Effect of V/III ratio on the growth of (11 2¯ 2) AlGaN by metalorganic vapour phase epitaxy

The effect of V/III ratio on the growth and properties of AlGaN layers grown on (112¯2) AlN templates grown on (101¯0) sapphire by metalorganic vapour phase epitaxy was studied. The surface morphology of the (112¯2) AlGaN layers and the (112¯2) AlN templates showed an undulation along [11¯00]_AlGaN,AlN. The Al-content and thickness of the layers increased with decreasing V/III ratio due to a reduction in the parasitic reactions of the precursors. The Al-content of the (112¯2) layers was found to be in the range of 29.5-47.9%, which is lower than the composition of the simultaneously grown (0001) reference layers (30.4-58.0%). This was attributed to a higher density of cation (nitrogen) dangling bonds on the (112¯2) surface. Low temperature photoluminescence measurements of the (112¯2) layers showed an emission wavelength that shifts gradually from 273 nm to 306 nm with increasing V/III ratio. A decreased PL intensity of the layers with decreasing V/III ratio was attributed to an increase in cation vacancies. The Stokes-shift of the (112¯2) layers was estimated to be about 60-194 meV, and this shift increases with increasing Al-content (decreasing V/III ratio) correlated to an increased exciton localization.