Large-signal simulations of non-stationary transport in GaAs and InP millimeter Impatt diodes have been performed. This study of the influence of non steady-state features on the performance of a 100 GHz operation shows that non punch-through structures still present interesting performances at this frequency. However, for this type of structure, InP exhibits significant advantages over GaAs for the manufacture of high efficiency diodes.A T FREQUENCIES below 30 GHz high power Impatt oscillators are dominated by non punch-through diodes using transferred electron velocity materials. The situation regarding millimeter wave Impatt is less clear. High efficiency oscillators have been fabricated from silicon punch-through diodes and GaAs impatt diodes have had little experimental success.This discrepancy could be explained by numerous effects, (difference between the saturation velocities or the build up times of the avalanche) but it is sufficiently large to raise the possibility that some novel physical mechanism is present in device operation in the millimeter frequency band and particularly for devices operating in the premature collection [ 1, 21 and surfing modes [3, 41.The premature collection mode refers to the collection of the avalanche current at drift angles smaller than the small signal angle, which is intentionally chosen to be longer than the optimum conventional one. The surfing mode is characterized by a carrier bunch drifting synchronously with the movement of the front edge of the depletion layer at drift velocity superior to the saturation value.The most important factors for successful operation in these high efficiency modes are the use of transferred electron velocity material, and a large depletion region modulation obtained with clump structures. It is obvious that if we extrapolate these conditions of operation and these types of structure up to the millimeter frequencies, very high field gradients and rapid time variations will be present in the device. These are the conditions under which the non-stationary transport effects are expected to be significant. In. all cases the effects of the energy relaxation seem to be sufficiently important to influence the high-frequency performances and t o be considered in simulations.We are interested here with the energy conserving transport properties of carriers in the drift region of GaAs and InP Read diodes in order to point out the fundamental limitation of the high efficiency modes of operation. In particular, we propose to study to what extent non punch-through structures could be used in the millimeter frequency range, because millimeterwave Impatt diodes generally studied [j] are punched through in order to avoid the performance deterioration due to diffusion and mobility effects.Because the purpose of this article is the study of the role played by the energy relaxation on the depletion region width modulation and transferred electron velocity modulation, we have divided the diode into two zones: the avalanche region and transit region. The in...
