Strain and thickness effects on the electronic structures of low-energy two-dimensional CdTe phases

Cadmium telluride (CdTe) has prime importance in photovoltaics due to its direct band gap of 1.45 eV. However, its two-dimensional counterparts have not been fully explored due to polymorphism. We investigated the energy phase diagram of 2D CdTe (x + y ≤ 8) using state-of-art computational methods and found the phases of CdTe and CdTe₂ on and near the energy convex-hull, respectively. Further screening of phonon and ab initio molecular dynamics simulations confirms their experimental viability. These structures reveal promising electronic properties. 2D CdTe has a robust direct band gap unaffected by thickness, monolayer to trilayer and bulk, and strain as high as ±7%. Such robust semiconductors are crucial for device applications because of challenges in the growth of wafer-scale uniform monolayers. In contrast, the direct band gap of 2D transition metal dichalcogenides is highly sensitive to thickness and strain, limiting their usage in devices. The 2D CdTe₂ has an indirect band gap whose magnitude is tunable by strain. The robust direct band gap of 2D CdTe and the tunable indirect band gap of CdTe₂ make them potential candidates for optoelectronic devices.