Rectifying Single GaAsSb Nanowire Devices Based on Self-Induced Compositional Gradients

Sb-saturated high-temperature growth of extended, self-catalyzed GaAsSb nanowires on silicon with high quality

Ternary GaAsSb nanowires (NW) are key materials for integrated high-speed photonic applications on silicon (Si), where homogeneous, high aspect-ratio dimensions and high-quality properties for controlled absorption, mode confinement and waveguiding are much desired. Here, we demonstrate a unique high-temperature (high-T >650 °C) molecular beam epitaxial (MBE) approach to realize self-catalyzed GaAsSb NWs site-selectively on Si with high aspect-ratio and non-tapered morphologies under antimony (Sb)-saturated conditions. While hitherto reported low-moderate temperature growth processes result in early growth termination and inhomogeneous morphologies, the non-tapered nature of NWs under high-T growth is independent of the supply rates of relevant growth species. Analysis of dedicated Ga-flux and growth time series, allows us to pinpoint the microscopic mechanisms responsible for the elimination of tapering, namely concurrent vapor-solid, step-flow growth along NW side-facets enabled by enhanced Ga diffusion under the high-T growth. Performing growth in an Sb-saturated regime, leads to high Sb-content in VLS-GaAsSb NW close to 30% that is independent of Ga-flux. This independence enables multi-step growth via sequentially increased Ga-flux to realize uniform and very long (>7μm) GaAsSb NWs. The excellent properties of these NWs are confirmed by a completely phase-pure, twin-free zincblende (ZB) crystal structure, a homogeneous Sb-content along the VLS-GaAsSb NW growth axis, along with remarkably narrow, single-peak low-temperature photoluminescence linewidth (<15 meV) at wavelengths of ∼1100-1200 nm.

Heterostructure axial GaAsSb ensemble near-infrared p-i-n based axial configured nanowire photodetectors

In this work, we present a systematic design of growth experiments and subsequent characterization of self-catalyzed molecular beam epitaxially grown GaAsSb heterostructure axial p-i-n nanowires (NWs) on p-Si <111> for the ensemble photodetector (PD) application in the near-infrared region. Diverse growth methods have been explored to gain a better insight into mitigating several growth challenges by systematically studying their impact on the NW electrical and optical properties to realize a high-quality p-i-n heterostructure. The successful growth approaches are Te-dopant compensation to suppress the p-type nature of intrinsic GaAsSb segment, growth interruption for strain relaxation at the interface, decreased substrate temperature to enhance supersaturation and minimize the reservoir effect, higher bandgap compositions of the n-segment of the heterostructure relative to the intrinsic region for boosting the absorption, and the high-temperature ultra-high vacuumin situannealing to reduce the parasitic radial overgrowth. The efficacy of these methods is supported by enhanced photoluminescence (PL) emission, suppressed dark current in the heterostructure p-i-n NWs accompanied by increased rectification ratio, photosensitivity, and a reduced low-frequency noise level. The PD fabricated utilizing the optimized GaAsSb axial p-i-n NWs exhibited the longer wavelength cutoff at ∼1.1μm with a significantly higher responsivity of ∼120 A W^-1(@-3 V bias) and a detectivity of 1.1 × 10¹³Jones operating at room temperature. Frequency and the bias independent capacitance in the pico-Farad (pF) range and substantially lower noise level at the reverse biased condition, show the prospects of p-i-n GaAsSb NWs PD for high-speed optoelectronic applications.

Sb-Mediated Tuning of Growth- and Exciton Dynamics in Entirely Catalyst-Free GaAsSb Nanowires

Vapor-liquid-solid (VLS) growth is the mainstream method in realizing advanced semiconductor nanowires (NWs), as widely applied to many III-V compounds. It is exclusively explored also for antimony (Sb) compounds, such as the relevant GaAsSb-based NW materials, although morphological inhomogeneities, phase segregation, and limitations in the supersaturation due to Sb strongly inhibit their growth dynamics. Fundamental advances are now reported here via entirely catalyst-free GaAsSb NWs, where particularly the Sb-mediated effects on the NW growth dynamics and physical properties are investigated in this novel growth regime. Remarkably, depending on GaAsSb composition and nature of the growth surface, both surfactant and anti-surfactant action is found, as seen by transitions between growth acceleration and deceleration characteristics. For threshold Sb-contents up to 3-4%, adatom diffusion lengths are increased ≈sevenfold compared to Sb-free GaAs NWs, evidencing the significant surfactant effect. Furthermore, microstructural analysis reveals unique Sb-mediated transitions in compositional structure, as well as substantial reduction in twin defect density, ≈tenfold over only small compositional range (1.5-6% Sb), exhibiting much larger dynamics as found in VLS-type GaAsSb NWs. The effect of such extended twin-free domains is corroborated by ≈threefold increases in exciton lifetime (≈4.5 ns) due to enlarged electron-hole pair separation in these phase-pure NWs.

