AVALANCHE AND DRIFT LAYER CONTRIBUTIONS TO THE NEGATIVE-RESISTANCE OFMILLIMETER-WAVE P+NN+ INP IMPATT DIODE FOR DIFFERENT CURRENT DENSITIES

An attempt is made to investigate the contributions of the avalanche a nd drift layers of a millimetre wave p+nn+ InP IMPATT diode towards hi gh frequency negative resistance for four biasing current densities by computer analysis of the negative resistance profiles in the depletio n layer of the diode and the diode admittance characteristics. The res ults show that the contribution of the avalanche layer to the negative resistance increases while that of the drift layer decreases apprecia bly with an increase of current density from 8 x 10(8) A m-2 to 10(9) A m-2. The negative resistance profiles exhibit a maximum in the drift layer and a minimum in the avalanche layer, while the reactance profi les illustrate the opposite behaviour. In addition, the optimum freque ncy is a window frequency (congruent-to 221 GHz) at an operating curre nt density of 6 x 10(8) A m-2 for which the device Q-factor is 6-6. Th e millimetre wave device performance is found to improve for an increa se of current density beyond 8 x 10(8) A m-2.