Investigation of Physical Mechanisms in Multi-band Tunneling in Layered Semiconductor Structures

Worcester Polytechnic Institute, Worcester MA

Investigators

Abstract

0084512 Ram-Mohan Layered quantum semiconductor structures such as multiple quantum wells, superlattices, and, multi-barrier resonant tunneling diode (RTD) structures have been realized as viable devices over the past several years. Here the PI proposes the investigation of carrier tunneling, with special, emphasis on hole tunneling, in such structures. The in-plane energy dispersion for holes in these structures displays large non-parabolicities of the energy sub-bands. It has also been found that in-plane dispersion in such quantum heterostructures significantly influences the tunneling spectrum in the growth direction. In the existing literature, these crucial aspects have not been included in (a) multi-band Schrodinger-Poisson self-consistent band bending calculations, (b) a tunneling theory including in-plane wavevector dependence, and (c) the full theory of the I-V characteristics of general layered systems including these effects. The modeling aspects of the theory are best done in a highly accurate finite element approach that was investigated earlier by the PI. A number of puzzling features in the I-V characteristics in Type-11 RTDs observed by Magno, et al., at the Naval Research Laboratory will be addressed. A proper understanding of the Type-II interband quantum cascade laser (proposed and later implemented by Meyer, Vurgaftman and the PI), under active device conditions also requires a detailed multi-band approach to tunneling. These device applications should permit the realization of wavefunction engineering of optimized structures for superior performance. In addition, nonequilibrium dissipative effects of phonon emission and phonon-assisted tunneling under active device conditions, will be investigated using a Numerical Green's Function approach proposed here. These investigations will have direct relevance to device design, to device performance, and to the implementation of mid-IR lasers and Type-II RTDs.