  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 ns-laser irradiation in SF6 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 dark show a
non-linear 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, due to their increased surface area and light
absorption.
