Burstein Shift of the Absorption Edge of nBi 2 Se 3

The spectral position of the absorption edge of n‐type Bi 2 Se 3 , 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 n 2 ‐ k 2 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 Bi 2 Se 3 is deduced with m   v *= 0.125 m 0 ± 10%.