Bulk GaSb Research Articles

Research on wet etching techniques for very long-wavelength InAs/GaSb superlattices

Manufacturing high-quality very long-wavelength infrared detectors (VLWIR) on GaSb substrate is significant for advancing the superlattices application in the field of infrared detection. In this study, superlattices with excellent surface and crystal quality were obtained. Based on it, we delved into the wet chemical etching fabrication for very long-wavelength InAs/GaSb superlattices. The impact of varying concentrations of different components on surface etching results along the growth direction was examined through univariate experiments. The analysis revealed that the concentration and ratios of phosphoric acid and hydrogen peroxide notably dictated both the etching rate and surface roughness. The surface chemistry of GaSb and InAs bulk materials treated with various etching solution components was investigated using X-ray photoelectron spectroscopy (XPS). The objective of this study is to provide a comprehensive understanding of the effects caused by different components in wet etching, thereby enhancing the understanding of the wet etching process for InAs/GaSb materials.

Ion track formation and porosity in InSb induced by swift heavy ion irradiation

Ion track formation, irradiation-induced damage (amorphization), and the formation of porosity in InSb after 185 MeV 197Au swift heavy ion irradiation are studied as a function of ion fluence and irradiation angle. Rutherford backscattering spectrometry in channeling geometry reveals an ion track radius of about 16 nm for irradiation normal to the surface and 21 nm for off-normal irradiation at 30° and 60°. Cross-sectional scanning electron microscopy shows significant porosity that increases when irradiation was performed off-normal to the surface. Off-normal irradiation shows a preferential orientation of the pores at about 45° relative to the surface normal. Moreover, when subjected to identical conditions, InSb samples demonstrate notably higher swelling compared to GaSb bulk samples.

Characterization of the quenched GaSb–MnSb composites with high fraction of the ferromagnetic component

In this work, we studied properties of the GaSb–MnSb composite (30 mol.% GaSb ＋ 70 mol.% MnSb), synthesized from a melt of elemental precursors and subjected to the post-growth quenching procedure. We used a combination of experimental methods to specify phase composition of studied systems and elemental composition of each phase. Presented results suggest that studied composites can be considered as an ensemble of large ferromagnetic MnSb inclusions (with sizes of order of 10 μm) embedded in GaSb matrix with small amount of diluted Mn atoms in it. We show that magnetic and magnetooptical properties of composites are primarily defined by the MnSb phase. However, transport and magnetotransport properties of GaSb-MnSb samples depends on both components. In general, low temperature magnetotransport is dominated by the contribution of the GaSb matrix, while at room temperature measured data are qualitatively similar to those for pristine MnSb polycrystals. Additive character of these contributions along with the absence of any magnetooptical response besides that characteristic for bulk MnSb polycrystals suggests that these composites do not contain any considerable fraction of nm-sized ferromagnetic inclusions. Nevertheless, our results suggests that bulk GaSb–MnSb nanocomposite can be obtained, e.g. by more aggressive quenching.

Electronic and optical properties of InAs/InAs0.625Sb0.375 superlattices and their application for far-infrared detectors

We calculate the electronic and optical properties of InAs/InAs0.625Sb0.375 superlattices (SLs) within relativistic density functional theory. To have a good description of the electronic and optical properties, the modified Becke–Johnson exchange-correlation functional is employed to describe the band gaps correctly. First, we analyze the electronic and optical characteristics of bulk InAs and InSb, and then we investigate the InAs/InAs0.625Sb0.375 SL. The optical gaps deduced from the imaginary part of the dielectric function are associated with the characteristic interband transitions. We investigate the electronic and optical properties of the InAs/InAs0.625Sb0.375 SL with three lattice constants of the bulk InAs, GaSb and AlSb, respectively. It is observed that the electronic and optical properties strongly depend on the lattice constant. Our results support the presence of two heavy-hole bands with increasing in-plane effective mass as we go far from the Fermi level. We notice a considerable decrease in the energy gaps and the effective masses of the heavy-holes in the k x –k y plane compared to the bulk phases of the parent compounds. We demonstrate that the electrons are s-orbitals delocalized in the entire SL, while the holes have mainly p-Sb character localized in the In(As,Sb) side of the SL. In the SL, the low-frequency absorption spectra greatly increase when the electric field is polarized orthogonal to the growth axis allowing the applicability of III–V compounds for the long-wavelength infrared detectors.

