Dynamical conductivity of type-I semiconductor superlattices

We calculated longitudinal and transverse macroscopic as well as microscopi c dynamical conductivity for a modulation-doped type-I superlattice. Our co mputed long wavelength macroscopic conductivity significantly differs from Drude conductivity in the low-frequency regime (microwave and infrared radi ations). Macroscopic conductivity shows oscillatory behaviour along the dir ection of growth of the superlattice. Propagation of transverse electromagn etic waves in a superlattice has been studied for all possible values of fr equency and wavevector. It is found that microscopic transverse conductivit y exhibits poles along both real and imaginary axes of frequency. Depending on the values of wavevector components, along and perpendicular to the dir ection of the superlattice, both poles can lie on real or imaginary axes of frequency. We also find that there can be more than one penetration depth for a superlattice and one of them decreases with frequency for frequencies below the microwave regime. (C) 2000 Academic Press.