experiments were performed on p-GaN and p-InGaN/GaN photocathodes activated to negative electron affinity. The photoemission quantum yield of the InGaN samples with more than 5% of indium drops by more than 1 order of magnitude when the temperature is decreased while it remains constant for lower indium content. This drop is attributed to a freezing of photoelectron transport in p-InGaN due to electron localization in the fluctuating potential induced by the alloy disorder. This interpretation is supported by the disappearance at low temperature of the peak in the photoemission spectrum that corresponds to the contribution of the photoelectrons relaxed at the bottom of the InGaN conduction band.
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Affiliation(s)
- Mylène Sauty
- Laboratoire de Physique de la Matière Condensée, Ecole polytechnique, CNRS, Institut Polytechnique de Paris, 91120 Palaiseau, France
| | - Nicolas M S Lopes
- Laboratoire de Physique de la Matière Condensée, Ecole polytechnique, CNRS, Institut Polytechnique de Paris, 91120 Palaiseau, France
| | - Jean-Philippe Banon
- Laboratoire de Physique de la Matière Condensée, Ecole polytechnique, CNRS, Institut Polytechnique de Paris, 91120 Palaiseau, France
| | - Yves Lassailly
- Laboratoire de Physique de la Matière Condensée, Ecole polytechnique, CNRS, Institut Polytechnique de Paris, 91120 Palaiseau, France
| | - Lucio Martinelli
- Laboratoire de Physique de la Matière Condensée, Ecole polytechnique, CNRS, Institut Polytechnique de Paris, 91120 Palaiseau, France
| | - Abdullah Alhassan
- Materials Department, University of California, Santa Barbara, California 93106, USA
| | - Yi Chao Chow
- Materials Department, University of California, Santa Barbara, California 93106, USA
| | - Shuji Nakamura
- Materials Department, University of California, Santa Barbara, California 93106, USA
| | - James S Speck
- Materials Department, University of California, Santa Barbara, California 93106, USA
| | - Claude Weisbuch
- Laboratoire de Physique de la Matière Condensée, Ecole polytechnique, CNRS, Institut Polytechnique de Paris, 91120 Palaiseau, France
- Materials Department, University of California, Santa Barbara, California 93106, USA
| | - Jacques Peretti
- Laboratoire de Physique de la Matière Condensée, Ecole polytechnique, CNRS, Institut Polytechnique de Paris, 91120 Palaiseau, France
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Li P, Li H, Yao Y, Zhang H, Lynsky C, Qwah KS, Iza M, Speck JS, Nakamura S, DenBaars SP. Fully transparent metal organic chemical vapor deposition-grown cascaded InGaN micro-light-emitting diodes with independent junction control. Opt Express 2021; 29:22001-22007. [PMID: 34265974 DOI: 10.1364/oe.430694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Accepted: 06/10/2021] [Indexed: 06/13/2023]
Abstract
In this work, we present fully transparent metal organic chemical vapor deposition (MOCVD)-grown InGaN cascaded micro-light-emitting diodes (µLEDs) with independent junction control. The cascaded µLEDs consisted of a blue emitting diode, a tunnel junction (TJ), a green emitting diode, and a TJ, without using any conductive oxide layer. We can control the injection of carriers into blue, green, and blue/green junctions in the same device independently, which show high optical and electrical performance. The forward voltage (Vf) at 20 A/cm2 for the TJ blue µLEDs and TJ green µLEDs is 4.06 and 3.13 V, respectively. These results demonstrate the efficient TJs and fully activated p-type GaN in the cascaded µLEDs. Such demonstration shows the important application of TJs for the integration of µLEDs with multiple color emissions.
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Chow YC, Lee C, Wong MS, Wu YR, Nakamura S, DenBaars SP, Bowers JE, Speck JS. Dependence of carrier escape lifetimes on quantum barrier thickness in InGaN/GaN multiple quantum well photodetectors. Opt Express 2020; 28:23796-23805. [PMID: 32752371 DOI: 10.1364/oe.399924] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2020] [Accepted: 07/11/2020] [Indexed: 06/11/2023]
Abstract
We reported significant improvements in device speed by reducing the quantum barrier (QB) thicknesses in the InGaN/GaN multiple quantum well (MQW) photodetectors (PDs). A 3-dB bandwidth of 700 MHz was achieved with a reverse bias of -6 V. Carrier escape lifetimes due to carrier trapping in the quantum wells (QWs) were obtained from both simulation and experimental fitting, identifying carrier trapping as the major speed limiting factor in the InGaN/GaN MQW PDs.
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Li P, Zhang H, Li H, Iza M, Yao Y, Wong MS, Palmquist N, Speck JS, Nakamura S, DenBaars SP. Size-independent low voltage of InGaN micro-light-emitting diodes with epitaxial tunnel junctions using selective area growth by metalorganic chemical vapor deposition. Opt Express 2020; 28:18707-18712. [PMID: 32672165 DOI: 10.1364/oe.394664] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Accepted: 06/01/2020] [Indexed: 06/11/2023]
Abstract
High performance InGaN micro-size light-emitting diodes (µLEDs) with epitaxial tunnel junctions (TJs) were successfully demonstrated using selective area growth (SAG) by metalorganic chemical vapor deposition (MOCVD). Patterned n + GaN/n-GaN layers with small holes were grown on top of standard InGaN blue LEDs to form TJs using SAG. TJ µLEDs with squared mesa ranging from 10×10 to 100×100 µm2 were fabricated. The forward voltage (Vf) in the reference TJ µLEDs without SAG is very high and decreases linearly from 4.6 to 3.7 V at 20 A/cm2 with reduction in area from 10000 to 100 µm2, which is caused by the lateral out diffusion of hydrogen through sidewall. By contrast, the Vf at 20 A/cm2 in the TJ µLEDs utilizing SAG is significantly reduced to be 3.24 to 3.31 V. Moreover, the Vf in the SAG TJ µLEDs is independent on sizes, suggesting that the hydrogen is effectively removed through the holes on top of the p-GaN surface by SAG. The output power of SAG TJ µLEDs is ∼10% higher than the common µLEDs with indium tin oxide (ITO) contact.
