Structural quality and ordering of MBE grown AlxGa1-xN-layers

Epitaxial AlxGa1-xN-layers (x = 1-0) with the hexagonal wurzite structure w ere grown on 6H-SiC- and alpha -Al2O3-substrates for the development of sem iconductor UV detectors. The experiments were performed in a plasma enhance d molecular beam epitaxy system (MBE) by varying substrate temperature, III /V ratio and growth rates. A detailed analysis of dislocations was performe d for pure AlN-layers by RBS-channeling and was compared to the analysis of cross sectional and plan view TEM images. The annihilation of threading di slocations during the growth process was observed by RBS-channeling dependi ng on the type of substrate and the growth mechanism. Lowest dislocation de nsities are obtained for 2D-growth on SIC substrate in the range of 2 x 10( 8) cm(-2). The decrease of the growth temperature from 1000 to 900 degreesC lead to an decrease of the dislocation density by about an order of magnit ude. Depending on the growth conditions chemical ordering was observed for ternary AlxGa1-xN-layers. The space group symmetry P6(3)mc of the wurzite s tructure is reduced to P3ml due to the ordering of the group III sublattice into alternating aluminium and gallium layers. The phenomenon was studied by XRD-measurements of the symmetric superlattice peaks. (C) 2001 Elsevier Science S.A. All rights reserved.