The density of states (DOS) of i-layers in a Si:H based pin cells determined by CPM measurements

In a systematic study, the spectral distribution of the optical absorption coefficient within the subbandgap energy range was estimated. This was done by constant photocurrent method (CPM) measurements on glow-discharge-deposited a-Si based pin cells. Typical CPM spectra were evaluated for pin cells with thicknesses ranging from 0.5 μm to 10 μm measured in various bias modes. Bias-mode-dependent occupations and transitions involving defect states are considered for two representative cells (d=0.64 μm or ´thin´ and d=3.4 μm or ´thick´). The density of states of the thick cell shows a characteristic minimum in the defect-controlled energy region for positive bias voltages while the number of deep defect states remains constant, N(E)=(1.5-3)×10¹⁵ cm^-3 . In the case of the thin cell, N(E) is on the order of 6×10¹⁵ cm^-3