Role of Si-H bonding in a-Si:H metastability

In plasma-deposited a-Si:H films, the time dependence and saturation value of the metastable defect density produced by high-intensity illumination are found to depend on the material properties. From a wide range of deposition techniques, we have observed a strong correlation between the steady-state defect density N_ss and the monohydride Si-H bond concentration observed in infrared transmission, with [SiH]₂₀₀₀ values between 2% and 16%. We propose a microscopic description of the light-induced defect creation and light-induced defect annealing phenomena in a-Si:H, based on the trapping of mobile H at two specific sites: the Si-H bond and the Si dangling bond. This model predicts a steady-state defect density proportional to the monohydride [SiH]. For the production of mobile H in three-center (Si-H-Si) configurations, a low-energy mechanism with no necessity for Si-H bond breaking is suggested from the observed changes in the infrared absorption of the various H-bonding configurations during light soaking. With the assistance of an electron-hole pair recombination, it consists of the excitation of two adjacent H atoms from a (Si-H H-Si) configuration along with a Si-Si bond reconstruction.