The characteristics of an oppositely placed double potential barrier photodetector structure were investigated under longitudinal illumination. The functional abilities of the silicon n+-p-n+ structure were studied under longitudinal illumination. The choice of impurity concentration in the n+- and p- regions provided the difference in heights of the potential barriers near-surface, rear, and oppositely directed regions and their conjoining in the high-resistance p-base. The widths of the depletion regions of these barriers varied with a step change in the bias voltage. The redistribution of the fraction of absorption of electromagnetic waves between the barriers and the change in their contribution to the total photocurrent was investigated. In connection with this, short-wavelength (490 nm) and long-wavelength (830 nm) spectral maxima were formed. In the voltage range commensurate with the difference in the heights of the potential barriers, the inversion of the sign of the spectral photocurrent and, using the developed algorithm, the spectral distribution of the absorbed radiation intensity, were obtained. A physical explanation of these results is provided. The structure under investigation enables the selective registration of individual waves and their intensities. The results reported here enable an optimistic spectrophotometric outlook for oppositely placed double-barrier photonic structures.

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.