Magneto Optical Properties Of Semiconductor Heterostructures

ABSTRACT: Next generation of semiconductor device will not only based on the charge transport properties of the carrier, but also their spin degree of freedom. In order to understand or predict how those devices work one need to understand the spin-dependent electronic structures of both bulk and low-dimensional semiconductors. We have theoretically studied the spin-dependent Landau levels for electrons or holes in bulk GaAs system and AlInSb/InSb multiple quantum wells system. We use the envelope function approximation for the electronic and magneto-optical properties of AlInSb/InSb superlattices. Our model includes the conduction electrons, heavy holes, light holes and the split-off holes for a total of 8 bands when spin is taken into account. It is a generalization of the Pidgeon-Brown model to include the wave vector dependence of the electronic states, as well as quantization of wave vector due to multiple quantum well superlattice effects. In addition, we take strain effects into account by assuming pseudomorphic growth conditions. For bulk GaAs system, we calculated the spin-dependent absorption coefficients which can be directly compared with the optically pumped NMR experiment. We show that the optically pumped NMR is a complimentary tool to traditional magneto optical absorption measurement, in the sense that optically pumped NMR is more sensitive to the light hole transitions which are very hard to resolve in the traditional magneto absorption measurement. For the AlInSb/InSb multiple quantum well system, we calculated both the magneto absorption spectra and 10 the cyclotron resonance spectra. We compare both spectra to experimental results and achieve a good agreement. This agreement assures us that our understanding of the valence band structure of the narrow gap InSb materials are correct.

The theoretical research performed under the auspices of this grant has played a central role in the investigation of optical and magneto-optical properties of semiconductor heterostructures. There are two major developments to report. One is that the method of finite elements has been proved to be a very effective, flexible, and powerful approach for the calculation of energy levels in semiconductor superlattices and quantum well structures. The second is the method of tight-binding which provides a full Brillouin-zone description of the energy bands of superlattices and quantum wells. These two approaches have allowed new theoretical insights in understanding the electronic and optical properties of heterostructures. The following items describe these new developments based on work supported by the research grant.