Dual phase two-color emission observed in van der Waals GaTe planes

Abstract After the eagerly study on two-dimensional (2D) electronic devices made by layered semiconductors, light-emitting devices based on 2D semiconductors have also flourished in recent years due to their special characters of flexibility, flatness surface, and thickness-tunable band gap modulation, etc. Among the 2D materials, III-VI layer compounds with hexagonal structure like GaSe and InSe are essentially direct semiconductors that own high band-edge luminescence efficiency and wide thickness tunable range from bulk to thin few-layer scale. In this work, dual-phase two-color emissions of multilayered gallium monotelluride positioned at 1.588 and 1.652 eV are simultaneously detected by micro-photoluminescence (μPL) measurement at 300 K. The lower-energy peak may originate from the hexagonal GaTe (H-GaTe) phase while the higher-energy luminescence might come from monoclinic GaTe (M-GaTe) phase and which are verified by micro-thermoreflectance (μTR) and high-resolution transmission electron microscopy (HRTEM). Micro-time-resolved photoluminescence (TRPL) and area fluorescence lifetime mapping (AFLM) of the multilayer GaTe indicated that the luminescence decay time constant of the H-GaTe is larger than that of the M-GaTe for verification of the dominant phase in multilayered GaTe is the monoclinic phase. In-plane structural and optical anisotropy of the multilayered GaTe were characterized by using polarized micro-Raman and polarized μPL measurements. The results clearly indicate that the monoclinic-phase GaTe possesses higher polarized extinction ratio with respect to that of the hexagonal GaTe for fully extinction of the Raman vibration mode and band-edge emission in the dual-phase gallium telluride. The existence of dual crystalline phases in multilayer GaTe may render it possible for fabrication of two-color emission device available for near-infrared (NIR) optical communication use.