Influence of growth temperature on laser molecular beam epitaxy and properties of GaN layers grown on c-plane sapphire

• Published in: Optical materials Vol. 66; pp. 142 - 148
• Main Authors: Dixit, Ripudaman, Tyagi, Prashant, Kushvaha, Sunil Singh, Chockalingam, Sreekumar, Yadav, Brajesh Singh, Sharma, Nita Dilawar, Kumar, M. Senthil
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.04.2017
• Subjects: Gallium nitride; Heteroepitaxy; Nanoindentation; Photoluminescence; Raman spectroscopy; X-ray diffraction; X-ray diffraction; Heteroepitaxy; Raman spectroscopy; Gallium nitride; Photoluminescence; Nanoindentation
• ISSN: 0925-3467; 1873-1252
• DOI: 10.1016/j.optmat.2017.01.053

We have investigated the influence of growth temperature on the in-plane strain, structural, optical and mechanical properties of heteroepitaxially grown GaN layers on sapphire (0001) substrate by laser molecular beam epitaxy (LMBE) technique in the temperature range 500–700 °C. The GaN epitaxial layers are found to have a large in-plane compressive stress of about 1 GPa for low growth temperatures but the strain drastically reduced in the layer grown at 700 °C. The nature of the in-plane strain has been analyzed using high resolution x-ray diffraction, atomic force microscopy (AFM), Raman spectroscopy and photoluminescence (PL) measurements. From AFM, a change in GaN growth mode from grain to island is observed at the high growth temperature above 600 °C. A blue shift of 20–30 meV in near band edge PL emission line has been noticed for the GaN layers containing the large in-plane strain. These observations indicate that the in-plane strain in the GaN layers is dominated by a biaxial strain. Using nanoindentation, it is found that the indentation hardness and Young's modulus of the GaN layers increases with increasing growth temperature. The results disclose the critical role of growth mode in determining the in-plane strain and mechanical properties of the GaN layers grown by LMBE technique. •GaN growth mode critically affects in-plane strain during laser MBE growth.•High growth temperature of 700 °C changes GaN growth mode from grains to islands.•Island growth largely relaxes in-plane strain in laser MBE grown GaN layer.•Structural, optical and mechanical properties improve drastically by island growth.