Structural defects and cathodoluminescence of In_xGa_1-xN layers

Correlation between structural defects and appearance of multiple cathodoluminescence and photoluminescence peaks of In_xGa_1-xN grown nominally with x = 0.1 and increasing layer thickness (100 nm to 1000 nm) is discussed. Cathodoluminescence studies were performed on the cross-section samples earlier characterized by electron microscopy including Z-contrast microscopy. Strained and relaxed layers with different In concentrations were observed for InGaN layers above the critical layer thickness. Stacking faults appear at high density in the relaxed layer which also roughens, created a saw-tooth surface profile due to V-shaped pits. Large domains of closely separated stacking faults (polytype-like) were observed. In Z-contrast microscopy stacking faults in upper/lower part of the layer appear with higher/lower brightness, suggesting different amount of In incorporation in agreement with x-ray and RBS results. Only thin, strained InGaN layers showed single band-edge CL peaks. Multiple CL peaks appear in the relaxed, defective portion of the InGaN layers. By comparison with GaN samples where structural defects are associated with CL peak shifts, we postulate that defects, their type and distribution are main contributors to the multiple peaks observed for InGaN samples. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.