Infrared reflectance study of n-type GaSb epitaxial layers

Reflectance measurements from 50 to 5000 cm−1 were made at room temperature on several GaSb layers grown by molecular beam epitaxy on GaAs substrates, and n-doped from ∼1016 to more than 1018 cm−3. A two-layer model, joined with Drude-Lorentz dielectric functions accounting for phonons and plasmons, was applied to calculate the reflectance spectra, which fitted the experimental data very well. With the optical parameters extracted it was possible to obtain the carrier concentration and mobility to be compared with the Hall measurements. Both the optical and transport analysis require a two-valley conduction model, because of the presence in GaSb of Γ and L conduction valleys, separated by only 80 meV. Populations and free-carrier scattering times in each valley were derived as a function of the phenomenological plasma frequency. Some discrepancies between optical and transport results were found and are discussed.