Characterization and modeling of a ZnO nanowire ultraviolet photodetector with graphene transparent contact

Abstract

We report the demonstration of a ZnO nanowire ultraviolet photodetector with a top transparent electrode made of a few-layered graphene sheet. The nanowires have been synthesized using a lowcost electrodeposition method. The detector is shown to be visible-blind and to present a responsivity larger than 10 4 A/W in the near ultraviolet range thanks to a high photoconductive gain in ZnO nanowires. The device exhibits a peak responsivity at 370 nm wavelength and shows a sub bandgap response down to 415 nm explained by an Urbach tail with a characteristic energy of 83 meV. The temporal response of the detector and the power dependence are discussed. A model of the photoconductive mechanism is proposed showing that the main process responsible for the photoconductive gain is the modulation of the conducting surface due to the variation of the surface depletion layer and not the reduction of recombination efficiency stemming from the electron-hole spatial separation. The gain is predicted to decrease at high incident power due to the flattening of the lateral band bending in agreement with experimental data. V C 2013 AIP Publishing LLC.

Ultrahigh Responsivity in Graphene-ZnO Nanorod Hybrid UV Photodetector

“…The R I value characterizes the ratio of generated photocurrent to incident UV intensity at a certain wavelength, , where I ph = I light − I dark is the photocurrent. G is defined as the ratio between the number of electrons collected per unit time and the number of absorbed photons per unit time, where hv is photon energy. The R I and G values of the hybrid‐channel FETs at various UV intensities are compared in Figure .…”

“…However, a drastic decrease in G occurred at low intensity, and G slowly decreased at high intensity. The lightly decrease of G at relatively high intensities was attributed to a manifestation of hole‐trap saturation and the shrinking of the depletion region . Indeed, under low‐intensity illumination, the holes that separated from photogenerated electron–hole pairs migrated to the ZnO surface and occupied surface states, then trapped at the surface and discharging adsorbed oxygen molecules.…”

UV Photosensing Characteristics of Nanowire-Based GaN/AlN Superlattices

“…14 In comparison with planar devices, almost defect-free semiconductor nanowires open the possibility of exploiting the photoconductive gain while avoiding the deleterious effects of grain boundaries and dislocations on the spectral response. 18 Both ZnO and (Al,Ga)N are promising choices to be used as miniature, visible-blind, ultraviolet (UV) photosensors, [11][12][13][14]16,19 but GaN presents advantages in terms of physical and chemical robustness as well as for controlled doping.…”

Effect of the nanowire diameter on the linearity of the response of GaN-based heterostructured nanowire photodetectors

“…Nanowire photoconductors are characterized by high photocurrent gains, which can reach 10 6 , and strong spectral contrast above and below the bandgap. A general feature in nanowire photoconductors is the fact that the photocurrent scales sublinearly with the impinging laser power, which has been shown for single GaN nanowires regardless of the presence of heterostructures [6][7][8][9][10], as well as for nanowires of other material systems such as ZnTe [11], ZnO [12,13], InP [14], CuO [15], and GaAs [16]. This sublinearity of the response hampers the use of such devices for quantification of the radiant fluence, and restricts their application domain to digital detection.…”