Titanium oxide nanoparticles spin-coated onto r-plane sapphire substrate: Effects on structural and optical properties of nonpolar a-plane GaN and InGaN/GaN multiple quantum wells

• Published in: Journal of crystal growth 2012-09, Vol.355 (1), p.101-108
• Main Authors: Hoon Kim, Ji, Hwang, Sung-Min, Son, Ji-Su, Hyeon Baik, Kwang, Man Song, Keun, Ho Park, Jung
• Format: Article
• Language: English
• Subjects: A3. Metalorganic chemical vapor deposition; Atomic force microscopy; B1. Nitrides; B1. Titanium compounds; B2. Semiconducting III–V materials; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Defects and impurities in crystals; microstructure; Exact sciences and technology; Gallium nitrides; Linear defects: dislocations, disclinations; Materials science; Nanoscale materials and structures: fabrication and characterization; Optical properties; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Other topics in nanoscale materials and structures; Physics; Quantum confinement; Sapphire; Stacking faults and other planar or extended defects; Structure of solids and liquids; crystallography; Titanium dioxide; Transmission electron microscopy
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2012.06.036

The structural and optical properties of nonpolar a-plane (11−20) GaN and In0.18GaN0.82/GaN multiple quantum wells (MQWs) grown on TiO2 nanoparticle (NP)-coated r-plane (1−102) sapphire substrate have been investigated. A smooth surface morphology was observed by atomic force microscopy (AFM), indicating a good lateral overgrowth on TiO2 NPs. Transmission electron microscopy (TEM) images revealed a reduction in the density of basal stacking faults (BSFs) and threading dislocations (TDs) in the TiO2 NP-coated sample. From X-ray diffraction measurements, the broadening of ω-scan full width at half maximum (FWHM) was influenced by the tilt of the mosaic due to TiO2 NPs. A reduced PL-integrated intensity ratio (IBSF/INBE) in low-temperature photoluminescence (PL) spectra of the a-plane GaN film grown over TiO2 NPs was consistent with TEM results. The improved room temperature-PL intensity of TiO2-embedded MQWs is associated with the increase in light extraction efficiency, due to the TiO2 NPs and air voids. Temperature-dependent PL spectra revealed that the dominant PL emission was attributed to localization of carriers in quantum wire-like regions, where the BSFs intersect the QWs. The observed quantum efficiency at 300K also showed a good quantum confinement, even though alloy fluctuations might be expected in the QWs. ► We investigated the effect of TiO2 nanoparticle on a-plane GaN-related structures. ► TEM images revealed a reduction in the density of BSFs and TDs in theTiO2-related sample. ► Broadening of omega scan is attributed to the tilt of mosaic crystals by the TiO2. ► High PL intensity of TiO2-embedded MQW is attributed to TiO2 nanoparticles. ► The high activation energy and PL efficiency show good quantum confinement effect.