Wavelength‐Selective, High‐Speed, Self‐Powered Isotype Heterojunction n ⁺ ‐ZnO/n‐Si Photodetector with Engineered and Tunable Spectral Response

Abstract An isotype heterojunction n ⁺ ‐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 UV–vis–NIR or as a NIR‐only photodetector, depending on the relative carrier concentrations of ZnO and silicon. In addition, 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. Photovoltage and photocurrent measurements for pulsed illumination reveal a high‐speed self‐powered response, with rise and fall times <100 µs across the UV–vis–NIR. The device can be engineered to reproduce undistorted pulsed light with frequencies as high as 1 kHz. Self‐powered responsivity reaches ≈70 mA W ⁻¹ , which becomes ≈4 A W ⁻¹ with an applied external bias.