摘要
使用气相沉积SiO2和普通光刻以及湿法腐蚀方法,在c面蓝宝石上开出不同尺寸的正方形窗口,在窗口区域中露出衬底,然后使用氢化物气相外延(HVPE)方法选区外延GaN薄膜.采用光学显微镜、原子力显微镜(AFM)、扫描电子显微镜(SEM)、高分辨率双晶X射线衍射(DCXRD)和喇曼谱测试(Ramanshift)对薄膜进行分析.结果表明,在c面蓝宝石衬底上独立的正方形窗口区域中外延生长的,厚度约20μm的GaN薄膜,当窗口面积为100μm×100μm时,GaN表面无裂纹;而当窗口面积为300μm×300μm和500μm×500μm时,GaN表面有裂纹.随着窗口面积的减小,GaN双晶衍射摇摆曲线的(0002)峰的半高宽(FWHM)减小,表明晶体的质量更好,最小的半高宽为530″.从正方形窗口区的角上到边缘再到中心,GaN的面内压应力逐渐减小,分析认为这与GaN横向外延区(ELO区)与SiO2掩膜之间的相互作用,以及窗口区到ELO区的线位错的90°扭转有关.
Square patterns with different sizes are prepared on c-sapphire by plasma-enhanced chemical vapor deposition of SiO2 ,conventional optical lithography,and wet chemical etching. The GaN film is selectively grown on this patterned c-sapphire by hydride vapor phase epitaxy. An optical microscope, atomic force microscope, scanning electron microscope, high resolution double crystal X- ray diffraction （DCXRD） ,and Raman shift spectrum are used to analyze the sample. The GaN layer with a thickness of about 20μm grown on an area of 100μm × 100μm is crack-free while the GaN layers grown on areas of 300μm × 300μm and 500μm × 500μm have cracks. Thus,the full width at half maximum （FWHM） of DCXRD of （0002） reflection of GaN grown on the independent square window of c-sapphire decreases when the area of window decreases, indicating better quality GaN single crystal. The minimum FWHM is 530″. From the corner of the square window towards its edge and center,the in-plane compressive stress of GaN decreases due to the interaction between the epitaxial lateral overgrown GaN wings and the SiO2 mask underneath,and the bending of 90° of threading dislocations at the border of the window regions.
