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

• Published in: IEEE transactions on electron devices Vol. 61; no. 2; pp. 394 - 399
• Main Authors: Zhong, Chun-Liang, Yao, Ruo-He, Geng, Kui-Wei
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.02.2014; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Capacitance; Diffusion potential; Discharges (electric); Electric potential; Heterojunctions; Interface states; inversion layer; Photovoltaic cells; Silicon; solar cells; Solar energy
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2013.2295459

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.