We present a study of hexagonal GaN thin films grown by low-pressure chemical vapor deposition on sapphire substrates. We used synchrotron radiation photoemission spectroscopy to probe the electronic density of states and test the validity of existing band structure calculations. Parallel studies of surface composition and atomic structure by means of Auger spectroscopy and reflection high-energy electron diffraction were performed following sputtering/annealing cycles using argon, xenon and nitrogen ions. We found that sputtering with nitrogen ions followed by annealing in vacuum is an effective method to reduce nitrogen surface depletion and produce quasi-stoichiometric ordered GaN(0 0 0 1)1 × 1 surfaces.
Bibliographical noteFunding Information:
This work was supported by the Office of Naval Research under grant No. N00014-89-J-1407a nd by the Center for Interfacial Engineering of the University of Minnesota. We are in debt to H. Morkos, M. Yoder, C. Van de Walle and G. Wright for useful discussions,a nd for providing us with their results prior to publication. The synchrotronr adiation photoemission measurementps resentedh ere were performeda t the Synchrotron Radiation Center of the University of Wisconsin-Madison, supported by NSF. We grat’efully acknowledge the cheerful assistancet o its staff.