Nonequilibrium Electrons in Semiconductor

The dynamics of nonequilibrium electron transport in submicron devices has been explored with the technique "Hot Electron Spectroscopy. " Using this method the evolution of an injected nonequilibrium electron momentum distribution with distance from the point of injection has been obtained for GaAs.1 To understand the scattering mechanisms giving rise to the observed hot electron spectra, a theory of nonequilibrium electron transport has been developed which takes into account the coupled nature of the longitudinal optic phonon and plasmon modes in n-type direct bandgap semiconductors.2 These studies have been extended to nonequilibrium conduction band electrons interacting with an ambient Fermi sea of holes in the valence band of GaAs. Hot electron spectroscopy measurements using a double heterojunction bipolar transistor structure indicate that nonequilibrium electrons interact strongly with holes and the transistors' electroluminescence shows that a potential well formed at the base collector junction acts as a preferential trap of low energy conduction band electrons in the base. At high current densities the trap saturates with the subsequent build-up of carriers in the base changing the transistor turn on characteristic.3 To gain deeper physical insight into the scattering of electrons with holes, a theory has been developed which takes into account the essential role of intervalence band and optic phonon excitations. More recently the transport of electrons across thin (is equal to or less than 100 Angstrom) layers of low mass semiconductors has been measured. A significant number of electrons traverse the material without scattering and, assuming reasonable electron velocities, their traversal time is much less than a picosecond.