Molecular orbital calculations for the formation of GaN layers on ultra-thin AlN/6H-SiC surface using alternating pulsative supply of gaseous trimethyl gallium (TMG) and NH3

The steps for the generation of very thin GaN films on ultrathin AlN/6H-SiC surface by alternating a pulsative supply (APS) of trimethyl gallium and N H3 gases have been examined by ASED-MO calculations. We postulate that the gallium culster was formed with the evaporation of CH4 gases via the decomp osition of trimethyl gallium (TMG), dimethyl gallium (DMG), and monomethyl galluim (MMG). During the injection of NH3 gas into the reactor, the atomic hydrogens were produced from the thermal decomposition of NH3 molecule. Th ese hydrogen gases activated the Ga-C bond cleavage. An energetically stabl e GaN nucleation site was formed via nitrogen incorporation into the layer of gallium cluster. The nitrogen atoms produced from the thermal degradatio n of NH3 were expected to incorporate into the edge of the gallium cluster since the galliums bind weakly to each other (0.19 eV). The structure was s tabilized by 2.08 eV, as an adsorbed N atom incorporated into a tetrahedral site of the Ca cluster. This suggests that the adhesion of the initial lay er can be reinforced by the incorporation of nitrogen atom through the form ation of large grain boundary GaN crystals at the early stage of GaN film g rowth.