Highly Narrow-Band Polarization-Sensitive Solar-Blind Photodetectors Based on β-Ga2O3 Single Crystals

Enhancement of solar blind full band absorption in photodetector with Ga2O3 nanopore and Al nanograting

In this paper, we presented a novel double-layer light-trapping structure consisting of nanopores and nanograting positioned on both the surface and bottom of a gallium oxide-based solar-blind photodetector. Utilizing the finite element method (FEM), we thoroughly investigated the light absorption enhancement capabilities of this innovative design. The simulation results show that the double-layer nanostructure effectively combines the light absorption advantages of nanopores and nanogratings. Compared with thin film devices and devices with only nanopore or nanograting structures, double-layer nanostructured devices have a higher light absorption, achieving high light absorption in the solar blind area.

Template-Confined Oriented Perovskite Nanowire Arrays Enable Polarization Detection and Imaging

Polarized light detection can effectively identify the difference between the polarization information on the target and the background, which is of great significance for detection in complex natural environments and/or extreme weather. Generally, polarized light detection inevitably relies on anisotropic structures of photodetector devices, while organic-inorganic hybrid perovskites are ideal for anisotropic patterning due to their simple and efficient preparation by solution method. Compared to patterned thin films, patterned arrays of aligned one-dimensional (1D) perovskite nanowires (PNWAs) have fewer grain boundaries and lower defect densities, making them well suited for high-performance polarization-sensitive photodetectors. Here, we fabricated PNWAs crystallographically aligned with variable line widths and alignment densities employing CD-ROM and DVD-ROM grating pattern template-confined growth (TCG) methods. The photodetectors constructed from MAPbI3 PNWAs achieved responsivity of 35.01 A/W, detectivity of 6.85 × 1013 Jones, and fast response with a rise time of 172 μs and fall time of 114 μs. They were successfully applied to high-performance polarization detection with a polarization ratio of 1.81, potentially applicable in polarized light detection systems.

Highly Polarization-Deep-Ultraviolet-Sensitive β-Ga2O3 Epitaxial Films by Disrupting Rotational Symmetry and Encrypted Solar-Blind Optical Communication Application

Ultrawide bandgap semiconductor β-Ga2O3 (4.9 eV), with its monoclinic crystal structure, exhibits distinct anisotropic characteristics both optically and electrically, making it an ideal material for solar-blind polarization photodetectors. In this work, β-Ga2O3 epitaxial films were deposited on sapphire substrates with different orientations, and the mechanisms underlying the anisotropy of these epitaxial films were investigated. Compared to c-plane sapphire, the lattice mismatch between m- or r-plane sapphire and β-Ga2O3 is more pronounced, disrupting the rotational symmetry of the films and rendering them anisotropic. Thanks to the improved anisotropy, the polarization ratio of the photodetector based on β-Ga2O3 films grown on r-plane substrates is 0.24, nearly ten times higher than that on c-plane substrates. Finally, by utilizing these polarization-sensitive photodetectors, we developed an encrypted solar-blind ultraviolet optical communication system. Our work provides a new approach to facilitate the fabrication and application of high-performance polarization-sensitive solar-blind photodetectors.

Low-Dimensional-Materials-Based Photodetectors for Next-Generation Polarized Detection and Imaging

The vector characteristics of light and the vectorial transformations during its transmission lay a foundation for polarized photodetection of objects, which broadens the applications of related detectors in complex environments. With the breakthrough of low-dimensional materials (LDMs) in optics and electronics over the past few years, the combination of these novel LDMs and traditional working modes is expected to bring new development opportunities in this field. Here, the state-of-the-art progress of LDMs, as polarization-sensitive components in polarized photodetection and even the imaging, is the main focus, with emphasis on the relationship between traditional working principle of polarized photodetectors (PPs) and photoresponse mechanisms of LDMs. Particularly, from the view of constitutive equations, the existing works are reorganized, reclassified, and reviewed. Perspectives on the opportunities and challenges are also discussed. It is hoped that this work can provide a more general overview in the use of LDMs in this field, sorting out the way of related devices for "more than Moore" or even the "beyond Moore" research.