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Lheureux G, Monavarian M, Anderson R, Decrescent RA, Bellessa J, Symonds C, Schuller JA, Speck JS, Nakamura S, DenBaars SP. Tamm plasmons in metal/nanoporous GaN distributed Bragg reflector cavities for active and passive optoelectronics. Opt Express 2020; 28:17934-17943. [PMID: 32679995 DOI: 10.1364/oe.392546] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Accepted: 05/09/2020] [Indexed: 06/11/2023]
Abstract
We theoretically and experimentally investigate Tamm plasmon (TP) modes in a metal/semiconductor distributed Bragg reflector (DBR) interface. A thin Ag (silver) layer with a thickness (55 nm from simulation) that is optimized to guarantee a low reflectivity at the resonance was deposited on nanoporous GaN DBRs fabricated using electrochemical (EC) etching on freestanding semipolar (2021¯) GaN substrates. The reflectivity spectra of the DBRs are compared before and after the Ag deposition and with that of a blanket Ag layer deposited on GaN. The experimental results indicate the presence of a TP mode at ∼ 454 nm on the structure after the Ag deposition, which is also supported by theoretical calculations using a transfer-matrix algorithm. The results from mode dispersion with energy-momentum reflectance spectroscopy measurements also support the presence of a TP mode at the metal-nanoporous GaN DBR interface. An active medium can also be accommodated within the mode for optoelectronics and photonics. Moreover, the simulation results predict a sensitivity of the TP mode wavelength to the ambient (∼ 4-7 nm shift when changing the ambient within the pores from air with n = 1 to isopropanol n = 1.3), suggesting an application of the nanoporous GaN-based TP structure for optical sensing.
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Khoury M, Li H, Bonef B, Mates T, Wu F, Li P, Wong MS, Zhang H, Song J, Choi J, Speck JS, Nakamura S, DenBaars SP. 560 nm InGaN micro-LEDs on low-defect-density and scalable (20-21) semipolar GaN on patterned sapphire substrates. Opt Express 2020; 28:18150-18159. [PMID: 32680016 DOI: 10.1364/oe.387561] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2020] [Accepted: 04/14/2020] [Indexed: 06/11/2023]
Abstract
We demonstrate InGaN-based semipolar 560 nm micro-light-emitting diodes with 2.5% EQE on high-quality and low-defect-density (20-21) GaN templates grown on scalable and low-cost sapphire substrates. Through transmission electron microscopy observations, we discuss how the management of misfit dislocations and their confinement in areas away from the active light-emitting region is necessary for improving device performance. We also discuss how the patterning of semipolar GaN on sapphire influences material properties in terms of surface roughness and undesired faceting in addition to indium segregation at the proximity of defected areas.
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Li H, Li P, Zhang H, Chow YC, Wong MS, Pinna S, Klamkin J, Speck JS, Nakamura S, DenBaars SP. Electrically driven, polarized, phosphor-free white semipolar (20-21) InGaN light-emitting diodes grown on semipolar bulk GaN substrate. Opt Express 2020; 28:13569-13575. [PMID: 32403828 DOI: 10.1364/oe.384139] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Accepted: 03/02/2020] [Indexed: 06/11/2023]
Abstract
We demonstrate a simple method to fabricate efficient, electrically driven, polarized, and phosphor-free white semipolar (20-21) InGaN light-emitting diodes (LEDs) by adopting a top blue quantum well (QW) and a bottom yellow QW directly grown on (20-21) semipolar bulk GaN substrate. At an injection current of 20 mA, the fabricated 0.1 mm2 size regular LEDs show an output power of 0.9 mW tested on wafer without any backside roughing, a forward voltage of 3.1 V and two emission peaks located at 427 and 560 nm. A high polarization ratio of 0.40 was measured in the semipolar monolithic white LEDs, making them promising candidates for backlighting sources in liquid crystal displays (LCDs). Furthermore, a 3dB modulation bandwidth of 410 MHz in visible light communication (VLC) was obtained in the micro-size LEDs (µLEDs) with a size of 20×20 µm2 and 40×40 µm2, which could overcome the limitation of slow frequency response of yellow phosphor in commercial white LEDs combing blue LEDs and yellow phosphor.
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Wong MS, Kearns JA, Lee C, Smith JM, Lynsky C, Lheureux G, Choi H, Kim J, Kim C, Nakamura S, Speck JS, DenBaars SP. Improved performance of AlGaInP red micro-light-emitting diodes with sidewall treatments. Opt Express 2020; 28:5787-5793. [PMID: 32121793 DOI: 10.1364/oe.384127] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The electrical and optical improvements of AlGaInP micro-light-emitting diodes (µLEDs) using atomic-layer deposition (ALD) sidewall passivation were demonstrated. Due to the high surface recombination velocity and minority carrier diffusion length of the AlGaInP material system, devices without sidewall passivation suffered from high leakage and severe drop in external quantum efficiency (EQE). By employing ALD sidewall treatments, the 20×20 µm2 µLEDs resulted in greater light output power, size-independent leakage current density, and lower ideality factor. The forward current-voltage characteristic was enhanced by using surface pretreatment. Furthermore, ALD sidewall treatments recovered the EQE of the 20×20 µm2 devices more than 150%. This indicated that AlGaInP µLEDs with ALD sidewall treatments can be used as the red emitter for full-color µLED display applications.
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Khoury M, Li H, Zhang H, Bonef B, Wong MS, Wu F, Cohen D, De Mierry P, Vennéguès P, Speck JS, Nakamura S, DenBaars SP. Demonstration of Electrically Injected Semipolar Laser Diodes Grown on Low-Cost and Scalable Sapphire Substrates. ACS Appl Mater Interfaces 2019; 11:47106-47111. [PMID: 31769651 DOI: 10.1021/acsami.9b17525] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The last two decades have shown an increasing need for GaN-based laser diodes (LDs), which are currently only grown on bulk GaN substrates, which remain to date very expensive and/or only available in small sizes. The ever growing laser market will expand in the coming years, thanks to the development of automotive laser lighting, high-speed Li-Fi optical data transmission, LiDAR sensing for autonomous vehicles and smart cities, head-up displays, and AR/VR systems, in addition to biomedical and further industrial applications. These emerging technologies demand for mass-production of GaN-based lasers to be produced on large-size, low-cost, and industrially compatible substrates. To address this issue, we demonstrate the first electrically injected semipolar 440 nm LD on high-quality and low-defect-density (11-22) GaN templates grown on scalable and low-cost sapphire substrates. The LDs exhibit a threshold current density of 17 kA/cm2, a single facet output power of more than 200 mW at 2 A with a slope efficiency of 0.85 W/A, and a TE polarization having a ratio of 97.6%. These results enable the advancement of ultra-low-cost LDs while benefiting from the inherent advantages of semipolar GaN properties.