Explore the correlation between intervalley scattering and phonon bottleneck effect on the hot carrier relaxation in bulk GaSb and InN for hot carrier solar cells

Slowed carrier intervalley scattering (IVS) may trap some photo-excited carriers within side valleys and reduce the overall thermalization rate. On the other hand, the thermalization rate could also be significantly retarded within the gamma valley by slowing the Klemens decay due to a large phononic bandgap via the phonon bottleneck effect (PBE). However, the correlation between IVS and PBE on slowing the carrier relaxation rate is still unclear. Herein, high-quality bulk InN and GaSb with similar electronic bandgap but remarkably different phononic structures are studied to clarify the above correlation through picosecond time-resolved photoluminescence. The occurrence of IVS is controlled by using different pump energies at high carrier density (∼1019 cm−3). The relaxations of carriers excited at the band edge just above and far above the side valley threshold are, therefore, studied in GaSb. It shows that the effective hot carrier lifetime (τ1) of GaSb gets significantly extended with higher pump energy mainly due to more carriers being trapped in side valleys through IVS. Nevertheless, the longest τ1 of GaSb is still shorter than the shortest τ1 of InN with a more polar nature and larger phononic bandgap. This implies that PBE plays a more decisive role in retarding Γ valley carrier relaxation than the slowed IVS. It indicates that the large phononic bandgap and Fröhlich coupling constant are keys to the slow thermalization rate if the Fröhlich interaction dominates. If the deformation potential interaction dominates this process, then low side valley threshold energy and the Fröhlich constant determine the reduction of the overall thermalization rate.

Growth and photo-electronic characteristics of short/mid wave dual-band infrared detectors based on GaSb bulk and InAs/GaSb superlattices

In this paper, we demonstrate a bias-selective short/mid wave dual-band infrared detector based on GaSb bulk materials and InAs/GaSb type-II superlattices with 50% cutoff wavelengths of 1.55 μm and 4.62 μm, respectively. At 77 K, the short wave channel exhibited a peak quantum efficiency of 35.86% at 1.43μm and a dark current density of 8.41 × 10−5A/cm2 under the forward 5.0 V bias, thereby providing a Johnson-noise-limited detectivity of 7.63 × 1011cm · Hz1/2/W. The mid-wave channel showed a quantum efficiency of 10.45% at 4.0μm and dark current density of 4.17 × 10−3A/cm2 under -1.35 V bias, resulting in a detectivity of4.05 × 1010cm · Hz1/2/W. The cross-talk was very low in the short wave channel, but existed in the mid wave channel originated from the contribution of the residual built-in electric field in the short wave channel. Furthermore, the schematic band alignment of N-I-P-P-I-N back-to-back structure was also discussed for further optimization.

Experimental and Simulation Analysis of Thermal Vertical Directional Solidification Grown Ni Doped Gasb

Due to high hole mobility, p-GaSb is an attractive III-V semiconducting material for high performance p-channel metal-oxide semiconductor field effect transistor (p-MOSFET). For that growth of undoped and Ni doped GaSb bulk crystal by thermal vertical directional solidification technique has been reported in this paper. X-ray diffraction (XRD) analysis confirms that the both grown compounds are polycrystalline in nature which have been supported by scanning electron microscope (SEM) image. The carrier charge density and mobility were measured by Hall Effect measurement in the temperature range 78K and 300K. From the sign of Hall co-efficient the both grown materials were confirmed p-type. The Current-Voltage (I-V) characteristic was studied for both the sample i.e. experimentally grown and also simulated using TCAD at 78K and 300K. The temperature dependence of the hole mobility were also investigated by TCAD tool using the models Auger recombination, Shockley-Read-Hall (SRH) and Band-gap narrowing (BGN). Comparison of experimental and simulated temperature dependencies of mobility shows good agreement, while their differences at some points suggests the contribution of compensating impurities.

