Phase separation in Al_xGa_1-xAs nanowhiskers grown by the solution-liquid-solid mechanism

Low-temperature growth of Al_xGa_1-xAs by the solution-liquid-solid mechanism affords nanowhiskers having two specific overall compositions: x = 0.1 and 0.8. Intermediate compositions (0.1 < x < 0.8) are inaccessible by the method employed. Examination of the nanowhiskers by transmission electron microscopy, photoluminescence spectroscopy, electron energy loss spectroscopy, and annealing studies indicates that they possess compositionally modulated nanostructures. The observed compositional modulation consists of alternating comparatively Al-rich and Ga-rich Al_xGa_1-xAs domains with dimensions of 3-20 nm. The spontaneous phase separation, which occurs during growth, appears to be kinetically driven, and the resulting phase-separated nanostructures appear to be, therefore, metastable rather than stable. Spontaneous phase separation in Al_xGa_1-xAs, which strongly influences its photoemission behavior, is not well understood theoretically.