An analysis of temperature-dependent absorption and photocurrent spectra in BaAl2Se4 layers

Abstract

The temperature-dependent photoresponse behavior of BaAl2Se4 layers has been investigated through the analysis of optical absorption and photocurrent (PC) spectra. Based on these results, the optical band gap was well expressed by Eg(T) = Eg(0) − 4.39 × 10−4T2/(T + 250), where Eg(0) is estimated to be 3.4205, 3.6234, and 3.8388 eV for the transitions corresponding to the valence band states Γ3(A), Γ4(B), and Γ5(C), respectively. From the PC measurement, three peaks A, B, and C corresponded with the intrinsic transitions from the valence band states of Γ3(A), Γ4(B), and Γ5(C) to the conduction band state of Γ1, respectively. According to the selection rule, the crystal field and spin orbit splitting were found to be 0.2029 and 0.2154 eV, respectively, through the direct use of PC spectroscopy. However, the PC intensities decreased with lowering temperature. In the log Jph versus 1/T plot, the dominant trap level at the high-temperature region was observed and its value was 12.7 meV. This level corresponds to the activation energy for the electronic transition from the shallow donor levels to the edge of the conduction band. It is estimated that the decrease in the PC intensity is caused by trapping centers related to native defects in the BaAl2Se4 layers. Consequently, this trap level limited the PC intensity with decreasing temperature.