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 co ncentration of (Tl, Ga)As. No approximations of the surrounding material ar e made, but the entire problem is addressed in full-scale calculations. Lat tice constants, bond lengths, band structure, effective mass and bulk modul us 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 geo metrical information oh lattice distortions and bond length distributions w as discovered. These symmetry-breaking lattice distortions were found to af fect the band structure. The bands varied smoothly over the entire composit ion range, except in the region where the material changed from semiconduct ing to semi-metallic character; a split-off band was found to exist for a s mall concentration interval before the conduction band reached the valence band. The effective mass was shown to decrease for increasing Tl concentrat ion up to 23%, supporting earlier predictions of enhanced electron transpor t properties in this alloy system. Calculations of bulk modulus and thermod ynamic stability of the alloy indicated that the material in zincblende for m may be more stable the higher the temperature is.