Surface Structures from NH 3 Chemisorption in CVD and ALD of AlN, GaN, and InN Films

Aluminum nitride (AlN), gallium nitride (GaN),and indium nitride (InN) form a family of technologicallyimportant semiconductors of high importance to light-emittingdiodes and high-frequency electronics. Although thinfilms of thesematerials are routinely manufactured by chemical vapor deposition(CVD) and atomic layer deposition (ALD), these methods are farfrom optimal and knowledge of the underlying chemical processesis lacking. In this work, we performed ab initio investigations of thesurface coverage of these materials under an ammonia-richatmosphere. Periodic density functional theory calculations wereused to test the probable surface structures, and their electronicand thermal energies were used to calculate their contribution tothe surface composition under the temperature and pressureconditions relevant for CVD and ALD processes of these materials. The results show similarities between the group of materials witha similar NHxsurface structure present for all three. Comparison of the coverage showed that at low growth temperatures, thesurface is expected to be covered by NH2, while at high temperatures, most surface sites would be vacant. The surface structureswere all found to be the most stable on AlN and least stable on InN. These results are important for further investigations of thematerial growth mechanisms.