A comparative investigation of the optical properties of polar and semipolar GaN epi-films grown by metalorganic chemical vapor deposition

We report on the structural and optical properties of polar gallium nitride on c-plane sapphire substrates and semi-polar (11-22) GaN films on m-plane sapphire substrates by metalorganic chemical vapor deposition. Polar GaN on c-plane sapphire and semi-polar GaN on m-plane sapphire both show good crystal quality, luminescence, absorption, and Raman characteristics. GaN on c-place sapphire shows a high crystal quality as compared to GaN on m-plane sapphire. Surface roughness of polar GaN is lesser than semi-polar GaN. The biaxial structural stress in GaN switches from compressive to tensile as the temperature is increased. This stress-switch temperature is higher in GaN/c-plane than GaN/m-plane. GaN in polar and semi-polar orientation shows ultraviolet emissions but yellow-emissions are only observed in GaN/c-plane sapphire. Raman spectroscopy-related oscillations show systematic variations with temperature in both GaN configurations (polar and semi-polar). This work provides a framework of characterizations for GaN with different crystal polarities. It contributes towards identifying suitable crystal growth mechanisms based on the application and requirements for doping (In, Al, etc), crystal quality, emission, absorption, and photonic oscillations.

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This study reports on the structural and optical properties of polar GaN on c-plane sapphire substrates and semi-polar GaN films on m-plane sapphire substrates. The results show that polar GaN has higher crystal quality and lower surface roughness compared to semi-polar GaN. The biaxial structural stress in GaN switches with increasing temperature, with a higher stress-switch temperature in GaN/c-plane than in GaN/m-plane. Only polar GaN exhibits yellow-emissions in addition to ultraviolet emissions. Raman spectroscopy-related oscillations show systematic variations with temperature in both polar and semi-polar GaN configurations. This research provides valuable insights into the characterization of GaN with different crystal polarities.