中文摘要：

室温300 K下,由于AlxGa1-xN的带隙宽度可以从GaN的3.42 eV到AlN的6.2 eV之间变化,所以AlxGa1-xN是紫外光探测器和深紫外LED所必需的外延材料。高质量高铝组分AlxGa1-xN材料生长的一大困难就是AlxGa1-xN与常用的蓝宝石衬底之间大的晶格失配和热失配。因而采用MOCVD在GaN/蓝宝石上生长的AlxGa1-xN薄膜由于受张应力作用非常容易发生龟裂。GaN/AlxGa1-xN超晶格插入层技术是释放应力和减少AlxGa1-xN薄膜中缺陷的有效方法。 研究了GaN/AlxGa1-xN超晶格插入层对GaN/蓝宝石上AlxGa1-xN外延薄膜应变状态和缺陷密度的影响。通过拉曼散射探测声子频率从而得到材料中的残余应力是一种简便常用的方法,AlxGa1-xN外延薄膜的应变状态可通过拉曼光谱测量得到。AlxGa1-xN外延薄膜的缺陷密度通过测量X射线衍射得到。对于具有相同阱垒厚度的超晶格,例如4 nm/4 nm,5 nm/5 nm,8 nm/8 nm的GaN/Al0.3Ga0.7N超晶格,研究发现随着超晶格周期厚度的增加AlxGa1-xN外延薄膜缺陷密度降低,AlxGa1-xN外延薄膜处于张应变状态,且5 nm/5 nmGaN/Al0.3Ga0.7N超晶格插入层AlxGa1-xN外延薄膜的张应变最小。在保持5 nm阱宽不变的情况下,将垒宽增大到8 nm,即十个周期的5 nm/8 nm GaN/Al0.3Ga0.7N超晶格插入层使AlxGa1-xN外延层应变状态由张应变变为压应变。由X射线衍射结果计算了AlxGa1-xN外延薄膜的刃型位错和螺型位错密度,结果表明超晶格插入层对螺型位错和刃型位错都有一定的抑制效果。透射电镜图像表明超晶格插入层使位错发生合并、转向或是使位错终止,且5 nm/8 nm GaN/Al0.3Ga0.7N超晶格插入层导致AlxGa1-xN外延薄膜中的刃型位错倾斜30°左右,释放一部分压应变。

英文摘要：

AlxGa1-xN material has a direct band gap between 3.42 eV and 6.2 eV at room temperature, the corresponding cut-off wavelength flexible from 36S nm to 200 nm. It also covers the spectrum obtained with conventional gas and solid-state ultraviolet （UV） lasers., therefore it is necessary for UV photo-detector and deep-ultraviolet light emitting diodes （deep UV-LED ）. For the fabrication of these devices, thick AlxGa1-xN layer with high AI composition and high crystalline quality are essential. A major obstacle concerning the growth of such AlxGa1-xN layer is the large mismatches in the lattice constants and thermal expansion coefficients between the AlxGa1-xN and the commonly used substrate of sapphire. Crack start to be generated because of tensile strain at a thickness of less than 100 nm for Alo25 Gao 75N once it directly grown on GaN/Sap- phire. The production of crack-free thick AlxGa1-xN ternary layer with high Al composition has also been a challenging issue. It has been reported that low temperature AlN（LT-AlN） IL, or high temperature AlN（ HT- AlN） IL, or AlN/AlxGa1-xN SLs IL is introduced to improve the quality of AlGa1-xN layer. Introduction of GaN/AlxGa1-xN superlattices （SLs） interlayer （IL） is an effective technique for releasing stress in AlxGa1-xN and decreasing TDs density in AlxGa1-xN epitaxial film. The influence of GaN/AlxGa1-xN superlattice （SLs） interlayer （IL） on the strain and threading dislocations （TDs） density of AlxGa1-xN epitaxial film grown on GaN/sapphire were investigated. Probing of phonon frequency by Raman scattering is one of the most convenient methods for charactering residual stress. The strain in AlGaN epitaxial film is obtained via Raman spectroscopy. Edge TDs density and screw TDs density of AlxGa1-x N film are obtained by X-Ray Diffraction （XRD）. As thickness of superlattices period increase （wel/ and barrier have the same thickness）, both the edge TDs and the screw TDs density of AlxGa1-x,N film decrease, and minimum tensile strai