S. S. Kubakaddi

Cyclotron‐phonon resonance in quasi‐two‐dimensional semiconducting structures

A theory of phonon‐assisted cyclotron resonance in quasi‐two‐dimensional semiconductor quantum‐well structures is given. Using perturbation technique, expressions for absorption coefficients are obtained when the electrons are scattered by acoustic, nonpolar, and polar optical phonons. Extra peaks in the absorption spectrum due to transitions between Landau levels accompanied by emission and absorption of phonons are predicted. Numerical results for the frequency, magnetic field, and temperature dependence are given for parameters characteristic of GaAs.

Free-carrier absorption in semiconducting quantum well wires

The theory of free-carrier absorption is developed for quasi-one-dimensional semiconducting structures (ultra-thin wires) for the case where the carriers are scattered by acoustic phonons via the deformation potential coupling and the radiation field is polarised along the length of the wire. The absorption is found to be an oscillatory function of the area of the cross section of the wire and is enhanced over its bulk value in going to wires of decreasing cross section.

Free carrier absorption in semiconducting quantum wells for confined LO phonon scattering

A theory of free carrier absorption is given for GaAs/GaAlAs quantum wells when the carriers are scattered by confined LO phonons. The Huang and Zhu approximation for the confined phonon modes is used. The absorption coefficient is calculated and is found to have, broadly, features similar to the calculations with bulk phonons. The well width dependence of absorption is found to be opposite to that exhibited by scattering rates.

Hot-electron transport in semiconducting quantum well wires

Velocity-field characteristics for electrons in quasi-one-dimensional semiconductor quantum well structures have been calculated at different lattice temperatures using the displaced-Maxwellian approximation for the distribution function and the energy and momentum balance conditions. The electrons are assumed to interact with acoustic phonons via deformation potential coupling and polar optical phonons. Calculations do not show any negative differential resistance at high fields.

Thermal Conductivity of GaAs Substrates in GaAs/GaAlAs Heterostructures

The thermal conductivity (TC) data of GaAs substrates in GaAs/GaAlAs heterostructures has been analysed in the temperature range where lattice TC is dominant. Hollands formalism which has been successful in describing the TC data in bulk semiconductors is employed. Scattering of phonons by boundaries, impurities, other phonons and carriers is considered. Good fits to the experimental data in literature are obtained. The values of various parameters characterising the scattering mechanisms obtained are of the same orders of magnitude as in the case of bulk GaAs.

Electron-interface LO phonon scattering rates in quantum wells in a quantizing magnetic field

Electron scattering rates due to interaction with interface phonon modes in semiconductor quantum‐well structures in a quantizing magnetic field are studied. Numerical results for scattering rates in GaAs/GaAlAs quantum wells show oscillatory behavior with magnetic field. The scattering rate due to interface phonon modes is found to decrease with the increase of well width in contrast to that seen with bulk confined phonons.

Two-photon magnetoabsorption in GaAs/GaAlAs quantum wells

A theory of two-photon magnetoabsorption has been given for GaAs/GaAlAs quantum wells for circularly polarized radiation. Numerical results are given for the specimen of Frohlich et al. (1988 Phys. Rev. Lett. vol.61 p.1878). A good fit is obtained between experimental and calculated values.

Phonon‐drag thermopower in semiconducting quantum well structures in a quantizing magnetic field

A theory of phonon‐drag thermopower (PDTP) of a quasi‐two‐dimensional electron gas in quantum well semiconductor heterostructures in the presence of a quantizing magnetic field is presented. At liquid‐helium temperatures PDTP is found to be of the order of a few mV/K which is two to three orders of magnitude larger than diffusion thermopower. The effect of screening is to suppress PDTP and to modify its variation with temperature.

Infra-red free-carrier absorption due to impurity scattering in semiconducting quantum well structures

The theory of free-carrier absorption (FCA) is developed, in the extreme quantum limit when the carriers are assumed to populate only the lowest quantized energy level, for quasi-two and one-dimensional semiconducting quantum well structures where the carriers are scattered by ionized impurities. The radiation field is assumed to be polarized in the plane of the layer in the quasi-two-dimensional case and along the length of the wire in the quasi-one-dimensional case. Expressions for FCA are obtained for the cases where the impurities are either in the well (background impurities) or outside the well (remote impurities). Variation of FCA is numerically studied with photon frequency and well width.

Warm electrons in quantum well wires

The energy relaxation time and the warm-electron coefficient are studied in quantum well wires. Calculations have been carried out by employing the drifted Maxwellian distribution function and the energy-momentum balance conditions. The electrons are assumed to be scattered by acoustic and polar optical phonons. Numerical results are given for parameters characteristic of GaAs. Both the quantities increase with the transverse dimension of the quantum well wire.