Effects of passivation-layer thickness and current gain enhancement of InGaP/GaAs -doped single heterojunction bipolar transistors using an InGaP passivation layer

This paper reports the fabrication and characterization of InGaP/GaAs -doped single heterojunction bipolar transistors (-SHBTs) with an InGaP passivation layer. Effects of passivation-layer thickness on device performance are investigated. Various passivation-layer thicknesses (, 75, 50, 25, 0 nm) are employed in the device fabrication. Experimental findings show that both collector current and current gain are enhanced at fixed base currents when an InGaP passivation layer is used. We obtain a current gain and a collector current of 340 (300) and 50 (42) mA at a base current of 200 for a -SHBT with a 50 nm thick (0 nm thick) InGaP passivation layer, respectively. All fabricated devices exhibit a small offset voltage of 50 mV. Furthermore, comparisons between passivated and unpassivated devices with a small emitter size are also included. It is found that a passivated -SHBT with an optimized InGaP layer shows little degradation in current gains as used emitter size is scaled.