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 with compositions around x = 0.5 have been determined using surface acoustic waves measured by Brillouin light scattering spectroscopy. Contrary to the case for the usual estimates, the experimentally obtained elastic constants are different from the ones calculated by simple linear combination of those of the corresponding constituent binary compounds. An averaging model combining 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 are not reproduced.