P-type doping of hydrogenated amorphous silicon films with boron by reactive radio-frequency co-sputtering

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 x 10(-3) and 5 x 10(-4) Torr. respectively. Substrates were kept at 200degreesC or 250degreesC during sputtering. The maximum B concentration in the film obtained was 2 x 10(19) cm(-3) from secondary ion mass spectroscopy measurement. Films with resistivity Of 10(4)-10(5)Omegacm 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. (C) 2001 Elsevier Science B.V. All rights reserved.