Highly Reliable Carbon-doped HBTs for Microwave Power Generation

The proposed project will develop a new technology capable of producing highly reliable npn heterojunction bipolar transistors (HBTs) using carbon-doping. Carbon is a very slow diffusant and has a higher solubility in GaAs than more conventional dopants, such as beryllium or zinc. A carbon-doped HBT base will provide sharp emitter-base np junctions with a simplified design. Spire proposes to achieve high quality carbon-doped (5 x 10 19 cm-3) np heterojunctions capable of sustaining accelerated-stress life tests. Spire has already succeeded in carbon doping GaAs grown by metalorganic chemical vapor deposition (MOCVD) using trimethylarsenic, and has demonstrated doping up to 10 20 cm-3. Trimethylarsenic appears to be the best candidate for replacing carbon tetrachloride, an ozone depleting gas banned by the Montreal Protocol, as a carbon doping source. The proposed work will expand the GaAs carbon-doping technique to In0.53Ga0.47As, a material of great interest for InP-based power HBTs. MOCVD is an alternative approach to molecular beam epitaxy particularly suitable to the high-quality high-volume HBT products that will be derived from this work. Phase I will demonstrate that Spire's approach is capable of producing high reliability np diodes. Ga0,.51In0.49P/GaAs and InP/Ga0.47 In0.53As np heterojunctions having carbon-doped p-layers and designed to mimic the HBT emitter-base junction will be grown, fabricated, and tested. While InP-based HBTs are potentially higher power devices than GaAs, the advanced state of GaAs manufacturing technology gives it a compelling advantage; both material systems should therefore be explored as the basis for high performance power HBTs. Accelerated stress life tests will validate our approach.