Gate-modulated optical transitions of tellurium-based field-effect transistors

Tellurium (Te) is a two-dimensional semiconducting material with significant potential for tunable device applications. Here, we perform optical transmission measurements on a Te-based field-effect transistor (FET) and reveal three major optical changes induced by electrical gating. (i) Intraband transition in Te evolves from localized Drude-Smith states to delocalized, standard Drude states as the hole carrier density increases. (ii) Interband transition and defect-level transition both shift to higher energies at distinct rates. (iii) The optical phonon peak of the SiO2 dielectric layer undergoes a subtle yet distinct shift. We calculate the variation of dc dielectric constant ϵ(0) of SiO2 induced by the optical phonon shift and support that the FET operates in practice within the linear charge response regime.