Properties of Ga2O3/Ga2O3:Sn/CIGS for visible light sensors

A Ga2O3/Ga2O3:Sn/CuIn1-xGa(Se1-ySy)(2)(CIGS) structure is proposed for use in visible light sensors. CIGS thin films have been investigated for high efficiency thin-film solar cells. The typical structure of CIGS solar cells consists of ZnO/CdS/CIGS. However, the quantum efficiency of this structure at short wavelengths is decreased due to optical absorption loss from the CdS layer. In this study, a Ga2O3 layer was adopted instead of a CdS layer. Ga2O3 has a wide band gap and high transmittance in the visible region. Furthermore, it was assumed that it could function as a hole-blocking layer to suppress hole injection from the anode. Additionally, a Ga2O3:Sn thin layer was laid on the CIGS layer to spread the depletion region to the CIGS layer, because the carrier density of the undoped Ga2O3 layer was much lower than that of the CIGS layer. In this structure, signal current multiplication and quantum efficiency greater than unity were observed at applied voltages over 3.5 V.