Unstable composition region in the wurtzite B1-x-yGaxAlyN system

The unstable composition region of B1-x-yGaxAlyN was calculated from the fr ee energy of mixing by using the strictly regular solution model. The inter action parameter used in this calculation was based on the delta-lattice-pa rameter method. The proportionality constant K of 1.15 x 10(7) cal/mol Angs trom(2.5) was determined by fitting the spinodal isotherms to the experimen tal data of B1-xGaxN grown at 1000 degrees C by MOVPE. Using this K value, the interaction parameters of BN-GaN, BN-AIN and AlN-GaN are 70 730, 54 872 and 1091 cal/mol, respectively. The high interaction parameters of BN-GaN and BN-AlN result in very wide unstable composition regions. From the calcu lated spinodal isotherms, the maximum boron solubility having a uniform sin gle-phase solid solution is 1.8% in B1-xGaxN and 2.8% in B1-yAlyN at 1000 d egrees C. However, the GaAlN alloy can be deposited over the entire composi tion range since the spinodal isotherms are parallel to the GaN-AlN line. ( C) 2000 Elsevier Science B.V. All rights reserved.