Current Gain and Offset Voltage in an InGaP/GaAsSb/GaAs Double Heterojunction Bipolar Transistor

An $\hbox{In}_{0.5}\hbox{Ga}_{0.5}\hbox{P/GaAs}_{0.93}\hbox{Sb}_{0.07}/ \hbox{GaAs}$ heterostructure is grown by metal–organic chemical vapor deposition and demonstrated to be an alternative to InGaP/GaAs systems for use in single heterojunction bipolar transistors (SHBTs). The $\hbox{In}_{0.5}\hbox{Ga}_{0.5}\hbox{P/GaAs}_{0.93}\hbox{Sb}_{0.07}/ \hbox{GaAs}$ double heterojunction bipolar transistor (DHBT) device structures are identical to the control SHBTs except for the incorporation of antimony to the base layer. The InGaP/GaAsSb/GaAs DHBT has a lower turn-on voltage than the control InGaP/GaAs SHBT. Details of the effect of the base current on the offset voltage in the studied devices are explored. The dc current gain $\beta$ of the InGaP/GaAsSb/GaAs DHBT is virtually independent of collector current at 300 K. The current gain of the GaAsSb-based DHBT is greater than 40 at a very small collector current of 1 $\mu \hbox{A}$ at 300 K. The dependence of the current gain on temperature at various collector currents is discussed. The variation of $\beta$ with temperature is slight at high currents over the range of 300 K–390 K. Furthermore, the current gain of the InGaP/GaAsSb/GaAs DHBT exhibits almost no dependence on the collector–base voltage $V_{\rm CB}$ , demonstrating the nonblocking “type-II” band lineup at the base/collector heterojunction.