Bipolar spintronics

By incorporating spin-dependent properties and magnetism in semiconductor structures, new applications can be considered which go beyond magnetoresistive effects based on metallic systems. Notwithstanding the prospects for spin/magnetism-enhanced logic in semiconductors, many important theoretical, experimental, and materials challenges remain. This chapter discusses the challenge for realizing a particular class of applications: the proposal here is for bipolar spintronic devices in which carriers of both polarities (electrons and holes) contribute to spin-charge coupling. Nonlinear current-voltage characteristics, large deviations from local charge neutrality, as well as inhomogeneous built-in and applied fields, all have important implications on the bipolar transport and potential spin-based logic applications. This chapter formulates the theoretical framework for bipolar spin-polarized transport, and describes the novel effects in two- and threeterminal structures which arise from the interplay between nonequilibrium spin and equilibrium magnetization.