A comprehensive experimental study on optical properties and photocarrier dynamics in Bi2O2Se monolayers and nanoplates is presented. Large and uniform Bi2O2Se nanoplates with various thicknesses down to the monolayer limit are fabricated. In nanoplates, a direct optical transition near 720 nm is identified by optical transmission, photoluminescence, and transient absorption spectroscopic measurements and is attributed to the transition between the valence and conduction bands in the Γ valley. Time‐resolved differential reflection measurements reveal ultrafast carrier thermalization and energy relaxation processes and a photocarrier recombination lifetime of about 200 ps in nanoplates. Furthermore, by spatially resolving the differential reflection signal, a photocarrier diffusion coefficient of about 4.8 cm2s−1is obtained, corresponding to a mobility of about 180 cm2V−1s−1. A similar direct transition is also observed in monolayer Bi2O2Se, suggesting that the states in the Γ valley do not change significantly with the thickness. The temporal dynamics of the excitons in the monolayer is quite different from the nanoplates, with a strong saturation effect and fast exciton–exciton annihilation at high densities. Spatially and temporally resolved measurements yield an exciton diffusion coefficient of about 20 cm2s−1.
Transient absorption spectroscopy is a powerful tool to monitor the out-of-equilibrium optical response of photoexcited semiconductors. When this method is applied to two-dimensional semiconductors deposited on different substrates, the excited state optical properties are inferred from the pump-induced changes in the transmission/reflection of the probe,
- NSF-PAR ID:
- 10386378
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Express
- Volume:
- 31
- Issue:
- 1
- ISSN:
- 1094-4087; OPEXFF
- Page Range / eLocation ID:
- Article No. 107
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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