用X射线衍射法测定氮化镓马赛克结构中的面内扭转角

Ⅲ-Ⅴ族氮化物半导体材料在发光二极管、激光器和探测器方面有着广泛的应用,采用高分辨X射线衍射来测定用金属有机化学气相沉淀法在蓝宝石衬底上生长的氮化镓外延层马赛克结构的扭转角,分别研究了(0002)、(1013)、(1012)、(1011)、(2021)五个面的X射线摇摆曲线,并且用Pseudo-Voigt方程拟合每一个面的摇摆曲线,我们利用外推法很方便地测得氮化镓外延薄膜的面内扭转角。另外我们采用同步辐射X射线掠入射衍射对样品进行(1100)面反射φ扫描直接测得面内扭转角,对第一种方法进行验证,两种方法测量结果相同。从而提供一种简单、方便的GaN外延层的面内扭转角的测试方法,为深入研究GaN材料奠定良好基础。

Twist Angle of Mosaic Structure in GaN Films Determined by X-ray Diffraction

GaN and its related Ⅲ - Ⅴ alloys have received much attention in recent years for their potential ability in short-wavelength light emitting diodes, laser diodes and photodetectors. However, due to the lack of a suitable latticematched bulk substrate, they are usually grown on Al2O3 or SiC substrates with a high density of threading dislocations (TDs). The origin of these dislocations has been suggested to be due to a peculiar growth mode-mosaic structure which can be characterized by means of tilt and twist angles. For wurtzite GaN the mean tilt angle of mosaic structure is related to the FWHM of (0002) diffraction peak,which can be easily measured by using XRD. Unfortunately, the twist of lattice planes is difficult to be measured directly. High-resolution X-ray diffraction was used to determine the twist angle of mosaic structure in GaN epitaxial layers grown on sapphire by metal-organic chemical vapor deposition (MOCVD). Rocking curves of five planes were investigated, (0002); (10(-1)3); (10(-1)2); (10(-1)1 ); and (20(-2)1) respectively. Pseudo-Voigt function was used to simulate the rocking-curve of every plane. The twist angles of GaN layers were easily obtained by extrapolating the full width at half maximum (FWHM) of diffraction peak of the planes. The twist angles of the films measured directly by φ-scans of the (1(-1)00) reflection in grazing-incidence X-ray diffraction (GIXRD) agree well with the extrapolated results. As far as we know, it's the first time that the extrapolated method was checked to be valid in this material, and the results are useful for the further study of GaN films.