Optimum doping level in a-Si:H and a-SiC:H materials

The changes in the optical and electrical properties of thick a-Si:H and a-SiC:H films doped with diborane are investigated. In situ spectroscopic ellipsometry measurements reveal that, at a ratio of diborane to silane C(g)=[B(2)H(6)]/[SiH(4)]<10(-3), the optical properties of both materials are not strongly modified by boron doping. However, in the case of a-Si:H films, an improvement of the morphological and optical properties is observed at C(g)=0.45X10(-3). The existence of an optimum doping level at C(g)<10(-3) in the case of an a-Si:H p layer is confirmed by the dependence of the open-circuit voltage of a-Si:H based solar cells on the doping level of the p layer. (C) 1998 American Institute of Physics. [S0021-8979(98)0720 1-6].