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Affiliation(s)
| | | | | | | | | | | | | | - Philippe De Mierry
- CNRS, Université Côte d'Azur, CRHEA , Rue Bernard Grégory , 06560 Valbonne , France
| | - Philippe Vennéguès
- CNRS, Université Côte d'Azur, CRHEA , Rue Bernard Grégory , 06560 Valbonne , France
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Kamikawa T, Gandrothula S, Araki M, Li H, Oliva VB, Wu F, Cohen D, Speck JS, Denbaars SP, Nakamura S. Realization of thin-film m-plane InGaN laser diode fabricated by epitaxial lateral overgrowth and mechanical separation from a reusable growth substrate. Opt Express 2019; 27:24717-24723. [PMID: 31510356 DOI: 10.1364/oe.27.024717] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2019] [Accepted: 07/06/2019] [Indexed: 06/10/2023]
Abstract
A nonpolar edge emitting thin film InGaN laser diode has been separated from its native substrate by mechanical tearing with adhesive tape, combining the benefits of Epitaxial Lateral Overgrowth (ELO) and cleavability of nonpolar GaN crystal. The essence of ELO is mainly to weakening strength between native substrate and the fabricated laser device on top of it. We report a 3 mm long laser bar removed from its native GaN substrate. We confirmed edge emitting lasing operation after cleaving facets on a separated thin bar. Threshold current density of the laser was measured to be as low as 2.15 kA/cm2.
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Saifaddin BK, Iza M, Foronda H, Almogbel A, Zollner CJ, Wu F, Alyamani A, Albadri A, Nakamura S, DenBaars SP, Speck JS. Impact of roughening density on the light extraction efficiency of thin-film flip-chip ultraviolet LEDs grown on SiC. Opt Express 2019; 27:A1074-A1083. [PMID: 31510492 DOI: 10.1364/oe.27.0a1074] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Accepted: 06/22/2019] [Indexed: 06/10/2023]
Abstract
Discovering ways to increase the LED light extraction efficiency (LEE) should help create the largest performance improvement in the power of UV AlGaN LEDs. Employing surface roughening to increase the LEE of typical AlGaN UV LEDs is challenging and not well understood, yet it can be achieved easily in AlGaN LEDs grown on SiC. We fabricate thin-film UV LEDs (~294-310 nm) grown on SiC-with reflective contacts and roughened emission surface-to study and optimize KOH roughening of N-face AlN on the LEE as a function of roughened AlN pyramid size and KOH solution temperature. The LEE increased the most (2X) when the average AlN pyramid base diagonals (d) were comparable to the electroluminescence (EL) wavelength in the AlN layer (d ~λEL; 42-52 pyramids/µm2), but the LEE enhancement diminished when d was much larger than λEL (d ~5.5λEL; 2-3 pyramids/µm2). The UV LEDs had a 10 nm p-GaN contact layer, and the forward voltage was ~6 V at ~8 A/cm2, with a voltage efficiency (VE) of ~70%. The VE of the LEDs did not change after KOH roughening. This work suggests important implications to increase the LEE of AlGaN LEDs.
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Hamdy KW, Young EC, Alhassan AI, Becerra DL, DenBaars SP, Speck JS, Nakamura S. Efficient tunnel junction contacts for high-power semipolar III-nitride edge-emitting laser diodes. Opt Express 2019; 27:8327-8334. [PMID: 31052652 DOI: 10.1364/oe.27.008327] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2018] [Accepted: 02/21/2019] [Indexed: 06/09/2023]
Abstract
We demonstrate high-power edge-emitting laser diodes (LDs) with tunnel junction contacts grown by molecular beam epitaxy (MBE). Under pulsed conditions, lower threshold current densities were observed from LDs with MBE-grown tunnel junctions than from similarly fabricated control LDs with ITO contacts. LDs with tunnel junction contacts grown by metal-organic chemical vapor deposition (MOCVD) were additionally demonstrated. These LDs were fabricated using a p-GaN activation scheme utilizing lateral diffusion of hydrogen through the LD ridge sidewalls. Secondary ion mass spectroscopy measurements of the [Si] and [Mg] profiles in the MBE-grown and MOCVD-grown tunnel junctions were conducted to further investigate the results.
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Seres J, Seres E, Serrat C, Young EC, Speck JS, Schumm T. All-solid-state VUV frequency comb at 160 nm using high-harmonic generation in nonlinear femtosecond enhancement cavity. Opt Express 2019; 27:6618-6628. [PMID: 30876243 DOI: 10.1364/oe.27.006618] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Accepted: 02/13/2019] [Indexed: 06/09/2023]
Abstract
We realized a solid-state-based vacuum ultraviolet frequency comb by harmonics generation in an external enhancement cavity. Optical conversions were so far reported by only using gaseous media. We present a theory that allows the most suited solid generation medium to be selected for specific target harmonics by adapting the material's bandgap. We experimentally use a thin AlN film grown on a sapphire substrate to realize a compact frequency comb high-harmonic source in the Deep Ultraviolet (DUV) / Vacuum Ultraviolet (VUV) spectral range. By extending our earlier VUV source [Opt. Express26, 21900 (2018)] with the enhancement cavity, a sub-Watt level Ti:sapphire femtosecond frequency comb is enhanced to 24 W stored average power, its 3rd, 5th, and 7th harmonics are generated, and the targeted 5th harmonic's power at 160 nm increased by two orders of magnitude. The emerging nonlinear effects in the solid medium, together with suitable intra-cavity dispersion management, support optimal enhancement and stable locking. To demonstrate the realized frequency comb's spectroscopic ability, we report on the beat measurement between the 3rd harmonic beam and a 266 nm CW laser reaching about 1 MHz accuracy.
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Kuritzky LY, Weisbuch C, Speck JS. Prospects for 100% wall-plug efficient III-nitride LEDs. Opt Express 2018; 26:16600-16608. [PMID: 30119487 DOI: 10.1364/oe.26.016600] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Accepted: 04/23/2018] [Indexed: 06/08/2023]
Abstract
The possibility of a III-nitride LED with 100% or greater wall-plug efficiency is examined considering recent observations of the phenomenon for smaller bandgap mid-IR LEDs under extremely low-bias operation [Phys. Rev. Lett. 108, 1 (2012)]. Thermoelectric pumping of carriers by lattice heat enables ≥ 100% WPE, but this effect is relatively weaker for the wider band gap III-nitrides. This work assesses the electrical and optical performance of several state-of-the-art nitride devices and summarizes the requirements and prospects for approaching ≥ 100% WPE for III-nitride LEDs operating at technologically relevant current densities (> 1 A/cm2).
