Electronic structure of ternary thallium chalcogenide compounds

The electronic structures of the ternary thallium chalcogenide compounds, TlGaSe ₂ and TlGaS ₂ are studied, using the linear muffin-tin orbital (LMTO) method. The calculated band dispersion shows that both compounds are indirect gap semiconductors. For both compounds, the top of the valence bands is located at Γ. For TlGaSe ₂, the bottom of the conduction band is located along the Z(0, 0, -5)-L(0.5, 0.5, -0.5) line. For TlGaS ₂, the bottom of the conduction band is located along the Γ-Y(0, 1, 0) line. An inspection of the LMTO wave functions shows that the valence band top has the character of Tl:6s-Se:4p or S:3p antibonding state, while the conduction band bottom has the character of Tl:6p-Se:4p or S:3p antibonding state.