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Abstract
This paper describes a fabrication and characterization of ultraviolet (UV) photodetectors based on Ohmic contacts using Pt electrode onto the epitaxial ZnO (0002) thin film. Plasma enhanced chemical vapor deposition (PECVD) system was employed to deposit ZnO (0002) thin films onto silicon substrates, and radio-frequency (RF) magnetron sputtering was used to deposit Pt top electrode onto the ZnO thin films. The as-deposited Pt/ZnO nanobilayer samples were then annealed at450∘Cin two different ambients (argon and nitrogen) to obtain optimal Ohmic contacts. The crystal structure, surface morphology, optical properties, and wettability of ZnO thin films were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), photoluminescence (PL), UV-Vis-NIR spectrophotometer, and contact angle meter, respectively. Moreover, the photoconductivity of the Pt/ZnO nanobilayers was also investigated for UV photodetector application. The above results showed that the optimum ZnO sample was synthesized with gas flow rate ratio of 1 : 3 diethylzinc [DEZn, Zn(C2H5)2] to carbon dioxide (CO2) and then combined with Pt electrode annealed at450∘Cin argon ambient, exhibiting good crystallinity as well as UV photo responsibility.
Highlights
It is known that only ultraviolet A (UVA) with wavelength ranging from 320 to 400 nm of the sunlight can pass through the atmosphere and reach the earth’s surface
The main aim of the present paper is to systematically study the effects of different gas flow rate ratios of DEZn to CO2 on crystalline quality and uniformity of epitaxial zinc oxide (ZnO) films, modification of native defects in ZnO films, and the electrical properties of Pt/ZnO nanobilayer films contact and explore the potential application of UV photodetector
During the ZnO phase growth, CO2 concentration played an important role due to the oxygen ions originating from CO2 which that were relatively low in the chamber when gas flow rate value was 1 : 1, which indicated the zinc ions had no sufficient chance to react with oxygen ions to form a high property ZnO phase
Summary
It is known that only ultraviolet A (UVA) with wavelength ranging from 320 to 400 nm of the sunlight can pass through the atmosphere and reach the earth’s surface. Many wide band gap materials such as GaN, AlGaN, ZnSe, and diamond have been used for the UV photodetector applications [1,2,3,4,5,6]. Either Ohmic contact based photoconductive type or Schottky contact based photovoltage type of ZnO metalsemiconductor-metal (MSM) is another way to develop UV photodetector [10, 11]. Comparing the differences between Ohmic and Schottky contact types, the Ohmic contact based photoconductive type device is typically more made and more understood. High quality ZnO films with good Ohmic contact are essential for fabricating high performance UV photodetector, which is based on a strong oxygen chemisorption and photodesorption mechanism on both the grain boundaries and surface [12, 13]
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