Adsorption of Cs on Al0.5Ga0.5N(0001) surface doped with Mg

The first-principles was employed to calculate the adsorption of Cs on (2 x 2) Al(Mg)(0.5)Ga0.5N and Al-0.5 Ga(Mg)(0.5)N surfaces using density-functional theory within a plane-wave ultrasoft pseudopotential scheme. Then, the surface morphology, stability, work functions and Cs adsorptions of Al(Mg)(0.5)Ga0.5N and Al-0.5 Ga(Mg)(0.5)N surfaces were investigated. The results reveal that Al(Mg)(0.5)Ga0.5N surface with Mg in the first layer was more suitable for ultraviolet cathode. The most stable adsorption site for adsorption of Cs on the Al(Mg)(0.5)Ga0.5N surface was found on N top. With the increase of Cs coverage, the interaction between Cs and atoms in the first layer of surface and that between Cs and Cs was enhanced, the surface dipole moment increased, the work function decreased, the carrier concentration and the absorption in visible light increased. When Cs coverage was greater than 0.5ML, the adsorption of Cs reached saturation, the deformation of surface structure appeared, the adsorption in visible light was greater than that in UV, and the surface was no longer suitable for UV detection. The results show that 0.5ML is the turning point of Cs coverage for the surface doped with Mg.