Dopant‐defect interactions in hydrogen‐free amorphous silicon

Abstract

Abstract Substitutional (B, P, As and Ga) and interstitial (K) dopants have been incorporated into H‐free amorphous Si (a‐Si) films produced by ion beam amorphization of crystalline silicon material. X‐ray absorption fine‐structure, photothermal deflection spectroscopy and electronic transport measurements have been performed on these films to monitor the annealing‐induced ordering phenomena around the implanted dopant impurity sites. We find that, in thermally relaxed a‐Si, substitutional dopant impurities have a strong tendency to enter the Si random network in the form of threefold‐coordinated, electrically inactive, alloying sites. It is shown that the bonding constraints associated with these sites retard the structural relaxation process of the a‐Si films and the crystallization of the a‐Si network in the immediate neighbourhood of these sites. In agreement with previous work, we find that high‐defect‐density a‐Si films can be electrically doped with interstitial K impurities. In such interstitially doped material, excess dangling‐bond densities are observed which are likely to arise from a charge‐induced bond‐breaking mechanism.