预成核对蓝宝石衬底上生长氮化镓低温层的影响

Influence of Pre-Nucleation on Growth of GaN Low Temperature Layer on Sapphire Substrate

金属有机物化学气相沉积(MOCVD)技术以气相源的热分解反应作为基础,其适合规模化生产,是现今生长半导体材料的主要制备方式。在MOCVD生长GaN的过程中,衬底表面初始条件直接影响到材料成核与生长,因此对于外延生长非常关键。本论文研究了GaN外延生长过程中蓝宝石衬底的表面预成核工艺对GaN低温成核的影响。通过对比未处理样品和高温预通TMGa、高温预通TMGa和NH3预成核以及高温预通TMAl和NH3预成核的样品上生长的低温层退火后的形貌,我们发现高温预成核形成的成核点有利于吸引其周围气相源并入,并降低成核岛的密度。结合光学实时反射率监测气相沉积中晶粒的成核过程,进一步横向比较可发现由于高温时AlN更稳定,预成核的效果更好,对退火以后GaN小岛形貌影响更加显著。X射线衍射表征成核层的晶体质量,发现预成核工艺可将退火后成核层的(002)衍射峰半高宽从1636 arcsec降低到最低1088 arcsec。通过对比分析,我们认为高温预成核工艺的优点可能来源于其可以改善成核初期小岛的晶向。这些研究为进一步提高GaN外延质量提供了新的工艺思路。

Metal-organic chemical vapor deposition(MOCVD)technology is based on the thermal decomposition of gas source,which is suitable for large-scale production and is the main preparation method for growing semiconductor materials.In the process of GaN growth by MOCVD,the initial conditions on the substrate surface directly affect the nucleation and growth of the material,so it is critical for epitaxial growth.In this paper,the effect of sapphire substrate surface prenucleation on GaN nucleation at low temperature during GaN epitaxial growth was studied.By comparing the annealed morphology of the low-temperature layer grown on untreated samples and samples with high temperature prenucleation of TMGa and NH3,and samples with high temperature prenucleation of TMAl and NH3,we found that the nucleation point formed by high temperature prenucleation is conducive to attracting the surrounding gas source into the site and reducing the density of the nucleation island.Combined with optical real-time reflectance monitoring the nucleation process of grains in vapor deposition,a further lateral comparison shows that AlN is more stable at high temperature,and the prenucleation effect is better,which has a more significant impact on the morphology of GaN islets after annealing.The crystal quality of the nucleated layer was characterized by X-ray diffraction,and it was found that the(002)half-height width of the diffraction peak of the annealed nucleated layer could be reduced from 1636 arcsec to 1088 arcsec.Through comparative analysis,we believe that the advantages of high temperature prenucleation process may come from its ability to improve the crystalline orientation of small islands at the early stage of nucleation.These studies provide new process ideas for further improving the epitaxial quality of GaN.