Interaction between Sm and GaN - a photoemission study

We report on a comprehensive study of the Sm/GaN(000 (1) under bar) interface using synchrotron radiation photoemission. Spectra were taken after stepwise Sm deposition onto a clean GaN(000 (1) under bar) surface at room temperature and after annealing. Based on the analysis of resonant photoemission spectra taken for hnu = 136 eV (divalent samarium resonance) and hnu = 141 eV (trivalent samarium resonance) we find that both divalent and trivalent samarium states are present in the GaN-Sm interface layer after each step of deposition. The average valence of the system increases from 2.57 for a coverage of 0.6 Angstrom to 2.73 for 3.2 Angstrom. Above this coverage the average valence drops and reaches a final value of 2.63 for a coverage of 10 Angstrom. The Ga3d core level evolution confirms that two valence Sm states are present in the interface region. A large chemical shift of the Ga3d core level after samarium deposition and a moderate decrease in the Ga3d attenuation curve indicate that a reactive interface is created when Sin atoms are deposited on the GaN(000 (1) under bar) surface. Annealing of the Sm/GaN system to 500 degreesC induces a valence change from Sm2+ to Sm3+ and promotes diffusion of Sm from the interface into the bulk. (C) 2004 Elsevier B.V. All rights reserved.