Capacitance studies of a-SiGe:H p-i-n solar cells

Abstract

An equivalent circuit model was used to fit the measured conductance (G) and capacitance (C) of a-Si:H and a-SiGe:H p-i-n and Schottky diodes using E/sub A/, g/sub 0/, and v as the main fitting parameters. The midgap density of states (MGDOS) was determined using steady-state admittance measurements on typical a-Si:H and a-SiGe:H p-i-n solar cells, C and G were measured as a function of temperature and frequency. The junction and bulk were each modeled by a capacitor and resistor, and the lumped equivalent circuit was analyzed. Good agreement is found between measured and predicted values of both C and G with the MGDOS and E/sub F/, as fitting parameters. Analysis of Schottky and p-i-n cells indicates that the influence of space charge in doped layers is negligible and that the p-i-n cell can be represented by a single space charge region in series with the bulk. The MGDOS values derived from the circuit model for a-Si:H and a-SiGe:H are in good agreement with those from other measurements. >