Surface passivation of InP/InGaAs heterojunction bipolar transistors

The effect of different dielectric films deposited by different techniques, on the electrical characteristics of InP/InGaAs heterojunction bipolar transistors was investigated. The electrical characteristics vary significantly depending on the type of dielectric film used for passivation. A significant increase in the forward biased base current, which resulted in lower transistor gain as well as an increased reverse leakage current in the base-collector junction, was observed when silicon nitride and silicon dioxide were deposited using plasma enhanced chemical vapour deposition. On the other hand, silicon monoxide and strontium fluoride films deposited using thermal evaporation, resulted in little degradation in the transistor characteristics. The low-temperature deposition was believed to have induced less surface states, resulting in the electrical characteristics being maintained long after deposition.