GaAs Nanowire Photodetectors Based on Au Nanoparticles Modification

A high-performance GaAs nanowire photodetector was fabricated based on the modification of Au nanoparticles (NPs). Au nanoparticles prepared by thermal evaporation were used to modify the defects on the surface of GaAs nanowires. Plasmons and Schottky barriers were also introduced on the surface of the GaAs nanowires, to enhance their light absorption and promote the separation of carriers inside the GaAs nanowires. The research results show that under the appropriate modification time, the dark current of GaAs nanowire photodetectors was reduced. In addition, photocurrent photodetectors increased from 2.39 × 10^-10 A to 1.26 × 10^-9 A. The responsivity of GaAs nanowire photodetectors correspondingly increased from 0.569 A∙W^-1 to 3.047 A∙W^-1. The reasons for the improvement of the photodetectors' performance after modification were analyzed through the energy band theory model. This work proposes a new method to improve the performance of GaAs nanowire photodetectors.

Passivation efficacy study of Al2O3dielectric on self-catalyzed molecular beam epitaxially grown GaAs1-xSbxnanowires

This work evaluates the passivation efficacy of thermal atomic layer deposited (ALD) Al₂O₃dielectric layer on self-catalyzed GaAs_1-xSb_xnanowires (NWs) grown using molecular beam epitaxy. A detailed assessment of surface chemical composition and optical properties of Al₂O₃passivated NWs with and without prior sulfur treatment were studied and compared to as-grown samples using x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and low-temperature photoluminescence (PL) spectroscopy. The XPS measurements reveal that prior sulfur treatment followed by Al₂O₃ALD deposition abates III-V native oxides from the NW surface. However, the degradation in 4K-PL intensity by an order of magnitude observed for NWs with Al₂O₃shell layer compared to the as-grown NWs, irrespective of prior sulfur treatment, suggests the formation of defect states at the NW/dielectric interface contributing to non-radiative recombination centers. This is corroborated by the Raman spectral broadening of LO and TO Raman modes, increased background scattering, and redshift observed for Al₂O₃deposited NWs relative to the as-grown. Thus, our work seems to indicate the unsuitability of ALD deposited Al₂O₃as a passivation layer for GaAsSb NWs.

Broadband GaAsSb Nanowire Array Photodetectors for Filter-Free Multispectral Imaging

Highly compact, filter-free multispectral photodetectors have important applications in biological imaging, face recognition, and remote sensing. In this work, we demonstrate room-temperature wavelength-selective multipixel photodetectors based on GaAs_0.94Sb_0.06 nanowire arrays grown by metalorganic vapor phase epitaxy, providing more than 10 light detection channels covering both visible and near-infrared ranges without using any optical filters. The nanowire array geometry-related tunable spectral photoresponse has been demonstrated both theoretically and experimentally and shown to be originated from the strong and tunable resonance modes that are supported in the GaAsSb array nanowires. High responsivity and detectivity (up to 44.9 A/W and 1.2 × 10¹² cm √Hz/W at 1 V, respectively) were obtained from the array photodetectors, enabling high-resolution RGB color imaging by applying such a nanowire array based single pixel imager. The results indicate that our filter-free wavelength-selective GaAsSb nanowire array photodetectors are promising candidates for the development of future high-quality multispectral imagers.

Light Absorption in Nanowire Photonic Crystal Slabs and the Physics of Exceptional Points: The Shape Shifter Modes

Semiconductor nanowire arrays have been demonstrated as promising candidates for nanoscale optoelectronics applications due to their high detectivity as well as tunable photoresponse and bandgap over a wide spectral range. In the infrared (IR), where these attributes are more difficult to obtain, nanowires will play a major role in developing practical devices for detection, imaging and energy harvesting. Due to their geometry and periodic nature, vertical nanowire and nanopillar devices naturally lend themselves to waveguide and photonic crystal mode engineering leading to multifunctional materials and devices. In this paper, we computationally develop theoretical basis to enable better understanding of the fundamental electromagnetics, modes and couplings that govern these structures. Tuning the photonic response of a nanowire array is contingent on manipulating electromagnetic power flow through the lossy nanowires, which requires an intimate knowledge of the photonic crystal modes responsible for the power flow. Prior published work on establishing the fundamental physical modes involved has been based either on the modes of individual nanowires or numerically computed modes of 2D photonic crystals. We show that a unified description of the array key electromagnetic modes and their behavior is obtainable by taking into account modal interactions that are governed by the physics of exceptional points. Such models that describe the underlying physics of the photoresponse of nanowire arrays will facilitate the design and optimization of ensembles with requisite performance. Since nanowire arrays represent photonic crystal slabs, the essence of our results is applicable to arbitrary lossy photonic crystals in any frequency range.

