Anomalous Temperature and Polarization Dependences of Photoluminescence of Metal‐Organic Chemical Vapor Deposition‐Grown GeSe2

Germanium diselenide (GeSe2) is a 2D semiconductor with air stability, a wide bandgap, and anisotropic optical properties. The absorption and photoluminescence (PL) of single‐crystalline 2D GeSe2 grown by metal‐organic chemical vapor deposition and their dependence on temperature and polarization are studied. The PL spectra exhibit peaks at 2.5 eV (peak A) and 1.8 eV (peak B); peak A displays a strongly polarized emission along the short axis of the crystal, and peak B displays a weak polarization perpendicular to that of peak A. With increasing temperature, peak B shows anomalous behaviors, i.e., an increasing PL energy and intensity. The excitation energy‐dependent PL, time‐resolved PL, and density functional theory calculations suggest that peak A corresponds to the band‐edge transition, whereas peak B originates from the inter‐band mid‐gap states caused by selenium vacancies passivated by oxygen atoms. The comprehensive study on the PL of single‐crystalline GeSe2 sheds light on the origins of light emission in terms of the band structure of anisotropic GeSe2, making it beneficial for the corresponding optoelectronic applications. 2D germanium diselenide (GeSe2) crystals are grown by metal‐organic chemical vapor deposition. Two peaks of absorption and photoluminescence spectra at 2.5 and 1.8 eV show the mutually perpendicular polarization and the apposite temperature dependence of the peak position. They are identified as the band‐edge transition and the mid‐gap states caused by the selenium vacancies passivated by oxygen atoms.