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InAs/GaSb superlattices sandwiched between conventional InAs layers were grown by low pressure metal organic chemical vapor deposition. Period and roughness of the superlattices were examined by field emission transmission electron microscopy. Room temperature infrared absorption spectra for InAs/GaSb superlattices were obtained by Fourier-transform infrared spectroscopy. The effects of varying the doping levels and thicknesses of the InAs sandwiching layers on the absorption spectra of InAs/GaSb superlattices were studied. It was found that by choice of suitable doping levels and cap/buffer thicknesses, the resulting fermi level equalization (as in normal homo or heterojunctions) thereby allowed the setting or “pinning” of the superlattice Fermi level to any desired value within the range made available by the original bulk material characteristics in conjunction with the doping conditions. When the thicknesses of the InAs sandwiching layers became less than 1 μm, the sandwiching effect and the intersubb...

The effects of elastic strain induced by lattice mismatch on the effective mass and band offset at Γ point are studied in this article. We found that the effective masses (electron, light‐ and heavy‐hole) become anisotropic in a strained layer. The theoretical calculations were made using a method of linear combination of atomic orbitals, and the overlapping integrals are adjusted in accordance with the change of atomic distance. In the kz direction, the effective mass ratios (strain: unstrain) of the electron of InxGa1−xSb/GaSb structure were found to vary from 1 to 3.38 for 0≤x≤1, the corresponding ratios of the light‐ and heavy‐hole are 1 to 3.38 and 1 to 0.99, respectively. In the kx and ky direction, the ratios of the light‐ and heavy‐hole are 1 to 1.02 and 1 to 1.13, respectively. For unstrained and strained interfaces, the band offset ratios of 90:10 and 57:43 (conduction band: valence band) are obtained, respectively. Experimental studies were also performed on the InxGa1−xSb/GaSb strained‐layer s...

We obtain undoped n‐type GaSb epilayers by low‐temperature metalorganic chemical vapor deposition at a low growth temperature of 450 °C reproducibly. Different conduction types of GaSb and different energy levels are compared by photoluminescence spectra. For n‐type undoped GaSb, the FWHM of dominant peak and bound exciton are 11 and 1.3 meV, respectively. Because semi‐insulating GaSb substrates cannot be obtained, we cannot use the Hall effect to determine the carrier concentration and mobility of the homoepilayer. In order to identify the conduction types of GaSb, ohmic contact and Schottky barrier are made by Au/Ge/Ni and Au, respectively. The concentrations of undoped n‐type GaSb homoepilayers obtained from I‐V and C‐V measurements are 1.44×1017–3.0×1017 cm−3, respectively. The mobility and concentration of undoped p‐type GaSb heteroepilayers are 758 cm2/V s and 9.0×1015 cm−3 at 300 K, respectively.

Undoped GaSb epilayers were grown on GaSb and GaAs substrates using the metalorganic chemical vapor deposition (MOCVD) technique, and photoluminescence (PL). Hall effect measurements were used to characterize the undoped epilayers. For undoped GaSb epilayers, four energy levels revealed by PL spectra are shown to be due to acceptors, using KTdp/dEf va Ef‐Ev data obtained from Hall effect results, where p is the hole concentration, Ef and Ev are the Fermi level and the top of valence band, respectively. The acceptor levels lie at 3, 58, 80, and 130 meV above the top of valence band, respectively. The donor level is 15 meV below the bottom of the conduction band. These acceptor levels exist in almost all of the undoped p‐type GaSb epilayers grown at high temperature, while the donor level exists only in the undoped n‐type GaSb epilayers grown by low‐temperature MOCVD. It is found that these levels may be changed using the different growth temperatures.

We have grown unstrained Al0.66In0.34As0.85Sb0.15/Ga0.64In0.36As0.84Sb0.16 multiple-quantum-well (MQW) structures on InP substrates by metalorganic vapor phase epitaxy. Low-temperature photoluminescence was performed for these MQW structures. By comparing the luminescence peak energies with the theoretical calculations, we estimated the conduction-band offset ratio to be 0.75±0.10 for the Al0.66In0.34As0.85Sb0.15/Ga0.64In0.36As0.84Sb0.16 heterostructure.

The transport properties of B-doped single-walled carbon nanotubes (SWNTs) are studied from both experimental and theoretical standpoints. Experimentally, it is found that the semiconducting behavior of SWNTs is drastically changed after B-doping, and the unusual abrupt current drops are observed at low temperatures, which may imply the possibility of superconducting transition in B-doped SWNTs. Using the density-functional tight-binding calculation, it is observed that B-doping induces the presence of density of state peaks near the Fermi level which shifts toward the valence band region, showing a clear charge-transfer characteristic, which agrees well with the experimental observations.

We present a systematic theoretical study of the Cerenkov acoustic-phonon emission from a polar semiconductor such as GaAs driven by dc electric field. The drift electron velocity and electron-temperature in the system are determined by solving self-consistently the momentum- and energy-balance equations derived from the Boltzmann equation. The intensity of the phonon emission via piezoelectric and deformation-potential coupling is evaluated on the basis of the energy-balance equation. We find that the electron velocity exceeds the sound velocity in GaAs even when electrons are still in the linear response regime. This implies that the Cerenkov phonon emission can be easily observed in GaAs-based electron gas systems. We also examine the frequency and angular dependence of the acoustic-phonon emission on the applied electric field and find that our results are in line with those observed experimentally. This study is pertinent to electrical generation of acoustic-phonon sources from polar semiconductor sy...