Comparative study of Cs,O coadsorption on Ga0.75Al0.25N (0001) and (001) surfaces

Based on first principle calculations, we carried out comparative research of Cs,O coadsorption on Ga0.75Al0.25N (0001) surface and Ga0.75Al0.25N (001) (2x2) reconstruction surface. On the (0001) surface, the average coordinate difference between Cs and O atoms along [0001] direction is obviously smaller than that along [001] direction on (001) (2x2) reconstruction surface. This is due to the existence of dimers and trenches on the (001) (2x2) reconstruction surface. Cs atoms are favored to locate on the dimers while O atoms are favored to locate in the trenches. As a result, Cs-O dipoles on (001) (2x2) reconstruction surface make an important contribution on lowering work function. For both (0001) and (001) (2x2) reconstruction surface, work function values fluctuate up and down at the stage of Cs,O alternative adsorption, and the valley values are smaller and smaller. The site of Mg dopant has an influence on work function of the surfaces, which results in the fish scale field effect.