Fig. 6: Electrical characteristics of the Bi₂Te₃/Te interface.

a Optical bandgap, work functions, and valence band maximum (VBM) levels of Bi₂Te₃ and Te. The band gap values were determined from Tauc plots of optical absorption coefficient (αhν)^1/n versus photon energy hν (h is the Planck constant and ν is the frequency of the photon), using Fourier transform infrared spectrometer (FTIR) measurements, where the value of n is taken to be 1/2 and 2 for indirect-gap^80,81,82 Bi₂Te₃ and direct-gap^51,83 Te, respectively. The work functions and VBM positions for Bi₂Te₃ and Te are extracted from ultraviolet photoelectron spectroscopy (UPS) spectra. b Schematic showing the experimentally determined energy-level alignment at the Bi₂Te₃/Te hetero-interface. E_vac vacuum level, E_CBM conduction band minimum, E_VBM valence band maximum, ΔΦ work function difference between Bi₂Te₃ and Te, χ electronic affinity, which can be calculated by the following formula: χ = E_vac − E_CBM; E_CBO conduction band offset, E_VBO valence band offset. c 3D charge density difference of the Bi₂Te₃/Te interface and corresponding planar-averaged differential charge density. The cyan and yellow areas denote electron depletion and accumulation, respectively. d Projected density of states (PDOS) of Bi₂Te₃/Te, bulk Te, and Bi₂Te₃. The Fermi level was set as zero.