Midinfrared injection-pumped laser based on a III–V/II–VI hybrid heterostructure with submonolayer InSb insets

Lasing at 3.075 μm (T = 60 K) in a regime of pulsed injection pumping has been obtained in an AlGaAsSb/InAs/CdMgSe double hybrid heterostructure with the active region comprising an InAs layer with submonolayer InSb insets. The electroluminescence (EL) spectrum of the heterostructure has been studied for various values of the pumping current up to the stimulated emission threshold. An increase in the pumping current leads to a short-wavelength shift and a change in the EL band structure, which is explained by the occupation of higher states by the charge carriers in InSb quantum dots and/or in the adjacent InAsSb layer.     

Structure-property relationships in heteroepitaxial InAs and InSb thin films

Heteroepitaxial thin films of InSb and InAs were evaporated onto sapphire and onto semi-insulating GaAs substrates. An in-line high vacuum evaporation set-up was used to deposit the semiconductor films by the three-temperature method at an ambient pressure of about 10^-5 mbar. The orientation and structure of the films were investigated as functions of substrate temperature and substrate orientation.The highest carrier mobilities were observed in (100)-oriented InAs and InSb films deposited on GaAs (100) substrates; these films had room temperature mobilities of 20 000 and 40 000 cm² V^-1 s^-1 respectively. InAs films on (0001) sapphire planes always showed (111) orientation with a maximum carrier mobility of 13 000 cm² V^-1 s^-1 at room temperature.     

Stress reduction and electric properties of InSb thin films grown by metalorganic vapor phase epitaxy on sapphire substrates with an InAs buffer layer

InSb thin films were grown by metalorganic vapor phase epitaxy using an InAs buffer layer on sapphire (0001) substrates. The stresses and strains in InSb were controlled by the thickness of the InAs buffer layer, and it was found that with decreasing compressive stress in InSb, the crystalline quality and the electrical properties improved. The thermoelectric properties of InSb were assessed and it was found that the power factor of InSb with a thickness of 5 μm reached as high as 5.8 × 10⁻³ W/mK² at 600 K.     

InSb/InAs quantum dots grown by liquid phase epitaxy

The first original results on the growth of quantum dots (QDs) in the InSb/InAs system by liquid phase epitaxy (LPE) are reported. The density and dimensions of QDs were studied by methods of scanning probe microscopy and atomic force microscopy. The surface density, shapes, and dimensions of LPE-grown nanoislands depend on the growth conditions (temperature, cooling rate, and solution melt-substrate contact time). In the interval of temperatures T = 420–445°C, homogeneous arrays of InSb quantum dots on InAs(100) substrates were obtained with an average height of H = 3.4 ± 1nm, a radius of R = 27.2 ± 7.5 nm, and a density of up to 1.9 × 10¹⁰ cm^?2.     

InSb-InAs alloys prepared by rapid quenching (106–108 K/s)

Homogeneous InSb-InAs alloys are prepared by rapid quenching (10⁶-10⁸ K/s) from the liquid state. As evidenced by x-ray diffraction studies, rapid quenching prevents liquid-phase segregation, so that solidification proceeds by a diffusionless mechanism. The lattice parameters of the rapidly quenched alloys are determined. The effects of melt overheating and sample thickness on the diffusionless solidification process are analyzed. The nonlinear composition dependence of the lattice parameter in the InSb-InAs system is accounted for using the calculated degrees of dissociation of InSb and InAs along the liquidus line and at 1000‡C and the covalent radii of the constituent elements.     