Photoelectric properties of glass-ceramics containing KTb2F7 nanocrystals for UV detection

In this work, a glass ceramics (GC) containing KTb2F7 nanocrystals was fabricated by controlled crystallization of an fluorosilicate glass via heat-treatment. The microstructure, luminescence, and photoelectric properties of the GCs are systematically studied by X-ray diffraction, transmission electron microscopy, spectral analysis, and current-voltage (I-V) curves. The results show that the GC containing KTb2F7 nanocrystals exhibit intense visible emission due to the 4f transition of Tb3+: 5Di (i = 3, 4) → 7Fj (j = 0-6) upon excitation of ultraviolet (UV) light. In addition, a UV detector device based on the GC was fabricated, which has a large dynamic linear response range, fast response speed and high sensitivity. This study not only provides a new material for UV detector that can simplify the process of UV detection, but also highlight a new strategy for UV detection.

Efficient Suppression of Persistent Photoconductivity in β-Ga2O3-Based Photodetectors with Square Nanopore Arrays

In this work, square nanopore arrays were developed on the surface of β-Ga₂O₃ microflakes using focused ion beam (FIB) etching, and solar-blind photodetectors (PDs) were fabricated based on the β-Ga₂O₃ microflakes with square nanopore arrays. The β-Ga₂O₃ microflake-based device was transformed from a gate voltage depletion mode to an oxygen depletion mode by FIB etching. The developed device exhibited excellent solar-blind PD performance with extremely high responsivity (1.8 × 10⁵ at 10 V), detectivity (3.4 × 10¹⁸ Jones at 10 V), and light-to-dark ratio (9.3 × 10⁸ at 5 V) as well as good repeatability and excellent stability. The intrinsic mechanism responsible for this performance was then systematically discussed. This work opens up a new avenue for the fabrication of high-performance β-Ga₂O₃-based low-dimensional PDs with high reproducibility by employing the FIB etching process.

Narrow-Band Solar-Blind Ultraviolet Detectors Based on AlSnO Films with Tunable Band Gap

Semiconductor materials with sufficiently wide band gaps are urgently desired for use in solar-blind ultraviolet detectors. In this work, the growth of AlSnO films was achieved through the magnetron sputtering technique. AlSnO films with band gaps in the range of 4.40-5.43 eV were obtained by varying the growth process, which demonstrates that the band gap of AlSnO is continuously tunable. What is more, based on the films prepared, narrow-band solar-blind ultraviolet detectors were fabricated with good solar-blind ultraviolet spectral selectivity, excellent detectivity, and narrow full widths at half-maximum in the response spectra, showing a great potential to be applied to solar-blind ultraviolet narrow-band detection. Therefore, based on the results above, this study focusing on the fabrication of detectors via band gap engineering can be a significant reference for researchers interested in solar-blind ultraviolet detection.

2D Ultrawide Bandgap Semiconductors: Odyssey and Challenges

2D ultrawide bandgap (UWBG) semiconductors have aroused increasing interest in the field of high-power transparent electronic devices, deep-ultraviolet photodetectors, flexible electronic skins, and energy-efficient displays, owing to their intriguing physical properties. Compared with dominant narrow bandgap semiconductor material families, 2D UWBG semiconductors are less investigated but stand out because of their propensity for high optical transparency, tunable electrical conductivity, high mobility, and ultrahigh gate dielectrics. At the current stage of research, the most intensively investigated 2D UWBG semiconductors are metal oxides, metal chalcogenides, metal halides, and metal nitrides. This paper provides an up-to-date review of recent research progress on new 2D UWBG semiconductor materials and novel physical properties. The widespread applications, i.e., transistors, photodetector, touch screen, and inverter are summarized, which employ 2D UWBG semiconductors as either a passive or active layer. Finally, the existing challenges and opportunities of the enticing class of 2D UWBG semiconductors are highlighted.

