DFT study on adduct reaction paths of GaN MOCVD growth

Abstract

The adduct reaction paths for GaN growth by metal organic chemical vapor deposition (MOCVD) were studied by quantum chemical calculations employing density functional theory (DFT). Five possible adduct reaction paths with or without the excess NH3 were proposed and the corresponding potential energy surfaces were calculated. From the calculation results, it is concluded that after the formation of DMGNH2 from TMG:NH3, the further decomposition paths have very slim probability because of the high energy barriers; whereas the oligomerization pathway to form oligomers [DMGNH2]x (x=2, 3) is probable, because of zero energy barrier. Since the oligomers tend to further polymerize, the nanoparticles are easily formed through this path. When NH3 is in excess, TMG:NH3 tends to combine with the second NH3 to form two new complexes: the coordination-bonded compound H3N:TMG:NH3 and the hydrogen-bonded compound TMG:NH3… NH3. The formation of hydrogen-bonded compound TMG:NH3… NH3 will be more probable because of the lower energy than H3N:TMG:NH3. By comparing the potential energy surfaces in five adduct reaction paths, we postulate that, under the growth conditions of GaN MOCVD, the formation of hydrogen-bonded compound TMG:NH3… NH3 followed by the reversible decomposition may be the main reaction path for GaN thin film growth; while the adduct oligomerization path to generate oligomers [DMGNH2]2 and [DMGNH2]3 might be the main reaction path for nanoparticles formation.