Spectral behavior of the temperature-dependent photoresponse of BaAl2S4 layers grown by using hot-wall epitaxy

The characteristic photocurrent (PC) property of BaAl 2 S 4 layers grown by using hot-wall epitaxy was investigated. With decreasing temperature, the PC peaks position shifted toward the short-wavelength region and its intensity decreased dramatically. The energy variation of the PC peaks shift at different temperatures could be matched well by using E g ( T ) = E g (0) − 7.556 × 10 −4 T 2 /( T + 523), where E g (0) was 4.0596, 4.1053, and 4.1094 eV corresponding to Γ 4 ( z ), Γ 5 ( y ), and Γ 5 ( x ) in the valence band in order of increasing energy, respectively. Thus, by the selection rule, the crystal field and the spin-orbit splitting were found to be 47.5 and −5.9 meV, respectively, through PC spectroscopy measurement. From the negative result for the spin-orbit parameter, the middle Γ 5 ( x ) and the lowest Γ 5 ( y ) levels in the valence band were found to be interchanged. By using the relation between the logarithm of the PC density and the reciprocal temperature, we extracted the dominant trap level as 23.2 in the high-temperature region and 5.4 meV in the low-temperature region. Consequently, we found that the dramatic decrease on the PC intensity was caused by these trapping centers.