MOCVD生长MgZnO薄膜及太阳盲紫外光电探测器

The Growth of MgZnO Thin Film by MOCVD and the Application in Solar Blind UV Detector

利用MOCVD在蓝宝石衬底上,通过低温生长实现了立方结构、吸收边在255nm的Mg0.52Zn0.48O合金薄膜,并采用传统湿法刻蚀的方法在薄膜上制备了梳状叉指金电极,构成金属-半导体-金属(MSM)结构,实现了在10V偏压下,器件的光响应峰值在250nm,截止边为273nm的MgZnO太阳盲光电探测器。

The application of UV detector in commerce and military are mainly focus on photomuhiplier tube and UV detector based on silicon at present. However, the ponderosity, large energy consumption, and the attachment of the filters have certain limitation on the application of the photomuhiplier tube as the UV detector. Recently, more attentions were paid on the solid wide gap semiconductor UV detector, especially for the potential application in solar blind region （220 nm to 280 nm） for the detection of the missile plume. The realization of GaN-based pn junction detector accelerated the development of UV detector in solar blind region. But the lack of the lattice mismatch substrate for the growth of GaN-based materials limited the rising of the devices efficiency. MgZnO appears to be an ideal material for the application of solar-blind photodetectors because it possesses 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 ℃ ）, nontoxic, and low defect density. Moreover, it also has a good potential application in deep UV region. In this paper, we obtained the pure cubic phase MgZnO alloy with 255 nm absorption edge by LP-MOCVD, and realized a solar-blind MgZnO photodetector. The peak responsivity of the detector locates at 250 nm, and cutoff wavelength at 273 nm. The MgZnO films were deposited on sapphire substrate by LP-MOCVD. We select bis（-η5-cyclopentadienyl） magnesium （Mg（ C5 H5 ）2 ） as Mg source, dimethylzinc as Zn source and high purity oxygen as O source.The growth temperature was fixed at 450 ℃, the pressure in growth chamber is at 20 kPa. The growth time lasts for 1.5 hour, then the films were taken out from the growth chamber. Energy-dispersive X-ray spectrum （EDX） measurement showed that the composition of the films is Mg0.52Zn0 480： Secondly, the interdigital Au electrodes were fabricated on 50 nm Au layer by conventional UV photolithography and wet etching. The interdigital fingers are 500 μm in length, 5 μm in width, and the spacing between the fingers is 2μm. The XRD patterns of MgZnO thin films show only one sharp and strong diffraction peak at 36.62°, which is assigned as cubic （111） orientation. The HMFM of the diffraction peak is only 0.16°, which shows the high quality of the thin film. The diffraction peak indicates that the sample has a metastable cubic phase without phase separation. The absorption spectrum shows that the band gap of the Mg0.52 Zn0.4s O is at 4.86 eV （ 255 nm）, which has step in the phase region reported in literature （4.0 - 5.0 eV）. As well known, the low growth temperature is beneficial to the cubic MgZnO film with large Mg composition, due to that the metastable state is more easily formed at low growth temperature. The responsivity of the detector exhibits the peak energy at 250 nm and cutoff wavelength at 273 nm, which satisfies for the wavelength-need of the missile flume detection in response wavelength region.