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Myzaferi A, Mughal AJ, Cohen DA, Farrell RM, Nakamura S, Speck JS, DenBaars SP. Zinc oxide clad limited area epitaxy semipolar III-nitride laser diodes. Opt Express 2018; 26:12490-12498. [PMID: 29801286 DOI: 10.1364/oe.26.012490] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Accepted: 03/26/2018] [Indexed: 06/08/2023]
Abstract
We report continuous-wave (CW) blue semipolar (202¯1) III-nitride laser diodes (LDs) that incorporate limited area epitaxy (LAE) n-AlGaN bottom cladding with thin p-GaN and ZnO top cladding layers. LAE mitigates LD design limitations that arise from stress relaxation, while ZnO layers reduce epitaxial growth time and temperature. Numerical modeling indicates that ZnO reduces the internal loss and increases the differential efficiency of TCO clad LDs. Room temperature CW lasing was achieved at 445 nm for a ridge waveguide LD with a threshold current density of 10.4 kA/cm2, a threshold voltage of 5.8 V, and a differential resistance of 1.1 Ω.
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Shen C, Ng TK, Lee C, Nakamura S, Speck JS, DenBaars SP, Alyamani AY, El-Desouki MM, Ooi BS. Semipolar InGaN quantum-well laser diode with integrated amplifier for visible light communications. Opt Express 2018; 26:A219-A226. [PMID: 29609284 DOI: 10.1364/oe.26.00a219] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Accepted: 01/14/2018] [Indexed: 06/08/2023]
Abstract
GaN-based semiconductor optical amplifier (SOA) and its integration with laser diode (LD) is an essential building block yet to be demonstrated for III-nitride photonic integrated circuits (PICs) at visible wavelength. This paper presents the InGaN/GaN quantum well (QW) based dual-section LD consisting of integrated amplifier and laser gain regions fabricated on a semipolar GaN substrate. The threshold current in the laser gain region was favorably reduced from 229mA to 135mA at SOA driving voltages, VSOA, of 0V and 6.25V, respectively. The amplification effect was measured based on a large gain of 5.7 dB at VSOA = 6.25V from the increased optical output power of 8.2 mW to 30.5 mW. Such integrated amplifier can be modulated to achieve Gbps data communication using on-off keying technique. The monolithically integrated amplifier-LD paves the way towards the III-nitride on-chip photonic system, providing a compact, low-cost, and multi-functional solution for applications such as smart lighting and visible light communications.
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Kuritzky LY, Espenlaub AC, Yonkee BP, Pynn CD, DenBaars SP, Nakamura S, Weisbuch C, Speck JS. High wall-plug efficiency blue III-nitride LEDs designed for low current density operation. Opt Express 2017; 25:30696-30707. [PMID: 29221097 DOI: 10.1364/oe.25.030696] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2017] [Accepted: 10/02/2017] [Indexed: 06/07/2023]
Abstract
Commercial LEDs for solid-state lighting are often designed for operation at current densities in the droop regime (~35 A/cm2) to minimize costly chip area; however, many benefits can be realized by operating at low current density (J ≈1 - 5 A/cm2). Along with mitigation of droop losses and reduction of the operating voltage, low J operation of LEDs opens the design space for high light extraction efficiency (LEE). This work presents detailed ray tracing simulations of an LED design for low J operation with LEE ≈94%. The design is realized experimentally resulting in a peak wall-plug efficiency of 78.1% occurring at 3.45 A/cm2 and producing an output power of 7.2 mW for a 0.1 mm2 emitting area. At this operation point, the photon voltage Vp=hνq exceeds the forward voltage (V), corresponding to a Vp/V = 103%.
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Li H, Khoury M, Bonef B, Alhassan AI, Mughal AJ, Azimah E, Samsudin MEA, De Mierry P, Nakamura S, Speck JS, DenBaars SP. Efficient Semipolar (11-22) 550 nm Yellow/Green InGaN Light-Emitting Diodes on Low Defect Density (11-22) GaN/Sapphire Templates. ACS Appl Mater Interfaces 2017; 9:36417-36422. [PMID: 28960058 DOI: 10.1021/acsami.7b11718] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
We demonstrate efficient semipolar (11-22) 550 nm yellow/green InGaN light-emitting diodes (LEDs) with In0.03Ga0.97N barriers on low defect density (11-22) GaN/patterned sapphire templates. The In0.03Ga0.97N barriers were clearly identified, and no InGaN clusters were observed by atom probe tomography measurements. The semipolar (11-22) 550 nm InGaN LEDs (0.1 mm2 size) show an output power of 2.4 mW at 100 mA and a peak external quantum efficiency of 1.3% with a low efficiency drop. In addition, the LEDs exhibit a small blue-shift of only 11 nm as injection current increases from 5 to 100 mA. These results suggest the potential to produce high efficiency semipolar InGaN LEDs with long emission wavelength on large-area sapphire substrates with economical feasibility.
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Affiliation(s)
- Hongjian Li
- Materials Department, University of California , Santa Barbara, California 93106, United States
| | - Michel Khoury
- Materials Department, University of California , Santa Barbara, California 93106, United States
| | - Bastien Bonef
- Materials Department, University of California , Santa Barbara, California 93106, United States
| | - Abdullah I Alhassan
- Materials Department, University of California , Santa Barbara, California 93106, United States
| | - Asad J Mughal
- Materials Department, University of California , Santa Barbara, California 93106, United States
| | - Ezzah Azimah
- Materials Department, University of California , Santa Barbara, California 93106, United States
- Institute of Nano Optoelectronics Research and Technology, Universiti Sains Malaysia , 11800 USM, Penang, Malaysia
| | - Muhammad E A Samsudin
- Materials Department, University of California , Santa Barbara, California 93106, United States
- Institute of Nano Optoelectronics Research and Technology, Universiti Sains Malaysia , 11800 USM, Penang, Malaysia
| | | | - Shuji Nakamura
- Materials Department, University of California , Santa Barbara, California 93106, United States
- Department of Electrical and Computer Engineering, University of California , Santa Barbara, California 93117, United States
| | - James S Speck
- Materials Department, University of California , Santa Barbara, California 93106, United States
| | - Steven P DenBaars
- Materials Department, University of California , Santa Barbara, California 93106, United States
- Department of Electrical and Computer Engineering, University of California , Santa Barbara, California 93117, United States
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Lee C, Shen C, Cozzan C, Farrell RM, Speck JS, Nakamura S, Ooi BS, DenBaars SP. Gigabit-per-second white light-based visible light communication using near-ultraviolet laser diode and red-, green-, and blue-emitting phosphors. Opt Express 2017; 25:17480-17487. [PMID: 28789239 DOI: 10.1364/oe.25.017480] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2017] [Accepted: 07/06/2017] [Indexed: 06/07/2023]
Abstract
Data communication based on white light generated using a near-ultraviolet (NUV) laser diode (LD) pumping red-, green-, and blue-emitting (RGB) phosphors was demonstrated for the first time. A III-nitride laser diode (LD) on a semipolar (2021¯) substrate emitting at 410 nm was used for the transmitter. The measured modulation bandwidth of the LD was 1 GHz, which was limited by the avalanche photodetector. The emission from the NUV LD and the RGB phosphor combination measured a color rendering index (CRI) of 79 and correlated color temperature (CCT) of 4050 K, indicating promise of this approach for creating high quality white lighting. Using this configuration, data was successfully transmitted at a rate of more than 1 Gbps. This NUV laser-based system is expected to have lower background noise from sunlight at the LD emission wavelength than a system that uses a blue LD due to the rapid fall off in intensity of the solar spectrum in the NUV spectral region.
