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A hidden phase uncovered by ultrafast carrier dynamics in thin Bi2O2Se
Hao Li1,2, Adeela Nairan3, Xiaoran Niu1,2
1State Key Laboratory on Tunable Laser Technology, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, P. R. China.
Nanoscale
|February 7, 2024
Summary
Researchers studied bismuth oxy-selenide (Bi2O2Se) thin films, revealing a hidden photoinduced ferroelectric transition in thinner films (<8 nm). This transition, influenced by strain and excitation density, deepens understanding for optoelectronic applications.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Solid-State Chemistry
Background:
- Bismuth oxy-selenide (Bi2O2Se) shows promise for electronics, optoelectronics, and ferroelectric devices.
- Limited ultrafast spectroscopy studies exist for Bi2O2Se thin films, with varying reported dynamics.
- A comprehensive understanding of thickness and fluence effects on carrier dynamics is needed.
Purpose of the Study:
- To systematically investigate thickness-dependent Raman spectroscopy and ultrafast carrier dynamics in Bi2O2Se thin films.
- To elucidate the influence of film thickness and pump fluence on carrier relaxation mechanisms.
- To explore potential photoinduced phase transitions in Bi2O2Se.
Main Methods:
- Chemical vapor deposition (CVD) growth of Bi2O2Se thin films with varying thicknesses (4.62 nm to 22.44 nm) on mica.
- Thickness-dependent Raman spectroscopy.
- Ultrafast time-resolved spectroscopy (pump-probe) across low and high pump fluence regimes.
Main Results:
- Observed thickness-dependent changes in Raman spectra and carrier dynamics.
- Identified a slow decay component influenced by film thickness and pump fluence.
- Demonstrated a hidden photoinduced ferroelectric transition in thinner (<8 nm) Bi2O2Se films below damage thresholds.
Conclusions:
- Substrate-induced compressive strain and non-equilibrium excitation contribute to the photoinduced ferroelectric transition.
- The transition is observable at high electronic excitation densities.
- Findings enhance the understanding of the interplay between ferroelectricity and semiconducting properties in Bi2O2Se, relevant for optoelectronics.
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