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Summary form only given. The authors present a comparison of single- and double-heterojunction devices formed in the InGaP/GaAs materials system. The HBT (heterojunction bipolar transistor) structures used for this study were grown by LP-MOCVD (low-pressure metal-organic chemical vapor deposition) using CCl4 as the base dopant. It was found that the use of a 25-Å spacer layer provided the highest gains in these device structures, with βMAX~210. A decrease in current gain with increasing spacer layer thickness was attributed to space-charge recombination current at the emitter-base junction. Despite the small conduction band discontinuity reported for this materials system, the gains for the double-heterojunction transistors were considerably lower (βMAX~25) than for single-heterojunction devices for which all other layers besides the collector were identical.