Progress in growth of high quality amorphous silicon materials

The band gap of hydrogenated amorphous silicon (a-Si:H) can be tuned from 1.5 eV to 2.1 eV by intentionally promoting structural relaxation during film growth by using chemically active species such as hydrogen atom or excited argon. No marked changes were observed in the local silicon-silicon bonds such as bond-length and bond-angle distribution for these films although the band gaps were significantly changed. The dielectric constants (ε₂) and weight of the films was markedly reduced in the wide gap a-Si:H materials, implying that the medium range structure of Si-network was significantly altered. The light soaking stability was improved in all cases where relaxation was promoted. The novel technique termed “Chemical Annealing” shows significant potential for fabrication of improved thin film silicon solar cells