The Distribution of Occupied Deep Levels in a-Si:H Determined from CPM Spectra

Abstract

ABSTRACTWe report the determination of the distribution of occupied defect states in hydrogenated amorphous silicon from the deconvolution of constant photocurrent measurement (CPM) spectra, and the modelling of the distribution with the defect pool.The CPM spectra were taken on undoped a-Si:H samples either in their as-grown state, in the annealed state, after quenching from high temperature, or after light-soaking. The spectra were deconvoluted to account for transitions from deep levels and from valence band tail states to a conduction band assumed to have a sharp edge. As-grown or annealed-state samples show a peak at 1.0 eV (0.2 eV FWHM) below the conduction band edge. Assuming a mobility gap of 1.9 eV, this peak lies 0.9 eV above the valence band edge. We ascribe this peak to the Do/+ transition. CPM spectra of light-soaked and thermally quenched samples show shifts in the peak position and increases in die peak height in accordance with the defect pool model. The model calculations agree with the CPM results, so that the applicability of CPM spectral analysis to obtaining detailed values of defect pool parameters is demonstrated.