An approach to the formation mechanism of the composition fluctuation in GaInNAs quantum wells

This work is focused on the study by transmission electron microscopy of the composition inhomogeneity of GaInNAs quantum wells. A variation of the contrast along the quantum well is reported which is related to phase separation in the alloy. This variation becomes more intense on increasing the growth temperature. From the intensity profiles taken from the images, we have calculated the energy of activation for surface diffusion in the alloy. The results suggest that the diffusion of indium controls the process of formation of phase separation. With regard to the thermodynamics of the process, we have extended the spinodal decomposition model of Ipatova to the quaternary alloy GaInNAs. Our calculations have shown that composition fluctuations of indium are stimulated by the introduction of nitrogen into the ternary alloy GaInAs. It is proposed that the observed compositional inhomogeneity of GaInNAs is composed mainly of a fluctuation of the indium content but secondly that N bonds preferentially to Ga-rich regions in the alloy.