Fabrication of GaInAs/InP Heterojunction Bipolar Transistors with a Single Tungsten Wire as Collector Electrode

GaInAs/InP heterojunction bipolar transistors (HBTs) with a single 0.1-mu m-wide W wire were fabricated. The W wire was buried in an undoped InP collector layer and functioned as a collector electrode. In a previous process of fabricating HBTs with buried wires, authors could not achieve a device operation with only a single wire. One of the possible reasons for this failure was the insufficient growth of the buried wire, because this wire requires a long growth time. The nonuniformity of facet formation in a previous wet etching process used to fabricate an InP emitter also contributed to the failure. By increasing the growth time of the buried wire and changing the wet etching solution used to enable uniform fabrication of emitter mesas, authors observed a transistor operation with a current gain of 20 in the fabricated HBT. The emitter area of the device was 0.1x 0.5 mu m2. 7 refs.