Online and in situ investigation of electron irradiation induced optical absorption in ZnGeP₂ single crystals

In the present study, the absorbance induced in Zinc germanium diphosphide, ZnGeP₂ (ZGP) crystals and new Sn-doped ZGP crystals has been investigated under irradiation with high energy electrons. Online and in situ experiments were performed in the range 720–1100 nm. The spectra of the induced absorbance are constituted by a “tail” and the maximum appears to be located at wavelengths lower than those of the investigated spectral range. A fraction of the induced absorbance disappears within one minute after the electron beam is switched off, revealing the presence of metastable effects. A low and a high fluence contribution to the induced absorbance have been observed at 800 nm. The first reaches a limit value and seems to be affected by the Sn doping or by the absence of post-growth annealing, while the high fluence contribution does not feature a saturation in the investigated range and does not depend on the sample type.