Monotonous alloying-driven band edge emission in two-dimensional hexagonal GaSe 1− x Te x semiconductors for visible to near-infrared photodetection

This work reports molecular beam epitaxy (MBE) of two-dimensional (2D) GaSe 1− x Te x ternary alloys that have recently attracted a lot of interest in physics for prospective electronics and optoelectronics even though they face crucial challenges in their epitaxial technology. Disregarding a distinction in crystal phase symmetry of two end-terminals, i.e. , hexagonal-GaSe (h-GaSe) and monoclinic-GaTe (m-GaTe), the majority of hexagonal-GaSe 1− x Te x (h-GaSe 1− x Te x ) phase on a GaN/sapphire platform is guaranteed under our specific growth conditions without a visible sign of phase transition. We have also proposed extracting the Te composition of the ternary alloy via the experimental in-plane lattice constant, which is consistent with those indicated from energy dispersion X-ray data. Fascinatingly, the experimental and predictable band emission versus Te content displays a continuous redshift from 1.78 eV (h-GaSe) to 1.25 eV (h-GaSe 0.4 Te 0.6 ) then a reversible blueshift to 1.46 eV (h-GaTe). Importantly, benefiting from the presence of Te incorporated atoms, the photoresponse performance of the hexagonal ternary alloy has greatly enhanced in comparison to the h-GaSe binary in terms of photocurrent density (up to 1250 nA cm −2 for h-GaSe 0.65 Te 0.35 at only 300 mV bias). Overall, the results pave a way for phase/physical engineering of the alloys through the MBE process and realizing self-powered wafer-scale photodetectors based on 2D Ga-based monochalcogenide epitaxial thin films.