Large-area photodetector with high-sensitivity and broadband spectral response based on composition-graded CdSSe nanowire-chip

The nanowire-chip based large-area and broad-band-response photodetector was realized by integrating the ternary bandgap-graded CdS_1-xSe_x nanowire-chip on proper substrate and optimizing electrode pattern. The actual light-to-dark current ratio (I_light/I_dark) is subject to the substrate type and the electrode pattern, as well the thickness of nanowires. Up to 10⁶ light-to-dark current ratio was obtained for the nanowire-chip photodetector with the optimized interdigital electrode parameters (0.5 mm in width, 0.5 mm in pitch), the suitable substrate - mica and appropriate nanowire thickness (70um). Although the carriers transmit from light-generated carrier centers to the electrodes through a complicated and long pathway, the photodetector of as-fabricated nanowire-chip shows much higher photocurrent and photoconductivity due to a higher photocarrier densities exist in the ternary compounds than that in binary CdS and CdSe nanowire and the intersection trap state existing between nanowires enhances the separation of electrons and holes. Uniform and broad photoresponse covering from ultraviolet to around 700 nm is attributed to the graded bandgap of different composition nanowires/nanobelts in the chip-type detector. Especially, the I_light/I_dark of nanowire-chip detector increases with the temperature decrease due to the dark noise and the scattering become lower. The chip detector with composition-graded nanowires shows good photoconductivity at room temperature and low temperature. More important, it can be fabricated by a commercial CVD route, which will satisfy the requirements in many application fields instead of Si-based detector.