DRIFT CURRENT AND THERMAL PRESSURE EFFECTS IN THE ELECTROMAGNETIC INSTABILITIES OF PERIODIC SEMICONDUCTOR SUPERLATTICES

We investigate the electromagnetic instabilities of an infinite period ic superlattice consisting of alternating spatially dispersive (nonloc al) and nonspatially dispersive (local) layers. We extend the results of Martin and Wallis [Phys. Rev. B 46, 12 448 (1992)] to include the e ffects of the electron thermal pressure gradient besides a dc drift cu rrent. In the case of zero pressure gradient, the dispersion relation shows branches not reported before. We also found that the thermal pre ssure changes the range of wave vectors where instabilities occur.