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 (GaX, 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 GaTe1-xSex for x = 0 to x = 1 are examined. The experimental results show that the whole series of GaTe1-xSex 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 GaTe1-xSex series. The micro-photoluminescence (mu PL) results indicate that the photon emission energy of M-phase GaTe1-xSex increases as the Se content increases from 1.652 eV (M-GaTe) to 1.779 eV (M-GaTe0.6Se0.4), whereas that of H-phase GaTe1-xSex 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 GaTe1-xSex 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 GaTe1-xSex (0 <= x <= 0.4). On the other hand, for H-phase GaTe1-xSex, the decay lifetime of the band-edge emission also increases as the Se content increases, owing to the surface effect. The dark resistivity of GaTe1-xSex for 0.5 <= x <= 1 (i.e., predominantly H phase) is greater than that of the other instance of majority M-phase GaTe1-xSex for 0 <= x <= 0.4, owing to the larger bandgaps. The predominantly H phase GaTe1-xSex (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 GaTe1-xSex multilayers (0 <= x <= 1) means that they can be used for future optoelectronic devices.

Automated summary

This study investigated the structural and optical properties of full-series multilayer GaTe1-xSex (0 ≤ x ≤ 1). Experimental results showed that the GaTe1-xSex layers may contain hexagonal (H) phase and monoclinic (M) phase, with the H-phase dominating when x ≥ 0.5. The photon emission energy of the M-phase GaTe1-xSex increased as the Se content increased, while that of the H-phase GaTe1-xSex decreased in the red to near-infrared (NIR) region. The decay lifetime of the band-edge emission was faster in the M phase than in the H phase for 0 ≤ x ≤ 0.4. The predominantly H phase GaTe1-xSex showed greater dark resistivity and photoconductive response under visible-light illumination. The GaTe1-xSex multilayers demonstrated superior light-emission and photodetection capability for future optoelectronic devices.