Sharp-line luminescence and absorption in ZnGeP2

Photoluminescence and optical absorption spectroscopies have been used to study bulk ZnGeP2. Two sharp zero-phonon lines with opposite polarizations are resolved in emission at 1.7849 eV (at 70 K) and 1.7784 eV (at 5 K), respectively. Thermalization occurs between these two lines, suggesting a split excited state of the center. Considerable structural detail is resolved in the vibronic sidebands of these lines, revealing phonon energies of 6.3 +/-0.1 meV and 43.7 +/-0.1 meV. Similar phonon energies are resolved in low-temperature absorption spectra. These results for ZnGeP2 are explained by a model of radiative recombination of excitons bound to an isoelectronic defect center. The observed polarization behavior of the sharp-line spectra can be produced by the built-in tetragonal distortion along the c axis associated with the chalcopyrite structure. (C) 2001 American Institute of Physics.