A Density Functional Study Of Small Molecule Adsorption On GaN(0001) Surface

GaN has very promising potential for short-wave length light-emitting diodes, semiconductor lasers, and optical detectors. In view of these exciting challenges it is currently under intensive theoretical and experimental investigations. To achieve its full technological potential, understanding the electronic properties of clean and adsorbate-covered surfaces is of particular importance. Since it is the first step in understanding fundamental issues of contact formation, chemical reactivity, growth processes, and structural stability. At present, the studies mainly concern the investigation of surface reconstructions and their electronic structures. However, the adsorption of small molecule on the GaN surfaces, are relatively in lack. In this dissertation, the adsorption and dissociation mechanism of some small molecules on GaN (0001) surface have been investigated. The main contents are as the following: - The adsorption of oxygen on GaN (0001) and ( 0001) surfaces is studied. It is found that molecular 62 parallel adsorption at the bridge site on the GaN (0001) surface is the precursor for its dissociation. And the dissociated O diffuses into the fee site on both polar orientations, causing the oxidation of the surfaces finally.2,The adsorption and dissociation of NH3 on the clean and O present GaN(0001) surface is investigated. The calculated results indicate, similar to the case of metal surfaces, the presence of oxygen atom has greatly decreased the barrier of NHsdissociation on the surface and the total energy of the reaction system, thussignificantly promotes the dissociation of NH3 on the GaN (0001) surface.3, The dissociative adsorption of Cl2 on the GaN (0001) surface is studied. The calculated results indicate almost no barrier exist for molecular Cl2 dissociation on the surface. The Mulliken charges analyses indicates the charges mainly transferred from the substrate to the antibonding 3p o orbital of Ch and the new bonds reforming are the main reason for the spontaneously dissociative process. No Ch molecular precursor is found in our calculation, therefore, our work supports direct dissociation mechanism for Cl2 dissociation on the surface.V4.9 The adsorption of N2O on the GaN (0001) surface is investigated. It is found the transferred charges play a crucial role in the N2O dissociation process: only when NiO is initially paralleled arranged at bridge site, the transferred charges flow from the substrate to the molecular antibonding orbital, and result in the dissociation of N2O; while in other adsorption configuration, the charges flow from the molecule to the substrate, and only weak interaction between the N2O and the surface.