无电极光助化学腐蚀法制备GaN微/纳米结构及其物性研究

Preparation and characterization of GaN micro/nanostructures by the electrodeless photo-assisted chemical etching

利用K2S2O8作为氧化剂,通过无电极光助化学腐蚀GaN外延层制备多种形貌的GaN微米/纳米结构.采用扫描电子显微镜(SEM)、阴极射线发光图(CL mapping)、高分辨X射线衍射(HRXRD)、拉曼光谱(Raman spectra)和光致发光谱(PL)等先进的表征手段研究腐蚀样品的形貌、晶体结构和光学性质.结果表明:在高浓度的KOH(1 mol/L)和低强度的紫外光照下,腐蚀出高质量的腐蚀坑、微米/纳米柱和纳米线;在低浓度KOH(0.4 mol/L)和高强度的紫外光照下,制备出GaN棱锥,研究发现此微米/纳米锥体阵列为包裹了位错的GaN晶体.在腐蚀液KOH浓度低至0.1 mol/L时,GaN腐蚀样品表面形成大量的晶须,聚集成束,晶须揭露了位错;并探讨了多形貌微米/纳米GaN的形成机理.腐蚀温度和GaN外延层极性对腐蚀形貌也具有明显的影响.

GaN micro/nano-structures of different morphology were successfully preparated by the electrodeless photo-assisted chemical etching in KOH solution, with K2S2O8 as the oxidizing agent. The structure, crystalline quality, stress state and optical property of both normal GaN and etched GaN were provided by the combined results of scanning electron microscopy（SEM） images, cathodoluminescence mapping（CL mapping）, high-resolution X-ray diffraction（HRXRD） detection, micro-Raman spectra and photoluminescence（PL）, respectively. The results show that pits, micro/ nanopillars and nanowires of high crystalline quality are formed in the high KOH concentrations（1 mol/L） and the low light intensity; Ga N pyramid arrays have been fabricated in 0.4 mol/L KOH solution with high UV light intensity, and CL mapping indicates that these pyramids are composed of crystalline GaN surrounding a dislocation; Whiskers can also be obtained in 0.1 mol/L KOH with high UV light intensity after etching. The whiskers are believed to be directly correlated with line-type defects of edge and mixed character. The formation mechanism and the feature of GaN different morphology were rationally explained. And the etching temperature and the polarity of Ga N surface have an evident influence on the surface morphology of GaN.