Near-Infrared Polarimetric Image Sensors Based on Ordered Sulfur-Passivation GaSb Nanowire Arrays

The near-infrared polarimetric image sensor has a wide range of applications in the military and civilian fields, thus developing into a research hotspot in recent years. Because of their distinguishing 1D structure features, the ordered GaSb nanowire (NW) arrays possess potential applications for near-infrared polarization photodetection. In this work, single-crystalline GaSb NWs are synthesized through a sulfur-catalyzed chemical vapor deposition process. A sulfur-passivation thin layer is formed on the NW surface, which prevents the GaSb NW core from being oxidized. The photodetector based on sulfur-passivation GaSb (S-GaSb) NWs has a lower dark current and higher responsivity than that built with pure GaSb NWs. The photodetector exhibits a large responsivity of 9.39 × 10² A/W and an ultrahigh detectivity of 1.10 × 10¹¹ Jones for 1.55 μm incident light. Furthermore, the dichroic ratio of the device is measured to reach 2.65 for polarized 1.55 μm light. Through a COMSOL simulation, it is elucidated that the origin of the polarized photoresponse is the attenuation of a light electric field inside the NW when the angle of incident polarization light rotates. Moreover, a flexible polarimetric image sensor with 5 × 5 pixels is successfully constructed on the ordered S-GaSb NW arrays, and it exhibits a good imaging ability for incident near-infrared polarization light. These good photoresponse properties and polarized imaging abilities can empower ordered S-GaSb NW arrays with technological potentials in next-generation large-scale near-infrared polarimetric imaging sensors.

Performance enhancement of GaSb vertical nanowire p-type MOSFETs on Si by rapid thermal annealing

GaSb is considered as an attractive p-type channel material for future III-V metal-oxide-semiconductor (MOS) technologies, but the processing conditions to utilize the full device potential such as low power logic applications and RF applications still need attention. In this work, applying rapid thermal annealing (RTA) to nanoscale GaSb vertical nanowire p-type MOS field-effect transistors, we have improved the average peak transconductance (g_m,peak) by 50% among 28 devices and achieved 70μSμm^-1atV_DS = -0.5 V in a device with 200 nm gate length. In addition, a low subthreshold swing down to 144 mV dec^-1as well as an off-current below 5 nAμm^-1which refers to the off-current specification in low-operation-power condition has been obtained. Based on the statistical analysis, the results show a great enhancement in both on- and off-state performance with respect to previous work mainly due to the improved electrostatics and contacts after RTA, leading to a potential in low-power logic applications. We have also examined a short channel device withL_g = 80 nm in RTA, which shows an increasedg_m,peakup to 149μSμm^-1atV_DS = -0.5 V as well as a low on-resistance of 4.7 kΩ·μm. The potential of further enhancement ing_mvia RTA offers a good alternative to obtain high-performance devices for RF applications which have less stringent requirement for off-state performance. Our results indicate that post-fabrication annealing provides a great option to improve the performance of GaSb-based p-type devices with different structures for various applications.

A Review on Thermophotovoltaic Cell and Its Applications in Energy Conversion: Issues and Recommendations

Generally, waste heat is redundantly released into the surrounding by anthropogenic activities without strategized planning. Consequently, urban heat islands and global warming chronically increases over time. Thermophotovoltaic (TPV) systems can be potentially deployed to harvest waste heat and recuperate energy to tackle this global issue with supplementary generation of electrical energy. This paper presents a critical review on two dominant types of semiconductor materials, namely gallium antimonide (GaSb) and indium gallium arsenide (InGaAs), as the potential candidates for TPV cells. The advantages and drawbacks of non-epitaxy and epitaxy growth methods are well-discussed based on different semiconductor materials. In addition, this paper critically examines and summarizes the electrical cell performance of TPV cells made of GaSb, InGaAs and other narrow bandgap semiconductor materials. The cell conversion efficiency improvement in terms of structural design and architectural optimization are also comprehensively analyzed and discussed. Lastly, the practical applications, current issues and challenges of TPV cells are critically reviewed and concluded with recommendations for future research. The highlighted insights of this review will contribute to the increase in effort towards development of future TPV systems with improved cell conversion efficiency.

Theoretical Characterization of GaSb Colloidal Quantum Dots and Their Application to Photocatalytic CO2 Reduction with Water

With a large exciton Bohr radius and a high hole mobility in the bulk, GaSb is an important semiconductor material for technological applications. Here, we present a theoretical investigation into the evolution of some of its most fundamental characteristics at the nanoscale. GaSb emerges as a widely tunable, potentially disruptive new colloidal material with huge potential for application in a wide range of fields.

