Anomalous Temperature and Polarization Dependences of Photoluminescence of Metal‐Organic Chemical Vapor Deposition‐Grown GeSe 2

Germanium diselenide (GeSe 2 ) is a 2D semiconductor with air stability, a wide bandgap, and anisotropic optical properties. The absorption and photoluminescence (PL) of single‐crystalline 2D GeSe 2 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 GeSe 2 sheds light on the origins of light emission in terms of the band structure of anisotropic GeSe 2 , making it beneficial for the corresponding optoelectronic applications.