Ultrafast and Ultrabroadband UV–vis-NIR Photosensitivity under Reverse and Self-Bias Conditions by n⁺-ZnO/n-Si Isotype Heterojunction with >1 kHz Bandwidth

A high-performance broadband photodetector has attracted significant attention due to its wide range of applications. We report an n + -ZnO/n-Si isotype heterojunction by depositing ZnO nanorods followed by a ZnO thin film on an n-type undoped Si wafer for detecting a broad wavelength from 300 to 940 nm with a high speed under reverse as well as zero bias conditions. Under 1.5 V reverse and zero bias, the device provides responsivity values up to ∼200 and ∼13 mA/W respectively. Under self-bias, the n + -ZnO/n-Si heterojunction exhibits up to 1.2 × 10 3 photosensitivity. The n + -ZnO/n-Si heterojunction can detect power as low as 10–12 μW/cm 2 . A photoresponse up to 2 kHz modulated illuminations has been measured, and the ultrafast n + -ZnO/n-Si heterojunction provides a stable and rapid photoresponse with a response time in the 60–120 μs range. The n + -ZnO/n-Si heterojunction exhibits a −3 dB cutoff frequency of >2000 and 1100 Hz under reverse and zero bias, respectively. Therefore, we unprecedentedly demonstrate an n + -ZnO/n-Si isotype heterojunction as a potential candidate for detecting light in a broad ultraviolet to infrared region with a very high speed and >1 kHz frequency bandwidth as well.