TERAHERTZ BALLISTIC CURRENT OSCILLATIONS FOR CARRIERS WITH NEGATIVE EFFECTIVE-MASS

It is shown that the stationary distribution of ballistic current carr iers moving across a thin doped base is unstable if there exists a neg ative effective mass (NEM) part in the carrier dispersion law. Under s uch a condition, a regime with a quasistationary current oscillations is established for a wide range of voltages across ballistic diode. Th e oscillation frequency and amplitude depend on the base length, dopin g concentration, and applied voltage. The current oscillations take pl ace in a short-circuit regime (in absence of an external resonator). W e consider asymmetric double quantum wells and/or composite Gamma X qu antum wells as possible structures allowing for the required dispersio n relation with NEM part. Carrier dynamics in these structures are des cribed quasiclassically and the validity of such a treatment is discus sed. (C) 1996 American Institute of Physics.