The application of a potential model to the analysis of differences between the Auger parameters of InSb and the elemental materials yields a value 1.82 +/- 0.07A for the core hole screening distance in InSb. It also yields a value of 0.22 +/- 0.49 e for the charge transfer in InSb. Shifts in the Auger parameters of elements between their metallic states and in a compound semiconductor are interpreted using a novel method based on quantifying atomic core potential, as a quantum mechanical observable, in terms of its dependence on the valence charge and the number of atomic core holes. The core hole screening distance is similar to 30% larger than half the interatomic distance between the nearest neighbors and, by the equivalent cores model, is expected to be the screening radius of Sn and Te impurities in InSb.

We demonstrate the operation of GaSbBi metal-semiconductor-metal photodetectors with different Bi concentration and compare performance with a reference GaSb device. A GaSbBi MSM-PDs is shown to have a 220 nm wavelength extension in cut-off wavelength, with 2.9% bismuth concentration, compared to the reference device. We also investigate the influences of electrode geometry and size on the final device performance.

The influence of postgrowth thermal annealing on GaSbBi Schottky barrier diodes has been investigated. The effects of the annealing temperature and time on the material quality and electrical characteristics of the diodes have been studied. The I-V characteristics indicated a better ideality factor and less leakage current at the reverse bias, as the annealing temperature increased up to 500 °C for a duration of 30 min. X-ray diffraction and scanning transmission electron microscope measurements were performed to verify that the bismuth composition was unaffected during the annealing process. Energy dispersive x-ray analysis indicated that Sb clustering occurs at high annealing temperatures, resulting in a concomitant degradation in the electrical performance. The optimum electrical characteristics of the diode were obtained with an annealing temperature of 500 °C for 30 min, resulting in an ideality factor of 1.3 being achieved.

The temperature dependence of the band gap of GaNxSb1-x films with x <= 1.3% has been studied in the 1.1-3.3 mu m (0.35-1.1 eV) range using infrared absorption spectroscopy between 4.2 and 300 K. As with other dilute nitride semiconductors, the temperature dependence of the band gap is reduced by alloying with nitrogen when compared to the host binary compound. However, for GaNSb, the smallest variation of the band gap with temperature is observed for samples with the lowest N content for which the band gap is almost totally insensitive to temperature changes. This contrasts with the more widely studied GaNxAs1-x alloys in which the band gap variation with temperature decreases with increasing N content. The temperature-dependent absorption spectra are simulated within the so-called band anticrossing model of the interaction between the extended conduction band states of the GaSb and the localized states associated with the N atoms. The N next-nearest neighbor pair states are found to be responsible for the temperature insensitivity of the band gap of the GaNSb alloys as a result of their proximity to the conduction band edge giving them a more pronounced role than in GaNAs alloys.

MnSb layers have been grown on In x Ga 1 − x As(111)A virtual substrates using molecular beam epitaxy (MBE). The effects of both substrate temperature ( T sub ) and Sb/Mn beam flux ratio ( J Sb/Mn) were investigated. The sur- face morphology, layer and interface structural quality, and magnetic prop- erties have been studied for a 3 × 3 grid of T sub and J Sb/Mn values. Com- pared to known optimal MBE conditions for MnSb/GaAs(111) [ T sub =415 ◦ C, J Sb/Mn =6.5], a lower substrate temperature is required for sharp interface formation when growing MnSb on In 0 . 48 Ga 0 . 52 As(111)A [ T sub =350 ◦ C, J Sb/Mn =6.5]. At high flux ratio ( J Sb/Mn =9.5) elemental Sb is readily incorporated into MnSb films. At higher substrate temperatures and lower flux ratios, (In,Ga)Sb inclusions in the MnSb are formed, as well as MnAs inclusions within the substrate. The Sb and (In,Ga)Sb inclusions are epitaxial, while MnAs in- clusions are endotaxial, i.e. all have a crytallographic relationship to the substrate and epilayer. MBE optimisation towards different device struc- tures is discussed along with results from a two-stage growth scheme.

We study acceptor-type defects in GaSb1-xBix grown by molecular beam epitaxy. The hole density of the GaSb1-xBix layers, from capacitance-voltage measurements of Schottky diodes, is higher than that of the binary alloys and increases linearly up to 10(19) cm(-3) with the Bi content. Positron annihilation spectroscopy and ab initio calculations show that both Ga vacancies and Ga antisites contribute to the hole density and that the proportion of the two acceptor-type defects vary in the layers. The modification of the band gap due to Bi incorporation as well as the growth parameters are suggested to affect the concentrations of acceptor-type defects.