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Rolland N, Vurpillot F, Duguay S, Mazumder B, Speck JS, Blavette D. New Atom Probe Tomography Reconstruction Algorithm for Multilayered Samples: Beyond the Hemispherical Constraint. Microsc Microanal 2017; 23:247-254. [PMID: 28327210 DOI: 10.1017/s1431927617000253] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Accuracy of atom probe tomography measurements is strongly degraded by the presence of phases that have different evaporation fields. In particular, when there are perpendicular interfaces to the tip axis in the specimen, layers thicknesses are systematically biased and the resolution is degraded near the interfaces. Based on an analytical model of field evaporated emitter end-form, a new algorithm dedicated to the 3D reconstruction of multilayered samples was developed. Simulations of field evaporation of bilayer were performed to evaluate the effectiveness of the new algorithm. Compared to the standard state-of-the-art reconstruction methods, the present approach provides much more accurate analyzed volume, and the resolution is clearly improved near the interface. The ability of the algorithm to handle experimental data was also demonstrated. It is shown that the standard algorithm applied to the same data can commit an error on the layers thicknesses up to a factor 2. This new method is not constrained by the classical hemispherical specimen shape assumption.
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Affiliation(s)
- Nicolas Rolland
- 1Groupe de Physique des Matériaux,Université et INSA de Rouen-UMR CNRS 6634-Normandie Université,76801 St Etienne du Rouvray,France
| | - François Vurpillot
- 1Groupe de Physique des Matériaux,Université et INSA de Rouen-UMR CNRS 6634-Normandie Université,76801 St Etienne du Rouvray,France
| | - Sébastien Duguay
- 1Groupe de Physique des Matériaux,Université et INSA de Rouen-UMR CNRS 6634-Normandie Université,76801 St Etienne du Rouvray,France
| | - Baishakhi Mazumder
- 2Department of Material Design and Innovation,University at Buffalo,Buffalo, NY 14260,USA
| | - James S Speck
- 3Materials Department,University of California,Santa Barbara,CA 93106,USA
| | - Didier Blavette
- 1Groupe de Physique des Matériaux,Université et INSA de Rouen-UMR CNRS 6634-Normandie Université,76801 St Etienne du Rouvray,France
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Kowsz SJ, Young EC, Yonkee BP, Pynn CD, Farrell RM, Speck JS, DenBaars SP, Nakamura S. Using tunnel junctions to grow monolithically integrated optically pumped semipolar III-nitride yellow quantum wells on top of electrically injected blue quantum wells. Opt Express 2017; 25:3841-3849. [PMID: 28241595 DOI: 10.1364/oe.25.003841] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We report a device that monolithically integrates optically pumped (20-21) III-nitride quantum wells (QWs) with 560 nm emission on top of electrically injected QWs with 450 nm emission. The higher temperature growth of the blue light-emitting diode (LED) was performed first, which prevented thermal damage to the higher indium content InGaN of the optically pumped QWs. A tunnel junction (TJ) was incorporated between the optically pumped and electrically injected QWs; this TJ enabled current spreading in the buried LED. Metalorganic chemical vapor deposition enabled the growth of InGaN QWs with high radiative efficiency, while molecular beam epitaxy was leveraged to achieve activated buried p-type GaN and the TJ. This initial device exhibited dichromatic optically polarized emission with a polarization ratio of 0.28. Future improvements in spectral distribution should enable phosphor-free polarized white light emission.
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Hwang D, Yonkee BP, Addin BS, Farrell RM, Nakamura S, Speck JS, DenBaars S. Photoelectrochemical liftoff of LEDs grown on freestanding c-plane GaN substrates. Opt Express 2016; 24:22875-22880. [PMID: 27828354 DOI: 10.1364/oe.24.022875] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We demonstrate a thin-film flip-chip (TFFC) process for LEDs grown on freestanding c-plane GaN substrates. LEDs are transferred from a bulk GaN substrate to a sapphire submount via a photoelectrochemical (PEC) undercut etch. This PEC liftoff method allows for substrate reuse and exposes the N-face of the LEDs for additional roughening. The LEDs emitted at a wavelength of 432 nm with a turn on voltage of ~3 V. Etching the LEDs in heated KOH after transferring them to a sapphire submount increased the peak external quantum efficiency (EQE) by 42.5% from 9.9% (unintentionally roughened) to 14.1% (intentionally roughened).
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Shen C, Lee C, Ng TK, Nakamura S, Speck JS, DenBaars SP, Alyamani AY, El-Desouki MM, Ooi BS. High-speed 405-nm superluminescent diode (SLD) with 807-MHz modulation bandwidth. Opt Express 2016; 24:20281-20286. [PMID: 27607634 DOI: 10.1364/oe.24.020281] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
III-nitride LEDs are fundamental components for visible-light communication (VLC). However, the modulation bandwidth is inherently limited by the relatively long carrier lifetime. In this letter, we present the 405 nm emitting superluminescent diode (SLD) with tilted facet design on semipolar GaN substrate, showing a broad emission of ~9 nm at 20 mW optical power. Owing to the fast recombination (τe<0.35 ns) through the amplified spontaneous emission, the SLD exhibits a significantly large 3-dB bandwidth of 807 MHz. A data rate of 1.3 Gbps with a bit-error rate of 2.9 × 10-3 was obtained using on-off keying modulation scheme, suggesting the SLD being a high-speed transmitter for VLC applications.
