Monte Carlo Simulation of Millimeter-Wave Gunn Effect Oscillators

Monte Carlo simulations have been carried out to investigate the performance of microwave Gunn oscillators. Three separate aspects of the simulation problem have been comprehensively addressed in this work. First, the presence of an external circuit has been self-consistently incorporated into the calculations. The inclusion of the external circuit facilitates a study of the circuit controlled regime, and correctly models effects arising from the time dependent boundary conditions. Secondly, microscopic details of the electronic relaxation mechanisms which ultimately control the frequency response limits, have been taken into account through an iterative Monte Carlo-Poisson scheme. This procedure overcomes a potential shortcoming of many previous analytical simulations which have relied on the steady state velocity-field characteristics for obtaining the microwave response. Comparisons between conventional GaAs Gunn diodes including a doping notch in the active layer have been made with AlxGa1.xAs heterojunction cathode structures. Particular attention has been focused on the heterojunction cathode effects. Impact on the changes in the operating characteristics, the ac conversion efficiency, and the power output arising from variations in the doping profile and alloy composition have been studied. Finally, results from some pertinent comparisons between conventional bulk oscillators and hetero-structure devices have also been obtained. We conclude that heterostructure Gunn diodes show improvements in performance over conventional Gunn devices at high voltages. In addition, appropriate tailoring of the doping profile can enhance the ac conversion efficiency.