Photoresponse properties of CdSe single-nanoribbon photodetectors

Photodetectors are fabricated from individual single-crystal CdSe nanoribbons, and the photoresponse properties of the devices are studied systematically. The photodetector shows a high sensitivity towards excitation wavelength with a sharp cut-off at 710 nm, corresponding to the bandgap of CdSe. The device exhibits a high photo-to-dark current ratio of five orders of magnitude at 650 nm, and can function with excellent stability, reproducibility, and high response speed ( < 1 ms) in a wide range of switching frequency (up to 300 Hz). The photocurrent of the device shows a power-law dependence on light intensity. This finding together with the analysis of the light intensity-dependent response speed reveals the existence of various traps at different energy levels (shallow and deep) in the bandgap. Coating with a thin SiO2 isolating layer increases the photocurrent but decreases the response speed of the CdSe nanoribbon, which is attributed to reduction of recombination centers on ribbon surface.