Obviously, BOC-H-200 sample possesses the highest donor density (1.1*10 17 cm -3 ) but does not show the highest photocurrent due to severe bulk recombination which is confirmed by photoluminescence measurements. The donor density of BOC-H-300 (5.20*10 16 cm -3 ) is 1.8 times and 3.6 times higher than that of BOC-S0 (2.88*10 16 cm -3 ) and BOC-O-300 (1.44*10 16 cm -3 ), respectively. Except for BOC-H-200, the photocurrent is proportional to the concentration of charge carriers, which reflects that both of defects and concentration of charge carriers affect the photocurrent density. The conductivity (σ) of semiconductors consists of mobility (μ) and concentration (n) of charge carriers according to the below equation: