OPTICALLY DETECTED ELECTRON-NUCLEAR DOUBLE-RESONANCE OF EPITAXIAL GAN

Optically detected electron-nuclear double resonance (ODENDOR) experim ents at 24 GHz performed on a set of GaN epitaxial layers grown on Al2 O3, substrates reveal Ga-69,Ga-71 signals with quadrupole splittings t hat reflect the crystal structure and degree of local strain. Searches were made between 1.5 and 140 MHz on both the effective-mass (EM) don or and deep defect resonances revealed from optically detected magneti c resonance (ODMR) studies of the 2.2-eV ''yellow'' emission bands. St rong Ga-69 and Ga-71 lines were found between 7 and 14 MHz on the EM d onor resonance from two high-resistivity films (n less than or equal t o 1x10(16) cm(-3)), and are attributed to neighboring Ga-69,Ga-71 latt ice nuclei. These resonances are split by the local electric-field gra dients through the nuclear quadrupole interaction. The quadrupole spli ttings of 2.16+/-0.08 and 2.40 +/- 0.05 MHz found for Ga-69 in these s amples are 15-25 % smaller than those reported for a free-standing bul k platelet and for a bulk powder. Similar signals were not observed on the EM-donor lines from two n-type GaN layers with n greater than or equal to 3x10(16) cm(-3). These concentration-dependence results revea l the ENDOR mechanisms in GaN. ODENDOR was not found on the deep-defec t ODMR. Possible reasons for the absence of signals are presented. [S0 163-1829(98)00216-1].