非极性(11-20)a面GaN薄膜MOCVD生长及性质研究

Growth and Characterization of Non-polar a-plane GaNEpi-layers Grown on r-plane Sapphire

本论文利用金属有机化合物化学气相沉积(MOCVD)方法生长了非极性(11-20)a面GaN薄膜,并利用光学显微镜(OM)、扫描电子显微镜(SEM)和高分辨率X射线衍射系统(HR-XRD)分别深入分析了生长薄膜的表面形貌、晶体质量和结构特性。研究结果表明,非极性(11-20)a面GaN薄膜在V/III为600时表面完全合并但存在大量的表面坑,而其在V/III为1200时出现大量的三角形表面坑。而且,V/III比为850~1000时有助于减少该薄膜的表面坑。由于非极性(11-20)a面GaN薄膜的Ga吸附原子扩散长度的各向异性,使其结构在a面内存在各向异性,因此这些薄膜在c和a方向上的XRD摇摆曲线的半高宽值也存在各向异性。另外,Ga原子沿c方向的迁移在相对较高的反应室压力(100 Torr)时被抑制,从而降低了非极性(11-20)a面GaN薄膜的结构各向异性。

In our work,the non-polar a-plane GaNepi-layers were grown with varied V/III ratio and reactor pressure on r-plane(1-102)sapphire substrates by metal-organic chemical vapor deposition(MOCVD)in a low pressure reactor.Moreover,the surfaces morphologies of these samples were studied by optical microscopy(OM)and scanning electron microscopy(SEM),respectively.The crystal property was also examined using high resolution X-ray diffraction(HRXRD).The XRDω-2θscan results showed that the as-deposited GaNepi-layers are the non-polar a-plane(11-20)GaN films.Furthermore,the non-polar a-GaNepi-layer with V/III ratio of 600 showed a fully coalesced surface morphology with a large amount of pits,while there existed the large triangular pits on the surface of the a-GaNepi-layers with V/III ratio of 1200.Moreover,a suitable V/III ratio of 850~1000 should be beneficial in reducing the pits on the surface of the a-GaNepi-layers.Due to the different migration length of Gaadatoms along c-and a-direction,the crystal structure of a-plane GaNepi-layers is in-plane anisotropic.Thus,the narrowest FWHM values of these epi-layers in the c-and a-direction were obtained at V/III ratio of 850 and 1200,respectively.In addition,for these epi-layers with varied reactor pressure,the narrowest FWHM values were achieved at reactor pressure of 40 Torr.Under the relatively high reactor pressure,the structural anisotropy for these epi-layers was reduced because of the suppressed Ga atomic migration along thec-axis.