Optical constants of Ga{sub 1{minus}x}In{sub x}As{sub y}Sb{sub 1{minus}y} lattice-matched to GaSb(001): Experiment and modeling

The optical constants {epsilon}(E)[={epsilon}{sub 1}(E)+i{epsilon}{sub 2}(E)] of two epitaxial layers of GaInAsSb/GaSb have been measured at 300 K using spectral ellipsometry in the range of 0.35--5.3 eV. The {epsilon}(E) spectra displayed distinct structures associated with critical points (CPs) at E{sub 0} (direct gap), spin-orbit split E{sub 0}+{Delta}{sub 0} component, spin-orbit split (E{sub 1}, E{sub 1}+{Delta}{sub 1}) and (E{sub 0}{prime}, E{sub 0}{prime}+{Delta}{sub 0}{prime}) doublets, as well as E{sub 2}. The experimental data over the entire measured spectral range (after oxide removal) has been fit using the Holder model dielectric function [Phys.Rev.B 56, 4037 (1997)] based on the electronic energy-band structure near these CPs plus excitonic and band-to-band Coulomb enhancement effects at E{sub 0.}, E{sub 0}+{Delta}{sub 0} and the E{sub 1}, E{sub 1}+{Delta}{sub 1} doublet. In addition to evaluating the energies of these various band-to-band CPs, information about the binding energy (R{sub 1}) of the two-dimensional exciton related to the E{sub 1}, E{sub 1}+{Delta}{sub 1} CPs was obtained. The value of R{sub 1} was in good agreement with effective mass/k{sup {rightharpoonup}}{center_dot}p{sup {rightharpoonup}} theory. The ability to evaluate R{sub 1} has important ramifications for recent first-principles band structure calculations which include exciton effects at E{sub 0}, E{sub 1}, and E{sub 2} [M.Rohlfing and S.G.Louie, Phys.Rev.Lett. 81, 2312 (1998) and S. Albrecht et al., Phys.Rev.Lett. 80, 4510 (1998)]. The experimental absorption coefficients in the region of E{sub 0} were in good agreement with values obtained from a linear interpolation of the end point materials. The experimental results were compared to a recent evaluation and fitting (Holden model) of the optical constants of GaSb