Experimental and Simulation Analysis of Thermal Vertical Directional Solidification Grown Ni Doped Bulk GASB

Due to high hole mobility, p-GaSb is an attractive III-V semiconducting material for high performance p-channel metal-oxide semiconductor field effect transistor (p-MOSFET). For that growth of undoped and Ni doped GaSb bulk crystal by thermal vertical directional solidification has been reported in this paper. Both structural and electrical characterization was carried out for both the samples. X-ray diffraction (XRD) analysis confirms that the compound grown is polycrystalline in nature which has been supported by scanning electron microscope (SEM) image. The carrier charge density and mobility were measured by Hall Effect measurement in the temperature range 78K and 300K. From the sign of Hall co-efficient the grown material was confirmed p-type. The Current-Voltage (I-V) characteristic was studied for the sample i.e. experimentally grown and also simulated using TCAD at 78K and 300K. The temperature dependence of the hole mobility were also investigated by TCAD tool using the models Auger recombination, Shockley-Read-Hall (SRH) and Band-gap narrowing (BGN). Comparison of experimental and simulated temperature dependencies of mobility shows good agreement, while their difference at some points suggests the contribution of compensating impurities.

Fabrication and characterization of n-ZnO/p-GaSb heterojunction diode

PurposeThe purpose of this paper is to examine the growth and characterization of the two different compound semiconductors, namely, n-zinc oxide (ZnO) and p-gallium antimonide (GaSb). In this paper, fabrication and characterization of n-ZnO/p-GaSb heterojunction diode is analyzed.Design/methodology/approachThermo vertical direction solidification (TVDS) method was used to synthesize undoped GaSb ingot from high purity Ga (5N) and Sb (4N) host materials. Thermal evaporation technique is used to prepare a film of GaSb on glass substrate from the pre-synthesized bulk material by TVDS method. Undoped ZnO film was grown on GaSb film by sol–gel method by using chemical wet and dry (CWD) technique to fabricate n-ZnO/p-GaSb heterojunction diode.FindingsThe formation of crystalline structure and surface morphological analysis of both the GaSb bulk and film have been carried out by x-ray diffraction (XRD) analysis and scanning electron microscopy analysis. From the XRD studies, the structural characterization and phase identification of ZnO/GaSb interface. The current–voltage characteristic of the n-ZnO/p-GaSb heterostructure is found to be rectifying in nature.Originality/valueGaSb film growth on any substrate by thermal evaporation method taking a small piece of the sample from the pre-synthesized GaSb bulk ingot has not been reported yet. Semiconductor device with heterojunction diode by using two different semiconductors such as ZnO/GaSb was used by this group for the first time.

Crystalline GaSb-core optical fibers with room-temperature photoluminescence

Glass-clad, GaSb-core fibers were drawn and subsequently laser annealed. The as-drawn fibers were found to be polycrystalline, possess Sb inclusions, and have oxide contamination concentrations of less than 3 at%. Melting and resolidifying regions in the cores using 10.6 µm CO2 laser radiation yielded single crystalline zones with enhanced photoluminescence (PL), including the first observation of strong room temperature PL from a crystalline core fiber. Annealed fibers show low values of tensile strain and a bandgap close to that of bulk GaSb.

ICP etching for InAs-based InAs/GaAsSb superlattice long wavelength infrared detectors

In this work, we study and report the dry etching processes for InAs-based InAs/GaAsSb strain-free superlattice long wavelength infrared (LWIR) detectors. The proper etching parameters were first obtained through the parametric studies of Inductively Coupled Plasma (ICP) etching of both InAs and GaSb bulk materials in Cl2/N2 plasmas. Then an InAs-based InAs/GaAsSb superlattice LWIR detector with PπN structure was fabricated by using the optimized etching parameters. At 80 K, the detector exhibits a 100% cut-off wavelength of 12 μm and a responsivity of 1.5 A/W. Moreover, the dark current density of the device under a bias of −200 mV reaches 5.5 × 10−4 A/cm2, and the R0A is 15 Ω cm2. Our results pave the way towards InAs-based superlattice LWIR detectors with better performances.