Formation of a Thin Continuous GaSb Film on Si(001) by Solid Phase Epitaxy

Nanocrystalline GaSb films were grown on Si(001) from the stoichiometric Ga⁻Sb mixture using solid-phase epitaxy at temperatures of 200⁻500 °C. Use of the solid-phase epitaxy method allowed the suppression of Ga surface diffusion and prevention of intense Sb desorption. At the annealing temperature of 300 °C, a 14-nm-thick GaSb film aggregates, while a 20-nm-thick GaSb film remains continuous with a roughness of 1.74 nm. A GaSb film with a thickness of 20 nm consists of crystalline grains with a size of 9⁻16 nm. They were compressed by ~2%. For some GaSb grains, new epitaxial relationships have been found: GaSb ( 111 ) ||Si ( 11 1 ¯ ) and GaSb [ 11 2 ¯ ] ||Si [ 1 1 ¯ 0 ] , GaSb ( 113 ) ||Si ( 11 1 ¯ ) and GaSb [ 1 1 ¯ 0 ] ||Si [ 1 1 ¯ 0 ] , and GaSb ( 11 1 ¯ ) ||Si ( 002 ) and GaSb [ 1 1 ¯ 0 ] ||Si [ 1 1 ¯ 0 ] .

Individual Defects in InAs/InGaAsSb/GaSb Nanowire Tunnel Field-Effect Transistors Operating below 60 mV/decade

Tunneling field-effect transistors (TunnelFET), a leading steep-slope transistor candidate, is still plagued by defect response, and there is a large discrepancy between measured and simulated device performance. In this work, highly scaled InAs/In_xGa_1-xAs_ySb_1-y/GaSb vertical nanowire TunnelFET with ability to operate well below 60 mV/decade at technically relevant currents are fabricated and characterized. The structure, composition, and strain is characterized using transmission electron microscopy with emphasis on the heterojunction. Using Technology Computer Aided Design (TCAD) simulations and Random Telegraph Signal (RTS) noise measurements, effects of different type of defects are studied. The study reveals that the bulk defects have the largest impact on the performance of these devices, although for these highly scaled devices interaction with even few oxide defects can have large impact on the performance. Understanding the contribution by individual defects, as outlined in this letter, is essential to verify the fundamental physics of device operation, and thus imperative for taking the III-V TunnelFETs to the next level.

Nanoporous Structure Formation in GaSb, InSb, and Ge by Ion Beam Irradiation under Controlled Point Defect Creation Conditions

Ion beam irradiation-induced nanoporous structure formation was investigated on GaSb, InSb, and Ge surfaces via controlled point defect creation using a focused ion beam (FIB). ‎This paper compares the nanoporous structure formation under the same extent of point defect creation while changing the accelerating voltage and ion dose. Although the same number of point defects were created in each case, different structures were formed on the different surfaces. The depth direction density of the point defects was an important factor in this trend. The number of point defects required for nanoporous structure formation was 4 × 10²² vacancies/m² at a depth of 18 nm under the surface, based on a comparison of similar nanoporous structure features in GaSb. The nanoporous structure formation by ion beam irradiation on GaSb, InSb, and Ge surfaces was controlled by the number and areal distribution of the created point defects.

High-Mobility GaSb Nanostructures Cointegrated with InAs on Si

GaSb nanostructures integrated on Si substrates are of high interest for p-type transistors and mid-IR photodetectors. Here, we investigate the metalorganic chemical vapor deposition and properties of GaSb nanostructures monolithically integrated onto silicon-on-insulator wafers using template-assisted selective epitaxy. A high degree of morphological control allows for GaSb nanostructures with critical dimensions down to 20 nm. Detailed investigation of growth parameters reveals that the GaSb growth rate is governed by the desorption processes of an Sb surface layer and, in turn, is insensitive to changes in material transport efficiency. The GaSb crystal structure is typically zinc-blende with a low density of rotational twin defects, and even occasional twin-free structures are observed. Hall/van der Pauw measurements are conducted on 20 nm-thick GaSb nanostructures, revealing high hole mobility of 760 cm²/(V s), which matches literature values for high-quality bulk GaSb crystals. Finally, we demonstrate a process that enables cointegration of GaSb and InAs nanostructures in close vicinity on Si, a preferred material combination ideally suited for high-performance complementary III-V metal-oxide-semiconductor technology.

III-V Nanowire Complementary Metal-Oxide Semiconductor Transistors Monolithically Integrated on Si

III-V semiconductors have attractive transport properties suitable for low-power, high-speed complementary metal-oxide-semiconductor (CMOS) implementation, but major challenges related to cointegration of III-V n- and p-type metal-oxide-semiconductor field-effect transistors (MOSFETs) on low-cost Si substrates have so far hindered their use for large scale logic circuits. By using a novel approach to grow both InAs and InAs/GaSb vertical nanowires of equal length simultaneously in one single growth step, we here demonstrate n- and p-type III-V MOSFETs monolithically integrated on a Si substrate with high I(on)/I(off) ratios using a dual channel, single gate-stack design processed simultaneously for both types of transistors. In addition, we demonstrate fundamental CMOS logic gates, such as inverters and NAND gates, which illustrate the viability of our approach for large scale III-V MOSFET circuits on Si.

