Heterojunction Bipolar Transistor Development for Semiconductor Laser Drivers

Heterojunction bipolar transistors (HBTs) were designed, grown by molecular beam epitaxy (MBE) and fabricated for applications as semiconductor laser drivers. The material growth technique of MBE and its added flexibility in the design of HBT structures for optimum performance in laser drivers was investigated. The HBT epitaxial layer structure was optimized to achieve the specifications necessary for multi-gigabit/sec laser drivers. The optimized HBT structure differs from conventional designs in the emitter, collector, and the base thicknesses and compositions. Numerical simulation was used to study carrier transport across the graded base region. HBTs with the optimized structure are shown to have characteristics superior to conventional HBTs. Thus the new design has great potential for microwave and optoelectronic integrated laser-array driver circuits.