Semiconductor Heterojunctions

Semiconductor heterojunctions offer unique electrical and optical properties not otherwise found in nature. Growth methods are now available to create new novel heterojunction structures with state-of-the-art physical properties for next generation electronics. This chapter covers the unique interface features of semiconductor heterojunctions in terms of their geometrical, chemical, and electronic structure. For a particular application, one chooses semiconductors or semiconductor alloys based on both their energy gaps and their good lattice match. The lattice mismatch between heterojunction constituents leads to strain and ultimately the formation of lattice dislocations. Semiconductor-semiconductor heterojunctions can exhibit a variety of chemical structures including interdiffusion, chemical reactions, and interlayer effects. The chapter reviews both experimental and theoretical work to understand the nature of heterojunction band offsets as well as atomic-scale methods to control them. One approach to describe band offsets involves the alignment of charge neutrality levels in the two semiconductors.