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Compositional dependence of the elastic constants and the lattice parameter of Al(x)Ga(1-x)As

Zusammensetzungsbedingte Abhängigkeit der elastischen Konstanten und Gitterparameter von Al(x)Ga(1-x)As


Physical Review. B 60 (1999), Nr.16, S.11601-11610
ISSN: 0163-1829
ISSN: 1098-0121
ISSN: 0556-2805
Fraunhofer IAF ()
Atom-Emissions-Spektroskopie; Brillouin scattering; Brillouin-Streuung; composition determination; elastic constant; elastische Konstante; Epitaxie; epitaxy; Gallium-Aluminium-Arsenid; gallium aluminum arsenide; high-resolution X-ray diffraction; hochauflösende Röntgenumgebung; HRXRD; ICP AES; inductively coupled plasma atomic emission spectroscopy; induktiv gekoppeltes Plasma; Poisson Verhältnis; poisson's ratio; Zusammensetzungsbestimmung

Near infrared Brillouin scattering and high resolution x-ray diffraction is used for a precise determination of the elastic constants and the relaxed lattice parameters of Al(x)Ga(1-x)As epitaxial layers (0.1 <= x <= 1.0). The composition of the layers is specified by inductively coupled plasma atomic emission spectroscopy, photoluminescence, and Raman spectroscopy. For the elastic constants we get a composition independent value of 118.9 ¤ 0.7 GPa for C11, a nonlinear increase in C12and a linear decrease in C44 with increasing AI composition. The Poisson ratio shows a linear increase for x < 0.8 and a downward bowing for higher Al concentrations to the AlAs value of v=0.325¤0.004. The effect of lattice mismatch induced strain on the elastic properties is investigated on free standing epitaxial layers. The trend in ionicity from the GaAs to the AlAs bonds are deduced from phenomenological expressions for the bond-bending and bond-stretching forces which are calculated from the elastic constants. The lattice parameters of the unstrained crystals are obtained from the measured full metric of the tetragonally strained layers and the Poisson ratios. The combined results of Brillouin scattering, x-ray diffraction, and compositional analysis confirm the deviation of the Al(x)Ga(1-x)As lattice parameter from Vegard's law, and provides the first direct and accurate determination of the quadratic bowing parameter.