Band gap variation and miscibility gaps of thallium-based pseudo-binary alloys

To stimulate further research on the Tl-based semiconductor alloys for long-wave infrared (LWIR) application, we carried out detailed calculations for the variation of band gaps versus lattice constants and the alloy miscibility gaps of cation-substituted pseudo-binary alloys. These results are used to identify promising Tl-based LWIR alloys and the lattice-matched non-TI bearing alloys for possible substrates and passivation caps. Although all the six Tl-bearing pseudo-binary alloys studied can have a 0.1 eV band gap, none of these systems are lattice matched to a pure III-V compound. Five of these six alloys can have a non-Tl-bearing lattice-matched ternary alloy as the substrate, but only two do not have a serious problem with the miscibility gap. When further considering the difficulty of incorporating Tl with a large concentration, the only promising LWIR pseudo-binary alloy left is In1-xTlxAs with x approximate to 0.16.