物理学报2017，Vol.66Issue(10)：229-234,6.DOI:10.7498/aps.66.106101
金属有机物化学气相沉积同质外延GaN薄膜表面形貌的改善
Surface morphology improvement of homoepitaxial GaN grown on free-standing GaN substrate by metalorganic chemical vapor deposition
摘要
Abstract
Free-standing GaN is generally regarded as an ideal substrate for GaN-based devices due to its advantage of low threading dislocation density (TDD) and good thermal conductivity.However,new surface features such as hillocks and ridges appear on the GaN homoepitaxy films.In this paper,the influences of the intermediate GaN (IM-GaN) layer on the surface defects and crystal quality of GaN homoepitaxy films grown on c-plane GaN substrates by metalorganic chemical vapor deposition are investigated.It is found that hexagonal hillocks and ridges on the surface can be avoided by inserting an IM-GaN layer grown at an intermediate temperature (650-850 ℃),prior to the growth of GaN at 1050 ℃.The results based on X-ray diffraction (XRD) measurements and differential interference contrast microscopy images demonstrate that the growth temperature of the IM-GaN layer has a significant influence on GaN homoepitaxy layer,which is one of the most critical parameters determining the surface morphology and crystal quality.As the IM-GaN growth temperature decreases from 1050 ℃ to 650 ℃,thed densities of hillocks and ridges on the surface reduce gradually.While,the XRD full width at half maximum (FWHM) values of (002) and (102) peaks for the homoepitaxy films are increased rapidly,indicating the adding of the TDD in the films.The atomic force microscopy (AFM) images show that the quasi-step growth mode change into layer-layer growth mode with the growth temperature decreasing from 1050 ℃ to 650 ℃ during the IM-GaN layer growing.It is speculated that the growth mode is determined by the diffusion length of adatom on the growing surface,which is proportional to the growth temperature.In the case of IM-GaN grown at low temperature,the formation of hillocks can be suppressed by reducing the adatom diffusion length.Finally,High crystal quality GaN homoepitaxy films (2 μm) without hillocks is achieved by optimizing the growth parameters of IM-GaN layer,which is about 150 nm in thickness and grown at 850 ℃.The crystal quality of GaN homoepitaxy film is assessed by XRD rocking curve measured with double-crystal optics.The FWHMs of the (002) and (102) peaks are 125arcsec and 85arcsec respectively,indicating that rather low TDD is formed in the film.And well defined steps are observed on the image of AFM test,the root-mean square roughness value of the which is only about 0.23 nm for 5 μm x 5 μm scan area.关键词
金属有机物化学气相沉积/同质外延GaN/插入层/生长模式Key words
metalorganic chemical vapor deposition/homoepitaxy GaN/intermediate layer/growth mode引用本文复制引用
李忠辉,李传皓,罗伟科,杨乾坤,李亮,周建军,董逊,彭大青,张东国,潘磊..金属有机物化学气相沉积同质外延GaN薄膜表面形貌的改善[J].物理学报,2017,66(10):229-234,6.基金项目
国家自然科学基金(批准号:61505181,61474101,61504125)、国家高技术研究发展计划(批准号:2015AA016800,2015AA033300)和国家重点研发计划(批准号:2016YFB0400902)资助的课题.Project supported by the National Natural Science Foundation of China (Grant Nos.61505181,61474101,61504125),the National High Technology Research and Development Program of China (Grant Nos.2015AA016800,2015AA033300) and the National Key Research and Development Program of China (Grant No.2016YFB0400902). （批准号:61505181,61474101,61504125）
