The electronic structure of the Cs/$n$-GaN(0001) nano-interface

Electronic structures of the $n$-GaN(0001) surface and Cs/$n$-GaN(0001) interface with submonolayer Cs coverages were studied for the first time in situ by the photoelectron spectroscopy (PES) method. The spectra of photoemission from the valence band, surface electron states, and core levels (Ga 3$d$, Cs 4$d$, Cs 5$p$) under synchrotron excitation were measured in a range of photon energies within 50–150 eV. Evolution of the spectrum of surface states near the valence-band maximum was revealed by PES during the adsorption of Cs atoms. A metallic character of the Cs/$n$-GaN(0001) nano-interface is demonstrated.