Abstract
Nitrogen solubility at GaAs and InAs (001) surfaces has been studied employing density-functional theory calculations. The effect of the surface reconstruction and the reconstruction-induced surface strain on N solubility was analyzed in detail, considering the various surface layers and sites. The stability phase diagrams for the considered systems were constructed, and based on them an estimate of the N concentration has been deduced for the thermodynamically accessible and relevant range of chemical potentials in the various surface layers and at a typical growth temperature of 500 degrees C. Our results show that the solubility of N at the surface is unexpectedly rich and a complex function of the surface reconstructions. We discuss the possible N incorporation mechanisms and the conditions that allow for an enhanced solubility which can be in GaAs up to five orders of magnitude higher than the equilibrium bulk solubility. In addition, we find that the solubility of N at the GaAs(001) surface is one to four orders of magnitude higher than that at the InAs(001) surface.