Photo-induced Carrier Dynamics Of Two-dimensional GaTe Nanoflakes

Gallium chalcogenides are promising building blocks for novel van der Waals heterostructures.This materials have many unique physical properties,such as wide light absorption range,suitable energy band gaps,significant nonlinear coefficient,high performance in carrier mobility,high switching ratio,and excellent light responsiveness in the visible-ultraviolet light region,etc.These unique features make them have great application prospects in photovoltaic devices,optoelectronic devices,nonlinear optics,microelectronics,and other fields.Gallium telluride(GaTe),as a represent of gallium chalcogenides,has become a strong competitor in the next generation of optoelectronics.Two-dimensional GaTe has excellent optoelectronic properties,such as anisotropic non-volatile memory,solar cells,and high-sensitivity photodetectors from ultraviolet to visible region.Further applications,however,have been impeded due to the limited understanding of their exciton dynamics.In order to further improve the performance of these devices,the study the luminescence process of GaTe materials to characterize its optical properties and understand its potential dynamics is very important(essential)for basic research and emerging applications.In this work,we perform temperature-and power-dependent photoluminescence(PL)spectra,as well as time-resolved PL measurements(TRPL),to investigate the exciton dynamics within GaTe nanoflakes.And we also observe and control the phonon-assisted exciton physics in 2D GaTe.Our results provides a new method for regulating the neutral and charged excitons of GaTe,and also provides important information for the development of transition metal chalcogenide-based optical devices and exciton circuits.The main contents of paper are as follows:1.In the experiment,we perform-temperature and power-dependent PL spectroscopy and time-resolved PL spectroscopy measurements,to study the dynamic behavior of excitons in GaTe nanosheets,comprehensively.Analysis of temperature-dependent PL measurement results shows that the free exciton(FE)of the GaTe nanosheets,the donor-acceptor pair transition(X^DAP)and shallow acceptor-bound excitons(X^SAB)dominate when excited at low power at low temperature.In terms of status,X^DAP and X^SAB quickly disappear with increasing temperature and tend to saturate with increasing power,while X^Texhibits a linear power dependence.2.We perform temperature-and power-dependent time-resolved PL spectra to comprehensively investigate the exciton dynamics of GaTe nanoflakes to explain the exciton dynamics of GaTe nanosheets.The temperature-dependent PL results show that GaTe nanosheets are dominated by free exciton(FE),donor-acceptor pair transitions(X^DAP)and shallow acceptor-bound excitons(X^SAB);while PL spectrum at room temperature is mainly composed of X^T and neutral excitation(X⁰).At the same time,the power-dependent PL spectrum reveals the complex exciton behavior in GaTe nanoflakes.The total PL intensity of GaTe increases rapidly with the increase of excitation power and then approaches saturation,even under high-power excitation due to exciton-exciton annihilation.The full width at half maximum of FE broadens significantly with increasing temperature and exhibits linear power dependence;while X^DAP and X^SABtends to saturate with increasing power intensity under low temperature.3.Based on the time-correlated single photon counting(TCSPC)technology,we further measured the time-resolved PL spectra of GaTe to explore the lifetime and evolution of FE,X^DAP and X^SAB.Furthermore,Combining the evolution of PL spectra and lifetimes,The lifetimes of X^DAP and X^SABare determined to be around 200 ns and 10 ns,which shorten with the increase in temperature.Although time-resolved PL of the GaTe nanoflakes presents sophisticated behaviors,their lifetimes become shorter gradually with the increasing temperature,originating from the enhanced interaction between the exciton with the longitudinal optical phonons.Our results offer a more thorough understanding of the exciton dynamics of GaTe nanoflakes,enabling further progress in engineering GaTe-based applications,such as photodetectors,light-emitting diodes,and nanoelectronics.