Elastic constants of InxGa1-xAs and InxGa1-xP determined using surface acoustic waves

The elastic constant tensors of thin layers of InxGa1-xAs and InxGa1-xP wit h compositions around x = 0.5 have been determined using surface acoustic w aves measured by Brillouin light scattering spectroscopy. Contrary to the c ase for the usual estimates, the experimentally obtained elastic constants are different from the ones calculated by simple linear combination of thos e of the corresponding constituent binary compounds. An averaging model com bining a parallel-serial disposition of springs with the elastic constants corresponding to the binary compounds has been used to explain the elastic constants of the ternary alloys. This model explains perfectly the elastic properties of the InxGa1-xAs system, while those of the InxGa1-xP system ar e not reproduced.