Investigation of the Photocurrent in Hot-Wall-Epitaxy-Grown BaIn2S4 Layers

The photocurrent (PC) of hot-wall-epitaxy-grown BaIn 2 S 4 layers was studied at different temperatures and for different photoresponse intensities. With increasing temperature, the position of the PC spectra tended to shift toward longer wavelength. These PC peaks corresponded to band-to-band transitions caused by intrinsic transitions from the valence band states to the conduction band states. Also, the bandgap variations were well matched by the equation E g ( T ) = E g (0) − 3.79 × 10 −3 T 2 /( T + 499), where E g (0) was estimated to be 3.0597 eV, 3.2301 eV, and 3.2606 eV for transitions corresponding to the valence band states Γ 4 (z), Γ 5 (x), and Γ 5 (y), respectively. By use of the selection rule and results from the PC spectroscopy, the crystal field and the spin–orbit splitting were found to be 0.1703 and 0.0306 eV, respectively. Thus, the PC intensity gradually decreased with decreasing temperature. The decrease of PC intensity was caused by the presence of trapping centers associated with native defects in the BaIn 2 S 4 layers. The trap level was found to be a shallow donor-level type of 20.4 meV, 1.6 meV below the conduction band. Consequently, these trap levels, which are related to native defects in BaIn 2 S 4 layers, are believed to limit PC intensity with decreasing temperature.