Electroless Deposition of III-V Semiconductor Nanostructures from Ionic Liquids at Room Temperature

Group III-V semiconductor nanostructures are important materials in optoelectronic devices and are being researched in energy-related fields. A simple approach for the synthesis of these semiconductors with well-defined nanostructures is desired. Electroless deposition (galvanic displacement) is a fast and versatile technique for deposition of one material on another and depends on the redox potentials of the two materials. Herein we show that GaSb can be directly synthesized at room temperature by galvanic displacement of SbCl3 /ionic liquid on electrodeposited Ga, on Ga nanowires, and also on commercial Ga. In situ AFM revealed the galvanic displacement process of Sb on Ga and showed that the displacement process continues even after the formation of GaSb. The bandgap of the deposited GaSb was 0.9±0.1 eV compared to its usual bandgap of 0.7 eV. By changing the cation in the ionic liquid, the redox process could be varied leading to GaSb with different optical properties.

Scanning Tunneling Spectroscopy on InAs-GaSb Esaki Diode Nanowire Devices during Operation

Using a scanning tunneling and atomic force microscope combined with in-vacuum atomic hydrogen cleaning we demonstrate stable scanning tunneling spectroscopy (STS) with nanoscale resolution on electrically active nanowire devices in the common lateral configuration. We use this method to map out the surface density of states on both the GaSb and InAs segments of GaSb-InAs Esaki diodes as well as the transition region between the two segments. Generally the surface shows small bandgaps centered around the Fermi level, which is attributed to a thin multielement surface layer, except in the diode transition region where we observe a sudden broadening of the bandgap. By applying a bias to the nanowire we find that the STS spectra shift according to the local nanoscale potential drop inside the wire. Importantly, this shows that we have a nanoscale probe with which we can infer both surface electronic structure and the local potential inside the nanowire and we can connect this information directly to the performance of the imaged device.

Evolution of morphology and microstructure of GaAs/GaSb nanowire heterostructures

In this paper, we successfully grow GaAs/GaSb core-shell heterostructure nanowires (NWs) by molecular beam epitaxy (MBE). The as-grown GaSb shell layer forms a wurtzite structure instead of the zinc blende structure that has been commonly reported. Meanwhile, a bulgy GaSb nanoplate also appears on top of GaAs/GaSb core-shell NWs and possesses a pure zinc blende phase. The growth mode for core-shell morphology and underlying mechanism for crystal phase selection of GaAs/GaSb nanowire heterostructures are discussed in detail.

Broadband 2.4 μm superluminescent GaInAsSb/AlGaAsSb quantum well diodes for optical sensing of biomolecules

High power, high radiance, broadband light sources emitting in the 2.0-2.5 μm wavelength range are important for optical sensing of biomolecules such as glucose in aqueous solutions. Here we demonstrate and analyze superluminescent diodes with output centered at 2.4 μm (range ~2.2-2.5 μm) from GaInAsSb/AlGaAsSb quantum wells in a separate confinement structure. Pulsed wave output of 1 mW (38 kW/cm2/sr) is achieved at room temperature for 40μm × 2mm devices. Superluminescence is evidenced in superlinear increase in emission, spectral narrowing, and angular narrowing of light output with increasing current injection. Optical output is analyzed and modeled with rate equations. Potential routes for future improvements are explored, such as additional Auger suppression and photonic mode engineering.

Optical Properties of GaSb Nanofibers

Amorphous GaSb nanofibers were obtained by ion beam irradiation of bulk GaSb single-crystal wafers, resulting in fibers with diameters of ~20 nm. The Raman spectra and photoluminescence (PL) of the ion irradiation-induced nanofibers before and after annealing were studied. Results show that the Raman intensity of the GaSb LO phonon mode decreased after ion beam irradiation as a result of the formation of the amorphous nanofibers. A new mode is observed at ~155 cm(-1) both from the unannealed and annealed GaSb nanofiber samples related to the A1g mode of Sb-Sb bond vibration. Room temperature PL measurements of the annealed nanofibers present a wide feature band at ~1.4-1.6 eV. The room temperature PL properties of the irradiated samples presents a large blue shift compared to bulk GaSb. Annealed nanofibers and annealed nanofibers with Au nanodots present two different PL peaks (400 and 540 nm), both of which may originate from Ga or O vacancies in GaO. The enhanced PL and new band characteristics in nanostructured GaSb suggest that the nanostructured fibers may have unique applications in optoelectronic devices.