An optical absorption investigation from 10 to 296K was performed on bulk crystals of ZnGeP2 grown by the horizontal-gradient-freeze method. Three broad absorption bands were identified, in the spectral range from 1 to 4µm, that were due to native defects. At low temperature, a band peaking near 1.2 µm and another band peaking near 2.2µm have intensities that correlate. The strength of these two absorption bands could be increased or decreased by illuminating the crystal with selected laser wavelengths. The 2.2 µm band was strongly polarized, with its greatest intensity occurring when E was parallel to the c axis of the crystal. A third absorption band, peaking near 2.3µm and extending from 1.5 µm to beyond 4µm, was observed at low temperature, during and immediately after illumination. Comparison of photo-induced changes in absorption with photo-induced changes in electron paramagnetic resonance spectra allowed specific defects to be associated with each of the three absorption bands. Both the 1.2 and the 2.2µm bands involve the singly ionized Zn vacancy. The third band at 2.3µm involves neutral P vacancies. Specific models for the optical transitions were discussed.

Infrared Absorption Bands Associated with Native Defects in ZnGeP2. N.C.Giles, L.Bai, M.M.Chirila, N.Y.Garces, K.T.Stevens, P.G.Schunemann, S.D.Setzler, T.M.Pollak: Journal of Applied Physics, 2003, 93[11], 8975-81