Surface structure for manipulating the near-field spectral radiative transfer of thermophotovoltaics

To improve the efficiency and output power of the nano-gap thermophotovoltaic (TPV) power generation system, surface rectangular grating structures are added to the top surface of the group Ⅲ-V semiconductor cell to control the spectrum of near-field radiative transfer. Doped zinc oxide that supports surface waves at near-infrared wavelengths is selected as the TPV emitter. When paired with GaSb grating structures, the surface plasmon polariton excited by the emitter and the light trapping effect by the grating tunnels will be coupled, which results in a significantly and selectively enhanced near-field radiative heat flux within a narrow spectral region above the cell bandgap, thereby fulfilling the design purpose. This physical mechanism is explained by a direct finite-difference time-domain (FDTD) simulation based on the Langevin approach. The material volume meshgrids filled with random dipole sources can act as the thermal emission source and the radiative heat flux is calculated by solving the Maxwell equations numerically. The spectral results show that adding rectangular grating structures to GaSb not only increases radiative transfer in the expected wavelength region over the unstructured case, resulting in a heat flux surpassing that of a far-field blackbody source at the same temperature, but also suppresses the unwanted long-wavelength heat flux that causes radiative loss and cell heating. With a vacuum gap of 200 nm between the emitter and the cell, using a bulk GaSb cell with rectangular gratings can double the spectral flux of the blackbody emitter case, and using an ultrathin GaSb cell with surface structures and back reflectors further increases this ratio to 2.84 due to the total internal reflection controlled by the cell thickness. The amplitude and wavelength of the spectral peak are controlled by the grating size parameters. Low filling ratio gratings with lower-aspect-ratio grating channels generally have sharper enhancement peaks but lower total radiative heat flux, while high filling ratio structures with higher-aspect-ratio channels have better heat flux improvement but might also result in lower conversion efficiency due to the broader spectrum. The rigorous approach reveals the detailed physical mechanism that is otherwise unseen with effective medium approaches for inhomogeneous structures or the Derjaguin proximity approximation. Overall the results of this study enable an enhancement of near-field radiative heat flux limited within a narrow wavelength range shorter than the cell bandgap, offering practical benefit to the application of TPV power generation with higher feasible power and conversion efficiency.

Electrical and optical property of annealed Te-doped GaSb**Project supported by the National Natural Science Foundation of China (Nos. 61474104, 61504131).

GaSb is the most suitable substrate in the epitaxial growth of mixed semiconductors of GaSb system. In this work, Te-doped GaSb bulk crystals with different doping concentration have been annealed at 550 °C for 100 h in ambient antimony. The annealed samples have been studied by Hall effect measurement, infrared (IR) optical transmission, Glow discharge mass spectroscopy (GDMS) and photoluminescence (PL) spectroscopy. After annealing, Te-doped GaSb samples exhibit a decrease of carrier concentration and increase of mobility, along with an improvement of below gap IR transmission. Native acceptor related electrical compensation analysis suggests a formation of donor defect with deeper energy level. The mechanism of the variation of the defect and its influence on the material properties are discussed.

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.

Room temperature operation of GaSb-based resonant tunneling diodes by prewell injection

We present room temperature resonant tunneling of GaSb/AlAsSb double barrier resonant tunneling diodes with pseudomorphically grown prewell emitter structures comprising the ternary compound semiconductors GaInSb and GaAsSb. At room temperature, resonant tunneling is absent for diode structures without prewell emitters. The incorporation of Ga0.84In0.16Sb and GaAs0.05Sb0.95 prewell emitters leads to room temperature resonant tunneling with peak-to-valley current ratios of 1.45 and 1.36, respectively. The room temperature operation is attributed to the enhanced Γ-L-valley energy separation and consequently depopulation of L-valley states in the conduction band of the ternary compound emitter prewell with respect to bulk GaSb.

A designing principle for low dark-current strained layer superlattices

A systematic study of native point defect states is carried out to understand the origin of gap states in strained layer superlattices. Using a combination of first principles Hamiltonian, tight-binding Hamiltonian, and Green's function approach, we calculate the native point defect states in bulk InAs, bulk GaSb, and ten InAs-GaSb strained layer superlattices. We observe that the defects in strained layer superlattices located away from the interface create fewer mid gap states if the constituent bulk materials do not have defect states in that energy interval. This can be used as a design principle to shift the superlattice band gap and reduce or eliminate the mid-gap states.