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Alhassan AI, Farrell RM, Saifaddin B, Mughal A, Wu F, DenBaars SP, Nakamura S, Speck JS. High luminous efficacy green light-emitting diodes with AlGaN cap layer. Opt Express 2016; 24:17868-17873. [PMID: 27505754 DOI: 10.1364/oe.24.017868] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We demonstrate very high luminous efficacy green light-emitting diodes employing Al0.30Ga0.70N cap layer grown on patterned sapphire substrates by metal organic chemical vapor deposition. The peak external quantum efficiency and luminous efficacies were 44.3% and 239 lm/w, respectively. At 20 mA (20 A/cm2) the light output power was 14.3 mW, the forward voltage was 3.5 V, the emission wavelength was 526.6 nm, and the external quantum efficiency was 30.2%. These results are among the highest reported luminous efficacy values for InGaN based green light-emitting diodes.
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Bierwagen O, Rombach J, Speck JS. Faceting control by the stoichiometry influence on the surface free energy of low-index bcc-In2O3 surfaces. J Phys Condens Matter 2016; 28:224006. [PMID: 26952816 DOI: 10.1088/0953-8984/28/22/224006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The faceting of In2O3(0 0 1), (0 1 1), and (1 1 1) grown by plasma-assisted molecular beam epitaxy on yttria-stabilised zirconia was investigated under different growth conditions-conventionally used oxygen-rich growth conditions with and without heavy Sn-doping, and indium-rich growth conditions-by in situ reflection high-energy electron diffraction, scanning electron microscopy, x-ray diffraction, and atomic force microscopy. In a simple thermodynamic model that considers surface free energy only, the observed faceting is compared to recent theoretical predictions of the surface tension (also termed surface free energy) anisotropy and the related equilibrium crystal shape derived from a Wulff construction. These predictions and our comparison include the variation with growth-condition-dependent oxygen chemical potential. Our results demonstrate how the experimentally changed oxygen chemical potential controls the faceting or island shape of In2O3 by changing the surface tension anisotropy. While the experimental results largely agree with the theoretically derived surface tension anisotropy, they strongly suggest a lower relative surface tension of the (0 0 1) surface at lower oxygen chemical potential (In-rich growth conditions) than theoretically predicted or a significant surface entropy contribution.
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Affiliation(s)
- Oliver Bierwagen
- Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany. Materials Department, University of California, Santa Barbara, California 93106, USA
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Shen C, Ng TK, Leonard JT, Pourhashemi A, Nakamura S, DenBaars SP, Speck JS, Alyamani AY, El-Desouki MM, Ooi BS. High-brightness semipolar (2021¯) blue InGaN/GaN superluminescent diodes for droop-free solid-state lighting and visible-light communications. Opt Lett 2016; 41:2608-2611. [PMID: 27244426 DOI: 10.1364/ol.41.002608] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
A high-brightness, droop-free, and speckle-free InGaN/GaN quantum well blue superluminescent diode (SLD) was demonstrated on a semipolar (2021¯) GaN substrate. The 447-nm emitting SLD has a broad spectral linewidth of 6.3 nm at an optical power of 123 mW. A peak optical power of 256 mW was achieved at 700 mA CW injection current. By combining YAG:Ce phosphor, SLD-generated white light shows a color-rendering index (CRI) of 68.9 and a correlated color temperature (CCT) of 4340 K. The measured frequency response of the SLD revealed a -3 dB bandwidth of 560 MHz, thus demonstrating the feasibility of the device for both solid-state lighting (SSL) and visible-light communication (VLC) applications.
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Yonkee BP, Young EC, Lee C, Leonard JT, DenBaars SP, Speck JS, Nakamura S. Demonstration of a III-nitride edge-emitting laser diode utilizing a GaN tunnel junction contact. Opt Express 2016; 24:7816-7822. [PMID: 27137064 DOI: 10.1364/oe.24.007816] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We demonstrate a III-nitride edge emitting laser diode (EELD) grown on a (2021) bulk GaN substrate with a GaN tunnel junction contact for hole injection. The tunnel junction was grown using a combination of metal-organic chemical-vapor deposition (MOCVD) and ammonia-based molecular-beam epitaxy (MBE) which allowed to be regrown over activated p-GaN. For a laser bar with dimensions of 1800 µm x 2.5 µm, without facet coatings, the threshold current was 284 mA (6.3 kA/cm2) and the single facet slope efficiency was 0.33 W/A (12% differential efficiency). A differential resistivity at high current density of 2.3 × 10-4 Ω cm2 was measured.
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Pimputkar S, Malkowski TF, Griffiths S, Espenlaub A, Suihkonen S, Speck JS, Nakamura S. Stability of materials in supercritical ammonia solutions. J Supercrit Fluids 2016. [DOI: 10.1016/j.supflu.2015.10.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Cantore M, Pfaff N, Farrell RM, Speck JS, Nakamura S, DenBaars SP. High luminous flux from single crystal phosphor-converted laser-based white lighting system. Opt Express 2016; 24:A215-A221. [PMID: 26832576 DOI: 10.1364/oe.24.00a215] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The efficiency droop of light emitting diodes (LEDs) with increasing current density limits the amount of light emitted per wafer area. Since low current densities are required for high efficiency operation, many LED die are needed for high power white light illumination systems. In contrast, the carrier density of laser diodes (LDs) clamps at threshold, so the efficiency of LDs does not droop above threshold and high efficiencies can be achieved at very high current densities. The use of a high power blue GaN-based LD coupled with a single crystal Ce-doped yttrium aluminum garnet (YAG:Ce) sample was investigated for white light illumination applications. Under CW operation, a single phosphor-converted LD (pc-LD) die produced a peak luminous efficacy of 86.7 lm/W at 1.4 A and 4.24 V and a peak luminous flux of 1100 lm at 3.0 A and 4.85 V with a luminous efficacy of 75.6 lm/W. Simulations of a pc-LD confirm that the single crystal YAG:Ce sample did not experience thermal quenching at peak LD operating efficiency. These results show that a single pc-LD die is capable of emitting enough luminous flux for use in a high power white light illumination system.
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Lee C, Shen C, Oubei HM, Cantore M, Janjua B, Ng TK, Farrell RM, El-Desouki MM, Speck JS, Nakamura S, Ooi BS, DenBaars SP. 2 Gbit/s data transmission from an unfiltered laser-based phosphor-converted white lighting communication system. Opt Express 2015; 23:29779-29787. [PMID: 26698461 DOI: 10.1364/oe.23.029779] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We demonstrate data transmission of unfiltered white light generated by direct modulation of a blue gallium nitride (GaN) laser diode (LD) exciting YAG:Ce phosphors. 1.1 GHz of modulation bandwidth was measured without a limitation from the slow 3.8 MHz phosphor response. A high data transmission rate of 2 Gbit/s was achieved without an optical blue-filter using a non-return-to-zero on-off keying (NRZ-OOK) modulation scheme. The measured bit error rate (BER) of 3.50 × 10(-3) was less than the forward error correction (FEC) limit of 3.8 × 10(-3). The generated white light exhibits CIE 1931 chromaticity coordinates of (0.3628, 0.4310) with a color rendering index (CRI) of 58 and a correlated color temperature (CCT) of 4740 K when the LD was operated at 300 mA. The demonstrated laser-based lighting system can be used simultaneously for indoor broadband access and illumination applications with good color stability.
