Grain boundary effects in Poly-Si as determined by low frequency capacitance and conductance data

The dependence of MIS capacitance (G_M) and conductance) on dc bias (U) at various frequencies (20 Hz to 50 kHz) is measured for MIS devices on the grain, grain boundary, and multiple grain boundaries for p-type silicon. Significant differences in C_M-V and G_M-U are seen when comparing devices with and without grain boundaries. The effective interface state density (N₈₃) is calculated from the above data. At mid-gap, AT SS = 1.5 X 10¹¹ cm^-2 eV^-1 without a grain boundary, whereas N_ss = 4 to 8 X 10¹¹ cm^-2 eV^-1 when grain boundaries are present. This can account for the 50 mV reduced U^oc on solar cells made from polycrystalline Si. This technique is also a useful tool for evaluating effects of grain boundary passivation.