DOPANT DEFECT INTERACTIONS IN HYDROGEN-FREE AMORPHOUS-SILICON

Substitutional (B, P, As and Ga) and interstitial(K) dopants have been incorporated into H-free amorphous Si (a-Si) films produced by ion be am amorphization of crystalline silicon material. X-ray absorption fin e-structure, photothermal deflection spectroscopy and electronic trans port measurements have been performed on these films to monitor the an nealing-induced ordering phenomena around the implanted dopant impurit y sites. We find that, in thermally relaxed a-Si, substitutional dopan t impurities have a strong tendency to enter the Si random network in the form of threefold-coordinated, electrically inactive, alloying sit es. It is shown that the bonding constraints associated with these sit es 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 impu rities. In such interstitially doped material, excess dangling-bond de nsities are observed which are likely to arise from a charge-induced b ond-breaking mechanism.