The Hydrogen Content of Multicomponent Amorphous Silicon Alloys by 19F Nuclear Reaction Analysis

Chemical vapor deposited (CVD) amorphous silicon alloyed with carbon or nitrogen (α-Si:X, X=C or N) to retard high temperature crystallization is a promising absorber material for photothermal solar energy conversion. Films are prepared by decomposing silane containing gas mixures, a technique which is known to incorporate hydrogen into α-Si in some cases. Using the 16.45 MeV resonance of the 1H(19F,αγ)16O reaction we made the first measurements of the hydrogen incorporation in CVD a-Si:X films (X=C,N). We have made three observations. First, the incorporation efficiency of hydrogen into CVD a-Si increases by a factor of twenty as the carbon content increases from 0 to 35 atomic percent which indicates that previous studies of multicomponent systems may need to be reevaluated since this enhancement in incorporation efficiency involves hydrogen--a key alloyant in a-Si. Second, the quantity of hydrogen incorporated increases at a greater than linear rate as a function of carbon content which implies that the presence of hydrogen in the films is not accidental but is a necessary part of film growth. Third, the hydrogen content of a-Si decreases to almost zero after high temperature anneal which may help explain reported shift in optical constants.