Role of boron in the structural and electronic properties of hydrogenated silicon films deposited by r.f. magnetron sputtering

Abstract

Results on the characterization of boron-doped hydrogenated silicon films prepared by r.f. magnetron sputtering technique are presented. The effect of gas-phase dopant concentration Y_g and r.f. power density P on the structure and electronic properties of the films were investigated. The films were characterized by X-ray diffractometry, Transmission electron microscopy and Raman spectroscopy. For X-ray diffraction, both the grazing-incidence diffraction mode and the Bragg-Brentano mode were used. In Raman spectroscopy, in addition to the regular spectra, polarization effects were studied for specific samples. The boron content of the films was obtained by secondary-ion mass spectroscopy and was compared with the camer concentration determined from Hall-effect measurements. The structural changes were correlated with the conductivity and mobility of the films. With an increase in the ratio P/Y_g, the growth pattern changed from homogeneous, similar to small-grained polysilicon, to anisotropic, with a large-grained matrix. In this region of P/Y_g, highly conducting (about 20 S cm^-1) films were obtained. With a further increase in P/Y_g, segregation of boron atoms with concomitant deterioration in the crystalline structure was observed.