D. N. Talwar

Ground and Excited State Exciton Spectra from GaN Grown by Molecular-Beam Epitaxy

The emission and reflection spectra of GaN have been investigated in the intrinsic region and the data have been interpreted in terms of the wurtzite crystal band structure. Three intrinsic exciton transitions have been observed, one associated with each of the valence bands. Exciton excited states associated with the two top valence bands were also observed. The exciton binding energies, the band‐gap energies, and the exciton Bohr radii are all reported along with the dielectric constant and the spin‐orbit and crystal‐field parameters for GaN.

Vibrational properties of HgCdTe system

The results of reflection spectra at 300 °K in the far‐infrared region (100–400 cm−1) are reported due to low concentration of Hg atoms in the Cd‐rich CdHgTe mixed crystals. A gap mode is observed at 131 cm−1 due to isolated Hg occupying Cd in CdTe. The experimental results are analyzed theoretically using the well‐know Green’s function technique. The perturbation caused by low concentration of Cd(Hg) is described by the mass change at the impurity site as well as local variation of impurity‐host interactions. In the nearest neighbor approximation, all the involved Green’s function matrix elements have been computed numerically by incorporating the lattice phonons from an eleven parameter rigid‐ion model fitted to recent neutron data of HgTe and CdTe. We find that different substitutional defects in Hg‐Cd tellurides can give rise to well‐defined symmetry vibrations both within the gap and outside the maximum phonon frequency regions. Our calculations suggest that a gap mode of Hg substituted to Te is like...

Elastic, structural, bonding, and defect properties of zinc-blende BN, AlN, GaN, InN and their alloys

Abstract Simple tight-binding simulations, incorporating only the Herman–Skillman atomic term values, are shown to provide valuable information about the bonding, elastic and structural properties of zinc-blende group III-nitrides. Our calculated values of the elastic parameters (viz., bulk modulus, elastic stiffness constants, Kleinmans internal displacement parameter, Keating force constants, etc.) for BN, AlN, GaN, and InN are shown to exist well within the range of values derived from more sophisticated methods. Despite the crude approximations used, the tight-binding method has clearly provided the meaningful trends to the local distortions around isoelectronic impurities and has described reasonably well the bond length variations as a function of composition in ternary alloys.

Incorporation of carbon in heavily doped AlxGa1−xAs grown by metalorganic molecular beam epitaxy

Hole concentrations in excess of 1020 cm−3 have been achieved in AlxGa1−xAs using carbon doping during metalorganic molecular beam epitaxy. Hall and secondary‐ion mass spectrometry measurements show a 1:1 correspondence between the hole density and carbon concentration in as‐grown samples, although post‐growth annealing at 900 °C leads to a reduction in the net free‐carrier concentration (typically a decrease of ∼40% for 30 s anneals). The carbon‐localized vibrational modes (LVMs) show fine structure due to the presence of three different symmetries for substitutional carbon CAs, namely Td, C2v, and C3v. The experimental CAs LVM line positions are in remarkable agreement with the predictions of a rigid ion model.

Thermal expansion coefficient of 3C–SiC

Theoretical results for the temperature dependence of the thermal expansion coefficient for 3C–SiC are reported using a phenomenological lattice dynamical theory in the quasiharmonic approximation. The linear thermal expansion coefficient α of 3C–SiC exhibits a variation with temperature much like that of the specific heat and, unlike other tetrahedrally coordinated materials, it does not attain a negative value at lower temperatures.

Surface plasmon resonance due to the interface of a metal and a chiral sculptured thin film

Multiple surface plasmon resonances are experimentally observed for p-polarized as well as s-polarized incident light at the planar interface of a metal and a chiral sculptured thin film. These experimental results confirm that four surface plasmon resonances can be supported at the interface of metal-chiral sculptured thin film. Multiple surface plasmon resonances may allow for multiple simultaneous measurements by devices that utilize surface plasmon resonance for detection.

Electronic structure of ternary alloy semiconductors

Abstract The results of energy gap variation in ternary alloy semiconductors (A1−xBxC) are reported within the tight-binding (TB) framework of Koster and Slater by universalizing TB parameters as a function of x, in which the effects of lattice relaxation and composition disorder are involved appropriately. A good agreement is obtained between the calculated results and existing experimental data.

Lattice distortion associated with isolated defects in semiconductors

Abstract A semi-empirical tight-binding (TB) method is used to investigate the lattice relaxation around isovalent impurities and its effect on the vibrational properties of semiconductors. In terms of the revised Hartree-Fock atomic-term values, this technique provides simple analytical expressions for the change in the impurity-host bond energy and suggests a computationally efficient and reasonable method to estimate the bond-length distortions. Numerical calculations for the symmetric lattice relaxations are reported for eighty cases of impurity-host systems in nineteen elemental and compound semiconductors. For GaAs: In, InAs: Ga, GaP:As, GaAs: P, ZnSe: Te and ZnTe: Se, the results are found to be in good agreement with the recent extended X-ray absorption fine structure (EXAFS) data and, in other cases, the bond-length distortions are seen to be compatible with the theoretical values reported by Martins and Zunger (1984). In almost all the systems studied here the calculated relaxation parameter e l...

Lattice dynamics of II–VI, III–V compounds

Abstract The lattice vibrations of II–VI compound ZnSe and III–V compound InSb have been calculated in the frame work of Banerjee-Varshnis second neighbour ionic [SNI] model utilizing critical-point phonons as an input to determine the required seven parameters and the experimentally determined three elastic constants C 11 , C 12 , C 44 as restraints on the values of the parameters. A reinvestigation of the experimental elastic constants particularly C 11 and C 44 for ZnSe has been suggested. Results are presented for the dispersion curves along high symmetry directions. A reasonable agreement with the recently measured inelastic nutron scattering data is observed.

Direct evidence of LO phonon-plasmon coupled modes in n-GaN

We report theoretical results of the far-infrared transmission in oblique incidence for undoped and doped GaN epilayers. For c-GaN, our results in p-polarization find transmission minima at LO and TO frequencies while in s-polarization only one minima corresponding to TO mode is revealed. For c-GaN/GaAs/AlN (buffer) layer we noticed minima in s-polarization corresponding to TO modes of c-GaN and c-AlN while in p-polarization the features related to TO modes as well as minima linked to LO modes are found. The shift in L+ modes with increasing carrier concentration (N) provided direct evidence of estimating N in doped GaN.