Growth of high-quality In-rich InGaN alloys by RF–MBE for the fabrication of InN-based quantum well structures

This paper describes studies performed for improving the quality of In-rich InxGa1−xN alloys. The crystalline quality and surface morphology of In-rich InxGa1−xN films was improved by using InN templates as underlying layers. It was also found that the crystalline quality of In-rich InxGa1−xN was strongly correlated with that of the underlying InN templates. High-quality InN templates with the (0 0 0 2) X-ray rocking curves (XRCs) as narrow as 1 arcmin, have recently been achieved by optimizing the nitridation conditions of (0 0 0 1) sapphire substrates (300 °C, 2 h). These InN templates have provided further improvement of the crystalline quality of In0.8Ga0.2N films. The (0 0 0 2) XRCs for these In0.8Ga0.2N films were approximately 18 arcmin (full-width at half-maximum), dramatically narrower than the 36 arcmin obtained with a previous substrate-nitridation process (550 °C, 1 h). By employing these high-quality In0.8Ga0.2N layers as not only growth templates but also bottom barrier layers, an InN/In0.8Ga0.2N multiple quantum well (MQW) structure and single-quantum well (SQW) structures with different well widths were fabricated. The MQW structure showed clear 1st and 2nd satellite peaks of X-ray diffraction. The SQW structures exhibited photoluminescence emission from their well layers.