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Lee C, Zhang C, Cantore M, Farrell RM, Oh SH, Margalith T, Speck JS, Nakamura S, Bowers JE, DenBaars SP. 4 Gbps direct modulation of 450 nm GaN laser for high-speed visible light communication. Opt Express 2015; 23:16232-16237. [PMID: 26193595 DOI: 10.1364/oe.23.016232] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We demonstrate high-speed data transmission with a commercial high power GaN laser diode at 450 nm. 2.6 GHz bandwidth was achieved at an injection current of 500 mA using a high-speed visible light communication setup. Record high 4 Gbps free-space data transmission rate was achieved at room temperature.
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Von Dollen P, Pimputkar S, Speck JS. Let There Be Light-With Gallium Nitride: The 2014 Nobel Prize in Physics. Angew Chem Int Ed Engl 2014; 53:13978-80. [DOI: 10.1002/anie.201410693] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Indexed: 11/11/2022]
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Perl EE, McMahon WE, Farrell RM, DenBaars SP, Speck JS, Bowers JE. Surface structured optical coatings with near-perfect broadband and wide-angle antireflective properties. Nano Lett 2014; 14:5960-5964. [PMID: 25238041 DOI: 10.1021/nl502977f] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Optical thin-film coatings are typically limited to designs where the refractive index varies in only a single dimension. However, additional control over the propagation of incoming light is possible by structuring the other two dimensions. In this work, we demonstrate a three-dimensional surface structured optical coating that combines the principles of thin-film optical design with bio-inspired nanostructures to yield near-perfect antireflection. Using this hybrid approach, we attain average reflection losses of 0.2% on sapphire and 0.6% on gallium nitride for 300-1800 nm light. This performance is maintained to very wide incidence angles, achieving less than 1% reflection at all measured wavelengths out to 45° for sapphire. This hybrid design has the potential to significantly enhance the broadband and wide-angle properties for a number of optical systems that require high transparency.
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Affiliation(s)
- Emmett E Perl
- Department of Electrical and Computer Engineering and ‡Materials Department, University of California, Santa Barbara , Santa Barbara, California 93106, United States
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Hu YL, Rind E, Speck JS. Antiphase boundaries and rotation domains in In2O3(001) films grown on yttria-stabilized zirconia (001). J Appl Crystallogr 2014. [DOI: 10.1107/s1600576713033864] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
In2O3is important because it has been widely used as a transparent contact material and an active gas sensor material. To understand and utilize its intrinsic physics as a semiconductor, it is necessary to have In2O3with a high material quality. In this article, single-crystalline (001)-oriented In2O3thin films were grown on yttria-stabilized zirconia (001) substrate, and a group theory analysis and transmission electron microscopy (TEM) experiments were conducted to investigate the defects within the In2O3film. Owing to the reduced symmetry of the bixbyite structure (space group Ia{\overline 3}) in comparison with the fluorite template (space group Fm {\overline 3}m), the formation of antiphase domains and 90° rotation domains in the In2O3thin films is anticipated. This prediction is confirmed experimentally by TEM and high-angle annular dark-field scanning transmission electron microscopy images. The size of the enclosed domains ranges from 50 to 300 nm, and the major domain boundaries are along the (110), (1{\overline 1}0), (010) and (100) planes. The rotation domains are related by a fourfold rotation operation along the 〈001〉 directions, which will cause the permutation of the axes of the bixbyite structure.
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Iveland J, Martinelli L, Peretti J, Speck JS, Weisbuch C. Direct measurement of Auger electrons emitted from a semiconductor light-emitting diode under electrical injection: identification of the dominant mechanism for efficiency droop. Phys Rev Lett 2013; 110:177406. [PMID: 23679777 DOI: 10.1103/physrevlett.110.177406] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/25/2012] [Indexed: 06/02/2023]
Abstract
We report on the unambiguous detection of Auger electrons by electron emission spectroscopy from a cesiated InGaN/GaN light-emitting diode under electrical injection. Electron emission spectra were measured as a function of the current injected in the device. The appearance of high energy electron peaks simultaneously with an observed drop in electroluminescence efficiency shows that hot carriers are being generated in the active region (InGaN quantum wells) by an Auger process. A linear correlation was measured between the high energy emitted electron current and the "droop current"--the missing component of the injected current for light emission. We conclude that the droop phenomenon in GaN light-emitting diodes originates from the excitation of Auger processes.
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Affiliation(s)
- Justin Iveland
- Materials Department, University of California, Santa Barbara, California 93106, USA
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Feezell DF, Speck JS, DenBaars SP, Nakamura S. Semipolar $({\hbox{20}}\bar{{\hbox{2}}}\bar{{\hbox{1}}})$ InGaN/GaN Light-Emitting Diodes for High-Efficiency Solid-State Lighting. ACTA ACUST UNITED AC 2013. [DOI: 10.1109/jdt.2012.2227682] [Citation(s) in RCA: 298] [Impact Index Per Article: 27.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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40
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Zhao Y, Yan Q, Feezell D, Fujito K, Van de Walle CG, Speck JS, DenBaars SP, Nakamura S. Optical polarization characteristics of semipolar (3031) and (3031) InGaN/GaN light-emitting diodes. Opt Express 2013; 21 Suppl 1:A53-A59. [PMID: 23389275 DOI: 10.1364/oe.21.000a53] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Linear polarized electroluminescence was investigated for semipolar (3031) and (3031) InGaN light-emitting diodes (LEDs) with various indium compositions. A high degree of optical polarization was observed for devices on both planes, ranging from 0.37 at 438 nm to 0.79 at 519 nm. The extracted valence band energy separation was consistent with the optical polarization ratios. The effect of anisotropic strain on the valance band structure was studied using k?p method for the above two planes. The theoretical calculations are consistent with the experimental results.
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Affiliation(s)
- Yuji Zhao
- Electrical Computer and Engineering Department, University of California, Santa Barbara, California 93106, USA.
