Photocurrents in semiconductors and semiconductor quantum wells analyzed by k.p-based Bloch equations

摘要

Using a microscopic theory that combines k.p band structure calculations with multisubband semiconductor Bloch equations we are capable of computing coherent optically-induced rectification, injection, and shift currents in semiconductors and semiconductor nanostructures. A 14-band k.p theory has been employed to obtain electron states in non-centrosymmetric semiconductor systems. Numerical solutions of the multisubband Bloch equations provide a detailed and transparent description of the dynamics of the material excitations in terms of interband and intersubband polarizations/coherences and occupations. Our approach allows us to calculate and analyze photocurrents in the time and the frequency domains for bulk as well as quantum well and quantum wire systems with various growth directions. As examples, we present theoretical results on the rectification and shift currents in bulk GaAs and GaAs-based quantum wells. Moreover, we compare our results with experiments on shift currents. In the experiments the terahertz radiation emitted from the transient currents is detected via electro-optic sampling. This comparison is important from two perspectives. First, it helps to validate the theoretical model. Second, it allows us to investigate the microscopic origins of interesting features observed in the experiments.