VALIDITY OF VEGARDS RULE FOR THE LATTICE-PARAMETER AND THE STIFFNESS ELASTIC-CONSTANT RATIOS OF THE ALGAAS TERNARY COMPOUND

A new procedure for the determination of the Poisson ratio, the elasti c stiffness constant ratios and the lattice parameter of epitaxial fil ms is presented which is based on the strain tensor determination by h igh-resolution X-ray diffraction by using epitaxial layers simultaneou sly grown on three different substrate orientations and different allo y compositions. Our method allows us to verify the validity of the Veg ard's rule and/or evidence a difference in the incorporation of group- III-elements in ternary III-V semiconductor films. We discuss the resu lts obtained from AlxGa1-xAs epilayers coherently grown simultaneously on(1 0 0)-, (2 1 0)and (3 1 1)-GaAs substrate crystals. Assuming a Ga As lattice parameter d(GaAs) = 0.565325 +/- 0.000002 nm our experiment yields the AlAs lattice parameter d(AlAs) = 0.566139 +/- 0.000005 nm. The stiffness elastic constant ratios for AlAs are C-12/C-11 = 0.475 +/- 0.003, which leads to a Poisson ratio nu = 0.322 +/- 0.001 and C-4 4/C-11 = 0.517 +/- 0.003. An analogous analysis for the ternary AlxGa1 -xAs compound with x = 0.5 yields a lattice parameter value and elasti c constant ratios which are in agreement with the Vegard's rule. Withi n the accuracy of our method no deviation for the Al incorporation in the differently oriented samples has been observed. (C) 1998 Elsevier Science Ltd. All rights reserved.