High-Performance Room-Temperature UV-IR Photodetector Based on the InAs Nanosheet and Its Wavelength- and Intensity-Dependent Negative Photoconductivity

Low-dimensional narrow-band-gap III-V semiconductors have great potential in high-performance electronics, photonics, and quantum devices. However, high-performance nanoscale infrared photodetectors based on isolated two-dimensional (2D) III-V compound semiconductors are still rare. In this work, we demonstrate a new type of photodetector based on the InAs nanosheet. The photodetector has high optoelectronic response in the ultraviolet-infrared band (325-2100 nm) at room temperature. The high-performance photodetector has very high responsivity (∼1231 A/W), EQE (2.2 × 10⁵ %), and detectivity (5.46 × 10¹⁰ Jones) to 700 nm light at low operating voltage (∼0.1 V). These results indicate that 2D InAs nanosheet devices have great potential in nano-optoelectronic devices and integrated optoelectronic devices. In addition, we observe for the first time that the InAs nanosheet devices have a negative photoconductivity (NPC) that is not only affected by the wavelength but also related to the optical power intensity of the light. After analyzing experimental data, we propose that the origin of the NPC may come from electron trapping, and two competing mechanisms of optical absorption and the photogating effect in the photoelectric response process cause the dependence on the light wavelength and optical power intensity.

Assembling your nanowire: an overview of composition tuning in ternary III-V nanowires

The ability to grow defect-free nanowires in lattice-mismatched material systems and to design their properties has made them ideal candidates for applications in fields as diverse as nanophotonics, nanoelectronics and medicine. After studying nanostructures consisting of elemental and binary compound semiconductors, scientists turned their attention to more complex systems-ternary nanowires. Composition control is key in these nanostructures since it enables bandgap engineering. The use of different combinations of compounds and different growth methods has resulted in numerous investigations. The aim of this review is to present a survey of the material systems studied to date, and to give a brief overview of the issues tackled and the progress achieved in nanowire composition tuning. We focus on ternary III _x III_1-x V nanowires (AlGaAs, AlGaP, AlInP, InGaAs, GaInP and InGaSb) and IIIV _x V_1-x nanowires (InAsP, InAsSb, InPSb, GaAsP, GaAsSb and GaSbP).

A study of n-doping in self-catalyzed GaAsSb nanowires using GaTe dopant source and ensemble nanowire near-infrared photodetector

This work reports a comprehensive investigation of the effect of gallium telluride (GaTe) cell temperature variation (T_GaTe) on the morphological, optical, and electrical properties of doped-GaAsSb nanowires (NWs) grown by Ga-assisted molecular beam epitaxy (MBE). These studies led to an optimum doping temperature of 550 °C for the growth of tellurium (Te)-doped GaAsSb NWs with the best optoelectronic and structural properties. Te incorporation resulted in a decrease in the aspect ratio of the NWs causing an increase in the Raman longitudinal optical/transverse optical vibrational mode intensity ratio, large photoluminescence emission with an exponential decay tail on the high energy side, promoting tunnel-assisted current conduction in ensemble NWs and significant photocurrent enhancement in the single nanowire. A Schottky barrier photodetector (PD) using Te-doped ensemble NWs with broad spectral range and a longer wavelength cutoff at ∼1.2 µm was demonstrated. These PDs exhibited responsivity in the range of 580-620 A W^-1 and detectivity of 1.2-3.8 × 10¹² Jones. The doped GaAsSb NWs have the potential for further improvement, paving the path for high-performance near-infrared (NIR) photodetection applications.

The role of As species in self-catalyzed growth of GaAs and GaAsSb nanowires

Precise control and broad tunability of the growth parameters are essential in engineering the optical and electrical properties of semiconductor nanowires (NWs) to make them suitable for practical applications. To this end, we report the effect of As species, namely As₂ and As₄, on the growth of self-catalyzed GaAs based NWs. The role of As species is further studied in the presence of Te as n-type dopant in GaAs NWs and Sb as an additional group V element to form GaAsSb NWs. Using As₄ enhances the growth of NWs in the axial direction over a wide range of growth parameters and diminishes the tendency of Te and Sb to reduce the NW aspect ratio. By extending the axial growth parameter window, As₄ allows growth of GaAsSb NWs with up to 47% in Sb composition. On the other hand, As₂ favors sidewall growth which enhances the growth in the radial direction. Thus, the selection of As species is critical for tuning not only the NW dimensions, but also the incorporation mechanisms of dopants and ternary elements. Moreover, the commonly observed dependence of twinning on Te and Sb remains unaffected by the As species. By exploiting the extended growth window associated with the use of As_4, enhanced Sb incorporation and optical emission up to 1400 nm wavelength range is demonstrated. This wavelength corresponds to the telecom E-band, which opens new prospects for this NW material system in future telecom applications while simultaneously enabling their integration to the silicon photonics platform.

