Gallium nitride (GaN), a wide band gap semiconductor (Eg=3.4 eV) has unique physical properties which opened up the door to widespread applications in modern electronic devices. The semiconductor is used as a base for fabrication of visible and UV lasers, light-emitting diodes, high temperature and frequency detectors, and transistors. In all these devices the electronic properties of bare and thin-covered GaN surfaces have impacts on their efficiencies.
Herein surface sensitive techniques with an emphasis on ultraviolet and X-ray photoelectron spectroscopies (UPS and XPS) are used to understand physical and chemical properties of bare and film-covered GaN(0001) surfaces. Thin films of several elements: nickel, palladium, manganese, arsenic and antimony (Ni, Pd, Mn, As, Sb) are included. The properties of bare GaN surfaces  as well as various adsorbate/GaN phase boundary are reported [2-7]. Different types of thin films behavior under an influence of annealing in ultrahigh vacuum conditions are distinguish. Metal films form surface alloys with gallium (NiGa, PdGa) while semi-metals layers easy evaporate from GaN surface, however, the layer in direct contact with the substrate can react with it causing a change in the surface properties of GaN(0001).
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