Magneto Optical Properties Of Narrow Gap 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.

This volume contains the Proceedings of the NATO Advanced Research Workshop on "Optical Properties of Narrow-Gap Low-Dimensional Structures", held from July 29th to August 1st, 1986, in St. Andrews, Scotland, under the auspices of the NATO International Scientific Exchange Program. The workshop was not limited to optical properties of narrow-gap semiconductor structures (Part III). Sessions on, for example, the growth methods and characterization of III-V, II-VI, and IV-VI materials, discussed in Part II, were an integral part of the workshop. Considering the small masses of the carriers in narrow-gap low dimensional structures (LOS), in Part I the enhanced band mixing and magnetic field effects are explored in the context of the envelope function approximation. Optical nonlinearities and energy relaxation phenomena applied to the well-known systems of HgCdTe and GaAs/GaAIAs, respectively, are reviewed with comments on their extension to narrow gap LOS. The relevance of optical observations in quantum transport studies is illustrated in Part IV. A review of devices based on epitaxial narrow-gap materials defines a frame of reference for future ones based on two-dimensional narrow-gap semiconductors; in addition, an analysis of the physics of quantum well lasers provides a guide to relevant parameters for narrow-gap laser devices for the infrared (Part V). The roles and potentials of special techniques are explored in Part VI, with emphasis on hydrostatic pressure techniques, since this has a pronounced effect in small-mass, narrow-gap, non-parabolic structures.

The calculations of CR spectra, valence Landau suband structure, and average z component of the spins explain the differences between the CR measurements that are observed in molecular beam epitaxy (MBE) and metal organic vapor phase epitaxy (MOVPE) samples, and the higher Curie temperature in the MOVPE structures. In the OPNMR experiments on AlGaAs/GaAs MQW, the sign change of the calculated electron spin polarization agrees with the sign change of the OPNMR signal. This sign change has not been observed in bulk GaAs. The strain effect and density of states in the strained MQW are responsible for this sign change. The calculated magneto-absorption with biaxial strain effects included more accurately reproduces the experimental results of AlInSb/InSb parabolic MQW. Comparing the results with that of the AlInSb/InSb square MQW indicates that the shape of the confinement affects the magneto-absorption significantly.

The field of narrow-gap II-VI materials is dominated by lhe compound mercury cadmium telluride, MCT or Hg1_ .. Cd .. Te. By varying the x value, material can be made to cover all the important infrared (lR) ranges of interest. It is probably true to say that MCT is the third most studied semiconductor after silicon and gallium arsenide. As current epitaxial layers of MCT are mainly grown on bulk CdTe family substrates these materials are included in this book, although strictly, of course, they are not 'narrow-gap'. This book is intended for readers who are either new to the field or are experienced workers in the field who need a comprehensive and up to date view of this rapidly expanding area. To satisfy the needs of the frrst group each chapter discusses the principles underlying each topic and some of the historical background before bringing the reader the most recent information available. For those currently in the field the book can be used as a collection of useful data, as a guide to the literature and as an overview of topics covering the wide range of work areas.