VALIDITY OF VEGARD 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 to evidence a difference in the incorporation of gro up-ill-elements in ternary ill-V semiconductor films. We discuss the r esults obtained from Al(x)Gal(1-x)As epilayers coherently grown simult aneously on(1 0 0)-, (2 1 0)and (3 1 1)-GaAs substrate crystals. Assum ing a GaAs lattice parameter d(GaAs) = 0.565325 +/- 0.000002 nm our ex periment yields the AlAs lattice parameter d(AlAs) = 0.566139 +/- 0.00 0005 nm. The stiffness elastic lattice constant ratios for AlAs is c(1 2)/c(11) = 0.475 +/- 0.003, which leads to a Poisson ratio v = 0.322 /- 0.001 and c(44)/c(11) = 0.517 +/- 0.003. An analogous analysis for the ternary AlxGa1-xAs compound with x = 0.5 yields a lattice paramete r value and elastic constant ratios which are in agreement with the Ve gard's rule. Within the accuracy of our method no deviation for the AI incorporation in the differently oriented samples has been observed. (C) 1998 Published by Elsevier Science Ltd.