Recent Progress on the Gold-Free Integration of Ternary III-As Antimonide Nanowires Directly on Silicon

During the last few years, there has been renewed interest in the monolithic integration of gold-free, Ternary III–As Antimonide (III–As–Sb) compound semiconductor materials on complementary metal-oxide-semiconductor (CMOS)—compatible silicon substrate to exploit its scalability, and relative abundance in high-performance and cost-effective integrated circuits based on the well-established technology. Ternary III–As–Sb nanowires (NWs) hold enormous promise for the fabrication of high-performance optoelectronic nanodevices with tunable bandgap. However, the direct epitaxial growth of gold-free ternary III–As–Sb NWs on silicon is extremely challenging, due to the surfactant effect of Sb. This review highlights the recent progress towards the monolithic integration of III–As–Sb NWs on Si. First, a comprehensive and in-depth review of recent progress made in the gold-free growth of III–As–Sb NWs directly on Si is explicated, followed by a detailed description of the root cause of Sb surfactant effect and its influence on the morphology and structural properties of Au-free ternary III–As–Sb NWs. Then, the various strategies that have been successfully deployed for mitigating the Sb surfactant effect for enhanced Sb incorporation are highlighted. Finally, recent advances made in the development of CMOS compatible, Ternary III–As–Sb NWs based, high-performance optoelectronic devices are elucidated.

In situ passivation of GaAsSb nanowires for enhanced infrared photoresponse

Surface passivation of semiconductor nanowires (NWs) is important for their optoelectronic properties and applications. Here, the in situ passivation effect of an epitaxial InP shell and the corresponding photodetector performance is experimentally studied. Compared with the unpassivated GaAs_{1- x} Sb _x core-only NWs, the GaAs_{1- x} Sb _x /InP core/shell NWs have shown much stronger photoluminescence and cathodoluminescence intensities. Correspondingly, the fabricated single GaAs_{1- x} Sb _x /InP core/shell NW photodetector shows a responsivity of 325.1 A W^-1 (@ 1.3 μm and 1.5 V) that is significantly enhanced compared to that of single GaAs_{1- x} Sb _x core-only NW photodetectors (143.5 A W^-1), with a comparable detectivity of 4.7 × 10¹⁰ and 5.3 × 10¹⁰ cm√Hz/W, respectively. This is ascribed to the enhanced carrier mobility and carrier concentration by the in situ passivation, which lead to both higher photoconductivity and dark-conductivity. Our results show that in situ passivation is an effective approach for performance enhancement of GaAs_1-x Sb _x NW based optoelectronic devices.

Review on III-V Semiconductor Single Nanowire-Based Room Temperature Infrared Photodetectors

Recently, III-V semiconductor nanowires have been widely explored as promising candidates for high-performance photodetectors due to their one-dimensional morphology, direct and tunable bandgap, as well as unique optical and electrical properties. Here, the recent development of III-V semiconductor-based single nanowire photodetectors for infrared photodetection is reviewed and compared, including material synthesis, representative types (under different operation principles and novel concepts), and device performance, as well as their challenges and future perspectives.

Space charge limited conduction mechanism in GaAsSb nanowires and the effect of in situ annealing in ultra-high vacuum

In this work, the first observation of the space charge limited conduction mechanism (SCLC) in GaAsSb nanowires (NWs) grown by Ga-assisted molecular beam epitaxial technique, and the effect of ultra-high vacuum in situ annealing have been investigated. The low onset voltage of the SCLC in the NW configuration has been advantageously exploited to extract trap density and trap distribution in the bandgap of this material system, using simple temperature dependent current-voltage measurements in both the ensemble and single nanowires. In situ annealing in ultra-high vacuum revealed significant reduction in the trap density from 10¹⁶ cm^-3 in as-grown NWs to a low level of 7 × 10¹⁴ cm^-3 and confining wider trap distribution to a single trap depth at 0.12 eV. A comparison of current conduction mechanism in the respective single nanowires using conductive atomic force microscopy (C-AFM) further confirms the SCLC mechanism identified in GaAsSb ensemble device to be intrinsic. Higher current observed in current mapping by C-AFM, increased 4 K photoluminescence (PL) intensity along with reduced full-width half maxima and more symmetric PL spectra, and reduced asymmetrical broadening with increased TO/LO mode in room temperature Raman spectra for in situ annealed NWs again attest to effective annihilation of traps leading to the improved optical quality of NWs compared to as-grown NWs. Hence, the I-V-T analysis of the SCLC mechanism has been demonstrated as a simple approach to obtain information on growth induced traps in the NWs.

