Intrinsic dangling-bond density in hydrogenated amorphous silicon

Abstract

Recently proposed models for the recombination-induced creation and thermally activated annealing of dangling bonds in hydrogenated amorphous silicon are discussed. While these models were proposed to explain dangling bonds produced by the recombination of electron-hole pairs created by optical generation or electrical injection, we propose that intrinsic-carrier recombination processes can produce the same effect. The dynamic equilibrium between this generation process and thermal annealing determines an intrinsic dangling-bond density. This intrinsic dangling-bond density is shown to be negligible at room temperature but may be sizable at growth temperatures commonly employed. We show that typical cooling rates after film growth could lead to a ‘‘freeze-in’’ of dangling-bond densities in the range ${10}^{15}$–${10}^{18}$ ${\mathrm{cm}}^{\mathrm{-}3}$. Furthermore, we show that this process can be used to explain the enhancement in performance observed when solar cells are annealed under reverse bias.