Improved Electrical Properties of Ga 2 O 3 :Sn/CIGS Hetero-Junction Photoconductor

We examined the potential application of CuIn 1-x Ga x Se 1-y S y (CIGS) film for visible light image sensors. CIGS chalcopyrite semiconductors, which are representative of high efficiency thin film solar cells, have both a high absorption coefficient and high quantum efficiency. However, their dark current is too high for image sensors. In this study, we applied gallium oxide (Ga 2 O 3 ) as a hole-blocking layer for CIGS thin film to reduce the dark current. The dark current of this hetero-junction was 10 -9 A/cm 2 at less than 7 V. Moreover, an avalanche multiplication phenomenon was observed at an applied voltage of over 8 V. However, this structure had sensitivity only in the ultraviolet light region due to the much lower carrier density of the Ga 2 O 3 layer. We therefore used a tin-doped Ga 2 O 3 (Ga 2 O 3 :Sn) layer deposited by pulsed laser deposition (PLD) for the n-type layer to increase the carrier density. The sensitivity of the visible region was observed in the Ga 2 O 3 :Sn/CIGS hetero-junction. We also investigated the influence of the laser frequency of the PLD on the transmittance of Ga 2 O 3 :Sn and the quantum efficiency of this hetero-junction. Ga 2 O 3 :Sn film deposited at a 0.1-Hz laser repetition rate had higher transmittance than at a 10-Hz repetition rate. The Ga 2 O 3 :Sn/CIGS hetero-junction also had a higher quantum efficiency with the lower rate (50%) than with the higher rate (30%).