ANALYSIS OF THE OFFSET VOLTAGE OF INGAP/GAAS SINGLE, DOUBLE, AND COMPOSITE DOUBLE-HETEROJUNCTION BIPOLAR-TRANSISTORS

The common-emitter offset voltages of In0.49Ga 0.51P/GaAs single-, double-, and composite double-heterojunction bipolar transistors have been investigated. The physical mechanisms behind variations in the offset voltage between these devices and versus base current for each device have been examined. We have found that the offset voltages of the composite collector devices decrease and remain more constant at low base currents as the composite spacer thickness decreases due to reduced space-charge recombination in the base-collector junction. An InGaP/GaAs composite-collector device with a thin spacer has an offset voltage that is almost as low and uniform as a double-heterojunction bipolar transistor (DHBT) with comparable breakdown voltage but without the poor common-emitter current characteristics of the DHBT. © 1995 American Institute of Physics.