Isotype Heterojunction n⁺-ZnO/n-Si Photodetector with Tunable Wavelength-Selective, High-Speed, and Self-Powered Operation

An isotype heterojunction n<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup>-ZnO/n-Si photodetector is developed, showing adjustable wavelength-selective operation at self-powered conditions. Without an external bias voltage, the device can operate either as a broadband ultraviolet-visible-near-infrared (UV-vis-NIR) or as a NIR-only photodetector. This is achieved by careful engineering of the relative carrier concentrations of the constituting materials, i.e., ZnO and silicon, which in turn affects the built-in potential barrier of the n<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup>-n junction. In addition to this self-powered behavior, the photodetector can be tuned to either broadband or NIR operation by the application of an external bias voltage, regardless of carrier concentrations. At negative bias, it demonstrates UV-vis-NIR photodetection, while at positive bias, NIR photodetection for any ratio of ZnO/Si carrier concentrations investigated here.