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 A1N 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 ν = 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 ~10¹⁰/cm² and ~10⁸/em² were determined for GaN films grown on vicinal and on-axis SiC, respectively. A 0.9% residual compressive strain at the GaN/AIN interface was observed by high resolution transmission electron microscopy (HRTEM).