Observation of singly ionized selenium vacancies in ZnSe grown by molecular beam epitaxy

Electron paramagnetic resonance (EPR) has been used to investigate singly ionized selenium vacancy $V_{\mathrm{Se}}^{+}$ centers in ZnSe epilayers grown by molecular beam epitaxy (MBE). The study included undoped and nitrogen-doped films. Spectra taken at 8 K and 9.45 GHz, as the magnetic field was rotated in the plane from [100] to [010], showed an isotropic signal at $g$ =2.0027±0.0004 with a linewidth of 5.8 G. In the two samples where this signal was observed, estimates of concentration were approximately ${\text{1.1×10}}^{17}$ and ${\text{6.3×10}}^{17}\hspace{0.5em}{\mathrm{cm}}^{\text{−3}}$ . The appearance of the EPR signal correlated with an increase in the Zn/Se beam equivalent pressure ratio (during growth) in undoped films and with an increase in the nitrogen concentration in doped films. We conclude that the singly ionized selenium vacancy may be a dominant point defect in many MBE-grown ZnSe layers and that these defects may play a role in the compensation mechanisms in heavily nitrogen-doped ZnSe thin films.