Metal-semiconductor-metal photodetectors (MSM-PDs) with transparent ITO contacts were studied. The RF-sputtered ITO layers were formed under various ambient gases Ar, Ar/N2, and Ar/O2. The ITO film fabricated under the Ar/O2 ambient has highest Schottky barrier-height, but the high resistivity limited the photocurrent of the photodetectors. Consequently, using Ar/N2 as the plasma gas would be a suitable choice for MSM-PD application. The photo/dark current ratios of the MSM-PDs were 5, 25 and 12 (measured under 0.2 V) using Ar, Ar/N2 and Ar/O2 as the plasma gases. To further improve the photo/dark current ratio, we fabricated the InGaAN-PDs using metal-insulator-metal-semiconductor (MIMS) structures. The dark current was greatly suppressed by the SiO 2 layer, and the highest photo/dark current ratio was 66 under 0.2 V bias.