Hydrogen collision model: Quantitative description of metastability in amorphous silicon

The hydrogen collision model of light-induced metastability in hydrogenated amorphous silicon is described in detail. Recombination of photogenerated carriers excites mobile H from Si-H bonds, leaving threefold-coordinated Si dangling-bond defects. When two mobile H atoms collide and associate in a metastable two-H complex, the two dangling bonds from which H was emitted also become metastable. The proposed microscopic mechanism is consistent with electron-spin-resonance experiments. Comprehensive rate equations for the dangling-bond and mobile-H densities are presented; these equations include light-induced creation and annealing. Important regimes are solved analytically and numerically. The model provides explanations for both the $t^{1/3}$ time dependence of the rise of defect density during continuous illumination and the $t^{1/2}$ time-dependence during intense laser-pulse illumination. Other consequences and predictions of the H collision model are described.