COMPETITION BETWEEN THERMALLY-INDUCED RESONANT-TUNNELING AND PHONON-ASSISTED TUNNELING IN SEMICONDUCTOR SUPERLATTICES

We employ time-dependent photocurrent measurements to study the temper ature dependence of the tunneling dynamics of electrons in GaAs-AlAs s uperlattices with similar coupling but different subband spacings. At low temperatures the transport characteristics are governed by resonan t tunneling as well as longitudinal optical phonon-assisted tunneling out of the lowest subband. However, for a smaller subband spacing, res onances due to elastic tunneling out of the thermally populated second subband are observed at higher temperatures. At room temperature thes e resonances dominate in comparison with the inelastic transport chann els out of the ground state. The thermal population of the second subb and is directly observed by electroluminescence spectroscopy.