Lateral epitaxy and dislocation density reduction in selectively grown GaNstructures

The results of a comparative study of the defect microstructures at differe nt regions in epitaxial, monocrystalline GaN structures grown selectively w ithin windows in and laterally over SiO2 masks deposited on GaN/AlN/6H-SiC heterostructures are presented. The defects in the GaN grown within the SiO 2 windows were predominantly threading dislocations of mostly mixed charact er with Burgers vector b = 1/3(1 1 (2) over bar 3) and edge dislocations wi th b = 1/3(1 1 (2) over bar 0) with a density range of 10(9)-10(10)cm(-2) a s determined using transmission electron microscopy (TEM). The regions of l ateral epitaxial overgrowth (LEO-GaN) contained short dislocation segments parallel to the interfacial planes, which were usually aligned parallel or nearly parallel to the (1 (1) over bar 0 0) or (1 1 (2) over bar 0) directi ons and with densities of less than or equal to 10(6) cm(-2) Specific morph ologies exhibited by the LEO-GaN were determined to be associated with the mechanism of stress relaxation. Finite element analysis of these complex he terostructures showed that the accommodation of the mismatches in the coeff icients of thermal expansion among the different phases in the heterostruct ures was manifest in the formation of the curved surfaces observed in cross -sectional TEM. (C) 2001 Elsevier Science B.V. All rights reserved.