Simulation of electron plasma instability in n+nn+ GaAs structure

High frequency microwave generation is feasible in n+nn+ structures because of the electron plasma instability in the device. The time and frequency behaviour of the current instability in the electron plasma of n+nn+ GaAs structure is simulated by Monte Carlo method. The simulation technique involves the particle-in-cell formalism. In the model for simulation, the energy dispersion band is taken to be parabolic and spherical. The other parameters like the effective mass, band gap etc. are taken from the standard literatures. The temperature is taken to be 25 K. Polar optical, acoustic phonon and impurity scatterings are taken into consideration. It is observed that the oscillation frequency in the THz region is affected by the structure length. The optical phonon dominated current instabilities show high peaks alternating with extremely high frequencies in the time scale of pico-seconds. For longer structures, the instability is found to be dominated strongly by the optic phonon scatterings while for short ones it is mainly by the ballistic mode. Smaller is the structure length higher is the instability frequency. It may also be remarked here that the structure length does not affect the carrier behavior very close to the cathode of the structure.