QUANTITATIVE TRANSMISSION ELECTRON-MICROSCOPY INVESTIGATION OF THE RELAXATION BY MISFIT DISLOCATIONS CONFINED AT THE INTERFACE OF GAN AL2O3(0001)/

A quantitative transmission electron microscopy (TEM) investigation of the relaxation of GaN grown on Al2O3(0001) has been carried out. Term inating {11 (2) over bar 0}-substrate fringes observed at the interfac e of the highly mismatched system have been characterized and the effi ciency of the relaxation was measured. Wurtzite type GaN was grown by plasma induced molecular beam epitaxy (MBE) on the (0001) basal plane of Al2O3. The in-plane orientation between GsN and substrate reveals a high lattice misfit of f = -13.9% and therefore the critical thicknes s of dislocation formation is reached when the first monolayer of GaN is grown. An expected interfacial relaxation process is characterized by the results of high resolution transmission electron microscopy (HR TEM) which reveals misfit dislocations confined in the GaN/Al2O3 inter face region, The quantitative evaluation of the HRTEM images on the on e hand and Moire pattern on the other hand shows the effectiveness of the observed relaxation process: here a degree of relaxation delta = ( -11.8 +/- 0.9)% and a residual strain of epsilon(r) = (-2.1 +/- 0.9)% was measured, and it seems that only epsilon(r) causes a dislocation d ensity of estimately 10(10) cm(-2) in the GaN epilayer.