Genuine wide-bandgap microcrystalline emitter Si-HBT with enhanced current gain by suppressing homocrystallization

The energy bandgap of microcrystalline silicon (μc-Si) emitter prepared by the plasma CVD method for Si-HBTs was investigated. The μc-Si films directly deposited on c-Si substrates were confirmed to have almost the same energy bandgap as c-Si because of μc-Si crystallization, resulting in formation of a homojunction. In order to suppress such a homojunction formation, a c-Si surface modification method using an a-SiC thin layer was proposed. The a-SiC layer was confirmed to have the effect of producing an abrupt and uniform heterojunction. A current gain as high as 523 was obtained by using the a-SiC thin layer, which was 24 times larger than that without the a-SiC layer