Recently observed photoluminescence (PL) in ZnO, positioned at 3.324 eV and known to be related to Ge impurities, is investigated here by uniaxial stress and Zeeman spectroscopy measurements. The 3.324-eV PL line shifts but does not split under uniaxial stress both parallel and perpendicular to the $c$ axis, indicating trigonal defect symmetry. This reinforces the findings of prior work that the defect center is related to a substitutional Ge impurity in ZnO. Applied magnetic fields result in linear splittings of the line into two components for fields parallel and perpendicular to the $c$ axis. This result, combined with the temperature dependence of the Zeeman spectra, enables the line to be assigned to neutral donor bound-exciton recombination, most likely at a partially compensated Ge${}_{\mathrm{Zn}}$ double-donor impurity.

• Received 15 February 2013

DOI:https://doi.org/10.1103/PhysRevB.87.165202