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 Vintaccounts 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 Vintalmost 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 Vintas 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.