Spontaneous polarization and piezoelectric field in nitride semiconductor heterostructures

Wide bandgap nitride semiconductors have recently attracted a great level o f attention owing to their direct bandgaps in the visible to ultraviolet re gions of the spectrum. A number of scientific challenges remain, however, i ncluding important issues such as the determination and control of film pol arity and relative extent of various polarization effects. Polarization eff ects arise from two sources: 1) spontaneous polarization at heterointerface s due to the ionic wurtzite nitride bonds, and 2) strain-induced piezoelect ric polarization caused by lattice misfit or thermal strain. Polarization e ffects can impact heterojunction structures such as MODFETs and quantum wel ls. In quantum wells, the fundamental electron-heavy-hole transition in GaN /AlGaN quantum wells is observed to red-shift well below the GaN bulk gap f or well widths larger than 3 nm for the specific quantum wells investigated . Polarization effects as pertained to nitride semiconductor heterostructur es and devices will be treated.