Broad-band photoluminescence from ZnGeP2

Abstract

The near-infrared photoluminescence from single crystals of bulk ZnGeP2 was studied as a function of excitation power, excitation wavelength, sample temperature, and polarization. The nature of this broad-band luminescence from large single crystals grown for nonlinear optical applications is established. Two distinct bands with quite different polarization, power, and temperature behaviors were resolved. At 5 K, these broad bands have peaks in intensity near 1.58 and 1.36 eV. The 1.58 eV band is partially polarized perpendicular to the crystal’s c axis, has a relatively small thermal quenching activation energy (45 meV), and excitation spectra show a resonance in intensity associated with a shallow level approximately 90 meV below the minimum conduction band. The 1.36 eV band is partially polarized parallel to c, has a much larger quenching activation energy (220 meV), and its excitation spectrum includes two weak resonances corresponding to the A′ and B′ n=1 excitons. The high-energy band was enhanced in crystals containing relatively larger concentrations of phosphorus vacancies (measured by electron paramagnetic resonance).