Layer design for GaAs-based DHBTs enabling 28V high-power microwave applications

We report on the realization of GaAs-based Double Heterojunction Bipolartransistors (DHBTs) using GaInP as collector material. With a collector thickness of 1.5 mum we achieved up to 70 V base-collector breakdown voltage. We used a GaAs spacer in conjunction with a highly doped n-type layer at the base-collector junction to compensate the reduction of the critical current density due to the base-collector heterojunction. The devices show a do current gain around 30 and proved to be very stable under on-wafer do conditions, i.e., we were able to obtain a dissipated power of up to 7.5 W and collector currents up to 1 A on a 4000 mum(2) area device. Regarding high-frequency behavior, the DHBTs exhibit cut-off frequencies up to 30 GHz, which are higher than that of a comparable SHBT (20 GHz). On-wafer load-pull measurements yielded 5 W of microwave output power for a 1680 mum(2) area device at 26 V bias and 2 GHz.