Controllable Synthesis of [11−2−2] Faceted InN Nanopyramids on ZnO for Photoelectrochemical Water Splitting

Indium nitride (InN) is one of the promising narrow band gap semiconductors for utilizing solar energy in photoelectrochemical (PEC) water splitting. However, its widespread application is still hindered by the difficulties in growing high‐quality InN samples. Here, high‐quality InN nanopyramid arrays are synthesized via epitaxial growth on ZnO single‐crystals. The as‐prepared InN nanopyramids have well‐defined exposed facets of [0001], [11?2?2], [1?212], and [?2112], which provide a possible routine for understanding water oxidation processes on the different facets of nanostructures in nanoscale. First‐principles density functional calculations reveal that the nonpolar [11?2?2] face has the highest catalytic activity for water oxidation. PEC investigations demonstrate that the band positions of the InN nanopyramids are strongly altered by the ZnO substrate and a heterogeneous n–n junction is naturally formed at the InN/ZnO interface. The formation of the n–n junction and the built‐in electric field is ascribed to the efficient separation of the photogenerated electron–hole pairs and the good PEC performance of the InN/ZnO. The InN/ZnO shows good photostability and the hydrogen evolution is about 0.56 µmol cm^?2 h^?1, which is about 30 times higher than that of the ZnO substrate. This study demonstrates the potential application of the InN/ZnO photoanodes for PEC water splitting.     

On the problem of elemental BV material in the interface of native oxide/AIIIBV structures

By means of voltammetry using electroactive graphite paste electrodes or slices of InAs and InSb directly as the working electrodes it was shown that elemental arsenic and antimony are generated during anodic oxidation and chemical etching together with the sesquioxides As₂O₃ and Sb₂O₃. The concentrations of the elements are in the range 10¹¹–10¹² cm^-2. It was found that arsenic and antimony are present in two modifications, amorphous and crystalline, and that the ratio between the amounts of these modifications depends on the native oxide growth conditions.     

Interaction of InAs and InSb with aqueous solutions of nitric acid

InSb dissolution in 7.8–15.6 N HNO₃ is controlled by the oxidizer diffusion to the surface. InAs dissolution in 15.6 N HNO₃ is controlled by diffusion in solution; at low acid concentrations, the dissolution rate is limited by diffusion through the loose oxide layer forming on the sample surface. The different dissolution kinetics of InAs and InSb in HNO₃ can be explained by the different properties of the surface layers of hydrous arsenic and antimony oxides.     

Effect of thin intermediate-layer of InAs quantum dots on the physical properties of InSb films grown on (001) GaAs

In this study the formation of a semiconducting InSb layer, preceded by the growth of an intermediate layer of InAs quantum dots, is attempted on (001) GaAs substrate. From the analysis of atomic-force-microscopy and transmission-electron-microscopy images together with Raman spectra of the InSb films, it is found that there exists a particular layer-thickness of ~ 0.5 μm above which the structural and transport qualities of the film are considerably enhanced. The resultant 2.60-μm-thick InSb layer, grown at the substrate temperature of 400 °C and under the Sb flux of 1.5 × 10^− 6 Torr, shows the electron mobility as high as 67,890 cm²/Vs.     

Characterisation of molecular nitrogen in ion-bombarded compound semiconductors by synchrotron-based absorption and emission spectroscopies

We have studied formation of molecular nitrogen under low-energy nitrogen bombardment in a range of compound semiconductors by synchrotron-based X-ray photoelectron spectroscopy (XPS) around N 1s core-level and near-edge X-ray absorption fine structure (NEXAFS) around N K-edge. We have found interstitial molecular nitrogen, N₂, in all samples under consideration. The presence of N₂ produces a sharp resonance in low-resolution NEXAFS spectra at around 400.8 eV, showing the characteristic vibrational fine structure in high-resolution measurements. At the same time, a new peak, shifted towards higher binding energies, emerges in all N 1s photoemission spectra. We have found a shift of 7.6 eV for In-based compounds and 6.7 eV for Ga-based compounds. Our results demonstrate that NEXAFS and core-level XPS are complementary techniques that form a powerful combination for studying molecular nitrogen in compound semiconductors, such as GaSb, InSb, GaAs, InN, GaN or ZnO.     

