The base contact recombination current and its effect on the current gain of surface-passivated InGaP/GaAs HBTs

In this study, the effect of the emitter-base contact spacing on the current gain of InGaP/GaAs HBTs has been described and the base contact recombination current has been experimentally studied. When devices were passivated by nitride, the current gain of InGaP/GaAs HBTs showed no variation with the perimeter to area ratio, which suggested that the surface recombination current of InGaP/GaAs HBTs was negligible, leading the base contact recombination current to affect the current gain. It was found that the base contact recombination current significantly degraded the current gain when the emitter-base contact spacing was reduced to below 0.5 μm. The diode equation was used to model the base contact recombination current, and an ideality factor of 1.76 was obtained.