Determination of the direct bandgap value in In₄Se₃thin films

Area of Science:

• Materials Science
• Solid State Physics
• Semiconductor Research

Background:

• The electronic properties, specifically the bandgap value and nature, of Indium Selenide (In$_{4}$Se$_{3}$) remain poorly defined, with experimental data showing significant variation (0.42–1.68 eV).
• Theoretical calculations predict an indirect bandgap, contrasting with potential direct transitions needed for optoelectronic applications.

Purpose of the Study:

• To accurately determine the bandgap energy and nature of In$_{4}$Se$_{3}$ thin films.
• To investigate excitonic transitions and stimulated emission in In$_{4}$Se$_{3}$.
• To provide a reliable value for the direct bandgap of In$_{4}$Se$_{3}$ for future research and applications.

Main Methods:

• Growth of high-quality In$_{4}$Se$_{3}$ thin films via coevaporation on sapphire substrates.
• Optical transmission and photoluminescence (PL) spectroscopy at low temperatures.
• Analysis of PL intensity dependence on optical excitation power to identify stimulated emission mechanisms.

Main Results:

• First detection of excitonic-like transitions in the optical absorption of In$_{4}$Se$_{3}$ at low temperature.
• Observation of bound exciton emission at 0.75 eV under weak laser excitation.
• Demonstration of stimulated emission at 0.79 eV attributed to exciton-exciton scattering, evidenced by quadratic PL intensity dependence.

Conclusions:

• The direct bandgap of In$_{4}$Se$_{3}$ was determined to be 0.82 ± 0.01 eV at low temperature, based on optical measurements and excitonic energy estimations.
• The study resolves ambiguities regarding the bandgap of In$_{4}$Se$_{3}$, providing a crucial parameter for its potential use in optoelectronics.
• High-quality In$_{4}$Se$_{3}$ films enable the observation of fundamental optical transitions and stimulated emission phenomena.