影响InN材料带隙的几个关键问题

确定了InN材料的带隙值并研究了影响InN材料带隙变化的导带电学结构和几个关键因素,以解释当前用不同方法生长不同质量的InN材料时出现的各种不同带隙值.用光致发光、光吸收和光调制反射方法测量确定InN材料的带隙值约为0.7eV;探讨了InN材料带隙与温度的函数关系,并分析了影响InN材料带隙的导带电学结构和有关因素.影响InN材料带隙的主要因素有Moss-Burstein效应、深能级俘获现象以及N:In化学计量比等,得出在不同质量样品和不同生长条件下,3种因素均影响InN材料的带隙值,但所起的作用却不尽相同.     

Structure and optical properties of InN and InAlN films grown by rf magnetron sputtering

The structure and optical properties of InN and In-rich InAlN films grown by magnetron sputtering were investigated. The XRD results show that these films are highly c-axis oriented. The film morphology and microstructure of these films were observed by AFM and SEM which reveals that the films grown in island growth mode. Optical properties of these films were studied by absorption method. The band gap energy of the InN film grown under substrate temperature of 400 °C is 1.38 eV. By studying the E _g values of InN films deposited under different substrate temperature, the Burstein-Moss effect on band gap of InN was examined. The significant band gap bowing of our In-rich InAlN films was found to be correlated with the In contents. The bowing parameter of 3.68 eV was obtained which is in agreement with previous theoretical predictions.     

Growth of InN layers on Si (111) using ultra thin silicon nitride buffer layer by NPA-MBE

Indium nitride (InN) epilayers have been successfully grown by nitrogen-plasma-assisted molecular beam epitaxy (NPA-MBE) on Si (111) substrates using different buffer layers. Growth of a (0001)-oriented single crystalline wurtzite-InN layer was confirmed by high resolution X-ray diffraction (HRXRD). The Raman studies show the high crystalline quality and the wurtzite lattice structure of InN films on the Si substrate using different buffer layers and the InN/β-Si₃N₄ double buffer layer achieves minimum FWHM of E₂ (high) mode. The energy gap of InN films was determined by optical absorption measurement and found to be in the range of ~ 0.73-0.78 eV with a direct band nature. It is found that a double-buffer technique (InN/β-Si₃N₄) insures improved crystallinity, smooth surface and good optical properties.     

Etching behavior of GaAs,GaSb, InAs,and InSb in aqueous H<Subscript>2</Subscript>O<Subscript>2</Subscript>-HBr-ethylene glycol solutions

The chemical interaction of GaAs, GaSb, InAs, and InSb single crystals with H₂O₂-HBr-ethylene glycol bromine-releasing etchants has been studied under reproducible hydrodynamic conditions. We have located boundaries between regions of polishing and nonpolishing solutions, assessed the surface condition of the crystals using microstructural analysis and surface profiling, and optimized the compositions of the polishing solutions and dynamic chemical polishing conditions for the materials studied.     

Modeling of InAs-InSb nanowires grown by Au-assisted chemical beam epitaxy

Interesting phenomena during the Au-assisted chemical beam epitaxy of InAs-InSb nanowire heterostructures have been observed and interpreted within the framework of a theoretical model. An unusual, non-monotonous diameter dependence of the InSb nanowire growth rate is demonstrated experimentally within a range of deposition conditions. Such a behavior is explained by competition between the Gibbs-Thomson effect and different diffusion-induced material fluxes. Theoretical fits to the experimental data obtained at different flux pressures of In and Sb precursors allow us to deduce some important kinetic coefficients. Furthermore, we discuss why the InAs nanowire stem forms in the wurtzite phase while the upper InSb part has a pure zinc blende crystal structure. It is hypothesized that the 30° angular rotation of nanowire when passing from InAs to the InSb part is driven by the lowest surface energy of (1100) wurtzite and (110) zinc blende facets.     

