Structural and Optical Properties of Nonpolar m-Plane GaN and GaN-Based LEDs on γ-LiAlO_₂

We report the structural and optical properties of nonpolar m-plane GaN and GaN-based LEDs grown by MOCVD on a γ-LiAlO₂ (100) substrate. The TMGa, TMIn and NH₃ are used as sources of Ga, In and N, respectively. The structural and surface properties of the epilayers are characterized by x-ray diffraction, polarized Raman scattering and atomic force microscopy (AFM). The films have a very smooth surface with rms roughness as low as 2nm for an area of 10×10μm² by AFM scan area. The XRD spectra show that the materials grown on γ-LiAlO₂ (100) have <1-100> m-plane orientation. The EL spectra of the m-plane InGaN/GaN multiple quantum wells LEDs are shown. This demonstrates that our nonpolar LED structure grown onthe γ-LiAlO₂ substrate is indeed free of internal electric field. The current voltage characteristics of these LEDs show the rectifying behaviour with a turn on oltage of 1--3V.