Defect and crystal structure variation in Tl-doped TlGaTe2 semiconductor alloys: An experimental and theoretical study

In this work, the structural and defect characteristics of TlGaTe 2 semiconductors doped with 5 % and 9 % thallium (Tl) were investigated using X-ray diffraction (XRD), positron annihilation lifetime spectroscopy (PALS), Doppler broadening spectroscopy (DBS), and first-principles calculations. XRD analysis confirmed the preservation of the tetragonal I4/mcm symmetry across all compositions, with increasing Tl content inducing local microstrain without long-range structural transitions. PALS revealed a dual defect evolution mechanism: sequential filling of micropores by Tl atoms alongside the creation of monovacancies (primarily monoGa). This was supported by the non-monotonic behavior of positron lifetime components and the ortho-positronium annihilation ratio. Electron Momentum Distribution (EMD) analysis further corroborated this, indicating Tl substitution for Ga and a modified bonding environment due to Tl occupying micropores. DBS showed a transition to a more homogeneous defect distribution with increased Tl concentration. These findings provide a detailed understanding of the complex defect dynamics induced by Tl doping in TlGaTe 2 , offering potential for defect engineering to tailor its properties for advanced technological applications. • XRD confirms structural stability with increased microstrain at higher Tl concentrations. • Tl doping in TlGaTe 2 induces dual defect mechanisms: monovacancies and micropore filling. • Combined positron annihilation spectroscopy and DFT calculations reveal strain-driven defect evolution in Tl-dopped TlGaTe 2 . • EMD and R parameter trends indicate Tl substitutes Ga and alters electron density. • The study provides insights into defect engineering strategies for tailoring the properties of ternary semiconductor alloys.