Vis-IR Wide-Spectrum Photodetector at Room Temperature Based on p-n Junction-Type GaAs1-xSbx/InAs Core-Shell Nanowire

Infrared (IR) detection at room temperature is very important in many fields. Nanoscale wide-spectrum photodetectors covering IR range are still rare, although they are desired in many applications, such as in integrated optoelectronic devices. Here, we report a new kind of photodetector based on p-n heterojunction-type GaAs_1-xSb_x/InAs core-shell nanowires. The photodetectors demonstrate high response to the lights ranging from visible light (488 nm) to short-wavelength IR (1800 nm) at room temperature under a very low bias voltage of 0.3 V. The high performance of the devices includes an ultralow dark current (32 pA at room temperature), a high response speed (0.45 ms) to 633 nm light, high responsivity to 1310 nm telecommunication light (0.12 A/W), high response even to 1800 nm light (on/off ratio of 2.5), etc. Besides, the devices also show excellent rectifying I-V characteristics (the current rectification ratio being ∼178 in a voltage range of ±0.3 V). These results suggest that the GaAs_1-xSb_x/InAs core-shell nanowire devices are promising for applications in nanoelectronic devices, optoelectronic devices, and integrated optoelectronic devices.

Enhanced Photoresponsivity of a GaAs Nanowire Metal-Semiconductor-Metal Photodetector by Adjusting the Fermi Level

Metal-semiconductor-metal (MSM)-structured GaAs-based nanowire photodetectors have been widely reported because they are promising as an alternative for high-performance devices. Owing to the Schottky built-in electric fields in the MSM structure photodetectors, enhancements in photoresponsivity can be realized. Thus, strengthening the built-in electric field is an efficacious way to make the detection capability better. In this study, we fabricate a single GaAs nanowire MSM photodetector with superior performance by doping-adjusting the Fermi level to strengthen the built-in electric field. An outstanding responsivity of 1175 A/W is obtained. This is two orders of magnitude better than the responsivity of the undoped sample. Scanning photocurrent mappings and simulations are performed to confirm that the enhancement in responsivity is because of the increase in the hole Schottky built-in electric field, which can separate and collect the photogenerated carriers more effectively. The eloquent evidence clearly proves that doping-adjusting the Fermi level has great potential applications in high-performance GaAs nanowire photodetectors and other functional photodetectors.

Synthesis and Applications of III-V Nanowires

Low-dimensional semiconductor materials structures, where nanowires are needle-like one-dimensional examples, have developed into one of the most intensely studied fields of science and technology. The subarea described in this review is compound semiconductor nanowires, with the materials covered limited to III-V materials (like GaAs, InAs, GaP, InP,...) and III-nitride materials (GaN, InGaN, AlGaN,...). We review the way in which several innovative synthesis methods constitute the basis for the realization of highly controlled nanowires, and we combine this perspective with one of how the different families of nanowires can contribute to applications. One reason for the very intense research in this field is motivated by what they can offer to main-stream semiconductors, by which ultrahigh performing electronic (e.g., transistors) and photonic (e.g., photovoltaics, photodetectors or LEDs) technologies can be merged with silicon and CMOS. Other important aspects, also covered in the review, deals with synthesis methods that can lead to dramatic reduction of cost of fabrication and opportunities for up-scaling to mass production methods.

Nanowire Electronics: From Nanoscale to Macroscale

Semiconductor nanowires have attracted extensive interest as one of the best-defined classes of nanoscale building blocks for the bottom-up assembly of functional electronic and optoelectronic devices over the past two decades. The article provides a comprehensive review of the continuing efforts in exploring semiconductor nanowires for the assembly of functional nanoscale electronics and macroelectronics. Specifically, we start with a brief overview of the synthetic control of various semiconductor nanowires and nanowire heterostructures with precisely controlled physical dimension, chemical composition, heterostructure interface, and electronic properties to define the material foundation for nanowire electronics. We then summarize a series of assembly strategies developed for creating well-ordered nanowire arrays with controlled spatial position, orientation, and density, which are essential for constructing increasingly complex electronic devices and circuits from synthetic semiconductor nanowires. Next, we review the fundamental electronic properties and various single nanowire transistor concepts. Combining the designable electronic properties and controllable assembly approaches, we then discuss a series of nanoscale devices and integrated circuits assembled from nanowire building blocks, as well as a unique design of solution-processable nanowire thin-film transistors for high-performance large-area flexible electronics. Last, we conclude with a brief perspective on the standing challenges and future opportunities.

Epitaxially grown III-arsenide-antimonide nanowires for optoelectronic applications

Epitaxially grown ternary III-arsenide-antimonide (III-As-Sb) nanowires (NWs) are increasingly attracting attention due to their feasibility as a platform for the integration of largely lattice-mismatched antimonide-based heterostructures while preserving the high crystal quality. This and the inherent bandgap tuning flexibility of III-As-Sb in the near- and mid-infrared wavelength regions are important and auspicious premises for a variety of optoelectronic applications. In this review, we summarize the current understanding of the nucleation, morphology-change and crystal phase evolution of GaAsSb and InAsSb NWs and their characterization, especially in relation to Sb incorporation during growth. By linking these findings to the optical properties in such ternary NWs and their heterostructures, a brief account of the ongoing development of III-As-Sb NW-based photodetectors and light emitters is also given.

