Native Defect Characterization in ZnGeP₂

Abstract

Electron paramagnetic resonance (EPR) as well as time-resolved and time-integrated photoluminescence (PL) are used to characterize the defect centers in ZnGeP 2 bulk crystals. The samples, as-grown, electron-irradiated and annealed, reveal a strong intensity dependence of the VZn-correlated EPR-transitions. Photo-EPR experiments show that this intensity behavior is mainly caused by a recharging of the VZn centers owing to the preparation induced shift of the Fermi-level. The luminescence spectra show a broad infrared emission with peak position at 1.23 eV that exhibits features of classical donor-acceptor recombination. The hyperbolic decay characteristics, investigated in energy range from 1.2 eV up to 1.5eV, suggest that this broad emission band is related to one energetic recombination center. This recombination is interpreted to be between donor-acceptor states related to residual disorder on the cation sublattice that is retained in metastable equilibrium during the formation of the chalcopyrite structure. The emission decay behavior in the energy range from 1.2 eV up to 1.6 eV is characterized by two hyperbolic time constants, and explained as the super-composition of the decays from the broad emission center peaked at 1.2 eV and an additional donor-acceptor recombination centers at 1.4 eV.

Energy levels of native defects in zinc germanium diphosphide

“…4. For the recharging of the V Zn À , Ge Zn + and V P 0 centers we determine E opt ¼ 1:7070:03 eV and for the decrease of the V Zn In agreement with [2], for samples irradiated with high-energy (2 MeV) electrons neither the V Zn À EPR signal nor the V P 0 signal could be detected before optical excitation, if the samples are cooled down in the dark and infrared irradiation by black body emission from the resonator walls is avoided. However, illumination with infrared light simultaneously generates the V Zn À -and the Ge Zn + -related EPR signals.…”

“…No clear defect assignments have been made for the usually broad photoluminescence bands in the range from 1.2 to 1.6 eV. However, a correlation with the concentration of the phosphorus vacancies was observed [5] and some parts of the broad infrared emission exhibit features of classical donor-acceptor recombination in dependence of the excitation density and time-decay character [2,6]. An assignment of the three identified native defects described above to energy levels in the ZnGeP 2 bandgap determined by electrical measurements [7] does not exist to date.…”

“…A large reduction of this unwanted absorption could be obtained by highenergy electron irradiation of the crystals. Electron paramagnetic resonance (EPR) and photo-EPR investigations of as-grown, electron-irradiated and annealed ZnGeP 2 samples have shown strong differences in the V Zn À -related EPR signal intensity, which are mainly caused by a meta-stable recharging of the V Zn À centers owing to the preparation induced shift of the Fermi-level [2]. Photoinduced EPR studies of such highly compensated bulk ZnGeP 2 crystals have identified two donor centers, that have been attributed to the neutral P vacancy (V P 0 ) [3] and the singly charged Ge Zn anti-site (Ge Zn + ) [4] centers, respectively.…”

Donor centers in zinc germanium diphosphide produced by electron irradiation

“…In agreement with [1,7], for samples irradiated with highenergy (2 MeV) electrons neither the V Zn -EPR signal nor the V P 0 and Ge Zn + signals could be detected before optical excitation, if the samples are cooled down in the dark. Illumination with infrared light generates the spectra of V Zn -, and Ge Zn + .…”

“…A large reduction of this absorption can be obtained by high-energy electron irradiation of the crystals. This reduction is mainly caused by a metastable recharging of the V Zn centers as result of the irradiation induced shift of the Fermi-level [1]. Both as-grown and annealed ZnGeP 2 samples grown by the horizontal gradient freeze technique exhibit commonly a strong EPR spectrum [2] that has been identified the singly negatively charged zinc vacancy (V Zn -) by ENDOR measurements [3,4].…”