Study of front panel electrode coatings for combined visible and short wavelength infrared photodetectors

Abstract

ZnO-Ga2O3 composite oxide films were RF sputtered and studied how the optical and electrical film properties are affected by the sputtering conditions and film thickness. The aim was to achieve low resistivity and at the same time, high transparency for the visible and short wavelength infrared (SWIR) electromagnetic range for the needs of simple, transparent and indium-free electrodes. A comparison was made with pristine ZnO films. We found that plasma voltage, respectively plasma power plays a crucial role in determining the optoelectronic properties of the deposited films for the fabrication of combined photodetectors. The effective surface roughness of the ZnO-Ga2O3 films varied between 12.9 nm and 16.7 nm when plasma power density varied between 35 and 54 W/cm2, respectively. The increase of the sputtering power narrowed the transmission band to the longer wavelength from the visible spectrum. The transparency in the SWIR range varied between 83 and 96% and decreased with the plasma power increase, while the corresponding transparency in the visible range varied between 60 and 82%. The sheet resistance for the films under the best parameters demonstrating the highest transmission in both electromagnetic ranges showed relatively low sheet resistance of 48 Ω/sq. The potential application of the prepared films is for VIS-IR detectors used in robotics for spatial information gain, gaming and virtual reality and autonomous car navigation, where the day and the night visions are equally important.