Isotropic dielectric functions of highly disordered AlxGa1-xInP (0 <= x <=1) lattice matched to GaAs

Determination of the complex dielectric function and the critical-point ene rgies of (AlxGa1-x)(0.51)In0.49P, over the full range of composition x and for photon energies E from 0.75 to 5 eV is reported from variable angle of incidence spectroscopic ellipsometry. Native-oxide effects on the (AlxGa1-x )(0.51)In0.49P optical functions are removed numerically. The highly disord ered state of the metalorganic vapor-phase epitaxy grown samples is analyze d by transmission electron microscopy. Optical anisotropy investigations re vealed that the order-induced optical birefringence is negligible throughou t. The augmentation of A. D. Rakic and M. L. Majewski [J. Appl. Phys. 80, 5 909 (1996)] to Adachi's critical-point model, i.e., consideration of Gaussi an-like broadening function instead of Lorentzian broadening, is used for c alculation of the isotropic (AlxGa1-x)(0.51)In0.49P dielectric function is an element of. The optical functions spectra consistently match the experim ental data, whereas previously reported model dielectric functions fail to reproduce the correct absorption behavior of the quaternary, especially nea r the fundamental band-to-band transition. The results are compared to thos e presented previously, and influence of spontaneous chemical ordering is d iscussed. (C) 1999 American Institute of Physics. [S0021-8979(99)04316-9].