Recent advances in Sb-based III-V nanowires

Owing to the high mobility, narrow bandgap, strong spin-orbit coupling and large g-factor, Sb-based III-V nanowires (NWs) attracted significant interests in high speed electronics, long-wavelength photodetectors and quantum superconductivity in the past decade. In this review, we aim to give an integrated summarization about the recent advances in binary as well as ternary Sb-based III-V NWs, starting from the fundamental properties, NWs growth mechanism, typical synthetic methods to their applications in transistors, photodetectors, and Majorana fermions detection. Up to now, famous NWs growth techniques of solid-source chemical vapor deposition (CVD), molecular beam epitaxy, metal organic vapor phase epitaxy and metal organic CVD etc have been adopted and developed for the controllable growth of Sb-based III-V NWs. Several parameters including heating temperature, III/V ratio of source materials, growth temperature, catalyst size and kinds, and growth substrate play important roles on the morphology, position, diameter distribution, growth orientation and crystal phase of Sb-based III-V NWs. Furthermore, we discuss the photoelectrical applications of Sb-based III-V NWs such as field-effect-transistors, tunnel diode, low-power inverter, and infrared detectors etc. Importantly, due to the strongest spin-orbit interaction and giant g-factor among all III-V semiconductors, InSb with the geometry of one-dimension NW is considered as the most promising candidate for the detection of Majorana fermions. In the end, we also summarize the main challenges remaining in the field and put forward some suggestions for the future development of Sb-based III-V NWs.

Improved performance of GaAsSb/AlGaAs nanowire ensemble Schottky barrier based photodetector via in situ annealing

In this work, we report on the p-i GaAsSb/AlGaAs nanowires (NWs) ensemble device exhibiting good spectral response up to 1.1 μm with a high responsivity of 311 A W^-1, an external quantum efficiency of 6.1 × 10⁴%, and a detectivity of 1.9 × 10¹⁰ Jones at 633 nm. The high responsivity of the NWs has been attributed to in situ post-growth annealing of GaAsSb axial NWs in the ultra-high vacuum. The enabling growth technology is molecular beam epitaxy for the Ga-assisted epitaxial growth of these NWs on Si (111) substrates. Room temperature Raman spectra, as well as temperature dependent micro-photoluminescence peak analysis indicated suppression of band tail states and non-radiative channels due to annealing. A similar improvement in in situ annealed p-i GaAsSb NW ensemble with an AlGaAs passivating shell was inferred from a reduction in the Schottky barrier height as well as the NW resistance compared to the as-grown NW ensemble. These results demonstrate in situ annealing of nanowires to be an effective pathway for improving the optoelectronic properties of the NWs and the device thereof.

Optical characteristics of GaAs/GaAsSb/GaAs coaxial single quantum-well nanowires with different Sb components

III–V ternary alloy quantum-wells have become a hot topic in recent years. Especially, GaAs/GaAsSb quantum wells have attracted increasing attention due to their numerous applications in the field of near-infrared optoelectronic devices. With the further reduction of dimensions, GaAs/GaAsSb nanowires show many special properties compared to their quantum well structures. In this work, GaAs/GaAs_1−xSb_x/GaAs coaxial single quantum-well nanowires with different Sb composition were grown by molecular beam epitaxy. The band structure and the optical properties were investigated through power-dependent and temperature-dependent photoluminescence measurement. It has been found that a deeper quantum well is created with the increase of Sb component. Thanks to the deeper quantum well, more effective electron confinement has been realized, the emission from the sample can still be detected up to room temperature. The different trend of peak position and shape at various temperatures also supports the improved temperature stability of the samples. These results will be beneficial for the design of alloy quantum wells, and will facilitate the development of alloy quantum-well based devices.

GaAs/GaAs_1−xSb_x/GaAs coaxial single quantum-well nanowires with larger Sb content result in better electron confinement, which greatly improves their thermal stability.

Low-Dimensional Materials and State-of-the-Art Architectures for Infrared Photodetection

Infrared photodetectors are gaining remarkable interest due to their widespread civil and military applications. Low-dimensional materials such as quantum dots, nanowires, and two-dimensional nanolayers are extensively employed for detecting ultraviolet to infrared lights. Moreover, in conjunction with plasmonic nanostructures and plasmonic waveguides, they exhibit appealing performance for practical applications, including sub-wavelength photon confinement, high response time, and functionalities. In this review, we have discussed recent advances and challenges in the prospective infrared photodetectors fabricated by low-dimensional nanostructured materials. In general, this review systematically summarizes the state-of-the-art device architectures, major developments, and future trends in infrared photodetection.

