The Residual Stress and Al Incorporation of AlGaN Epilayers by Metalorganic Chemical Vapor Deposition

AlxGa1-xN/GaN heterostructures with different Al content ranging from 0.14 to 0.49 have been grown on sapphire substrates by metalorganic chemical vapor deposition. The Al composition and residual stress of AlGaN were investigated by high resolution X-ray diffraction. Based on the corrected band gap of AlGaN calculated by photoluminescence measurements and residual stress, the direct bandgap bowing parameter was estimated to be 0.5. Besides, the Al incorporation of AlGaN was found to depend not only on the parasitic reaction between Trimethylaluminium and NH3 but also on the Ga desorption. The Al/Ga molar fraction ratio in gas phase increased faster than the Al/Ga content ratio in solid phase due to the alleviative Ga desorption.