Comparison of surface recombination effect in GaAs-based heterostructure-emitter and heterostructure-base transistors (HEHBTs)

In this paper, the surface recombination effect of a GaAs-based heterostructure-emitter and heterostructure-base transistor (HEHBT) with a pseudomorphic base structure are compared and investigated. Due to the insertion of InGaAs quantum well between emitter-base (E-B) junction, the valence band discontinuity can be enhanced and a high emitter injection efficiency may be achieved. The excellent transistor characteristics including high current gain of 280 and low offset voltage of 100 mV are obtained when the base metal is deposited on the lower surface recombination velocity InGaAs layer. However, a lower current gain of only 135 and large offset voltage of 300 m V are acquired as the base metal is deposited on the GaAs layer. This is mainly attributed to the significant difference of surface recombination effect of the studied devices. The surface recombination velocity of InGaAs is substantially lower than that of GaAs layer. Thus, a reduced surface recombination current and an enhanced current gain can be obtained when the InGaAs is used as base contact layer,