Laser-Microstructured ZnO/p-Si Photodetector with Enhanced and Broadband Responsivity across the Ultraviolet–Visible–Near-Infrared Range

We develop ZnO/p-Si photodetectors by atomic layer deposition (ALD) of ZnO thin films on laser-microstructured silicon, and we investigate their electrical and optical behavior, demonstrating high sensitivity and broadband operation. Microstructured p-type silicon was obtained by nanosecond laser irradiation in SF 6 gas, which results in the formation of quasi-ordered and uniform microspikes on the silicon surface. The irradiated silicon contains sulfur impurities, which extend its absorbance to the near-infrared. A thin film of ZnO was conformally deposited on the microstructured silicon substrates by ALD. Photoluminescence measurements indicate high crystalline quality of the ZnO film after annealing. Current–voltage ( I − V ) measurements of the ZnO/p-Si heterodiodes in the dark show a nonlinear behavior with unusual high current values in reverse bias. Under illumination photocurrent is observed for reverse bias, even for wavelengths below the silicon bandgap in the case of the laser-microstructured photodetectors. Higher current values are measured for the microstructured photodetectors compared to planar ones. Photoconductivity measurements show enhanced responsivity across the UV–vis–NIR spectral range for the laser-microstructured devices because of their increased surface area and light absorption.