Heterojunction bipolar transistors using GaInAs/InP

Demonstrates the integration of GaInAs/InP HBTs by the fabrication of a monolithic differential amplifier. The eventual aim of this work is the integration of these HBTs with 1.3/1.55 μm optoelectronic components. The epitaxial material for the HBTs was grown by atmospheric pressure MOCVD onto semi-insulating InP substrates. The wide bandgap emitter and collector were formed from sulphur doped InP, with zinc doped GaInAs forming the base layer. Contact to the base layer was made either by magnesium implantation or by a selective wet-etch. After making contact to the heavily doped region of the collector, the devices were isolated by etching down to the substrate. A schematic diagram of the implanted transistor is shown. Resistors were fabricated at the same time as the transistors by using the epitaxial base layer; these were also isolated by mesa etching. The mesas were then planarised by a layer of polyimide and the process was completed by running an interconnection level of metallisation over this