Modelo e propriedades de heterojunções não-abruptas GaAs/AlxGa1-xAs

Abstract

A model was depeloped to study the properties of nonabrupt semiconductor heterojunctions GaAs/ Alx Ga1-x As. It is a generalization of the model of Freire, Auto e Farias [Superlattices and Microstr-uctures 1, 17 (1992)). It is included the possibility of any variation of the semiconductor alloy in the interface region, and also the possibility of the existence of random roughness. Kinetic energy operators with position dependent effective mass are used to calculate carrier transmission through nonabrupt GaAs/ Alx Ga1- x As heterojunctions. The multistep method of Ando and Itoh [J. Appl. Phys. 61, 1497 (1987)) is generalized for a class of kinetic energy operators, and used to obtain numerical solution of the eigenvalue problems necessary for the calculation of the transmission. By using a linear profile for the interfacial aluminium molar fraction variation, it is shown the limits of the constant effective mass approximation in the interfa .. e. ln this case, resonant peaks whose existence was early supposed hy Freire, Auto, and Faria.s, it is shown to disappear when the spacial dependence of the effective mass i::; considered. The role of five types of growth patterns in the heterojunction proper.ties is studied. It is shown that carrier transmission, in particular the existence of resonant peaks, is dependent of the type of growth pattern of -the aluminium molar fraction in the interface region. Effects of growth patterns are more important to heavy holes than electrons. When ranclom roughness are incluclecl in the variation of the aluminium molar fraction in the interface region, it is obtained a growth of the transmission. It is shown that the type of the kinetic energy operator is important, principally in the case of heavy holes, and when the interface wiclth is small. Our results inclicate the limitations of models that consider an abrupt picture of the interface, anel those that consider the constant effective mass approximation in the inter-facial region.