Analysis of Temperature Dependence of GaAs DHBT Terminal Resistances Using the Observed Kink Effect

Large parasitic series resistances of heterojunction bipolar transistor (HBT) are shown to cause a sharp kink in the base current (IB) of the Gummel plot at elevated temperatures under high collector currents (IC) and low base-collector (b-c) applied bias (VBC). This effect was analyzed and attributed to the temperature dependence of low-field and high field mobilities of undepleted and depleted areas at the b-c region. Using this observed kink a simple technique is presented to extract terminal resistances variation with temperature for an InGaP/GaAs DHBT. These extracted values are compared and verified with those extracted from s-parameter measurements. By incorporating these values into a temperature-dependent large signal DHBT model more accurate thermal behavior of IB at high current is demonstrated