Absorption measurements of doped thin film InP for solar cell modeling

Abstract

The first direct transmission measurement of above bandedge absorption coefficients in InP are reported. A novel technique for fabricating high-quality single crystal InP thin films is used to fabricate the thin films for transmission measurements. Two InP thin films were fabricated in this manner, one with a doping concentration of 1.4*10/sup 17/ cm/sup -3/ and the other with a doping concentration of 32*10/sup 18/ cm/sup -3/. Absorption coefficients were obtained from transmission measurements made on these two films, and were used to calculate the cell performance and quantum efficiency of an InP solar cell. These results were then compared with similar calculations made on the same cell using absorption coefficients for undoped InP, which are commonly used due to the lack of absorption coefficient data for doped InP. Model calculations with the directly measured absorption coefficients resulted in a cell efficiency which was significantly different from the efficiency of the cell with undoped InP absorption coefficients. This demonstrates that correct absorption coefficients are necessary to accurately model InP devices which utilize highly doped regions. >