Exciton and interband optical transitions in hBN single crystal

TL;DR

This study investigates excitonic and interband optical transitions in hBN single crystals at cryogenic temperatures, revealing details about defect-related and free excitons, band gap, and exciton binding energy.

Contribution

It provides new experimental insights into the excitonic states, defect trapping, and precise band gap and exciton binding energy measurements in hBN.

Findings

Dominance of defect-trapped excitons in PL signal

Observation of self-trapped excitons at specific energies

Band gap transition energy determined to be 6.4 eV

Abstract

Near band gap photoluminescence (PL) of hBN single crystal has been studied at cryogenic temperatures with synchrotron radiation excitation. The PL signal is dominated by the D-series previously assigned to excitons trapped on structural defects. A much weaker S-series of self-trapped excitons at 5.778 eV and 5.804 eV has been observed using time-window PL technique. The S-series excitation spectrum shows a strong peak at 6.02 eV, assigned to free exciton absorption. Complementary photoconductivity and PL measurements set the band gap transition energy to 6.4 eV and the Frenkel exciton binding energy larger than 380 meV.