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

Self-Assembled BiGaSeAs Composite Superlattice-Structured Nanowire for Broad-Band Photodetection

Photodetectors with a broad-band response range are widely used in many fields and are regarded as pivotal components of the modern miniaturized electronics industry. However, commercial broad-band photodetectors composed of traditional bulk semiconductor materials are still limited by complex preparation techniques, high costs, and a lack of mechanical strength and flexibility, which are difficult to satisfy the increasing demand for flexible and wearable optoelectronics. Therefore, researchers have been devoted to finding new strategies to obtain flexible, stable, and high-performance broad-band photodetectors. In this work, a novel self-assembled BiGaSeAs composite superlattice-structured nanowire was developed with a simple chemical vapor deposition method for easy fabrication. After the device assembling, the photodetector showed outstanding performance in terms of obvious Ion/Ioff (13.9), broad-band photoresponse (365-940 nm), excellent responsivity (1007.67 A/W), high detectivity (9.38 × 109 Jones), and rapid response (21 and 23 ms). The formation of microheterojunctions among various materials inside the nanowires also contributed to their extended broad-spectrum response and outstanding detection ability. These results indicate that the BiGaSeAs nanowires have potential applications in the field of flexible and wearable electronics.

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.

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.

Controlling the morphology and wavelength of self-assembled coaxial GaAs/Ga(As)Sb/GaAs single quantum-well nanowires

Antimonide-based ternary III-V nanowires (NWs) provide a tunable bandgap over a wide range, and the GaAsSb material system has prospective applications in the 1.3-1.55 μm spectral range of optical communications. In this paper, GaAs/Ga(As)Sb/GaAs single quantum well (SQW) NWs were grown on Si(111) substrates by molecular beam epitaxy (MBE). In addition, the morphologies and tunable wavelengths of the GaAs/Ga(As)Sb/GaAs SQWs were adjusted by interrupting the Ga droplets and changing the growth temperatures and V/III ratios. The four morphologies of the GaAs/Ga(As)Sb/GaAs SQW NWs were observed by scanning electron microscopy (SEM). The microscale lattice structure related to the incorporation of Sb in GaAs/Ga(As)Sb/GaAs SQWs was studied by Raman spectroscopy. The crystal quality of the GaAs/Ga(As)Sb/GaAs SQW NWs was researched by X-ray diffraction (XRD) and transmission electron microscopy (TEM). In addition, the optical properties of the GaAs/Ga(As)Sb/GaAs SQWs were investigated by photoluminescence (PL) spectroscopy. The PL spectra showed the peak emission wavelength range of ∼818 nm (GaAs) to ∼1628 nm (GaSb) at 10 K. This study provides an approach to enhance the effective control of the morphology, structure and wavelength of quantum well or core-shell NWs.

Atomic-Scale Observation of Unusual Dislocations in GaAs-GaAsSb Heterostructured Nanowires

Cognizing the structural characteristics of a heterointerface is significant to understand the growth mechanism of heterostructured nanowires. Here, the structural characteristics of a heterointerface in GaAs-GaAsSb heterostructured nanowires were investigated by employing spherical aberration (C_S)-corrected transmission electron microscopy (TEM). It is found that some unusual dislocations are formed at the heterointerface, leading to the bending of nanowires. Further, the atomically inhomogeneous distribution of Sb content near the heterointerface is revealed, which is responsible for the formation of dislocations. By applying a thermal electric system equipped in the Cs-corrected TEM, a direct observation of structural evolution at the heterointerface was enabled and the stability of GaAs-GaAsSb heterostructured nanowires was evaluated. In situ high-resolution TEM imaging indicates that the destabilization of the heterointerface occurs during nanowire annealing. This study builds a direct correlation between the nanowire heterointerfacial structure with nanowire growth behavior and its stability, which is of importance for heterostructured nanowire design for practical use.

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.