We report here the temperature-dependent incorporation kinetics of dimeric arsenic in InAs(001) homoepitaxy, using reflection high-energy electron diffraction (RHEED). Surface reconstructions, in combination with the RHEED investigation have provided insight into the growth of InAs(001), developing an accurate method of controlling the V:III ratio, which has been utilised to probe the low temperature epitaxial growth of indium arsenide epitaxial layers.

Ga(In)SbBi alloys grown by molecular-beam epitaxy on GaSb substrates with up to 5.5% In and 1.8% Bi were studied by temperature- and power-dependent photoluminescence (PL) and compared to previous photoreflectance (PR) results. High energy and low energy PL peaks were observed and attributed respectively to Ga(In) SbBi bandgap-related emission and native acceptor-related emission. For GaSbBi below 100 K, the HE peak is at slightly lower energy than the bandgap determined from PR, indicating carrier localization. This phenomenon is significantly weaker in PL of GaInSbBi alloys, suggesting that the presence of indium improves the optical quality over that of GaSbBi.

The simultaneous use of symmetric and grazing incidence X-ray diffraction in the characterisation of a pnictide material is demonstrated using MnSb epi-layers grown on compound semiconductor substrates. This combination of diffraction geometries enables a comprehensive determination of the lattice parameters and complex structural behaviour of MnSb. For example, in the ultra-thin limit (<;5 nm) of layers grown on GaAs an evolution from coherently strained to relaxed islands is observed with increasing thickness. However, a mixture of both strained and relaxed islands is seen beyond the calculated critical thickness. As film thickness increases, a cubic polymorph is observed and the relative content of this polymorph was probed using reciprocal space maps. Finally, recent surface X-ray diffraction work performed under ambient conditions is compared with similar data obtained at ultra-high vacuum conditions. The information found using these complementary diffraction geometries can readily be applied to a range of compound semiconductors.

Using infrared absorption, the room temperature band gap of InSb is found to reduce from 174 (7.1 μm) to 85 meV (14.6 μm) upon incorporation of up to 1.13% N, a reduction of ∼79 meV/%N. The experimentally observed band gap reduction in molecular-beam epitaxial InNSb thin films is reproduced by a five band k · P band anticrossing model incorporating a nitrogen level, EN, 0.75 eV above the valence band maximum of the host InSb and an interaction coupling matrix element between the host conduction band and the N level of β = 1.80 eV. This observation is consistent with the presented results from hybrid density functional theory.

We have investigated the growth by molecular beam epitaxy (MBE) of GaAs on MnSb. MnSb epilayers on GaAs(111), GaAs(001) and In0.5Ga0.5As(111) of thickness approximate to 50nm were used as substrates for GaAs films. The MBE growth of GaAs was monitored in situ using synchrotron X-ray diffraction and reflection high energy electron diffraction. We show data on strain relaxation and growth mode, and discuss the epitaxial relationship between GaAs(001) and MnSb(11 (0) over bar1). Schematic of the molecular beam epitaxy/X-ray diffraction insitu experiment and typical 2D detector data, with GaAs(111) and MnSb(0001) diffraction features.

The ferromagnetic material MnSb can exist in two polymorphs in epitaxial thin-film form, namely niccolite n-MnSb and cubic c-MnSb. We investigate the behavior of these polymorphs using grazing incidence depth-dependent in-plane X-ray diffraction. The in-plane lattice parameter evolution of a nominal 3000 angstrom thin film reveals a small near-surface compression of approximate to 0.1% in the majority n-MnSb component. A similar effect is also observed for the cubic polymorph, suggesting that the local strain environment of these crystallites is dominated by the n-MnSb matrix. Collated in-plane X-ray diffraction data from a GaAs/ In0.5Ga0.5As(111)/MnSb heterostructure in the near-surface region with probing depths ranging between 20 and 450 angstrom. Present are two of the polymorphs of MnSb: the niccolite (n-) and cubic zincblende (c-) phases.

