Thermal activation of deep oxygen defect formation and hydrogen effusion in hydrogenated nanocrystalline silicon thin films

Deep oxygen related defects form in hydrogenated nanocrystalline silicon (nc-Si:H) as a consequence of thermal annealing, but their microscopic origins and formation mechanisms are not well understood. To gain insight to this behavior we intentionally drive-out hydrogen from nc-Si:H films by thermal annealing and monitor accompanying changes in the electronic and vibrational structure of the films with photoluminescence (PL) and Fourier transform infrared (FTIR) absorption spectroscopy. Hydrogen effusion (HE) data provide additional insight, because the annealing temperature range shown to induce a defect band, centered at ~0.7 eV in PL studies, and that corresponding to the onset of thermally activated hydrogen desorption from grain boundaries, coincide. This coincidence suggests a probable link between the two processes. The activation energy obtained from correlated annealing-PL experiments, of ~0.6 eV, for defect formation with thermal exposure, provides substantial insight regarding the mechanism.