InN and related alloys are very attractive materials for future photonic and electronic devices. Extensive studies on InN and In-rich In_xGa_1-xN have been hindered for a long time by the difficulties of growing high-quality crystals because of high vapor pressure of nitrogen and low dissociation temperature. Recent developments of high-quality InN by MOVPE and MBE, coupled with discussion on true band-gap energy of InN, revived extensive attentions on this material system.

We already reported high-quality InN growth by RF-MBE. Comprehensive characterization of the grown films using XRD, TEM, EXAFS and Raman scattering clearly demonstrated that InN films grown in this study had ideal hexagonal wurtzite structure. We also reported successful growth of In_xGa_1-xN films in full compositional range without noticeable phase separation.

In this presentation, we will report on our recent developments of InN and In_xGa_1-xN growth. We have found that the insertion of a high-temperature-grown InN layer as a growth template was very effective for improving the surface morphology and crystalline quality of In-rich In_xGa_1-xN layers. We have also succeeded in dramatically improving the crystalline quality of InN films by optimizing nitridation conditions of (0001) sapphire substrates. These high-quality InN films showed their excellent c-axis orientation with the FWHMs of (0002) XRCs as narrow as 1 arcmin without deteriorating their a-axis orientation. By using these high-quality InN layers as growth templates, the crystalline quality of In_0.8Ga_0.2N layers was dramatically improved. Based on these studies, an InN/In_0.8Ga_0.2N multiple quantum well structure and InN/In_0.8Ga_0.2N single quantum well structures with various well widths were successfully grown on these high-quality InN templates. The MQW structure showed clear 1st and 2nd satellite peaks of XRD. The SQW structures exhibited photoluminescence emission from their well layers.

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1. Valence band structure of InN from x-ray photoemission studies