High-Responsivity Photodetection by a Self-Catalyzed Phase-Pure p-GaAs Nanowire

Defects are detrimental for optoelectronics devices, such as stacking faults can form carrier-transportation barriers, and foreign impurities (Au) with deep-energy levels can form carrier traps and nonradiative recombination centers. Here, self-catalyzed p-type GaAs nanowires (NWs) with a pure zinc blende (ZB) structure are first developed, and then a photodetector made from these NWs is fabricated. Due to the absence of stacking faults and suppression of large amount of defects with deep energy levels, the photodetector exhibits room-temperature high photoresponsivity of 1.45 × 10⁵ A W^-1 and excellent specific detectivity (D*) up to 1.48 × 10¹⁴ Jones for a low-intensity light signal of wavelength 632.8 nm, which outperforms previously reported NW-based photodetectors. These results demonstrate these self-catalyzed pure-ZB GaAs NWs to be promising candidates for optoelectronics applications.

A Two-Step Growth Pathway for High Sb Incorporation in GaAsSb Nanowires in the Telecommunication Wavelength Range

Self-catalyzed growth of axial GaAs_1−xSb_x nanowire (NW) arrays with bandgap tuning corresponding to the telecommunication wavelength of 1.3 µm poses a challenge, as the growth mechanism for axial configuration is primarily thermodynamically driven by the vapor-liquid-solid growth process. A systematic study carried out on the effects of group V/III beam equivalent (BEP) ratios and substrate temperature (T_sub) on the chemical composition in NWs and NW density revealed the efficacy of a two-step growth temperature sequence (initiating the growth at relatively higher T_sub = 620 °C and then continuing the growth at lower T_sub) as a promising approach for obtaining high-density NWs at higher Sb compositions. The dependence of the Sb composition in the NWs on the growth parameters investigated has been explained by an analytical relationship between the effective vapor composition and NW composition using relevant kinetic parameters. A two-step growth approach along with a gradual variation in Ga-BEP for offsetting the consumption of the droplets has been explored to realize long NWs with homogeneous Sb composition up to 34 at.% and photoluminescence emission reaching 1.3 µm at room temperature.

Near Full-Composition-Range High-Quality GaAs1-xSbx Nanowires Grown by Molecular-Beam Epitaxy

Here we report on the Ga self-catalyzed growth of near full-composition-range energy-gap-tunable GaAs_1-xSb_x nanowires by molecular-beam epitaxy. GaAs_1-xSb_x nanowires with different Sb content are systematically grown by tuning the Sb and As fluxes, and the As background. We find that GaAs_1-xSb_x nanowires with low Sb content can be grown directly on Si(111) substrates (0 ≤ x ≤ 0.60) and GaAs nanowire stems (0 ≤ x ≤ 0.50) by tuning the Sb and As fluxes. To obtain GaAs_1-xSb_x nanowires with x ranging from 0.60 to 0.93, we grow the GaAs_1-xSb_x nanowires on GaAs nanowire stems by tuning the As background. Photoluminescence measurements confirm that the emission wavelength of the GaAs_1-xSb_x nanowires is tunable from 844 nm (GaAs) to 1760 nm (GaAs_0.07Sb_0.93). High-resolution transmission electron microscopy images show that the grown GaAs_1-xSb_x nanowires have pure zinc-blende crystal structure. Room-temperature Raman spectra reveal a redshift of the optical phonons in the GaAs_1-xSb_x nanowires with x increasing from 0 to 0.93. Field-effect transistors based on individual GaAs_1-xSb_x nanowires are fabricated, and rectifying behavior is observed in devices with low Sb content, which disappears in devices with high Sb content. The successful growth of high-quality GaAs_1-xSb_x nanowires with near full-range bandgap tuning may speed up the development of high-performance nanowire devices based on such ternaries.

Mapping of the electronic band gap along the axis of a single InAs/InSbxAs1-x heterostructured nanowire

Herein, we report the graded electronic band gap along the axis of individual heterostructured WZ-ZB InAs/InSb_0.12As_0.88 nanowires. Resonance Raman imaging has been exploited to map the axial variation in the second excitation gap energy (E₁) at the high symmetry point (L point) of the Brillouin zone. We relate the origin of the observed evolution of the gap energy to the fine tuning of the alloy composition from the tip towards the interface of the nanowire. The electronic band structures of InAs, InSb and InSb_xAs_1-x alloy systems at x = 0.125, 0.25, 0.50, 0.75 and 0.875, using the all electron density functional theory code Wien2k, are reported. The measured band gap along the axis of the InAs/InSb_0.12As_0.88 nanowire is correlated with the calculated gap energy at the A point and the L point of the Brillouin zone for InAs and InSb_0.125As_0.875, respectively. We draw a one-to-one correspondence between the variation of the E₁ gap and the fundamental E₀ gap in the calculated electronic band structure and propose the graded fundamental gap energy across the axis of the nanowire.

