Structural Control of Defect‐Bound Exciton Emission in α‐In 2 Se 3
Rahul Rao, Pijush Bhattacharya, Thuc T. Mai, Michael A. Altvater, Tyler Matos, Christopher E. Stevens, Sandy A. Ekahana, Md Nasim Afroj Taj, Aalok Tiwari, Nguyen Tuan Hung, Andrea N. Giordano, Timothy Gustafson, Mona Zebarjadi, Jyoti Katoch, Joshua R. Hendrickson, Nicholas R. Glavin, Michael A. SusnerABSTRACT
Native lattice defects strongly govern the optoelectronic properties of ‐, an emerging van der Waals material. At room temperature, its photoluminescence (PL) spectrum features a band‐edge excitonic “A” peak at 1.36 eV and a defect‐related sub‐bandgap “B” peak at 1.3 eV. While the B peak emission brightens significantly below 150 K, its exact origin and its connection to the low‐temperature phase transition of have remained unclear. Here, we demonstrate that the B peak emission originates from excitons trapped at Se vacancies. Upon cooling below 150 K, ‐ undergoes a structural transformation to the phase, which increases the localized electron density at Se vacancies and drives the brightening of the B peak emission. X‐ray photoelectron spectroscopy and a negative Seebeck coefficient confirm the presence of Se vacancies, which introduce electron doping and form a surface two‐dimensional electron gas observed using angle‐resolved photoemission spectroscopy. The trapped excitons exhibit strong electron–phonon coupling, with a PL lifetime of 28 ns and a large Huang–Rhys factor of 14. These results offer a framework for the deterministic control of defect‐bound excitons in ‐ for optoelectronics applications.