Correlation of biaxial strains, bound exciton energies, and defect microstructures in GaN films grown on AlN/6H-SiC(0001) substrates

Biaxial strains resulting from mismatches in thermal expansion coefficients and lattice parameters in 22 GaN films grown on AlN buffer layers previously deposited on vicinal and on-axis 6H-SiC(0001) substrates were measured via changes in the c-axis lattice parameter. A Poisson's ratio of v = 0.18 was calculated. The bound exciton energy (E(BX)) was a linear function of these strains. The shift in E(BX) with film stress was 23 meV/GPa. Threading dislocations densities of similar to 10(10)/cm(2) and similar to 10(8)/cm(2) were determined for GaN Rims grown on vicinal and on-axis SiC, respectively. A 0.9% residual compressive strain at the GaN/AlN interface was observed by high resolution transmission electron microscopy (HRTEM).