Preparation And Photoelectric Properties Of ZnO-based Ultraviolet Detector

Zinc oxide (ZnO) is a kind of semiconductor materials with a wide direct band gap of3.37eV and a large exction binding energy of60meV at room temperature. ZnO has goodchemical and thermal stability, has potential application in short-wavelength optoelectronicdevices especially for ultraviolet (UV) photodetectors, and has become the focus after GaNmaterial. In this study, we prepared photoconductive type and PN junction type two kind ofZnO-based UV photodetector by pulsed laer deposition (PLD) and hydrothermal synthesis,and the optoelectronic properties of them have been studied.We prepared Ti/ZnO/Ti structure photoconductive UV detector on sapphire substrate byPLD method, and the photoelectric properties were studied. It is showed good Ohmic contactbetween metal Ti and ZnO, the best annealing temperature is400℃. The ZnO films preparedby PLD method show a good c axis preferred orientation and high crystallization quality. ZnOphotoconductive UV detector has the strong response to UV light, at the-5V reverse bias, thephotocurrent was7.025mA under the UV illuminated of360nm, and the response side of thedetector was about370nm. However, there is a long response time of the detector, rise timeand fall were10s and40s, respectively.Three kinds of ZnO-based heterojunction UV photodetectors, n-ZnO films/p-Si, n-ZnOfilms/p-GaN and n-ZnO nanorods/p-GaN, were prepared by PLD and hydrothermal method,and the photoelectric properties of them were studied. The spectral response of n-ZnOfilms/p-Si heterojunction UV photodetectors constituted by a UV response peak located at365nm which come from ZnO and a wide response band from visible to infrared which comefrom p-Si substrate. The peak responsivity in UV region and visible-infrared region was20.9A/W and more than23A/W, respectively. This kind of deteceor can’t realize detection ofUV illuminate under visible light environment. The spectral response of n-ZnO films/p-GaNheterojunction UV photodetectors showed a UV response peak located at364nm. When thereverse voltage reached-5V, the photocurrent of the detector saturated and the peakresponsivity reached1.19A/W. The detectivity curves under various reverse voltages showthat the detector has a high selectivity for UV light around364nm, and the peak detectivitywas8.9×1010cm Hz1/2/W at-2V reverse bias. However, the reverse leakage current of the device is large, which would affect the performance of the device more or less. The n-ZnOnanorods/p-GaN heterojunction UV photodetector had a small reverse leakage, which only5.76×10-7A under the-5V reverse bias. The spectral response of device showed a UVresponse peak located at362nm. When the reverse voltage reached-10V, the photocurrent ofthe detector saturated and the peak responsivity reached1.85A/W. The detector to achieve thebest working state at-4V reverse bias, and the peak detectivity reaches2.26×1011cmHz1/2/W.