Improved InGaP/GaAs/InGaP δ-doped double-HBT with InGaP passivation layer and effects of layer-thickness on device performance

Abstract

This paper reports on the fabrication and characterization of InGaP/GaAs/InGaP δ-doped double heterojunction bipolar transistors (δ-DHBTs) with an InGaP passivation layer. Effects of passivation layer thickness on the performance of the studied devices were investigated. Various passivation layer thicknesses (1000Å to 0Å at a rate of −200Å) were employed in the device fabrication. Experimental findings show that both collector current and current gain are enhanced at fixed base currents when a 400∼ 600-Å thick InGaP passivation layer is used. We obtained current gains of 350 and 280 at a base current of 100 μÅ for δ-DHBTs with a 400-Å thick InGaP passivation layer and without one, respectively. Furthermore, all devices exhibit a collector current saturation voltage (knee voltage) of less than 2.5 V. A control DHBT without a doping spike at the B–C heterointerface has a knee voltage of 3.5 V. At the same time, its current gains as a function of collector current are strongly dependent on the B–C reverse voltage. These high current gains with small knee voltages obtained in improved δ-DHBTs suggested that both the E–B and the B–C potential spikes are eliminated by δ-doped spikes.