Electronic structure of a Ba/n-AlGaN(0001) interface and the formation of a degenerate 2D electron gas

The electronic structure of ultrathin Ba/n-AlGaN(0001) interfaces has been investigated in situ in an ultra-high vacuum by the ultraviolet photoelectron spectroscopy method. The photoemission spectra from the n-AlGaN valence band and the spectra of the core levels Ga 3d, Al 2p, and Ba 4d have been studied under synchrotron excitation with photon energies of 60–400 eV. The modification of the spectra in the process of the formation of the Ba/n-AlGaN interface in the mode of the Ba submonolayer coverages has been revealed. It has been found that a decrease in the intensity in some spectral regions of the valence band is attributed to the interaction of the surface states of the AlGaN substrate with the Ba adatoms. It has been revealed that the interface formation results in the appearance of a new photoemission peak of the quasimetallic character at the Fermi level in the AlGaN bandgap. It has been established that the peak is due to the formation of the degenerate electron gas in the accumulation nanolayer induced by adsorption near the n-AlGaN surface.