Optical properties of InAsP alloys

Optical properties of InAs$_x$P$_{1-x}$ ternary alloys grown by chemical beam epitaxy (CBE) on S-doped InP(100) substrates are presented. Room-temperature pseudodielectric function spectra from 1.5 to 6.0 eV were measured by spectroscopic ellipsometry. The $E_0$, $E_1$, $E_1+\Delta_1$, $E'_0$, $E_2$, and $E_2+\delta$ interband critical point (CP) structures were observed in the spectra. By applying the parabolic-band critical point model to numerically calculated second-energy-derivatives of these spectra, accurate values of the CP parameters and their dependence on alloy composition $x$ were obtained. The experimentally determined variation of the $E_1$ and $E_2$ CP energies and the spin-orbit splitting $\Delta_1$ with alloy composition were in good agreement with the theoretical calculation based on the Van-Vechten-Berolo-Woolley (VV-B-C) model.