ZnO/Black Silicon Hybrid Composite with Enhanced Optoelectronic and Gas-Sensing Properties

We performed a comparative study of ZnO films synthesized by the sol–gel method on planar silicon surface (ZnO/Si) and on nanostructured black silicon layer (ZnO/b-Si) formed by reactive ion etching. The influence of b-Si on ZnO morphology, composition, and optical, wetting, photoelectric, and gas-sensing properties was investigated. The ZnO/b-Si hybrid composite exhibits significantly higher optical absorption in the 350–1100 nm range and a lower contact angle (36° vs. 59°) than ZnO/Si. The current–voltage characteristics show an increase in the n-ZnO/p-Si heterojunction current when b-Si is used as an interlayer, under both forward and reverse bias. Under illumination at 370 nm, the photocurrent of both samples increases, with a stronger photoresponse for ZnO/b-Si. The spectral responsivity in the 350–1000 nm range exhibits maxima near 370 and 860 nm. Cyclic transient measurements confirm the reproducibility of the photoresponse and a higher absolute photocurrent for ZnO/b-Si. Gas-sensing measurements showed that ZnO/b-Si exhibits a higher response to NO2 than ZnO/Si over the entire studied temperature (125–250 °C) and concentration (10–100 ppm) ranges. These results demonstrate that combining a nanostructured b-Si layer with a ZnO film can effectively tailor the optoelectronic and gas-sensing properties of this hybrid composite.