Correlating optical infrared and electronic properties of low tellurium doped GaSb bulk crystals

Control over the Te doping concentration is especially challenging in the mass-production of optically transparent, high-resistivity Te-doped GaSb crystals. Driven by the necessity to perform fast, robust, and non-destructive quality control of the Te doping homogeneity of the optically transparent large-diameter GaSb wafers, we correlated electronic and optical infrared properties of Te-doped GaSb crystals. The study was based on the experimental Hall and Fourier-Transform Infrared (FTIR) data collected from over 50 samples of the low-doped n-type material (carrier concentration of 6 × 1016 cm−3 to 7 × 1017 cm−3) and the Te-doped p-type GaSb (4.6 × 1015 cm−3 to 1 × 1016 cm−3). For the n-type GaSb, the analysis of the FTIR data was performed using free carrier absorption model, while for the p-type material, the absorption was modeled using inter-valence band absorption mechanism. Using the correlation between the Hall and the IR data, FTIR maps across the wafers allow a fast and reliable way to estimate carrier concentration profile within the wafer.

A theoretical discussion on the internal quantum efficiencies of the epitaxial single crystal GaSb thin film cells with different p–n junctions

As promising candidates for thermophotovoltaic energy conversion systems, epitaxial thin film III–V cells have gained increasing attention due to their potential for reduced weight. However, few studies have been done to date to enhance the performance of epitaxial single crystal GaSb thin film cells. In this work, the internal quantum efficiencies of epitaxial single crystal GaSb thin film cells with Zn-diffused and epitaxial p–n junctions were predicted with models verified using the corresponding experimental results. The results are the first to indicate that, for the former, when the base region thickness is approximately equal to minority carrier diffusion length, the maximal IQE can be obtained and it is notably higher than the IQE of GaSb bulk cell at wavelengths from 800 to 1700nm. Reducing bottom surface recombination velocity and increasing hole Shockley–Read–Hall lifetime could also increase the IQE. While for the latter, the results demonstrated that the optimal base region thickness is also approximately equal to minority diffusion length, and reducing emitter region thickness will increase the IQE when the base region is optimized. The comparison of the two optimized GaSb thin film cells showed that the GaSb thin film cell with epitaxial p–n junction has a higher IQE.

Increased p-type conductivity in GaNxSb1−x, experimental and theoretical aspects

The large increase in the p-type conductivity observed when nitrogen is added to GaSb has been studied using positron annihilation spectroscopy and ab initio calculations. Doppler broadening measurements have been conducted on samples of GaNxSb1−x layers grown by molecular beam epitaxy, and the results have been compared with calculated first-principle results corresponding to different defect structures. From the calculated data, binding energies for nitrogen-related defects have also been estimated. Based on the results, the increase in residual hole concentration is explained by an increase in the fraction of negative acceptor-type defects in the material. As the band gap decreases with increasing N concentration, the ionization levels of the defects move closer to the valence band. Ga vacancy-type defects are found to act as positron trapping defects in the material, and the ratio of Ga vacancy-type defects to Ga antisites is found to be higher than that of the p-type bulk GaSb substrate. Beside Ga vacancies, the calculated results imply that complexes of a Ga vacancy and nitrogen could be present in the material.

Thin-film 'Thermal Well' Emitters and Absorbers for High-Efficiency Thermophotovoltaics.

A new approach is introduced to significantly improve the performance of thermophotovoltaic (TPV) systems using low-dimensional thermal emitters and photovoltaic (PV) cells. By reducing the thickness of both the emitter and the PV cell, strong spectral selectivity in thermal emission and absorption can be achieved by confining photons in trapped waveguide modes inside the thin-films that act as thermal analogs to quantum wells. Simultaneously, photo-excited carriers travel shorter distances across the thin-films reducing bulk recombination losses resulting in a lower saturation current in the PV cell. We predict a TPV efficiency enhancement with near-field coupling between the thermal emitter and the PV cell up to 38.7% using a thin-film germanium (Ge) emitter at 1000 K and an ultra-thin gallium antimonide (GaSb) cell supported by perfect back reflectors separated by 100 nm. Even in the far-field limit, the efficiency is predicted to reach 31.5%, which is over an order of magnitude higher than the Shockley Queisser limit of 1.6% for a bulk GaSb cell and a blackbody emitter at 1000 K. The proposed design approach does not require nanoscale patterning of the emitter and PV cell surfaces, but instead offers a simple low-cost solution to improve the performance of thermophotovoltaic systems.