Pressure and temperature tuning of the valence band offset in cubic superlattices: The effects of piezoelectric fields

Abstract

Theoretical calculations have been performed to study the effects of piezoelectric fields in superlattice systems. The results show that cubic strained superlattices and quantum wells subjected to variable temperature and pressure exhibit changes in their piezoelectric fields. We consider superlattice systems grown in arbitrary directions, with a thickness smaller and larger than the critical thickness value (undercritical and overcritical systems). In both cases (including the partially relaxed case), theory predicts the existence of a critical temperature Tm and a critical pressure pm, above which the sign of the piezoelectric fields in each layer reverses. As applications to practical systems, we calculated (1) the piezoelectric fields as a function of temperature in GaAs∕ZnSe superlattice and (2) the piezoelectric fields as a function of pressure in GaAs∕InAs, GaAs∕Si, and ZnSe∕GaAs superlattice systems. We present here the results of the effects of piezoelectric fields for three different systems (undercritical systems, overcritical systems, and partially relaxed systems), where the piezoelectric field changes under variable temperature, pressure, and thickness of the layers. We also discuss the valence band offset, which is induced by piezoelectric fields, and its dependence on temperature and pressure. In addition, we present data on the valence band offset for some practical undercritical systems. All results and conclusions are valid in a linear region of strain or stress where no phase transitions occur.