Deep traps in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy

Deep level defects in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy were characterized using deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) and compared with polar c-plane GaN that was grown simultaneously in the same growth run. Significant differences in both the levels present and their concentrations were observed upon comparison of both growth orientations. DLTS revealed electron traps with activation energies of 0.14 eV, 0.20 eV, and 0.66 eV in the m-plane material, with concentrations that were similar to 10-50 x higher than traps of similar activation energies in the c-plane material. Likewise, DLOS measurements showed similar to 20 x higher concentrations of both a C-N acceptor-like state at E-C - 3.26 eV, which correlates with a high background carbon concentration observed by secondary ion mass spectroscopy for the m-plane material [A. Armstrong, A.R. Arehart, B. Moran, S.P. DenBaars, U. K. Mishra, J.S. Speck, and S.A. Ringel, Appl. Phys. Lett. 84, 374 (2004)], and the V-Ga-related state level at E-C - 2.49 eV, which is consistent with an enhanced yellow luminescence observed by photoluminescence. The findings suggest a strong impact of growth dynamics on the incorporation of impurities and electrically active native point defects as a function of GaN growth plane polarity. (C) 2012 American Institute of Physics. [doi:10.1063/1.3682528]