Growth dynamics and compositional structure in periodic InAsSb nanowire arrays on Si (111) grown by selective area molecular beam epitaxy

We report a comprehensive study of the growth dynamics in highly periodic, composition tunable InAsSb nanowire (NW) arrays using catalyst-free selective area molecular beam epitaxy. Employing periodically patterned SiO₂-masks on Si (111) with various mask opening sizes (20-150 nm) and pitches (0.25-2 μm), high NW yield of >90% (irrespective of the InAsSb alloy composition) is realized by the creation of an As-terminated 1 × 1-Si(111) surface prior to NW nucleation. While the NW aspect ratio decreases continually with increasing Sb content (x _Sb from 0% to 30%), we find a remarkable dependence of the aspect ratio on the mask opening size yielding up to ∼8-fold increase for openings decreasing from 150 to 20 nm. The effects of the interwire separation (pitch) on the NW aspect ratio are strongest for pure InAs NWs and gradually vanish for increasing Sb content, suggesting that growth of InAsSb NW arrays is governed by an In surface diffusion limited regime even for the smallest investigated pitches. Compositional analysis using high-resolution x-ray diffraction reveals a substantial impact of the pitch on the alloy composition in homogeneous InAsSb NW arrays, leading to much larger x _Sb as the pitch increases due to decreasing competition for Sb adatoms. Scanning transmission electron microscopy and associated energy-dispersive x-ray spectroscopy performed on the cross-sections of individual NWs reveal an interesting growth-axis dependent core-shell like structure with a discontinuous few-nm thick Sb-deficient coaxial boundary layer and six Sb-deficient corner bands. Further analysis evidences the presence of a nanoscale facet at the truncation of the (111)B growth front and {1-10} sidewall surfaces that is found responsible for the formation of the characteristic core-shell structure.

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).

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.

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.

Modeling selective-area growth of InAsSb nanowires

An analytical growth model is presented to explain the influence of antimony fractional flux on the morphology evolution of catalyst-free InAs_1-x Sb _x semiconductor nanowires grown by the selective-area vapor-solid mechanism on a Si (111) substrate by molecular beam epitaxy. Increasing Sb fractional flux promoted radial growth and suppressed axial growth, resulting in 'nano-disks'. This behavior is explained by a model of indium adatom diffusion along nanowire facets.

Molecular beam epitaxial growth of GaAsSb/GaAsSbN/GaAlAs core-multishell nanowires for near-infrared applications

We report on the bandgap engineering of the GaAsSb/GaAsSbN heterostructured nanowires (NWs) in the core-shell architecture using the unique properties of dilute nitride material system for near-infrared photodetection. A high density of vertical GaAsSb/GaAsSb(N)/GaAlAs core-multishell configured NWs with well faceted, smooth surface morphology has been grown on Si (111) substrates using Ga-assisted molecular beam epitaxy. A low Sb content GaAsSb core has been shown to enable the coherently strained growth of dilute nitride shell with higher Sb content in GaAsSbN shell NWs. A systematic study of N and V/III beam equivalent pressure ratios is carried out to achieve the large band-gap reduction, while successfully incorporating higher Sb content in the dilute nitride shells (GaAs_1-x Sb _x N; x = 0.27). The incorporation of N acts to relieve strain and provide a smooth surface morphology as well as redshift the 4K photoluminescence (PL) peak energy by ∼160 meV in comparison to a non-nitride shell. The selected area diffraction pattern confirms zinc-blende structure in all the NWs and did not show any noticeable planar defects in dilute nitride NWs. We successfully, thus demonstrate GaAsSb/GaAsSbN/GaAlAs core-shell NWs by engineering the lattice strain of nitride shell with the non-nitride ternary core, for extending the 4K photoemission up to 1.43 μm.

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.

Recent advances in III-Sb nanowires: from synthesis to applications

The excellent properties of III-V semiconductors make them intriguing candidates for next-generation electronics and optoelectronics. Their nanowire (NW) counterparts further provide interesting geometry and a quantum confinement effect which benefits various applications. Among the many members of all the III-V semiconductors, III-antimonide NWs have attracted significant research interest due to their narrow, direct bandgap and high carrier mobility. However, due to the difficulty of NW fabrication, the development of III-antimonide NWs and their corresponding applications are always a step behind the other III-V semiconductors. Until recent years, because of advances in understanding and fabrication techniques, electronic and optoelectronic devices based on III-antimonide NWs with novel performance have been fabricated. In this review, we will focus on the development of the synthesis of III-antimonide NWs using different techniques and strategies for fine-tuning the crystal structure and composition as well as fabricating their corresponding heterostructures. With such development, the recent progress in the applications of III-antimonide NWs in electronics and optoelectronics is also surveyed. All these discussions provide valuable guidelines for the design of III-antimonide NWs for next-generation device utilization.

