an amorphous silicon alloy material for example p layer 13 may be comprised of a silicon carbon alloy in this case methane ch 4 is mixed in the deposition chamber with the silane and diborane in conjunction with the deposition of p layer 13 in accordance with the present invention the deposition chamber is then flushed with a decontamination means for substantially removing residual p layer doping contaminants in a gaseous state when diborane is used to dope p layer 13 with boron one preferable decontamination means as embodied herein is nitrogen trifluoride nf 3 the concentration of nitrogen trifluoride is preferably within the range between 0 1 to 100 although a concentration of at least 10 is more preferred a carrier gas such as argon or hydrogen may optionally be used to introduce the nitrogen trifluoride into the deposition chamber the deposition chamber is preferably flushed for about 10 minutes at a gas flow rate of 100 sccm and 0 5 torr the substrate temperature is preferably 250 u00b0 c although temperatures typically range between 200 u00b0 300 u00b0 c other decontamination means which can be used in accordance with the invention include the following gases nh 2 f nhf 2 cnl 3 nhcl 2 nh 2 cl xef 6 xef 4 xef 2 hf f 2 clf 2 clf 4 clf 6 pf 3 pf 5 pcl 5 and cof 2 the reduction in boron concentration in the chamber can be calculated according to the formula c t c o e ft v for a well mixed system where c o is the initial concentration of boron c t is the concentration of boron at time t f is the flow rate corrected.