Band-edge Optical Anisotropy and Carrier Dynamics in Photoexcited Tellurium-nanoflakes*

Tellurium is a hexagonal chiral crystal with covalently bonded left- or right-spiral chains of atoms along the c-axis, with much weaker van der Waals interactions between the chains. Here we use transient polarized reflectivity measurements to study this complex band structure and carrier dynamics at 10 K and 300 K from 0.3 to 1.2 eV (4000 to 1000 nm). The transient spectra reveal a series of transitions with strong polarization anisotropy. We see optical transitions between all three VB (H₄, H₅ and H₆ symmetries) with the doubly degenerate CB (H₆ Symmetry). While the ground state energies are stable with time, higher lying states exhibit dynamic shifts to lower energy as a function of pump delay, showing strong correlation with relaxation processes of photoexcited carriers. The main decay of photoexcited carriers occurs within the first 60 ps, followed by a weak long-lived decay which perhaps suggest some inter-valley scattering before recombination. These results will help in understanding photoconductive properties in Te-based novel devices for thermoelectric as well as optoelectronic applications.