Optical constants of Ga1-xInxAsySb1-y lattice matched to GaSb (001): Experiment and modeling

The optical constants epsilon(E)[= epsilon(1)(E) + i epsilon(2)(E)] of two epitaxial layers of GaInAsSb/GaSb have been measured at 300 K using spectra l ellipsometry in the range of 0.35-5.3 eV. The epsilon(E) spectra displaye d distinct structures associated with critical points (CPs) at E-0 (direct gap), spin-orbit split E-0 + Delta(0) component, spin-orbit split (E-1,E-1 + Delta(1)) and (E-0',E-0' + Delta(0)') doublets, as well as E-2. The exper imental data over the entire measured spectral range (after oxide removal) has been fit using the Holden model dielectric function [Holden , Phys. Rev . B 56, 4037 (1997)] based on the electronic energy-band structure near the se CPs plus excitonic and band-to-band Coulomb-enhancement effects at E-0, E-0 + Delta(0), and the E-1, E-1 + Delta(1) doublet. In addition to evaluat ing the energies of these various band-to-band CPs, information about the b inding energy (R-1) of the two-dimensional exciton related to the E-1, E-1 + Delta(1) CPs was obtained. The value of R-1 was in good agreement with ef fective mass/k.p theory. The ability to evaluate R-1 has important ramifica tions for recent first-principles band-structure calculations which include exciton effects at E-0, E-1, and E-2 [M. Rohlfing and S. G. Louie, Phys. R ev. Lett. 81, 2312 (1998); S. Albrecht , Phys. Rev. Lett. 80, 4510 (1998)]. The experimental absorption coefficients in the region of E-0 were in good agreement with values obtained from a linear interpolation of the end-poin t materials. Our experimental results were compared to a recent evaluation and fitting (Holden model) of the optical constants of GaSb. (C) 2000 Ameri can Institute of Physics. [S0021-8979(00)04004-4].