Comparison of In/sub 0.5/Ga/sub 0.5/P/GaAs single- and double-heterojunction bipolar transistors with a carbon-doped base

A comparison of MOCVD-grown, n-p-n In/sub 0.5/Ga/sub 0.5/P/GaAs single- and double-heterojunction bipolar transistors (SHBTs and DHBTs) with a carbon-doped base is presented. A base doping level of 2.5*10/sup 19/ cm/sup -3/ was employed in both device structures, resulting in a base sheet resistance of 500 Omega /sq. Common-emitter current gains as high as 210 and 150 were measured for the SHBTs and DHBTs, respectively. Results of a DC performance optimization study indicate that a 15- and 25-AA undoped set-back layer at the emitter-base junction provides optimal common-emitter current gain. The DHBTs exhibited a 40% improvement in common-base breakdown voltage compared to SHBTs (25 versus 18 V), indicating that In/sub 0.5/Ga/sub 0.5/P/GaAs DHBTs may prove suitable for power device applications.>