Highly Weak-light Sensitive and Dual-band Switchable Photodetector Based on CuI/Si Unilateral Heterojunction

In recent years, copper iodide (CuI) is an emerging p-type wide bandgap semiconductor with high intrinsic Hall mobility, high optical absorption and large exciton binding energy. However, the spectral response and the photoelectric conversion efficiency are limited for CuI-based heterostructure devices, which is related to the difficulty in fabrication of high-quality CuI thin films on other semiconductors. In this study, a p-CuI/n-Si photodiode has been fabricated through a facile solid-phase iodination method. Although the CuI thin film is polycrystalline with obvious structural defects, the CuI/Si diode shows a high weak-light sensitivity and a high rectification ratio of 7.6×10⁴, indicating a good defect tolerance. This is because of the unilateral heterojunction behavior of the formation of the p⁺n diode. In this work, the mechanism of photocurrent of the p⁺n diode has been studied comprehensively. Different monochromatic lasers with wavelengths of 400, 505, 635 and 780 nm have been selected for testing the photoresponse. Under zero-bias voltage, the device is a unilateral heterojunction, and only visible light can be absorbed at the Si side. On the other hand, when a bias voltage of –3 V is applied, the photodiode is switched to a broader “UV-visible” band response mode. Therefore, the detection wavelength range can be switched between the “Visible” and “UV-visible” bands by adjusting the bias voltage. Moreover, the obtained CuI/Si diode was very sensitive to weak light illumination. A very high detectivity of 10¹³–10¹⁴ Jones can be achieved with a power density as low as 0.5 μW/cm², which is significantly higher than that of other Cu-based diodes. These findings underscore the high application potential of CuI when integrated with the traditional Si industry.