Pt/(InGa)2O3/n-Si Heterojunction-Based Solar-Blind Ultraviolet Photovoltaic Detectors with an Ideal Absorption Cutoff Edge of 280 nm

Ga₂O₃ is a popular material for research on solar-blind ultraviolet detectors. However, its absorption cutoff edge is 253 nm, which is not an ideal cutoff edge of 280 nm. In this work, by adjusting the ratio of In/Ga elements in the films, a high-quality (In_0.11Ga_0.89)₂O₃ film with an absorption cutoff edge of 280 nm was obtained, which owns a uniform surface and preferred orientation. On this basis, a solar-blind ultraviolet photovoltaic detector was constructed based on the Pt/(In_0.11Ga_0.89)₂O₃/n-Si heterojunction. When the device is exposed to 254 nm UV light, its open-circuit voltage (V_OC) can reach 354 mV. Under 0 V bias, the device has a responsivity of 0.48 mA/W with a rise time of 0.47 s and a decay time of 0.37 s; under -7 V bias, the device achieves a responsivity of 16.96 mA/W with a rise time of 0.17 s and a decay time of 0.33 s. The spectral response characteristics of the device show that it has a selective response to solar-blind ultraviolet light (cutoff wavelength is 280 nm) with a rejection ratio (R_{254 nm}/R_{310 nm}), which is greater by more than two orders of magnitude. This work provides a good reference for adjusting the band gap of Ga₂O₃-based films and broadening their application fields.

Recent advances in development of nanostructured photodetectors from ultraviolet to infrared region: A review

Herein, we aim to evaluate the photodetector performance of various nanostructured materials (thin films, 2-D nanolayers, 1-D nanowires, and 0-D quantum dots) in ultraviolet (UV), visible, and infrared (IR) regions. Specifically, semiconductor-based metal oxides such as ZnO, Ga₂O₃, SnO₂, TiO₂, and WO₃ are the majority preferred materials for UV photodetection due to their broad band gap, stability, and relatively simple fabrication processes. Whereas, the graphene-based hetero- and nano-structured composites are considered as prominent visible light active photodetectors. Interestingly, graphene exhibits broad band spectral absorption and ultra-high mobility, which derives graphene as a suitable candidate for visible detector. Further, due to the very low absorption rate of graphene (2%), various materials have been integrated with graphene (rGO-CZS, PQD-rGO, N-SLG, and GO doped PbI₂). In the case of IR photodetectors, quantum dot IR detectors prevails significant advantage over the quantum well IR detectors due to the 0-D quantum confinement and ability to absorb the light with any polarization. In such a way, we discussed the most recent developments on IR detectors using InAs and PbS quantum dot nanostructures. Overall, this review gives clear view on the development of suitable device architecture under prominent nanostructures to tune the photodetector performance from UV to IR spectral regions for wide-band photodetectors.

Stable and Self-Powered Solar-Blind Ultraviolet Photodetectors Based on a Cs3Cu2I5/β-Ga2O3 Heterojunction Prepared by Dual-Source Vapor Codeposition

Self-powered solar-blind ultraviolet (UV) photodetectors have drawn worldwide attention in recent years because of their important applications in military and civilian areas. In this study, a dual-source vapor codeposition technique was employed, for the first time, to prepare a nontoxic copper halide Cs₃Cu₂I₅, which was integrated with the β-Ga₂O₃ wafer to construct a type-II heterojunction for photodetection applications. By optimizing the annealing conditions, high-quality Cs₃Cu₂I₅ films with dense morphology, high crystallinity, and a long carrier lifetime of 1.02 μs were acquired. Because of the high material integrity of Cs₃Cu₂I₅ films and effective interfacial carrier transfer from Cs₃Cu₂I₅ to β-Ga₂O₃, a heterojunction device demonstrates a good solar-blind UV response property and operates at zero bias. Typically, the photodetector presents a low dark current (∼1.2 pA), a high solar-blind/UVA rejection ratio (∼1.0 × 10³), a relatively fast photoresponse speed (37/45 ms), and a high photo-to-dark current ratio (∼5.1 × 10⁴) at zero bias. Moreover, even after 12-h continuous working and 2-month storage without encapsulation in ambient air, the photodetection ability of the device can almost be maintained, demonstrating outstanding air stability. Our results suggest that nontoxic Cs₃Cu₂I₅ is able to serve as a prospective candidate for stable solar-blind UV photodetection.

