QUANTUM-WELL INTERSUBBAND RELAXATION IN RESONANT TUNNELING DIODES AND TRANSISTORS

The intersubband relaxation rate due to electron-electron interaction is calculated in analytical form and compared to the intersubband relaxation rates for polar optical phonon emission and for impurity scattering. It is found that for resonant tunneling diodes biased into the second resonance, the intersubband relaxation rate due to electron-electron scattering can become comparable to that due to phonon emission and can involve subpicosecond relaxation times. Taken together, these intersubband relaxation rates are sufficiently strong to significantly reduce the gain of a resonant tunneling transistor, i.e., a device in which an ohmic contact is made to the quantum well of a resonant tunneling diode. This leads us to propose a novel device structure similar to the resonant tunneling transistor, but where the subband for base potential modulation and the subband for hot charge transfer are located at different points in the Brillouin zone. This structure has the advantage that the intersubband relaxation rate is significantly reduced due to the increased momentum exchange on intersubband scattering. A possible material system that has all the needed band lineups to implement this device structure is the GaAs/AlAs/Ge material system.