Structural and luminescence properties of In-rich InGaN layers grown on InN templates by RF-MBE

Structural and luminescence properties of In-rich ln(x)Ga(1-x)N (0.71 <= x <= 1) layers are comprehensively studied. The layers were grown on (0001) sapphire substrates by radio-frequency plasma-assisted molecular-beam epitaxy, employing two types of underlying structures: low-temperature-grown InN (LT-InN) buffer layers and high-temperature-grown InN templates grown on LT-InN buffer layers. The insertion of the InN templates has improved not only surface morphology but also both a-axis and c-axis orientations of In-rich InxGa1-xN layers. In addition, by using InN templates of dramatically improved crystalline quality with the full width at half maximum of (0002) X-ray rocking curves as narrow as I arcmin, which have been recently achieved by optimizing nitridation conditions of sapphire substrates, the crystalline quality of In0.8Ga0.2N layers was even further improved. On the other hand, however, photoluminescence (PL) line width showed no noticeable variation between the InxGa1-xN layers grown on InN templates and those on LT-InN buffer layers. Possible factors that determine PL line width and compositional fluctuation of these In-rich InxGa1-xN are discussed. Interference fringes of X-ray diffraction (omega-2 theta scan) have been observed from the high crystalline-quality InN templates of the excellent c-axis orientation for the first time.