Band structure of TlGaSe 2

A model of the TlGaSe 2 ‐I band structure of the monoclinic modification is proposed. The monoclinic modification of TlGaSe 2 ‐I is considered as a deformed tetragonal one. The band structure of the metastable tetragonal modification of TlGaSe 2 ‐II is calculated by the pseudopotential method. The irreducible representations of the D 18 4h group (TlGaSe 2 ‐II) are expanded in irreducible representations of the C 4 s group (TlGaSe 2 ‐I). It is found that the top of the valence band is located at the point Y (0,2π/ b m , 0) of the TlGaSe 2 ‐I Brillouin zone and is formed from band states N 2 , N 4 of the tetragonal modification. The bottom of the conduction band is located at the point Γ of the TlGaSe 4 ‐I Brillouin zone and is formed from T 4 states. An additional extremum of the valence and conduction bands is located at the points Γ(A 2 ) and Y(N 6 , N 8 ), respectively. An interpretation of the absorption spectra of TlGaSe 2 ‐I near the fundamental edge is proposed.