B has been successfully doped into the hydrogenated amorphous Si films without using explosive and/or toxic gases SiH4 or B2H6 by reactive radio-frequency co-sputtering. The target used for co-sputtering was a composite target composed of a B-doped Si wafer and B chips attached on the Si wafer with silver powder bond. The maximum area fraction of B chips used was 0.11. Argon and hydrogen pressures were 5 × 10-3 and 5 × 10-4 Torr, respectively. Substrates were kept at 200°C or 250°C during sputtering. The maximum B concentration in the film obtained was 2 × 1019 cm-3 from secondary ion mass spectroscopy measurement. Films with resistivity of 104-105 Ωcm were obtained, which was low for the above acceptor concentration, compared with other group III impurities doping, indicating the high doping efficiency of B. A heterostructure, which was prepared by co-sputtering these B-doped films on an n-type crystalline Si, shows a good rectification characteristic. A small photovoltaic effect is also observed.
- Hydrogenated amorphous silicon