On the application of the photo-EPR technique to the studies of photoionization, DAP recombination, and non-radiative recombination processes

Godlewski, M.

doi:10.1002/pssa.2210900102

Cited by 76 publications

(29 citation statements)

References 107 publications

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“…The different methods for the determination of the optical cross section are discussed in Ref. [11]. How the relation between the DI EPR values and the optical cross section can be obtained within the framework of the saturation value method is described in detail in Ref.…”

Section: Resultsmentioning

confidence: 99%

“…Using only values from the linear regime DI EPR ðnÞBa and assuming that only one dominant photoionization process is responsible for the decrease or enhancement of the studied EPR signal, we see that DI EPR ðnÞ is directly proportional to the corresponding optical cross section [12]. Fitting the spectral dependence sðnÞ of the considered photoexcitation by the modified Lucovsky formula extended to account for the electron-phonon interaction [11] s n ð Þp…”

Section: Resultsmentioning

confidence: 99%

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Energy levels of native defects in zinc germanium diphosphide

Gehlhoff

Pereira

Azamat

et al. 2001

Physica B: Condensed Matter

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Electron paramagnetic resonance (EPR) and photo-EPR investigations of as-grown, post-growth annealed and electron irradiated zinc germanium diphosphide (ZnGeP 2 ) crystals allowed the determination of native acceptor-and donor-related defect levels in the ZnGeP 2 bandgap. From the photoinduced generation of the V Zn À EPR spectrum for electron-irradiated samples with the Fermi-level above the recharging level it is inferred that the V Zn ÀÀ/À acceptor state is located at 1.0270.03 eV below the conduction band. Observation of the recharging process in as-grown and postgrowth annealed samples yields the localization of the Ge anti-site donor level Ge Zn +/++ at E opt ¼ E V þ 1:7070:03 eV. Moreover, photoinduced processes involving the quenching and generation of the V Zn À and V P 0 EPR spectra, respectively, are observed with an energy of E opt ¼ 0:6470:03 eV. A model that can explain the complementary changes of the V Zn À and V P 0 EPR intensities is briefly discussed. r

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Energy levels of native defects in zinc germanium diphosphide

Gehlhoff

Pereira

Azamat

et al. 2001

Physica B: Condensed Matter

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“…Furthermore, the EPR signal intensities obtained by those measurements have to be corrected due to the fact that the optical absorption of the sample is also wavelength dependent, as described by Godlewski. 13 Since the EPR intensity is proportional to the square root of the light intensity, the correction factor ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 À expðÀadÞ p is introduced. The values of ad were obtained by optical transmittance and reflectance measurements on our samples.…”

Section: Photo-eprmentioning

confidence: 99%

Electron paramagnetic resonance and photo-electron paramagnetic resonance investigation on the recharging of the substitutional nitrogen acceptor in ZnO

Stehr

Hofmann

Meyer

2012

Journal of Applied Physics

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We investigated the substitutional nitrogen center in ZnO single crystals by electron paramagnetic resonance (EPR) and photo-EPR spectroscopy. Aside the three principle hyperfine lines due to the interaction of the N 0 (2p5) electron spin with the nitrogen nucleus (I ¼ 1, natural abundance 99.6%), we identify additional satellite lines which arise from Dm S ¼ 61 and Dm I ¼ 61, 62 transitions becoming allowed due to quadrupole interaction. The quadrupole coupling constant e 2 qQ/h is determined to À5.9 MHz with an asymmetry parameter of g ¼ 0.05. These values are somewhat different from those obtained for the nitrogen center in ZnO powders, but are closer to the theoretical calculations of Gallino et al. We further carefully investigated the photon induced recharging of the N centers. We determine the energy ht required for the process N O À þ ht ! N O 0 þ e cb À to 2.1 6 0.05 eV, the dependence of the EPR signal intensity on the illumination time shows a mono-exponential behavior which gives evidence that a direct ionization process is monitored.

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“…By solving the appropriate kinetic equations [4] it can be shown that τ -1( hv) is proportional to the optical cross-section σ(hv) for this transition. Thus, the spectral dependence of the Eu2+ ionization can be determined.…”

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confidence: 99%

Recombination Processes in ZnSe:Eu

Świątek

Godlewski

1991

Acta Phys. Pol. A

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The photo-ESR and photoluminescence experiments have been performed on high-resistivity ZnSe:Eu crystals. We report the first evidence that the energy 1evel of Eu2+ ground state is located within the ZnSe forbidden gap, approximately 2.1 eV below the bottom of the conduction band. Contrary to practically all transition-metal impurities only some rare-earth (RE) ions have been assumed to introduce energy levels into the forbidden gap of II-VI compounds [1]. Recently, we have analyzed this problem in ZnS and other sulphides doped with RE ions [2]. Until now, the only RE impurity observed in ZnSe 1attice in 2+ charge state is europium [3]. In this communication we present the first evidence that the Eu 2 +/3+ energy level is located within the ZnSe gap.The electron spin resonance (ESR) experiments were performed on a Bruker 418s X-band equipped with an Oxford Instruments ESR-900 continuous-gas-flow cryostat, working in the temperature range of 4-300 K. A high-pressure XBO 150 xenon lamp and a set of Carl-Zeiss interference filters were used for the optical ' excitation. The photoESR experiments have been performed on high-resistivity ZnSe:Eu crystals. An ESR signal f Eu2+ (4f7) has been observed at 4.2 K prior to illumination. After illuminating the sample with hv 1 > 1.9 eV light a quenching of the intensity of this signal has been observed, i.e., the concentration of Eu 2 + centers was found to decrease due to the population of the Eu 3+(4f6 ) state which cannot be easily detected by ESR technique. Then the light was turned off and a small increase of the Eu 2 + ESR signal was observed. After equilibrium was reached, a secondary infrared illumination (0.9 eV < hv2 < 1.1 eV) was applied leading to rapid enhancement f the Eu2+ signal intensity. Still a small, further increase occurred after the light was turned off. The sequence of steps in the experiment is shown in Fig. 1. Before each measurement, a primary hv 2 illumination was applied to ensure the same initial conditions. The spectral distribution of the photoquenching rate constant (τ -1 ) normalized to constant light intensity is shown in Fig. 2.(381)

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On the application of the photo-EPR technique to the studies of photoionization, DAP recombination, and non-radiative recombination processes

Cited by 76 publications

References 107 publications

Energy levels of native defects in zinc germanium diphosphide

Energy levels of native defects in zinc germanium diphosphide

Electron paramagnetic resonance and photo-electron paramagnetic resonance investigation on the recharging of the substitutional nitrogen acceptor in ZnO

Recombination Processes in ZnSe:Eu

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