Heterojunction cathode injectors for D-band InP gunn devices

Abstract InP Gunn devices with InGaAsP heterojunction-cathode injectors have been investigated for operation at D-band frequencies (110–170 GHz). The energy barrier to electron flow associated with the InGaAsP/InP heterojunction increases the electric field strength in the active region. Monte Carlo simulation reveals that a large barrier height could produce an excessive electric field near the cathode. As a result, the majority of electrons remain in the upper conduction band valleys throughout the active region which is to be avoided. Compared to a conventional structure, the heterojunction-cathode structure tends to operate at lower frequencies due to the reduction of the “dead zone” or equivalently the increase in the effective transit region length. Simulation of a structure with 0.8 μm long active region and a 0.1 eV barrier height predicts optimum performance at 140 GHz with an output power of 156 mW and a conversion efficiency of 5.5%. Including quantum tunneling in the model results in a larger average current density and degradation in performance. However with the barrier height increased to 0.125 eV, simulation results predict more than twofold increase in power and more than 50% increase in efficiency compared to a conventional structure with a graded doping profile.