电子束蒸发结合热处理方法制备高质量Mg_xZn_(1-x)O薄膜

High Quality Mg_xZn_(1-x)O Films Fabricated by Electron Beam Evaporation Combined with Heat Treatment

利用电子束蒸发结合热处理方法在150℃下,石英衬底上生长了纤锌矿结构的MgxZn1-xO薄膜。用X射线衍射(XRD),扫描电镜(SEM),吸收光谱和室温光致发光(PL)光谱研究了退火条件和降温方式对MgxZn1-xO薄膜的微结构和光学性质的影响。在吸收光谱中,吸收边和吸收峰的蓝移说明:通过改变退火条件和降温方式,可以将MgxZn1-xO薄膜的带隙从3.37eV提高到3.61eV。从SEM的结果得出:吸收边和吸收峰的蓝移不是由量子限制效应引起的,而是形成了MgxZn1-xO合金薄膜。在XRD谱图中,没观察到属于MgO的衍射峰,700℃退火快速降温至室温薄膜的衍射峰的半高全宽(FWHM)较其他薄膜的衍射峰有所展宽,说明Mg2+已经成功地取代了ZnO中的Zn2+。薄膜的室温光致发光谱说明:通过采用快速降温,可制得高质量的MgxZn1-xO薄膜。

Recently, much attention has been paid to wurtzite MgxZn1-xO alloys as a promising candidate for applications in optoelectronic devices in the ultraviolet region. ZnO is a wide-band-gap semiconductor with a direct gap of - 3.37 eV. The band gap becomes even larger if Zn atoms are substituted by Mg atoms, which have a similar ionic radius, allowing the construction of ZnO/MgxZn1-xO quantum-well and superlattice devices. One of the important problems that limits the fabrication of MgxZn1-xO alloy is the fact that the thermo- dynamic solubility limit of MgO in ZnO is about 4%. The problem of Mg concentration in ZnO is excess of 4% without phase segregation is important and necessary to be studied in details. In this paper, MgxZn1-xO films with wurtzite-type structure were fabricated on quartz substrates at 150 ℃ by electron beam evaporation （EBE） using Mg0. 15 Zn0.85 O target combined with heat treatment. The dependence of the microstructure and optical properties of MgxZn1-xO films on the annealing conditions and cooling modes has been investigated using X-ray diffraction （XRD）, scanning electron microscope （SEM）, absorption and photoluminescence （PL） spectra. In the XRD spectra, no diffraction peaks belonging to MgO were observed. The results showed that MgxZn1-xO films were single wurtzite-type structure. The increasing band gap is not due to quantum confinement effect according to SEM images, but attributed to the formation of MgxZn1-xO alloy films. In the absorption spectra, the blueshift of absorption edges and absorption peaks indicated that the band gap of MgxZn1-xO films was tuned from 3.37 eV to 3.61 eV by changing annealing conditions and cooling modes. As it can be seen, the full-width at half-maximum of the XRD peak for MgxZn1-xO films annealed at 700 ℃ followed with rapid cooling increases, which indicated the Zn^2＋ ions in ZnO lattice were successfully substituted by Mg^2＋ ions. Accordingly, an evident blueshift is observed in photoluminescence spectra for the MgxZn1-xO films annealed at 700 ℃ followed with rapid cooling, and the PL intensity of near-band-edge （NBE） emission is much higher than that of its visible emission, showing that high quality MgxZn1-xO films were obtained. We controlled on the Mg^2＋ concentration by changing annealing conditions and cooling modes. By using rapid cooling at high annealing temperature, the high-quality MgxZn1-xO films were achieved. The fabrication of high-quality MgxZn1-xO films makes it possible to obtain light detecting and emitting devices in the UV region.