Effects of point defects and doping in ?-GeTe monolayer for optoelectronic and spintronic applications

Utilizing the first-principles projector augmented wave approach, we examined how point defects and doping influence the structural, electronic, optical and magnetic characteristics of the α-GeTe monolayer for optoelectronic and spintronic applications. The GeTe compound exhibits a rhombohedral distorted NaCl-like crystal structure, categorized under the space group R3m. It is characterized by a narrow band gap and functions as a semiconducting material at room temperature. However, the exfoliated monolayer α-GeTe is indirect gap semiconductor with a relatively big band gap of 1.81 eV which can be further tuned by defect engineering and doping. Various defect types include single vacancy of Ge (Va: Ge) and Te (Va: Te), Ge+Te divacancy (????a: GeTe), Te_Ge: antisite defect formed by replacing one Ge atom by one Te atom and GeTe: antisite defect formed by replacing one Te atom by one Ge atom. Vacancies lead to half metallic nature in the monolayer whereas antisites preserve the nonmagnetic nature and reduces the band gap considerably. By doping with TM (Transition Metal) dopants like Cr, Fe, Mn and V large total magnetic moments of the order of 5 μ_B was obtained (Mn doping) which confirms induced ferromagnetism. The electronic and magnetic characteristics of the monolayer are primarily influenced by the 3d orbital of the transition metal dopants, leading to either a half-metallic or diluted magnetic semiconductor behaviour. These findings indicate a viable method for functionalizing the α-GeTe monolayer for use in optoelectronic and spintronic applications.

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