Heterojunction bipolar transistors with hydrogenated amorphous silicon contacts on crystalline silicon

Heterojunction bipolar transistors with hydrogenated amorphous silicon (a-Si:H) contact layers on crystalline silicon (c-Si) substrates are reported. In particular, current gains exceeding 500 were achieved by heterojunction contacts further including embedded homo-junctions comprised of hydrogenated crystalline silicon (c-Si:H), having thicknesses much shorter than the diffusion length of minority carriers. The a-Si:H and c-Si:H layers were grown by plasma-enhanced chemical vapour deposition at temperatures close to 200°C.