Absorption measurements of doped thin film InP for solar cell modeling
The first direct transmission measurement of above bandedge absorption coefficients in InP are reported in this paper. A new 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 × 1017 cm-3 and the other with a doping concentration of 3.2 × 1018 cm-3. Absorption coefficients were obtained from transmission measurements made on these two films. These measured absorption coefficients were used to calculate the cell performance and quantum efficiency of an InP solar ceil. 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 effficiency 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.
