| AVS 66th International Symposium & Exhibition | |
| Spectroscopic Ellipsometry Focus Topic | Wednesday Sessions |
| Session EL+EM-WeA |
| Session: | Spectroscopic Ellipsometry: Novel Applications and Theoretical Approaches |
| Presenter: | Farzin Abadizaman, New Mexico State University |
| Authors: | F. Abadizaman, New Mexico State University C. Emminger, New Mexico State University S. Knight, University of Nebraska-Lincoln M. Schubert, University of Nebraska-Lincoln, Linköping University, Sweden, Leibniz Institute of Polymer Research Dresden, Germany S. Zollner, New Mexico State University |
| Correspondent: | Click to Email |
The authors conducted optical Hall effect (OHE) measurements on Te-doped GaSb (n-type) at room temperature in the far-infrared between 30 cm-1 and 700 cm-1 at magnetic fields of ±7 T and 0 T. The measurements were performed at an angle of incidence of 45̊ and a resolution of 2 cm-1. The complex dielectric functions and Mueller Matrix (MM) elements were determined from spectroscopic ellipsometry at 0 T in the range of 300 cm-1 to 8000 cm-1 using an FTIR-VASE ellipsometer and from 30 cm-1 to 700 cm-1 using the FIR ellipsometer. Using a sum of a Lorentzian oscillator and two Drude terms, the experimental data at zero magnetic field were modeled. From the Lorentzian term, we found the transverse optical (TO) phonon energy at 226 cm-1 and the longitudinal optical (LO) phonon energy at 237 cm-1.
Although GaSb is a direct band gap semiconductor, a calculation of the electron concentration indicates that at T = 300 K and a total electron density below 1018 cm-3, the majority of carriers are located at the L-valley (67%) while the Γ-valley contains only 33% of the carriers. This implies that in the absence of the magnetic field, two Drude terms are needed to model the data. The surfaces of constant energy at the L-point in the Brillouin zone form eight half-ellipsoids at L, which are characterized by their anisotropic masses. However, due to the symmetry, the valleys at this point are two by two equivalent, which leads to the total number of four valleys. In the absence of a magnetic field, the contribution of all eight half-ellipsoids in the L-valley is reduced to only one Drude term, where the effective mass is the harmonic average of the transverse and longitudinal masses. As the magnetic field is turned on, each ellipsoid contributes to the anisotropic dielectric tensor, which, depending on the effective mass tensor, contributes differently to the total dielectric tensor. Therefore, in the presence of a magnetic field, the data is modeled by the sum of a Lorentzian, a Drude tensor at the Γ-valley and four Drude tensors at the L-valley.