SWITCHING MECHANISM IN THE HETEROSTRUCTURE HOT-ELECTRON DIODE.

In the heterostructure hot-electron diode (H**2ED) two possible conduction mechanisms exist. At low fields, the current is limited by tunneling through a wide-bandgap heterostructure barrier, resulting in a relatively large device series resistance. At higher fields, electrons are heated to sufficient energies so that thermionic emission over the barrier becomes dominant and the series resistance in this region become negligible. Since the energy distribution of electrons is confined to a narrow range of energies, one or the other of these modes will dominate conduction. The transition between these current conduction modes is shown to result in a negative differential resistance (NDR) and switching speeds that may be extremely fast. Results of both theoretical and experimental investigations of the H**2ED that verify the proposed mechanism and determine more precisely the underlying physical phenomena involved are presented. It is shown using an analytical theory that the field switching mechanism previously proposed is consistent with the NDR observed in the H**2ED. In addition to the tunneling and thermionic emission of hot electrons, the accumulation of electrons at the heterointerface is identified as an important mechanism in the operation of the device.