Explicit photogain principle for polycrystalline nanowire photoconductors

This study establishes an explicit photoresponse theory for polycrystalline nanowire photoconductors, addressing the gap in understanding gain mechanisms in scalable polycrystalline systems. Traditional photoconductive gain models assume uniform carrier distribution and equal electron–hole contributions, which fail to account for grain boundary effects in polycrystalline materials. The proposed theory introduces the photogating effect as the origin of high gain, where light-induced photovoltage modulates conduction barriers at grain boundaries. Experimental validation utilized silicon nanowires with multiple transparent ITO gates to mimic grain boundary potential barriers. Photoresponse measurements under varying gate voltages and light intensities (532 nm LED) demonstrated excellent agreement with derived analytical equations, enabling the extraction of critical parameters such as minority carrier recombination lifetime (τ0) and critical light intensity. Silvaco TCAD simulations further corroborated the theory, showing barrier height and number-dependent photocurrent trends consistent with experiments. Additionally, polycrystalline ZnO thin-film devices and literature data from other polycrystalline systems were successfully fitted to the model, confirming its universality. This work provides a unified framework for optimizing responsivity and bandwidth in low-dimensional photodetectors, bridging theoretical insights with practical applications in next-generation optoelectronics.