In this study, we compare our InAlAs-InP/GaAsSb DHBT with other published GaAsSb-based DHBTs in the dc characteristics by examining the Gummel plot and simulation analysis. The InAlAs-InP and InP-InAlAs composite emitters can effectively reduce electron pile-Up as found in the InP/GaAsSb DHBT, thus increasing current gain significantly at low current density. Although electron pile-up is found in the InP/GaAsSb DHBT from the type-II conduction band barrier, it shows better operation at the high Current regime than composite emitter structures because at high bias the abrupt heterojunction formed at the InP-InAlAs interface blocks carriers and degrades the inject efficiency. (C) 2009 Elsevier Ltd, All rights reserved.