Burstein Shift of the Absorption Edge of nBi2Se3

The spectral position of the absorption edge of n‐type Bi2Se3, single crystals was determined from reflectivity measurements on cleavage planes at nearly normal incidence of the radiation (E ⊥ c). A small reflectivity peak yields a maximum of the real part n2 ‐ k2 of the dielectric constant, which is correlated to the critical photon energy of the direct absorption edge. A direct optical gap of 160 me V at 77 K is extrapolated for an empty conduction band. The temperature coefficient between 77 and 300 K is ‐2 × 10−4 eV/K. Assuming a linear temperature dependence down to T = 0 a gap of 175 me V at T = 0 and of 115 me V at 300 K is derived. For E ⊥ c a parabolic ϵ(k) relation of the valence band of Bi2Se3 is deduced with m = 0.125 m0 ± 10%.