太阳盲MgZnO光电探测器

Solar-blind Photodetectors Based on MgZnO Thin Films

利用射频磁控溅射技术在石英衬底上制备了MgZnO合金薄膜,并采用传统湿法刻蚀的方法在薄膜上制备了梳妆叉指Au电极,构成金属-半导体-金属(MSM)结构。在室温下,实现了太阳盲MgZnO光电探测器,器件的探测峰值位于225 nm,截止边为230 nm。

In recent years, solar-blind photodetectors have attracted much attention due to their applications in missile plume sensors, flame detectors, chemical-biological agent sensors, and space-to-space communications. MgZnO appears to be an ideal material for the development of solar-blind photodetectors because it possess unique figures of merit, such as availability of lattice-matched single-crystal substrates, tunable band-gap （3.3 to 7.8 eV）, relative low growth temperatures （ 100 -750 ℃ ）, and high radiation hardness. In this paper, we demonstrate a solar-blind MgZnO photodetector made from MgZnO films. The peak responsivity of the detector lies at 225 nm, and cutoff wavelength at 230 nm. Solar-blind photodetectors based on MgZnO thin films were fabricated through two steps： the preparation of Mg0.7 Zn0.30 thin films and the interdigital Au-electrodes. The experimental procedure was as follows： Firstly, high-purity Mg0 5Zn0.50 ceramic disk was used as the target. The sputtering chamber was evacuated down to 3 × 10^-4 Pa before introducing the sputtering gas. Ar and O2 gases were introduced into the sputtering chamber through two separate mass flow controllers with the rates of 60 and 20 sccm （ standard cubic centime-ter per minute）, respectively. The working pressure in chamber was kept at 1 Pa, the substrate temperature at about 450 ℃, and the rf power at 100 W. The sputtering process lasted one hour, then the films were taken out of the growth chamber. Energy-dispersive X-ray spectrometer （EDX） measurement showed that the composition of the films is Mg0 7Zn0.30. Secondly, the interdigital Au electrodesl which were defined on 50 nm Au layer by conventional UV photolithography and wet etching were coated onto the film surface. The interdi- gital fingers are 500 μm in length, 5 μm in width, and the spacing between the fingers is 5 μm. The absorption spectrum of the MgZnO films shows strong absorption at 230 nm, and very weak absorp- tion from 320 to 600 nm. Note that there is a tail in the range from 245 nm to 300 nm in the absorption spectrum, which may be attributed to the nonuniformly distribution of Mg composition or the phase separation. The photodetector shows a peak response at 225 nm with the cutoff wavelength at 230 nm, which is in accordance with the absorption spectrum. Until now, none report on the MgZnO photodetector prepared by RF magnetron sputtering with the peak spectral response short to 225 nm can be found to the best of our knowledge. We think that by optimizing the growth conditions and reducing the composition fluctuations and phase separation occurred in the films, photodetector with improved performance can be expected.