Ag-assisted CBE growth of ordered InSb nanowire arrays

We present growth studies of InSb nanowires grown directly on [Formula: see text] and [Formula: see text] substrates. The nanowires were synthesized in a chemical beam epitaxy (CBE) system and are of cubic zinc blende structure. To initiate nanowire nucleation we used lithographically positioned silver (Ag) seed particles. Up to 87% of the nanowires nucleate at the lithographically pre-defined positions. Transmission electron microscopy (TEM) investigations furthermore showed that, typically, a parasitic InSb thin film forms on the substrates. This thin film is more pronounced for InSb((111)B) substrates than for InAs((111)B) substrates, where it is completely absent at low growth temperatures. Thus, using InAs((111)B) substrates and growth temperatures below 360?°C free-standing InSb nanowires can be synthesized.     

Chemical interaction of InAs,InSb, GaAs,and GaSb crystal surfaces with (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>Cr<Subscript>2</Subscript>O<Subscript>7</Subscript>–HBr–citric acid etching solutions

We have studied the chemical dissolution of InAs, InSb, GaAs, and GaSb crystals in (NH₄)₂Cr₂O₇–HBr–C₆H₈O₇ solutions. The dissolution rate of the crystals has been measured as a function of etchant composition, and the kinetics of the chemical interaction of the semiconductors with solutions have been investigated in detail. The dissolution rate has been shown to be diffusion-limited. Citric acid helps to reduce the etch rate and improves the polishing performance of the etching solutions.     

Calculation of the electronic structure and exchange interaction in the InSb and GaAs semiconductors codoped with Mn and Ni

Density functional theory calculations have been used to study the electronic structure of Mn-doped, Ni-doped, and Mn/Ni-codoped InSb and GaAs semiconductors. The ferromagnetic transition energy has been calculated using a multiscale method in which exchange interaction is calculated by the Hartree–Fock exact atomic method and is then included as a Hubbard parameter in calculation of the electronic structure of the material. The present calculation results demonstrate that, in all cases, there is hybridization of the impurity d states with the valence band of the host semiconductor. The contributions of the Ni and Mn dopants are approximately additive.     

Determination of the surface band bending in InxGa1−xN films by hard x-ray photoemission spectroscopy

Core-level and valence band spectra of In_xGa_1−xN films were measured using hard x-ray photoemission spectroscopy (HX-PES). Fine structure, caused by the coupling of the localized Ga 3d and In 4d with N 2s states, was experimentally observed in the films. Because of the large detection depth of HX-PES (∼20 nm), the spectra contain both surface and bulk information due to the surface band bending. The In_xGa_1−xN films (x = 0–0.21) exhibited upward surface band bending, and the valence band maximum was shifted to lower binding energy when the mole fraction of InN was increased. On the other hand, downward surface band bending was confirmed for an InN film with low carrier density despite its n-type conduction. Although the Fermi level (E_F) near the surface of the InN film was detected inside the conduction band as reported previously, it can be concluded that E_F in the bulk of the film must be located in the band gap below the conduction band minimum.     

Structure and bandgap determination of InN grown by RP-MOCVD

InN thin films are grown on sapphire substrates by remote plasma-assisted metal organic chemical vapor deposition while varying the indium pulse length and substrate temperature. The effects of the indium pulse length and temperature on the structural, morphological, electronic, and optical properties of the thin films are studied. The structural parameters are determined by X-ray diffraction and X-ray photoelectron spectroscopy and the effects of incorporating oxygen atoms in the structure is described. The N K-edge X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) measurements are used to determine the band gap and it is found to be 1.80?±?0.25 eV for all samples. A complementary measurement namely, X-ray excited optical luminescence measurement is performed to confirm the band gap value obtained from XAS and XES measurements. O K-edge XAS measurements are performed to determine the presence of oxygen impurities in the samples. Meanwhile, we carry out the density functional theory calculations for Wurtzite InN, hypothetical Wurtzite-type InO_0.5N_0.5, and InO_0.0625N_0.9375 structures. We find that the measured N-edge spectra agree well with our Wurtzite InN calculations and the measured O K-edge spectra agree better with hypothetical Wurtzite-type InO_0.0625N_0.9375 than Wurtzite-type InO_0.5N_0.5.