Charge accumulation layer on the n-GaN (0001) surface with ultrathin Ba coatings

The adsorption of Ba on the n-type GaN(0001) surface is studied. It is found that submonolayer Ba coatings induce cardinal changes in the electronic properties of the surface with the formation of a charge accumulation layer in the region of the near-surface band bending. The excitation of the Ba/n-GaN system by light from the region of GaN transparency results in photoemission. The lowest value of the work function corresponds to ∼1.90 eV at a Ba coverage of ∼0.4 ML. Two surface bands induced by Ba adsorption are found in the surface photoemission spectra.