Layer-Dependent Ultrafast Coherent Acoustic Phonon Dynamics in GaTe Driven by Native Oxidation

Gallium telluride (GaTe) has recently emerged as a promising material platform for optoelectronic applications due to its excellent electronic and optical properties. However, GaTe is highly susceptible to oxidation under ambient conditions, and the influence of oxidation on its excited-state carrier dynamics has rarely been investigated. In this work, the effects of ambient oxidation on the photoinduced carrier dynamics and phonon behavior in mechanically exfoliated GaTe nanosheets are systematically studied using femtosecond transient absorption microscopy combined with density functional theory calculations. The results indicate that oxidation of GaTe not only reconstructs the electronic band structure but also activates coherent acoustic phonon oscillations originating from interlayer breathing modes excited by femtosecond pulses. The oscillation frequency exhibits a pronounced thickness dependence, enabling the extraction of key mechanical parameters, including an out-of-plane sound velocity of 3,200 m/s, a Young's modulus of 56.5 GPa, and an interlayer force constant of 8.1 x 10¹⁹ N/m³. This study deepens the understanding of oxidation-induced ultrafast processes in layered semiconductors and provides important opportunities for the development of oxidized GaTe-based ultrafast optoelectronic, photoacoustic, and nanomechanical devices.