Ab initio investigation of the electronic and geometric structure of zincblende Ga1-xTlxAs alloys

Unique extensive ab initio band structure calculations have been performed to investigate the electronic and atomic structural dependency on the Tl concentration of (Tl, Ga)As. No approximations of the surrounding material are made, but the entire problem is addressed in full-scale calculations. Lattice constants, bond lengths, band structure, effective mass and bulk modulus were calculated, some for the first time ever for any material with this method. As a result of the choice of theoretical method, very detailed geometrical information on lattice distortions and bond length distributions was discovered. These symmetry-breaking lattice distortions were found to affect the band structure. The bands varied smoothly over the entire composition range, except in the region where the material changed from semiconducting to semi-metallic character; a split-off band was found to exist for a small concentration interval before the conduction band reached the valence band. The effective mass was shown to decrease for increasing Tl concentration up to 23%, supporting earlier predictions of enhanced electron transport properties in this alloy system. Calculations of bulk modulus and thermodynamic stability of the alloy indicated that the material in zincblende form may be more stable the higher the temperature is.

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