Electrical and optical properties of Ga₂O₃/ CuGaSe₂ heterojunction photoconductors

In this study, the feasibility of using a photoconductor with a Ga ₂O₃/CuGaSe₂ heterojunction for visible light sensors was investigated. We propose a hole-blocking structure using gallium oxide (Ga₂O₃) for CuIn_{1 - x}Ga _xSe_{1 - y}S_y (CIGS) thin film to reduce dark current. Experimental results showed that this structure drastically reduced the dark current. Then, avalanche multiplication phenomenon was observed at an applied voltage of over 6 V. However, this structure had sensitivity only in the ultraviolet light region. It seemed the depletion region in the heterojunction spread almost completely in the Ga₂O₃ layer but not in the CIGS layer because the carrier density of the non-doped Ga₂O ₃ layer was much lower than that of the CIGS layer. We therefore used tin-doped Ga₂O₃ (Ga₂O₃:Sn) for the n-type layer to increase carrier density. As a result, the depletion region shifted to the CIGS film and the cells had sensitivity in all visible regions. These results indicate that the Ga₂O₃:Sn/CuGaSe ₂ heterojunction is feasible for visible light photoconductors.