THE DENSITY OF STATES (DOS) OF i-LAYERS IN a-Si:H BASED PIN CELLS

In a systematic study we estimated the spectral distribution of the optical absorption coeffici ent b\(hv) within the subbandgap energy range. This was done by constant photocurrent method (CPM) measurements on glow-discharge depostited a-Si based pin cells. We evaluated typical CPM spectra for pin cells with thicknesses ranging from 0.5 pm to 10 pm measured in various bias modes. We restrict our discussions of the bias mode dependent occupations and transitions i nvolving defect s tates on two representative cells ( d = 0.64 Am: "thin" and d = 3.4 pn : "thick"). The density of states DOS of the thick cell (or the derivative dd/ d(hu 1) shows a characteristic minimum in the defect controlled energy region for positive bias voltages while t he number of deep defect s tates remains constant (N(E) = (1.5 - 3) x 1015 cm-3). In the case of the thin c ell N(E) is in the order of 6 x 1015 cm-3.