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Schematic for the fabricated UV MSM PDs with ZnO NR arrays.
(a) XRD result of ZnO NRs on ZnO/glass substrate. The inset shows the room temperature PL spectrum of ZnO NRs. (b) HRTEM image of an individual ZnO NR. The lattice spacing is 0.52 nm along the  direction. The inset is the corresponding SAED image.
FESEM image with 45° tilt angle for the ZnO NR MSM PDs. The inset shows the cross-sectional image of the ZnO NR arrays.
characteristics of the NR MSM PDs measured in dark and under 370 nm illumination.
Measured spectral reponsivities of the ZnO MSM PDs at 5 V applied bias.
Energy band illustration for photoconduction mechanism in this investigation: (a) In the dark case, oxygen molecules are adsorbed onto the ZnO surfaces by capturing free electrons , which creates a low-conductivity depletion layer near the surface. (b) Under UV illumination at photon energy more than the bandgap , electron-hole pairs are photogenerated. The holes migrate along the potential gradient and discharge the oxygen ions , consequently, oxygen is photodesorbed from the surfaces.
Photocurrent, dark current, photoresponsivity, and UV-to-visible rejection ratio of the ZnO MSM PDs measured at 5 V bias and 370 nm illumination.
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