Optical Anisotropic Properties of m-Plane GaN Film Grown by Metalorganic Chemical Vapor Deposition

Spontaneous and piezoelectric polarization could lower the efficiency of GaN-based light-emitting diodes. In order to eliminate or reduce this undesirable effect, m-plane GaN film was prepared by metalorganic chemical vapor deposition (MOCVD) on LiAlO2(100) substrate with a GaN buffer layer. Since the c axis of the m-plane GaN lays in the grown plane, the breakage of in-plane symmetry gave rise to an optical anisotropy, which was revealed by a difference in refractive indexes of E-field parallel and perpendicular to the c axis of the m-plane GaN measured by polarized reflection measurement. In addition, in-plane strain anisotropy due to the lattice mismatch between the GaN film and the LiAlO2 substrate changed the Electronic Band Structure (EBS). The change of EBS also led to an in-plane optical anisotropy. Polarized absorption and Photoluminescence (PL) measurements showed a split in energy of 32 meV for optical absorption edge and 37 meV for PL peak energy respectively.