STRAIN EFFECTS ON EXCITONIC TRANSITIONS IN GAN - DEFORMATION POTENTIALS

We present thr results of experimental studies of the strain effects o n the excitonic transitions in GaN epitaxial layers on sapphire and Si C substrates, with the emphasis on the determination of deformation po tentials for wurtzite GaN. Photoluminescence and reflectance spectrosc opies were performed to measure the energy positions of exciton transi tions and x-ray-diffraction measurements were conducted to examine the lattice parameters of GaN epitaxial layers grown on different substra tes. Residual strain induced by the mismatch of lattice constants and thermal expansion between GaN epitaxial layers and substrates was foun d to have a strong influence in determining the energies of excitonic transitions. The overall effects of the strain generated in GaN is com pressive for GaN grown on sapphire and tensile for GaN on SIC substrat e. The uniaxial and hydrostatic deformation potentials of wurtzite GaN were derived from the experimental results. Our results yield the uni axial deformation potentials b(1) approximate to-5.3 eV and b(2) appro ximate to 2.7 eV, as well as the hydrostatic components a(1) approxima te to-6.5 eV and a(2) approximate to-11.8 eV.