Spectral ellipsometry of GaSb: Experiment and modeling

The optical constants epsilon(E)[ = epsilon(1)(E) + i epsilon(2)(E)] of sin gle crystal GaSb at 300 K have been measured using spectral ellipsometry in the range of 0.3-5.3 eV. The epsilon(E) spectra displayed distinct structu res associated with critical points (CP's) 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 experimental data ov er the entire measured spectral range (after oxide removal) has been fit us ing the Holden model dielectric function [Phys. Rev. B 56, 4037 (1997)] bas ed on the electronic energy-band structure near these CP's plus excitonic a nd 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 evaluating the energies of the se various band-to-band CP's, information about the binding energy (R-1) of the two-dimensional exciton related to the E-1, E-1 + Delta(1) CP's was ob tained. The value of R-1 was in good agreement with effective mass/k.p theo ry. The ability to evaluate R1 has important ramifications 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. Rev. Lett. 81, 2312 (1 998); S. Albrecht et al., Phys. Rev. Lett. 80, 4510 (1998)]. Our experiment al results were compared to other evaluations of the optical constants of G aSb. [S0163-1829(99)02035-4].