An Improvement of the Capacitance–Voltage Method to Determine the Band Offsets in a-Si:H/c-Si Heterojunctions

Due to the strong inversion layer at the c-Si interface, there may be errors in the determination of the band offsets in a-Si:H/c-Si heterojunctions from the usual capacitance-voltage (C-V) method. Considering the charge effect in the strong inversion layer, the theoretical differential capacitance in (n⁺) a-Si:H/(p) c-Si heterojunctions at high frequency is developed. The calculated results of the capacitance show that, the errors depend on the minority carrier density at the c-Si interface, and increase with increasing conduction band offset in (n⁺) a-Si:H/(p) c-Si heterojunction solar cells. The apparent diffusion potential V_int accounts for the charge effect in the inversion layer. Particularly, a modification to the apparent diffusion potential is presented, and the simulation results show that the modified apparent diffusion potential V_int almost agrees with the theoretical value for various conduction band offsets. Accordingly, the band offsets are determined more precisely from the improved C-V method. However, there is still a small difference between VD and V_int as well as slight errors at the high values of AEC. The improved C-V method is based on the usual C-V method and the static coplanar conductance measurement to determine the band offsets.