InP-based heterojunction bipolar transistors: Recent advances and thermal properties

InP-based heterojunction bipolar transistor technology has been progressing rapidly over the past few years. Both the current-gain cutoff frequency and maximum frequency of oscillation have broken the 200-GHz performance barrier. The limitation of single-heterojunction bipolar transistors arises from their dc characteristics. Double-heterojunction bipolar transistors offer better output conductance and breakdown characteristics, but require more careful base-collector heterojunction design. The use of thick low-thermal-conductivity InGaAs in the collector and subcollector layers significantly increases the device junction temperature and base-collector reverse saturation current. For complicated device structures, such as InP power double-heterojunction bipolar transistors, we demonstrate that small collector-emitter saturation voltage, large breakdown voltage, and high maximum oscillation frequency can be achieved by putting as little as 194-Å InGaAs in the > 8300-Å-thick collector.