The transition between the a(1×3) and c(4×4) surface reconstructions of InSb(001) has been carefully monitored by reflection high energy electron diffraction as a function of temperature and Sb2 flux, without incident In flux. Arrhenius-like behaviour is observed across the whole range of Sb2 fluxes and temperatures, allowing accurate internal calibration of substrate temperature. This behaviour is in contrast to aggregated data obtained under dynamic molecular beam epitaxy conditions, which show two regimes rather than a single Arrhenius-like phase boundary. The results are explained qualitatively by the atomistic kinetics in static versus dynamic conditions.

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 GaN x Sb 1− 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.

We report the direct deposition of indium antimonide, by molecular beam epitaxy (MBE) on gallium antimonide, resulting in the formation of quantum dots (QDs) with a maximum density of ~5.3×1010 cm−2. Using reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) for the analysis of samples with InSb depositions of 1–6 ML equivalent thickness, we observe an apparent value for the critical thickness for InSb/GaSb (001) deposition of 2.3±0.3 ML, for the growth temperatures of 275 °C and 320 °C.

The incorporation of Bi in GaSb1-xBix alloys grown by molecular beam epitaxy is investigated as a function of Bi flux at fixed growth temperature (275 degrees'C) and growth rate (1 mu m h(-1)). The Bi content is found to vary proportionally with Bi flux with Bi contents, as measured by Rutherford backscattering, in the range 0 < x <= 4.5%. The GaSbBi samples grown at the lowest Bi fluxes have smooth surfaces free of metallic droplets. The higher Bi flux samples have surface Bi droplets. The room temperature band gap of the GaSbBi epitaxial layers determined from optical absorption decreases linearly with increasing Bi content with a reduction of similar to 32 meV/'%'Bi. (C) 2015 The Authors. Published by Elsevier B.V.

Molecular beam epitaxy is used to grow Ga1−yInySb1−xBix (y ≤ 5.5% and x ≤ 2.5%) and AlyGa1−ySb1−xBix alloys (y ≤ 6.6% and x ≤ 2.0%). The alloy composition and film thickness are determined by high resolution x-ray diffraction. The band gap of the alloys is determined by photomodulated reflectance (PR) spectroscopy. The band gap energy reduces with increasing In and Bi contents and decreasing Al content. The band gap energy reduction between 15 and 290 K is in the range of 60–75 meV, somewhat lower than the 82 meV for GaSb. The broadening of the band gap-related PR feature is between 16 and 28 meV.

The properties of molecular beam epitaxy-grown InSb1−xBix alloys are investigated. Rutherford backscattering spectrometry shows that the Bi content increases from 0.6% for growth at 350 °C to 2.4% at 200 °C. X-ray diffraction indicates Bi-induced lattice dilation and suggests a zinc-blende InBi lattice parameter of 6.626 Å. Scanning electron microscopy reveals surface InSbBi nanostructures on the InSbBi films for the lowest growth temperatures, Bi droplets at intermediate temperatures, and smooth surfaces for the highest temperature. The room temperature optical absorption edge was found to change from 172 meV (7.2 μm) for InSb to ∼88 meV (14.1 μm) for InSb0.976Bi0.024, a reduction of ∼35 meV/%Bi.

Photoreflectance (PR) spectroscopy was applied to study the band gap in GaSb1-xBix alloys with Bi < 5%. Obtained results have been interpreted in the context of ab initio electronic band structure calculations in which the supercell (SC) based calculations are joined with the alchemical mixing (AM) approximation applied to a single atom in the cell. This approach, which we call SC-AM, allows on the one hand to study alloys with a very small Bi content, and on the other hand to avoid limitations characteristic of a pure AM approximation. It has been shown that the pure AM does not reproduce the GaSb1-xBix band gap determined from PR while the agreement between experimental data and the ab initio calculations of the band gap obtained within the SC-AM approach is excellent. These calculations show that the incorporation of Bi atoms into the GaSb host modifies both the conduction and the valence band. The shift rates found in this work are respectively -26.0 meV per % Bi for the conduction band and 9.6 meV per % Bi for the valence band that consequently leads to a reduction in the band gap by 35.6 meV per % Bi. The shifts found for the conduction and valence band give a similar to 27% (73%) valence (conduction) band offset between GaSb1-xBix and GaSb. The rate of the Bi-related shift for the split-off band is -7.0 meV per % Bi and the respective increase in the spin-orbit split-off is 16.6 meV per % Bi.