Abstract
We report the ultrafast carrier dynamics of an SnSe2–SnSe composite thin film (∼150 nm thick) deposited using thermal evaporation of in-house synthesized SnSe2 powder. Raman and UV–visible spectroscopy supports the optical properties (direct and indirect bandgaps of 1.86 eV and 0.96 eV, respectively). Ultrafast transient spectroscopy is used to study the charge excited state dynamics in the SnSe2–SnSe composite thin film in the femtosecond to nanosecond interval. An energy model has been proposed based on the ultrafast transient absorption and the thin film's steady-state absorption studies. This article provides comprehensive knowledge about the excited carriers and their relaxations in 0.9 ps–31.1 ns via different trap states.
Highlights
The optically addressable valley degree of freedom in twodimensional materials (2DM) makes them an extraordinary resource for new technologies.1–9 The charge and the spin characteristics provide an opportunity for the advancement in device fabrication for optoelectronic applications7–11 and frequency generation.6,12–15 the presence of a novel valley degree of freedom in 2DM has intrigued/inspired the scientific community as it provides an additional technological advantage.1–5 The reduced screening and quantum confinement in the atomically thin 2D limit provide many electronic states such as biexciton, trion, and exciton, which give the valley dynamics.1,2,16–19 The binding energies of these particles are more significant than conventional materials
2020 Elsevier. (b) Raman spectra of the SnSe2–SnSe composite thin film fitted with a Lorentzian shape
The negative signal in the region of 940 nm–1200 nm indicates the presence of the trap-assisted states at “C” and stimulated emission (SE) at “D,” and a broad absorption is due to the extended trap states in the material having the density scitation.org/journal/adv of states proportional to the absorption amplitude
Summary
The optically addressable valley degree of freedom in twodimensional materials (2DM) makes them an extraordinary resource for new technologies.1–9 The charge and the spin characteristics provide an opportunity for the advancement in device fabrication for optoelectronic applications7–11 and frequency generation.6,12–15 the presence of a novel valley degree of freedom in 2DM has intrigued/inspired the scientific community as it provides an additional technological advantage.1–5 The reduced screening and quantum confinement in the atomically thin 2D limit provide many electronic states such as biexciton, trion, and exciton, which give the valley dynamics.1,2,16–19 The binding energies of these particles are more significant than conventional materials. The existence of trap states in the film may be due to many reasons, including the presence of SnSe as a secondary phase (as confirmed by the Raman peak at 68.69 cm−1), substrate effect44 (the interface may introduce trap states), or defect or impurity in the film at the time of growth.44 It is to be noted that the photoluminescence study did not show any peak, which may be due to the indirect bandgap nature of SnSe245
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