James Speck , University of California, Santa Barbara, DMR 0906805

1. Carbon as a source of yellow luminescence in GaN James Speck, University of California, Santa Barbara, DMR 0906805 CN Gallium nitride (GaN) is used for blue lasers, light-emitting diodes, and high-frequency transistors. Carbon is frequently added to GaN to alter its electrical properties; it is also often present as an unintentional impurity. Carbon-containing GaN typically exhibits yellow luminescence (YL); in spite of over 30 years of research the mechanism of this luminescence has remained unexplained. The UCSB Computational Materials group led by Prof. Van de Walle has now cracked this problem using advanced first-principles calculations. They find that carbon incorporates on the nitrogen site in GaN, acting as an acceptor. However, contrary to the commonly accepted view that carbon is a shallow acceptor, they find that carbon is a deep acceptor, with a transition level 0.9 eV above the valence band. Because of the position of this level the carbon acceptor itself can give rise a broad luminescence line near 2.14 eV, resolving the longstanding mystery of the C-related center that gives rise to YL in GaN. These results are of high relevance for researchers growing GaN-based devices, in which the YL can play a detrimental role. Model of the GaN lattice with a carbon impurity, and isosurface of the spin density Conduction band CN0 Valence Band GaN Mechanism for C-related luminescence