Low frequency noise in single GaAsSb nanowires with self-induced compositional gradients

Due to bandgap tunability, GaAsSb nanowires (NWs) have received a great deal of attention for a variety of optoelectronic device applications. However, electrical and optical properties of GaAsSb are strongly affected by Sb-related defects and scattering from surface states and/or defects, which can limit the performance of GaAsSb NW devices. Thus, in order to utilize the GaAsSb NWs for high performance electronic and optoelectronic devices, it is required to study the material and interface properties (e.g. the interface trap density) in the GaAsSb NW devices. Here, we investigate the low frequency noise in single GaAsSb NWs with self-induced compositional gradients. The current noise spectral density of the GaAsSb NW device showed a typical 1/f noise behavior. The Hooge's noise parameter and the interface trap density of the GaAsSb NW device were found to be ∼2.2 × 10(-2) and ∼2 × 10(12) eV(-1) cm(-2), respectively. By applying low frequency noise measurements, the noise equivalent power, a key figure of merit of photodetectors, was calculated. The observed low frequency noise properties can be useful as guidance for quality and reliability of GaAsSb NW based electronic devices, especially for photodetectors.

An organic-inorganic broadband photodetector based on a single polyaniline nanowire doped with quantum dots

The capability to detect light over a broad waveband is highly important for practical optoelectronic applications and has been achieved with photodetectors of one-dimensional inorganic nanomaterials such as Si, ZnO, and GaN. However, achieving high speed responsivity over an entire waveband within such a photodetector remains a challenge. Here we demonstrate a broadband photodetector using a single polyaniline nanowire doped with quantum dots that is highly responsive over a broadband from 350 to 700 nm. The high responsivity is due to the high density of trapping states at the enormous interfaces between polyaniline and quantum dots. The interface trapping can effectively reduce the recombination rate and enhance the efficiency for light detection. Furthermore, a tunable spectral range can be achieved by size-based spectral tuning of quantum dots. The use of organic-inorganic hybrid polyaniline nanowires in broadband photodetection may offer novel functionalities in optoelectronic devices and circuits.

In Situ Heat-Induced Replacement of GaAs Nanowires by Au

Here we report on the heat-induced solid-state replacement of GaAs by Au in nanowires. Such replacement of semiconductor nanowires by metals is envisioned as a method to achieve well-defined junctions within nanowires. To better understand the mechanisms and dynamics that govern the replacement reaction, we performed in situ heating studies using high-resolution scanning transmission electron microscopy. The dynamic evolution of the phase boundary was investigated, as well as the crystal structure and orientation of the different phases at reaction temperatures. In general, the replacement proceeds one GaAs(111) bilayer at a time, and no fixed epitaxial relation could be found between the two phases. The relative orientation of the phases affects the replacement dynamics and can induce growth twins in the Au nanowire phase. In the case of a limited Au supply, the metal phase can also become liquid.

New Insights into the Origins of Sb-Induced Effects on Self-Catalyzed GaAsSb Nanowire Arrays

Ternary semiconductor nanowire arrays enable scalable fabrication of nano-optoelectronic devices with tunable bandgap. However, the lack of insight into the effects of the incorporation of Vy element results in lack of control on the growth of ternary III-V(1-y)Vy nanowires and hinders the development of high-performance nanowire devices based on such ternaries. Here, we report on the origins of Sb-induced effects affecting the morphology and crystal structure of self-catalyzed GaAsSb nanowire arrays. The nanowire growth by molecular beam epitaxy is changed both kinetically and thermodynamically by the introduction of Sb. An anomalous decrease of the axial growth rate with increased Sb2 flux is found to be due to both the indirect kinetic influence via the Ga adatom diffusion induced catalyst geometry evolution and the direct composition modulation. From the fundamental growth analyses and the crystal phase evolution mechanism proposed in this Letter, the phase transition/stability in catalyst-assisted ternary III-V-V nanowire growth can be well explained. Wavelength tunability with good homogeneity of the optical emission from the self-catalyzed GaAsSb nanowire arrays with high crystal phase purity is demonstrated by only adjusting the Sb2 flux.

Room temperature GaAsSb single nanowire infrared photodetectors

Antimonide-based ternary III-V nanowires (NWs) allow for a tunable bandgap over a wide range, which is highly interesting for optoelectronics applications, and in particular for infrared photodetection. Here we demonstrate room temperature operation of GaAs0.56Sb0.44 NW infrared photodetectors grown by metal organic vapor phase epitaxy. These GaAs0.56Sb0.44 NWs have uniform axial composition and show p-type conductivity with a peak field-effect mobility of ∼12 cm(2) V(-1) s(-1)). Under light illumination, single GaAs0.56Sb0.44 NW photodetectors exhibited typical photoconductor behavior with an increased photocurrent observed with the increase of temperature owing to thermal activation of carrier trap states. A broadband infrared photoresponse with a long wavelength cutoff at ∼1.66 μm was obtained at room temperature. At a low operating bias voltage of 0.15 V a responsivity of 2.37 (1.44) A/W with corresponding detectivity of 1.08 × 10(9) (6.55 × 10(8)) cm√Hz/W were achieved at the wavelength of 1.3 (1.55) μm, indicating that ternary GaAs0.56Sb0.44 NWs are promising photodetector candidates for small footprint integrated optical telecommunication systems.