MOCVD外延Al_2O_3基AlGaN/GaN超晶格的结构和光学特性

通过X射线衍射分析、透射电镜观察、红外透射光谱分析、紫外-可见吸收光谱分析和光致发光试验,研究了用金属有机物化学汽相沉积(MOCVD)的方法,在带有GaN缓冲层的蓝宝石(Al2O3)衬底上生长的AlGaN/GaN超晶格材料的微观结构、光吸收性质和发光特性。X射线衍射结果表明,GaN基材料均为纤锌矿六方结构,薄膜具有良好的结晶质量,薄膜生长沿c轴择优取向。透射电镜观察表明,超晶格试样的周期结构分布均匀,实际周期为13.3nm,且观察到高密度的位错存在于外延膜中。通过光学试验数据,确定了试样的光学吸收边都是在370nm附近,理论计算显示试样为直接跃迁型半导体,禁带宽度约为3.4eV。试样的折射率随光子能量的增加而增加、随波长的增加而减小,计算表明消光系数的极小值位于370nm处。光致发光测试分析表明,超晶格有很好的发光性能,并发现存在黄带发光。

Microstructures and Optical Characteristics of AlGaN/GaN Based on Al_2O_3 Prepared by MOCVD

The microstructure, optical absorption properties and luminescence function of GaN thin films grown on the sapphire substrate with the buffer layer of GaN by MOCVD have been studied by means of XRD, TEM, infrared transmission spectrum, and photoluminescence. The XRD results show that the crystal of GaN is hexagonal wurtzite structure. The thin films have perferred orientation in c axis with very high quality. The TEM images of cross-sectional specimen show that the thicknesses of every layer in the superlattices are uniform with the average period of 13.3 nm, but there are high-density dislocations in the superlattices region. With the related optical experimental data, it had been found that the optical absorption edge was at about 370 nm. The theory calculation indicates that the five samples are direct transition semiconductor with band-gaps of about 3.4 eV. The refractive indexes of the samples increase with the photon energy enhance and decrease with the wavelength increasing. The results show that the extinction coefficients have the minimum at 370 nm. Photoluminescence test results show that the superlattice has preferable luminescence property and a yellow luminescence is found.