■ Example of research topics ■
Extremely high-speed GaAs growth by MOVPE for low-cost PV application
H. Sodabanlu, Hao Xu, K. Watanabe, Y. Nakano, M. Sugiyama
III-V semiconductor including GaAs-based solar cells have very high conversion efficiency owing to their excellent material properties. From price per watt analysis, the reduction in the overhead time of MOVPE reactors, together with the improvement in material utilization efficiency, can reduce the cost of GaAs single junction solar cells by 74%, when the growth rate of GaAs is boosted from 14 to 56 µm/h with performance loss less than 1%. Our group has demonstrated ultrafast GaAs growth with a growth rate up to 90 µm/h. GaAs p-n solar cells with growth rates of 20, 60, and 90 µm/h were successfully fabricated. The average efficiency of approximately 22-23% could be realized, which no degradation of performance was evidenced from the samples grown at 60 and 90 µm/h compared with those at 20 µm/h. The epitaxial growth had a good uniformity, resulting in good distribution of cell performance from center to edge of wafer.
Fig. 1 Dependence of GaAs growth rate on TMGa supply
Fig. 2 (a) current-voltage characteristics and (b) external quantum efficiency spectra of GaAs solar cells grown at 20, 60, and 90 µm/h with ZnS/SiO2 ARC.