High-Performance X-ray Detector Based on Single-Crystal β-Ga2O3:Mg

X-ray detection plays an important role in medical imaging, scientific research, and security inspection. Recently, the β-Ga₂O₃ single-crystal-based X-ray detector has attracted extensive attention due to its excellent intrinsic properties such as good absorption for X-ray photons, a high breakdown electric field, high stability, and low cost. However, developing a high-performance β-Ga₂O₃-based X-ray detector remains a challenge because of the large dark current and the high oxygen vacancy concentration in the crystals. In this paper, we report a high-performance Mg-doped β-Ga₂O₃ single-crystal-based X-ray detector with a sandwich structure. The reduced dark current enables the detector to have a high sensitivity of 338.9 μC Gy^-1 cm^-2 under 50 keV X-ray irradiation with a dose rate of 69.5 μGy/s. The sensitivity is 16-fold higher than that of the commercial amorphous selenium detector. Furthermore, the reduced oxygen vacancy concentration can improve the response speed (<0.2 s) of the detector. The present studies provide a promising method to obtain the high performances for the X-ray detector based on β-Ga₂O₃ single crystals.

High-energy x-ray radiation effects on the exfoliated quasi-two-dimensional β-Ga2O3 nanoflake field-effect transistors

The effects of x-ray irradiation on the mechanically exfoliated quasi-two-dimensional (quasi-2D) β-Ga₂O₃ nanoflake field-effect transistors (FETs) under the condition of biasing voltage were systematically investigated for the first time. It has been revealed that the device experienced two stages during irradiation. At low ionizing doses (<240 krad), the device performance is mainly influenced by the photo-effect and the subsequent persistent photocurrent (PPC) effect as a result of the pre-existing electron traps (e-trap) in the oxides far away from the SiO₂/β-Ga₂O₃ interface. At larger doses (>240 krad), the device characteristics are dominated by the radiation-induced structural or compositional deterioration. The newly-generated e-traps are found located at the SiO₂/β-Ga₂O₃ interface. This study shed light on the future radiation-tolerant device fabrication process development, paving a way towards the feasibility and practicability of β-Ga₂O₃-based devices in extreme-environment applications.

Polarization detection in deep-ultraviolet light with monoclinic gallium oxide nanobelts

Detection of polarization in deep-ultraviolet (DUV) wavelength is of great importance, especially in secure UV communication. In this paper, we report DUV polarization detectors based on ultra-wide bandgap β-Ga₂O₃ nanobelts, which belong to a monoclinic system with a strong anisotropic lattice structure. Single-crystalline β-Ga₂O₃ nanobelts are synthesized at high-temperature via chemical vapor deposition (CVD). Crystallographic investigation is performed to determine the crystal orientation of the nanobelts, by the combination of selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), crystal modeling and diffraction simulation. The photoresponse to unpolarized DUV light shows a high responsivity of 335 A W^-1 and high sensitivity even to a low illumination power of pW. Strong anisotropy in responsivity and response speed, depending on incident light polarization, is observed. The underlying mechanism is attributed to the combination of internal dichroism and 1D morphology, as indicated by the DFT calculation and FDTD simulation. This work shows a way of DUV polarization detection using CVD grown Ga₂O₃ nanobelts, which could broaden the investigation of the Ga₂O₃ material and DUV photodetection.

Surface/Interface Engineering for Constructing Advanced Nanostructured Photodetectors with Improved Performance: A Brief Review

Semiconductor-based photodetectors (PDs) convert light signals into electrical signals via a photon–matter interaction process, which involves surface/interface carrier generation, separation, and transportation of the photo-induced charge media in the active media, as well as the extraction of these charge carriers to external circuits of the constructed nanostructured photodetector devices. Because of the specific electronic and optoelectronic properties in the low-dimensional devices built with nanomaterial, surface/interface engineering is broadly studied with widespread research on constructing advanced devices with excellent performance. However, there still exist some challenges for the researchers to explore corresponding mechanisms in depth, and the detection sensitivity, response speed, spectral selectivity, signal-to-noise ratio, and stability are much more important factors to judge the performance of PDs. Hence, researchers have proposed several strategies, including modification of light absorption, design of novel PD heterostructures, construction of specific geometries, and adoption of specific electrode configurations to modulate the charge-carrier behaviors and improve the photoelectric performance of related PDs. Here, in this brief review, we would like to introduce and summarize the latest research on enhancing the photoelectric performance of PDs based on the designed structures by considering their surface/interface engineering and how to obtain advanced nanostructured photo-detectors with improved performance, which could be applied to design and fabricate novel low-dimensional PDs with ideal properties in the near future.

