Both the rise and decay edges of the photocurrent
match the mentioned exponential equation. The time constant τ r decreases from 1.18 to 0.26 s when the light intensity increases learn more from 0.49 to 508 mW cm−2. Furthermore, the time constant τ d decreases from 2.65 to 0.40 s when the light intensity increases from 0.49 to 508 mW cm−2. In this case, both τ r and τ d decrease with an increasing light intensity because of the distribution of traps in the energy band of the InSb nanowires. When the light is switched on, the excess electrons and holes are generated, and subsequently, two quasi-Fermi levels (one for electrons and one for holes) are induced. When the light intensity increases, the quasi-Fermi levels for electrons and holes shift toward the conduction and valence bands, respectively, and an increasing number of traps are converted to recombination centers [5, 44]. Therefore, the rise and decay times decrease significantly, and the response and recovery speeds increase. In this work, the time constants are higher than
those reported elsewhere because of the defect trapping (surface vacancy) in this process. VX-770 ic50 The photogenerated electrons might first fill traps to saturate them and subsequently reach the maximum number, which delays reaching a steady photocurrent. Moreover, the photogenerated electron, in returning to the valence band from the conduction, might first become trapped by the defects before reaching the valence band, which delays reaching a steady dark current [36, 45]. The defect trapping can increase the carrier lifetime (enhancing QE); however, the response and recovery times also increase. Furthermore, the rise time τ r is smaller than the decay time τ d. The long decay time can be attributed to the trapping and
adsorption processes of the oxygen surface . Figure 4 The photocurrent properties of middle-infrared PD184352 (CI-1040) photodetector based on InSb nanowire. (a) The photocurrent behaviors of the InSb nanowire illuminated under light intensity of 508 mW cm−2 as switch on and off states. (b) I on/I off ratio under light different intensities. (c) Rise and (d) decay of time constant at different light intensities. In this work, the high QE for the InSb nanowires is ascribed to the high this website surface-to-volume ratio and superior crystallinity of the InSb nanowires and the M-S-M structure. The high surface-to-volume ratio can significantly increase the number of hole-trap states and prolong the carrier lifetime. In the dark, oxygen molecules are adsorbed on the nanowire surface and capture free electrons (O2(g) + e − → O2 − (ad)), and thus, the depletion layer forms near the surface, which reduces the density and mobility of the carrier. When illuminated (hν → e − + h +), electron–hole pairs are generated; the holes migrate to the surface and discharge the adsorbed oxygen ions through an electron–hole recombination (h + + O2 − (ad) →O2(g)).