We report on the surprising observation of negative photoconductivity (NPC) in GaN nanorods (NRs) by bandgap and super bandgap excitations. A metal-semiconductor-metal (MSM) type of device configuration using Ni/Au as an electrode at both ends, has been used to study the NPC phenomenon. On exposing the device to the light sources with 363 nm (bandgap excitation) and 250 nm (super bandgap excitation) wavelengths, NPC with a drop of approximately 50 and 60% was observed, respectively. To explain this phenomenon, a model of trapping of photogenerated electrons by the trap states is proposed. Interestingly, a significant drop in the illumination current is observed at low values of power density (up to 3 μW/mm²) of the incident light. It has been interpreted that on increasing the power density, the density of trapped electrons starts approaching the density of available trap states. The de-trapping process is observed to be very slow as the illumination current reached the dark current value in nearly 2 h after switching off the incident light. The observation of NPC and saturation of trap states with high intensity of incident light are also validated by Kelvin Probe Force Microscopy (KPFM) characterization performed in the dark and on illumination with varying intensity of the incident light. Furthermore, on increasing the temperature from room temperature (RT) to 300 °C, the NPC was found to reduce to almost zero, which indicates the de-trapping of trapped electrons on increasing the temperature.

我们报告了通过带隙和超带隙激发对 GaN 纳米棒 (NRs) 中负光电导 (NPC) 的惊人观察。在两端使用 Ni/Au 作为电极的金属-半导体-金属 (MSM) 类型的器件配置已被用于研究 NPC 现象。将设备暴露于 363 nm（带隙激发）和 250 nm（超带隙激发）波长的光源后，分别观察到 NPC 下降约 50% 和 60%。为了解释这种现象，提出了陷阱态捕获光生电子的模型。有趣的是，在低功率密度值（高达 3 μW/mm ²) 的入射光。据解释，随着功率密度的增加，俘获电子的密度开始接近可用俘获态的密度。由于在关闭入射光后近 2 小时内照明电流达到暗电流值，因此观察到去捕获过程非常缓慢。NPC 的观察和具有高强度入射光的陷阱状态的饱和度也通过开尔文探针力显微镜 (KPFM) 表征在黑暗和不同入射光强度的照明下进行验证。此外，当温度从室温 (RT) 增加到 300 °C 时，发现 NPC 减少到几乎为零，这表明在增加温度时被捕获的电子被解陷。