The lattice constant of Al x Ga 1−x As epitaxial alloys with various Al-As(x) content is determined for Al x Ga 1−x As/GaAs (100) heterostructures grown by MOVPE epitaxy using X-ray diffractometry and X-ray back-reflections method. An ordered AlGaAs 2 (superstructural) phase was found in epitaxial heterostructures for x ∼ 0.50. The lattice constant of this phase along c axis is smaller than the double lattice constants of an Al 0.50 Ga 0.50 As alloy. Infrared (IR) reflection spectra of lattice vibrations were investigated in epitaxial heterostructures of Al x Ga 1−x As/GaAs (100) with different concentrations of Al in cation sublattice. In the sample with x ∼ 0.50, besides two main vibration modes some additional ones were found that correspond to superstructure ordered phase AlGaAs 2 . Atomic-force microscopy (AFM) of the sample surface with x ∼ 0.50 demonstrated the presence of areas with ordered nano-relief having period of ∼115 nm that can be related with superstructure phase of AlGaAs 2 .

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