Clarifying the high on/off ratio mechanism of nanowire UV photodetector by characterizing surface barrier height

Abstract

The response of semiconductor nanowire UV sensors represented by ZnO nanowire UV sensor is usually explained by the adsorption and desorption of oxygen molecules, but with the great increase of these sensors' on/off ratio in recent years, this explanation is inadequate and the inner mechanism for the large on/off ratio urgently needs to be explored. Here, the distribution of carrier concentration in a ZnO nanowire is found to be determined as a function of the radius of the nanowire, using a calibrated surface photovoltage method and space charge model. A critical radius is indicated which determines the carrier concentration and photoresponse behavior of the nanowire. When the radius is below this critical value, the carrier concentration in the dark decreases dramatically compared with that of the nanowire under UV light illumination. Specifically, a decrease of carrier concentration by 4-5 orders of magnitude occurs when the radius is below 50 nm, which causes the on/off ratio to vary by the same orders of magnitude. When the radius is above the critical value, the influence of radius on carrier concentration is nonsignificant and the on/off ratio is below 100. Finally, we found that the high on/off ratio of the ZnO nanowire should be ascribed to the complete depletion of the nanowire led by the interplay of radius and surface band bending rather than the change in width of the depletion layer as most papers have suggested.

Self‐Polarized BaTiO3 for Greatly Enhanced Performance of ZnO UV Photodetector by Regulating the Distribution of Electron Concentration

“…It is generally accepted that the response time and conductivity of the ZnO devices are greatly influenced by the depletion layer formed . Therefore, it is accessible to regulate the depletion layer by built‐in electric fields of ferroelectric material .…”

Effects of UV Irradiation and Storage on the Performance of Inverted Red Quantum-Dot Light-Emitting Diodes

“…The adsorbed oxygen can also create a potential barrier of upward band bending by a depletion region along the ZnO surface, causing a high work function (WF) [ 24 , 25 , 26 ]. After UV irradiation, the adsorbed oxygen in the ZnO is released, which leads to less band bending and lower WF [ 27 ]. As shown in Figure 3 c, the WF of the ZnO film exhibited a gradual drop with the exposure of ZnO to a 365 nm UV lamp for 15 min.…”

Crystallization of ZnO thin films without polymer substrate deformation via thermal dissipation annealing method for next generation wearable devices

“…). [32][33][34] When the ZnO thin lms based UV photodetector are exposed to UV light, electron-hole pairs generated, and some photogenerated holes migrate to the surface of the ZnO thin lms to combine with electrons that capture the oxygen molecules, resulting in a reduction in the depletion barrier thickness (h + + O 2 / O 2 ). 35,36 At the same time, the photogenerated electrons move to the electrode based on the bias voltage, resulting in a photocurrent increase.…”