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Keller S, Dora Y, Chowdhury S, Wu F, Chen X, DenBaars SP, Speck JS, Mishra UK. Growth and characterization of N-polar GaN and AlGaN/GaN HEMTs on (111) silicon. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/pssc.201000958] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Golan Y, Fini P, Denbaars SP, Speck JS. Substrate Surface Treatments and “Controlled Contamination” in GaN / Sapphire MOCVD. ACTA ACUST UNITED AC 2011. [DOI: 10.1557/proc-482-57] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
AbstractWe have used atomic force microscopy (AFM) to study the effect of common substrate surface treatments for the metal-organic chemical vapor deposition (MOCVD) of GaN on sapphire. It appears that contaminants play a major role in the surface chemistry and strongly influence the morphology of the treated surfaces. In order to investigate the role of these contaminants, we have introduced the concept of “controlled contamination” (CC), namely, exposure of the sapphire surfaces to controlled amounts of potential contaminants in-situ and investigation of the resulting sapphire morphology. The results showed that sapphire, considered to be a very stable oxide surface, is clearly reactive in the GaN MOCVD chemical environment at the high temperatures (HT) employed, allowing us to use CC for obtaining sapphire substrates with controlled roughness. Nevertheless, epitaxial growth using the two-step GaN MOCVD process appears to be very robust and practically insensitive to the (submicronscale) substrate morphology.
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Garrett GA, Shen H, Wraback M, Tyagi A, Schmidt MC, Speck JS, DenBaars SP, Nakamaura S. Comparison of time-resolved photoluminescence from InGaN single quantum wells grown on nonpolar and semipolar bulk GaN substrates. ACTA ACUST UNITED AC 2009. [DOI: 10.1002/pssc.200880974] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Reurings F, Tuomisto F, Gallinat CS, Koblmüller G, Speck JS. Vacancy defects probed with positron annihilation spectroscopy in In-polar InN grown by plasma-assisted molecular beam epitaxy: Effects of growth conditions. ACTA ACUST UNITED AC 2009. [DOI: 10.1002/pssc.200880952] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Schaake CA, Fichtenbaum NA, Neufeld CJ, Keller S, DenBaars SP, Speck JS, Mishra UK. M-plane InGaN/GaN light emitting diodes fabricated by MOCVD regrowth onc-plane patterned templates. ACTA ACUST UNITED AC 2008. [DOI: 10.1002/pssc.200779284] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Choi YS, Iza M, Matioli E, Koblmüller G, Speck JS, Weisbuch C, Hu EL. Submicron-thick microcavity InGaN light emitting diodes. ACTA ACUST UNITED AC 2008. [DOI: 10.1117/12.764696] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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Hashimoto T, Wu F, Speck JS, Nakamura S. A GaN bulk crystal with improved structural quality grown by the ammonothermal method. Nat Mater 2007; 6:568-71. [PMID: 17603489 DOI: 10.1038/nmat1955] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2007] [Accepted: 06/01/2007] [Indexed: 05/16/2023]
Abstract
The realization of high-performance optoelectronic devices, based on GaN and other nitride semiconductors, requires the existence of a high-quality substrate. Non-polar or semipolar substrates have recently been proven to provide superior optical devices to those on conventional c-plane substrates. Bulk GaN growth enables GaN substrates sliced along various favourable crystal orientations. Ammonothermal growth is an attractive method for bulk GaN growth owing to its potential to grow GaN ingots at low cost. Here we report on improvement in the structural quality of GaN grown by the ammonothermal method. The threading dislocation densities estimated by plan-view transmission electron microscopy observations were less than 1 x 10(6) cm(-2) for the Ga face and 1 x 10(7) cm(-2) for the N face. No dislocation generation at the interface was observed on the Ga face, although a few defects were generated at the interface on the N face. The improvement in the structural quality, together with the previous report on growth rate and scalability, demonstrates the commercial feasibility of the ammonothermal GaN growth.
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Affiliation(s)
- Tadao Hashimoto
- Materials Department, University of California, Santa Barbara, California 93106-5050, USA.
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Fehlberg TB, Umana-Membreno GA, Gallinat CS, Koblmüller G, Bernardis S, Nener BD, Parish G, Speck JS. Characterisation of multiple carrier transport in indium nitride grown by molecular beam epitaxy. ACTA ACUST UNITED AC 2007. [DOI: 10.1002/pssc.200674780] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Chichibu SF, Uedono A, Onuma T, Haskell BA, Chakraborty A, Koyama T, Fini PT, Keller S, Denbaars SP, Speck JS, Mishra UK, Nakamura S, Yamaguchi S, Kamiyama S, Amano H, Akasaki I, Han J, Sota T. Origin of defect-insensitive emission probability in In-containing (Al,In,Ga)N alloy semiconductors. Nat Mater 2006; 5:810-6. [PMID: 16951678 DOI: 10.1038/nmat1726] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2005] [Accepted: 07/12/2006] [Indexed: 05/11/2023]
Abstract
Group-III-nitride semiconductors have shown enormous potential as light sources for full-colour displays, optical storage and solid-state lighting. Remarkably, InGaN blue- and green-light-emitting diodes (LEDs) emit brilliant light although the threading dislocation density generated due to lattice mismatch is six orders of magnitude higher than that in conventional LEDs. Here we explain why In-containing (Al,In,Ga)N bulk films exhibit a defect-insensitive emission probability. From the extremely short positron diffusion lengths (<4 nm) and short radiative lifetimes of excitonic emissions, we conclude that localizing valence states associated with atomic condensates of In-N preferentially capture holes, which have a positive charge similar to positrons. The holes form localized excitons to emit the light, although some of the excitons recombine at non-radiative centres. The enterprising use of atomically inhomogeneous crystals is proposed for future innovation in light emitters even when using defective crystals.
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Affiliation(s)
- Shigefusa F Chichibu
- Institute of Applied Physics and 21st Century COE Office, Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8573, Japan.
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Im HJ, Ding Y, Pelz JP, Heying B, Speck JS. Characterization of individual threading dislocations in GaN using ballistic electron emission microscopy. Phys Rev Lett 2001; 87:106802. [PMID: 11531495 DOI: 10.1103/physrevlett.87.106802] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2001] [Indexed: 05/23/2023]
Abstract
Threading dislocations (TDs) of molecular beam epitaxy grown GaN film were studied with ultrahigh vacuum ballistic electron emission microscopy in order to quantify any fixed negative charge at identifiable TDs, with approximately 3 nm spatial and approximately 10 meV local barrier resolution. In contrast to several prior studies, we find no indication of fixed negative dislocation charge at specific TD structures, with a conservative upper limit of approximately 0.25 e(-) per c-axis unit cell. We do observe evidence of positive surface charge at TDs and at GaN step edges, which may be due to local piezoelectric fields.
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Affiliation(s)
- H J Im
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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