Near-infrared to red-light emission and carrier dynamics in full series multilayer GaTe1−xSex (0≤x≤1) with structural evolution

Two-dimensional layered gallium monochalcogenide (Ga X , where X = S, Se, Te) semiconductors possess great potential for use in optoelectronic and photonic applications, owing to their direct band edge. In this work, the structural and optical properties of full-series multilayer GaTe 1− x Se x for x = 0 to x = 1 are examined. The experimental results show that the whole series of GaTe 1− x Se x layers may contain one hexagonal (H) phase from GaTe to GaSe, whereas the monoclinic (M) phase predominates at 0 ≤ x ≤ 0.4. For x ≥ 0.5, the H-phase dominates the GaTe 1− x Se x series. The micro-photoluminescence (μPL) results indicate that the photon emission energy of M-phase GaTe 1− x Se x increases as the Se content increases from 1.652 eV (M-GaTe) to 1.779 eV (M-GaTe 0.6 Se 0.4 ), whereas that of H-phase GaTe 1− x Se x decreases from 1.998 eV (H-GaSe) to 1.588 eV (H-GaTe) in the red to near-infrared (NIR) region. Micro-time-resolved photoluminescence (TRPL) and area-fluorescence lifetime mapping (AFLM) of the few-layer GaTe 1− x Se x series indicates that the decay lifetime of the band-edge emission of the M phase is faster than that of the H phase in the mixed alloys of layered GaTe 1− x Se x (0 ≤ x ≤ 0.4). On the other hand, for H-phase GaTe 1− x Se x , the decay lifetime of the band-edge emission also increases as the Se content increases, owing to the surface effect. The dark resistivity of GaTe 1− x Se x for 0.5 ≤ x ≤ 1 (i.e., predominantly H phase) is greater than that of the other instance of majority M-phase GaTe 1−x Se x for 0 ≤ x ≤ 0.4, owing to the larger bandgaps. The predominantly H phase GaTe 1− x Se x (0.5 ≤ x ≤ 1) also shows a greater photoconductive response under visible-light illumination because of the greater contribution from surface states. The superior light-emission and photodetection capability of the GaTe 1− x Se x multilayers (0 ≤ x ≤ 1) means that they can be used for future optoelectronic devices.