Device characteristics of GaAs-based heterojunction bipolar transistors using an InGaAs/GaAsP strain-compensated layer as a base material

An InGaAs/GaAsP strain-compensated layer has been proposed as a base material for GaAs-based double heterojunction bipolar transistors (DHBTs). As known, decreasing bandgap energy of the base layer in heterojunction bipolar transistors (HBTs) can result in a smaller turn-on voltage. Using InGaAs as a base material is one possible approach to achieve the aim. However, compressive strain induced by InGaAs diminishes the influence of indium-adding-induced bandgap energy reduction, and thus abates the advantage of turn-on voltage reduction. In this study, a 280 Å GaAs_0.81P_0.19 layer has been inserted below the In_0.054Ga_0.946As base layer to compensate the compressive strain induced by the InGaAs base layer. The result shows that the utilization of an InGaAs/GaAsP strain-compensated layer results in a reduction of the turn-on voltage by 20 mV. A turn-on voltage reduction of 190 mV over a conventional HBT with a GaAs base layer is achieved by utilizing the In_0.054Ga_0.946As/GaAs _0.841P_0.19 strain-compensated base layer. This particular DHBT has a small offset voltage of 55 mV and a knee voltage of 0.6 V. A peak current gain of 58.98, a unity-current-gain cut-off frequency fT of 22 GHz and a unilateral power gain cut-off frequency fMAX of 25 GHz are also achieved for this particular DHBT.