Localized surface plasmon enhanced Ga2O3 solar blind photodetectors

Enhancement in the light interaction between plasmonic nanoparticles (NPs) and semiconductors is a promising way to enhance the performance of optoelectronic devices beyond the conventional limit. In this work, we demonstrated improved performance of Ga₂O₃ solar-blind photodetectors (PDs) by the decoration of Rh metal nanoparticles (NPs). Integrated with Rh NPs on oxidized Ga₂O₃ surface, the resultant device exhibits a reduced dark current of about 10 pA, an obvious enhancement in peak responsivity of 2.76 A/W at around 255 nm, relatively fast response and recovery decay times of 1.76 ms/0.80 ms and thus a high detectivity of ∼10¹³ Jones. Simultaneously, the photoresponsivity above 290 nm wavelength decreases significantly with improved rejection ratio between ultraviolet A (UVA) and ultraviolet B (UVB) regions, indicative of enhanced wavelength detecting selectivity. The plasmonic resonance features observed in transmittance spectra are consistent with the finite difference time-domain (FDTD) calculations. This agreement indicates that the enhanced electric field strength induced by the localized surface plasmon resonance is responsible for the enhanced absorption and photoresponsivity. The formed localized Schottky barrier at the interface of Rh/Ga₂O₃ will deplete the carriers at the Ga₂O₃ surface and lead to the remarkable reduced dark current and thus improve the detectivity. These findings provide direct evidence for Rh plasmonic enhancement in solar-blind spectral region, offering an alternative pathway for the rational design of high-performance solar-blind PDs.

Nanoplasmonically Enhanced High-Performance Metastable Phase α-Ga2O3 Solar-Blind Photodetectors

In this work, nanoplasmonically enhanced α-Ga₂O₃ solar-blind photodetectors with an interdigital structure were fabricated on sapphire. By introducing Al nanoparticles (NPs) onto the device surface, the photodetector obtained a significant increase in responsivity at the solar-blind region, and the response peak located at 244 nm reached 3.36 A/W under an applied voltage of 5 V. Compared with the responsivity at 320 nm, the response ratio exceeds 240, demonstrating a superior solar-blind cut-off edge. It also presents that the photocurrent was dramatically increased under 254 nm ultraviolet irradiation for the enhanced device while the dark current remains below 1 pA at 20 V. To explicitly elucidate the enhancement effects by Al NPs under ultraviolet illumination, Kelvin probe force microscopy was employed and directly revealed the physical mechanism of surface plasmon oscillation, which promoted the formation of localized electric fields on α-Ga₂O₃. In addition, we illustrated the effects of interdigital spacing on device performances through experimental measurements and theoretical calculations. These results not only provide direct evidences for Al nanoplasmonic enhancement on the α-Ga₂O₃ device but also facilitate design and fabrication of solar-blind photodetectors.

Enhanced Deep-Ultraviolet Responsivity in Aluminum-Gallium Oxide Photodetectors via Structure Deformation by High-Oxygen-Pressure Pulsed Laser Deposition

Aluminum-gallium oxide (AGO) thin films with wide bandgaps of greater than 5.0 eV were grown using pulsed laser deposition. As evidenced by X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy, the oxygen chamber pressure considerably affected the lattice deformation in the AGO materials. Under high oxygen pressure, the lattice deformation reduced the d-spacing of the AGO(-201) plane. In the measured transmittance spectra of the AGO films, this narrowing of the d-spacing in the main plane manifested as a high-energy shift of the absorption edge. The AGO films were then installed as the active layers in the metal-semiconductor-metal photodetectors (PDs). The lattice deformation was observed to enhance the photocurrent and reduce the dark current of the device. The responsivity was 20.7 times higher in the lattice-deformed AGO-based PD sample than that in the nondeformed sample. It appeared that the lattice deformation induced the separation of the piezopotential, improving the efficiency of the photogenerated carrier recombination and, consequently, shortening the decay time of the photodetector.