Theoretical and Experimental Investigation of Heterojunction Interfaces

Abstract : A technique based on the use of x-ray photoelectron spectroscopy was developed to measure heterojunction band discontinuities with an uncertainty of + or - 0.04 eV and changes in band discontinuities for a specific heterojunction interface with an uncertainty of + or - 0.01 eV. This technique was used to investigate Ge-GaAs, GaAs-A1As, ZnSe-GaAs, and ZnSe-Ge heterojunctions. It was discovered that microscopic dipoles present at abrupt heterojunction interfaces can substantially affect observed band discontinuities. Variations in heterojunction band discontinuities as functions of crystallographic orientation, growth sequence, and growth conditions were observed. It was established that heterojunction band discontinuities depend on microscopic properties of the interface and cannot be predicted from individual semiconductor properties alone. Based on electrostatic considerations, it was shown that polar heterojunction interfaces cannot be atomically abrupt but must require at least two interfacial transition planes to be consistent with experimental observations.