ZnO/p-Si heterostructure for UV sensing and long-range IoT environmental monitoring

Abstract

The development of low-cost photoconductive ultraviolet sensors with long-range wireless communication remains an attractive approach for environmental monitoring applications. In this work, a ZnO/p-Si photoconductive heterostructure was fabricated by spray pyrolysis and experimentally characterized for ultraviolet sensing and IoT integration. X-ray diffraction confirmed the formation of polycrystalline wurtzite ZnO with reflections indexed to the (100), (002), (101), and (102) crystallographic planes. Scherrer analysis yielded crystallite sizes ranging from approximately 13–28 nm. Surface profilometry measured an average film thickness of approximately 490 nm, while SEM and EDS analyses revealed a continuous granular morphology and homogeneous elemental distribution of the deposited ZnO layer. Optical characterization by UV–Vis spectroscopy showed visible-light transmittance between approximately 80 and 85%, and the Tauc analysis yielded a direct optical band gap of 3.285 eV. Electrical characterization demonstrated that the Ag/ZnO/p-Si/Cu device exhibits a photoconductive current-voltage response under ultraviolet illumination, confirming that its electrical conductivity is modulated by photogenerated charge carriers. Finally, the proposed sensor was successfully integrated with a signal-conditioning stage, an ESP32 microcontroller, and Long Range (LoRa) wireless communication, demonstrating its feasibility as a low-cost photoconductive ultraviolet sensor for long-range IoT environmental monitoring.