Solubility of nitrogen in binary III-V systems

A version of the valance-force-field (VFF) model has been developed specifically for the calculation of the nitrogen solubility in conventional III-V binary compounds. At very low N concentrations, i.e., in the dilute limit, the atoms surrounding the N are allowed to relax. It is found that the energy due to bond stretching and bond bending is lowered and the solubility limit is increased substantially when both sublattices are allowed to relax to distances as large as the sixth nearest neighbor positions. Using this model, the equilibrium mole fraction of N in GaP was calculated to be 6 x 10(-7) cm(-3) at 700 degrees C, which agrees with experimental data and closely approximates the results of the semi-empirical delta-lattice parameter model. It is more than three orders of magnitude larger than the result obtained using the simplest VFF model with relaxation of only the first neighbor bonds. Other nitride systems such as GaAsN, AlPN, AlAsN, InPN, and InAsN were investigated as well. The equilibrium mole fraction of nitrogen in InAs is the highest (about 0.002 at 700 degrees C). A miscibility gap is also predicted for the commercially important GaInN system.