Abstract
Since AlGaN offers new opportunities for the development of the solid state ultraviolet (UV) luminescence, detectors and high-power electronic devices, the growth of AlN buffer substrate is concerned. However, the growth of AlN buffer substrate during MOCVD is regulated by an intricate interplay of gas-phase and surface reactions that are beyond the resolution of experimental techniques, especially the surface growth process. We used density-functional ab initio calculations to analyze the adsorption, decomposition and desorption of group-III and group-V sources on AlN surfaces during MOCVD growth in molecular-scale. For AlCH3 molecule the group-III source, the results indicate that AlCH3 is more easily adsorbed on AlN (0001) than (000overline{1}) surface on the top site. For the group-V source decomposition we found that NH2 molecule is the most favorable adsorption source and adsorbed on the top site. We investigated the adsorption of group-III source on the reconstructed AlN (0001) surface which demonstrates that NH2-rich condition has a repulsion effect to it. Furthermore, the desorption path of group-III and group-V radicals has been proposed. Our study explained the molecular-scale surface reaction mechanism of AlN during MOCVD and established the surface growth model on AlN (0001) surface.
Highlights
Since AlGaN offers new opportunities for the development of the solid state ultraviolet (UV) luminescence, detectors and high-power electronic devices, the growth of AlN buffer substrate is concerned
The results indicated that the adsorption energy and the stable adsorption site of group-III source A lCH3 molecule on AlN surface are affected by the topmost surface atoms, and the AlCH3 molecule is easier adsorbed on the top site of AlN (0001) surface which explained in theory why the epitaxial growth of AlN for devices has usually been grown along the [0001] direction
We have found that when N and H atoms cover the surface in the form of NH2 molecular structure, they will inhibit the adsorption of Al source on AlN (0001) surface, which indicated that the desorption of H atom has a greater impact on the initial surface growth process on AlN (0001) surface than the adsorption of N atom
Summary
Since AlGaN offers new opportunities for the development of the solid state ultraviolet (UV) luminescence, detectors and high-power electronic devices, the growth of AlN buffer substrate is concerned. The structures that group-III source adsorbed on the adsorption site on AlN (0001) and AlN (0001 ) surfaces (shown in Fig. 2) were optimized.
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