Phase Transformation and Tunable Optoelectrical Properties of Two-Dimensional Layered GaTe1–xSex Crystals

The phase transformation threshold and mechanism of layered GaTe1–xSex crystals have been controversial for a long time. Herein, we demonstrate that an extremely low Se content of 20% can induce the phase transformation of GaTe1–xSex from monoclinic structure to hexagonal structure. Theoretical and experimental studies reveal that the introducing of Se dopants effectively stabilizes the host lattice of metastable h-GaTe and thus induces the transformation of GaTe1–xSex from monoclinic to hexagonal lattice in the low Se doping range. The obtained GaTe1–xSex crystals also display tunable band gaps from 1.65 to 1. 85 eV and near band edge emission from 755 to 675 nm with increasing Se content from x = 0 to x = 0.44. More importantly, in comparison with GaTe and GaSe, layered GaTe1–xSex nanosheets exhibit p-type conductivity, higher carrier concentration, excellent photoresponse, and air stability. The fabricated GaTe1–xSex nanosheet photodetectors also show outstanding performance in the UV and visible range including a high responsivity of 91.3 A/W, an excellent EQE of 3.16 × 104%, and a specific detectivity of 5.05 × 109 Jones.