Comparisons between InGaP/GaAs heterojunction bipolar transistors with a sulfur- and an InGaP-passivated base surface

This paper reports on InGaP/GaAs heterojunction bipolar transistors (HBTs) with a sulfur-treated base layer, which are then compared to InGaP/GaAs HBTs with an InGaP-passivated base layer. Experimental results reveal that the improvement in base leakage current for InGaP-passivated HBTs is due to the inherent low surface recombination velocity associated with an InGaP layer while it is the electronic modification of the GaAs surface for sulfur-treated HBTs. The maximum dc current gain available is β=75 with a base sheet resistance of RB=220Ω/□ for a sulfur-passivated HBT. The sulfur-passivated HBTs also exhibit very good linearity over a wide collector current range of 10−5 to 10−1 A. Furthermore, detailed sulfur treatment conditions and effects on device performances including post-treatment stability are investigated.