Extremely High-Speed GaAs Growth by MOVPE for Low-Cost PV Application

Epitaxial growth of GaAs in a horizontal metalorganic vapor phase epitaxy reactor was investigated to realize ultrafast growth rate, which has been demonstrated to be 90 μm/h at maximum. The GaAs growth rate had more or less a linear relationship with the amount of trimethylgallium supply. With extremely fast deposition >70 μm/h, slight saturation of growth rate was observed, which is most likely due to parasitic gas-phase reactions and/or limitation in bubbling. The impact of growth rates was examined using GaAs p-n solar cells, with the 2-μm-thick n-GaAs base layers grown at 20, 60, and 80 μm/h. The studies have not evidenced a significant change in performance as a function of growth rate. The base thickness was expanded to 3.5 μm with the growth rate of 80 μm/h to increase light absorption. The growth rate of 80 μm/h did not induce significant degradation in the efficiency of the cells as compared with the ones grown at 20 and 60 μm/h. The average efficiency of 23.6% (16.3% on the basis of a mesa area) under AM1.5G was realized in the cells with 3.5-μm-thick bases grown at 80 μm/h.