Study of the ion implantation of Sn-119 in a-Si1-xCx : H

The Mossbauer spectroscopy and Rutherford backscattering spectroscopy studi es presented here allow an investigation of the origins of the previously o bserved changes in optical absorption in sputter deposited a-Si1-xCx:H film s caused by high dose Sn implantations. To this end, we investigate the mic roscopic surroundings and the bonding structures of the Sn atoms. At doses up to 1 x 10(17) cm(-2) a major fraction of Sn takes a quasi-substitutional site, sp(3) bonded to four Si neighbours, while a smaller fraction is pres ent as Sn2+, presumably due to SnO formation. The latter fraction increases at the higher doses and the increase is paralleled by the formation of Sn4 + and a prominent metallic sn component. This beta-Sn fraction, presumably in the form of nanosized precipitates, becomes dominant at the higher doses , thus explaining the complete lack of optical transmission. (C) 1999 Elsev ier Science B.V. All rights reserved.