The CuPt-type ordering and dopant effects of ${\mathrm{In}}_{0.5}$${\mathrm{Ga}}_{0.5}$P/GaAs epitaxial layers have been studied using spectroscopic ellipsometry and transmission electron microscopy. The degree of ordering was estimated by both transmission electron diffraction and the position of the direct band edge $E_0$. Conventional line-shape fitting of $E_1$, $E_1+{\Delta }_1$, and $E_0$ gaps using the second derivative of pseudodielectric functions shows that the peak position of the $E_1$ gap is a function of CuPt-type ordering and carrier concentration whereas the linewidth and phase depend mainly on carrier concentration. The decrease of the $E_1$ gap is explained in terms of CuPt-type ordering and doping related band-gap renormalization. In contrast to the $E_1$ gap, all these line-shape parameters of the $E_0^{\prime }$ gap depend mainly on CuPt-type ordering. Finally, we compare our data with a recent band-structure calculation.

• Received 18 November 1994

DOI:https://doi.org/10.1103/PhysRevB.53.4015