Centers In ZnS Research Articles

X centers in ZnSe〈Ga〉 and ZnSe〈As〉 single crystals

The results of experimental studies of the energy spectrum of X centers in ZnSe〈Ga〉 and ZnSe〈As〉 single crystals are presented; the results are in accord with the available calculations. The Stokes shift, the stabilization of the Fermi level near the extrema of allowed bands of ZnSe, anomalies in thermoluminescence and interband photoluminescence, and some other effects are explained on the basis of configuration-coordinate diagrams for associated defects VZn-Gai and VSe-Asi, taking into account tetrahedral and hexagonal positions of interstitial atoms. The absence of residual photoconductivity is attributed to the presence of r-and s-recombination centers in the crystals.

Pressure behavior of Te isoelectronic centers in ZnS:Te

ZnS:Te epilayers with Te concentration from 0.5% to 3.1% were studied by photoluminescence under hydrostatic pressure at 15 K. Two emission bands related to the isolated Te1 and Te2 pair isoelectronic centers were observed in the samples with Te concentrations of 0.5% and 0.65%. For the samples with Te concentrations of 1.4% and 3.1%, only the Te2-related peak was observed. The pressure coefficients of all the Te1-related bands were found to be unexpectedly much larger than that of the ZnS band gap. The pressure coefficients for all the Te2-related bands are, however, rather smaller than that of ZnS band gap as usually observed. Analysis based on a Koster–Slater model indicates that an increase of the valence bandwidth with pressure is the main reason for the faster pressure shift of the Te1 centers, and the huge difference in the pressure behavior of the Te1 and Te2 centers is due mainly to the difference in the pressure-induced enhancement of the impurity potential on the Te1 and Te2 centers.

Optical and paramagnetic properties of titanium centres in ZnS

ZnS:Ti crystals grown by different methods are investigated at low temperatures (2 K K) by electron paramagnetic resonance (EPR) and optical spectroscopies, mainly with regard to their photoluminescence properties, including excitation and sensitisation spectra. The more familiar lattice-neutral Ti2+(d 2 ) ion on a cubic site (AN) presents an isotropic EPR signal with g=1.928 observable up to 80 K. Signals of axial PN and AS sites are detected in the same temperature range. This Ti2+ ion exhibits the transition in emission, structured by no-phonon lines (NPL) of centres in various environments, with the AN site represented at 3613 cm-1, and the 3 T 1 (F) and 3 T 1 (P) bands in excitation spectra. Substitutional Ti3+(d 1 ) is identified by an anisotropic EPR spectrum at T = 3.5 K, indicating a quasistatic Jahn-Teller effect at the doubly degenerate 2 E(D) ground state, while in the first excited vibronic state a quasidynamic JT effect in the strain-split vibronic 2 E/2 A 2 manifold is found. A new luminescence band centred at 4500 cm-1 with NPL structures near 5000 cm-1 represents AN, PN and AS sites in the transition. Charge-transfer processes are described in a one-particle model, depicting the Ti3+/Ti2+ donor level at 12 900 cm-1 below the conduction-band edge.

Incorporation of Cu Zn centers in ZnSe far from equilibrium

An investigation employing nuclear transmutation to probe the effects of copper doping in ZnSe is presented. Three experimental techniques are developed in the investigation. With the first, as-grown ZnSe is irradiated with thermal neutrons which results, after thermal annealing, in the incorporation of Cu Zn centers. Observations are consistent with isolated Cu Zn being involved in the copper red and copper green emissions in ZnSe but not in the I d 1 excitonic emission. With the second, it is shown that zinc annealing can be used effectively in investigations involving the irradiation of as-grown ZnSe since the zinc annealing treatment significantly reduces background PL emissions in bulk ZnSe. The third technique employs homoepitaxial ZnSe layer growth from previously irradiated elemental sources. The epitaxial layers display no dominant I d 1 excitonic emission and a very low level of deep emissions. Because, with the techniques described here, the copper atoms are introduced at zinc sites after crystal growth processes are complete, the copper atoms are not able to interact with other dopants or lattice defects during growth as they can when incorporated by other means. The absence of interactions during crystal growth permits the unambiguous incorporation, far from equilibrium, of isolated Cu Zn centers in ZnSe.

Nature of optical transitions in the charge-transfer region of ZnS:Co and ZnSe:Co.