Suppression of axial growth by boron incorporation in GaAs nanowires grown by self-catalyzed molecular beam epitaxy

The addition of boron to GaAs nanowires grown by self-catalyzed molecular beam epitaxy was found to have a strong effect on the nanowire morphology, with axial growth greatly reduced as the nominal boron concentration was increased. Transmission electron microscopy measurements show that the Ga catalyst droplet was unintentionally consumed during growth. Concurrent radial growth, a rough surface morphology and tapering of nanowires grown under boron flux suggest that this droplet consumption is due to reduced Ga adatom diffusion on the nanowire sidewalls in the presence of boron. Modelling of the nanowire growth puts the diffusion length of Ga adatoms under boron flux at around 700-1000 nm. Analyses of the nanowire surfaces show regions of high boron concentration, indicating the surfactant nature of boron in GaAs.

Single-Mode Near-Infrared Lasing in a GaAsSb-Based Nanowire Superlattice at Room Temperature

Semiconductor nanowire lasers can produce guided coherent light emission with miniaturized geometry, bringing about new possibilities for a variety of applications including nanophotonic circuits, optical sensing, and on-chip and chip-to-chip optical communications. Here, we report on the realization of single-mode and room-temperature lasing from 890 to 990 nm, utilizing a novel design of single nanowires with GaAsSb-based multiple axial superlattices as a gain medium under optical pumping. The control of lasing wavelength via compositional tuning with excellent room-temperature lasing performance is shown to result from the unique nanowire structure with efficient gain material, which delivers a low lasing threshold of ∼6 kW/cm² (75 μJ/cm² per pulse), a lasing quality factor as high as 1250, and a high characteristic temperature of ∼129 K. These results present a major advancement for the design and synthesis of nanowire laser structures, which can pave the way toward future nanoscale integrated optoelectronic systems with superior performance.

Semiconductor Solid-Solution Nanostructures: Synthesis, Property Tailoring, and Applications

The innovation of band-gap engineering in advanced materials caused by the alloying of different semiconductors into solid-solution nanostructures provides numerous opportunities and advantages in optoelectronic property tailoring. The semiconductor solid-solution nanostructures have multifarious emission wavelength, adjustability of absorption edge, tunable electrical resistivity, and cutting-edge photoredox capability, and these advantages can be rationalized by the assorted synthesis strategies such as, binary, ternary, and quaternary solid-solutions. In addition, the abundance of elements in groups IIB, IIIA, VA, VIA, and VIIA provides sufficient room to tailor-make the semiconductor solid-solution nanostructures with the desired properties. Recent progress of semiconductor solid-solution nanostructures including synthesis strategies, structure and composition design, band-gap engineering related to the optical and electrical properties, and their applications in different fields is comprehensively reviewed. The classification, formation principle, synthesis routes, and the advantage of semiconductor solid-solution nanostructures are systematically reviewed. Moreover, the challenges faced in this area and the future prospects are discussed. By combining the information together, it is strongly anticipated that this Review may shed new light on understanding semiconductor solid-solution nanostructures while expected to have continuous breakthroughs in band-gap engineering and advanced optoelectronic nanodevices.

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.

Selective-Area MOCVD Growth and Carrier-Transport-Type Control of InAs(Sb)/GaSb Core-Shell Nanowires

We report the first selective-area growth of high quality InAs(Sb)/GaSb core-shell nanowires on Si substrates using metal-organic chemical vapor deposition (MOCVD) without foreign catalysts. Transmission electron microscopy (TEM) analysis reveals that the overgrowth of the GaSb shell is highly uniform and coherent with the InAs(Sb) core without any misfit dislocations. To control the structural properties and reduce the planar defect density in the self-catalyzed InAs core nanowires, a trace amount of Sb was introduced during their growth. As the Sb content increases from 0 to 9.4%, the crystal structure of the nanowires changes from a mixed wurtzite (WZ)/zinc-blende (ZB) structure to a perfect ZB phase. Electrical measurements reveal that both the n-type InAsSb core and p-type GaSb shell can work as active carrier transport channels, and the transport type of core-shell nanowires can be tuned by the GaSb shell thickness and back-gate voltage. This study furthers our understanding of the Sb-induced crystal-phase control of nanowires. Furthermore, the high quality InAs(Sb)/GaSb core-shell nanowire arrays obtained here pave the foundation for the fabrication of the vertical nanowire-based devices on a large scale and for the study of fundamental quantum physics.

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.