The cobalt center in ZnS:Co and ZnSe:Co has long been considered as a possible candidate for the observation of so-called bound-electron levels. The optical transitions in the vicinity of the charge-transfer transition from the ${\mathit{d}}^{6}$/${\mathit{d}}^{7}$ charge-transfer level to the conduction band are therefore investigated by their magneto-optical properties. These clearly reveal the identical origin of the observed transitions in the two materials. With the aid of the known charge-transfer energies the transitions are identified as internal ${\mathit{d}}^{7}$\ensuremath{\rightarrow}${\mathit{d}}^{7}$* excitations. Possible assignments are discussed within the framework of ligand-field theory, which also delivers an explanation of why similar internal transitions were not yet observed in other II-VI or even III-V compound semiconductors doped with cobalt. A uniform picture of the cobalt center in these semiconductor host materials is thus derived. \textcopyright{} 1996 The American Physical Society.

Nonlinear Zeeman behavior of Cu2+ centers in ZnS and CdS explained by a Jahn-Teller effect.

The copper defect is that transition-metal impurity in II-VI compounds for which the most complete set of information has been compiled so far experimentally and theoretically. This makes it a favored system to study the mechanisms determining the optical spectra. The interpretation of the observed ${\mathrm{Cu}}^{2+}$ transitions in ZnS and CdS crystals is made using a coupling of the electronic states to a local vibrational mode of E symmetry and a moderate Jahn-Teller effect with a Huang-Rhys factor of S=0.8 for ZnS and S=1.1 for CdS. We report on parameter-free calculations of the magnetic-field splitting of ${\mathrm{Cu}}^{2+}$ centers in II-VI compounds, which show a general agreement with the observed spectra. For ZnS:${\mathrm{Cu}}^{2+}$ the calculated g factors agree with the observed values, though a stronger nonlinear behavior with respect to the magnetic field had been found for some of the calculated energy levels. For CdS:${\mathrm{Cu}}^{2+}$ the nonlinear behavior of the magnetic-field splitting is also reproduced by the calculation and the g factors agree for the $^{2}$E excited-state doublets, whereas there are some differences for the g factors of the $^{2}$${\mathit{T}}_{2}$ ground-state doublets, which are due to the neglect of the ${\mathit{T}}_{2}$ mode coupling in the Jahn-Teller calculation. \textcopyright{} 1996 The American Physical Society.

Electron-paramagnetic-resonance study of the Mn2+ luminescence center in ZnS:Mn powder and thin films

The number of isolated Mn2+ ions and Mn2+ clusters in ZnS:Mn powder and thin films has been studied using Mn2+ spectra measured at room temperature with an X-band electron-paramagnetic-resonance spectrometer. While the concentration of the isolated Mn2+ ions decreases with increasing Mn concentration, the concentration of the clusters increases. At low Mn concentration, the Mn2+ ion substitutes for the Zn ion in ZnS:Mn in the cubic phase. At high Mn concentrations, where the ZnS powder has a dominant hexagonal phase, the Mn ion still prefers to substitute for Zn in ZnS:Mn at the cubic site rather than at the hexagonal site.

Ho centres in ZnS in the 3+ and 2+ state studied by optical and electron paramagnetic resonance spectroscopy

Ho centres in mixed-polytype ZnS crystals codoped with Ag are studied by measuring polarized site-selective photoluminescence and photoluminescence excitation spectra as well as by EPR spectroscopy. The optical data give evidence of Ho in the charge state 3+ (4f10), while in the EPR measurements, which are performed under illumination in the interband range, centres in the 2+ state (4d11) are detected. From a crystal-field analysis we conclude that the dominant centres seen in the two kinds of experiment are identical with respect to the atomic configuration, apart from small nearest-neighbour relaxation effects which accompany the change of the charge state. The crystal field is found to have approximately cubic symmetry, with a small trigonal field component, whose axis is parallel to the (111)w direction. Our data indicate that the Ho occupies zincblende-type interstitial sites with four metallic ions as nearest neighbours, most probably Ag substituting for Zn ions. The Ho2+ ground state involved in the charge transfer process is thought to lie close to the bottom of the conduction band; this explains the optical behaviour observed in our experiments.

Nonlinear Zeeman Behaviour of Copper Centers in ZnS and CdS

Nonlinear Zeeman Behaviour of Copper Centers in ZnS and CdS

Photo-ESR Studies of Ni doped ZnS and ZnSe

Transition metal impurities, such as iron [1, 2], chromium [2, 3], or nickel, belong to the most active centers of nonradiative recombination in wide band gap II-VI compounds [4, 5]. In this communication we present the results of electron spin resonance experiments performed under the photo-excitation (photoESR) for Ni doped ZnS and ZnSe. Nonradiative recombination processes in Ni doped samples are discussed. Efficiency of electron and hole trapping by Fe and Ni centers is compared. We verify also previous estimations of energy level position of Nil+ center in ZnS and ZnSe.

XPS study of TbF3 and TbOF centres in ZnS

physica status solidi (a)Volume 146, Issue 2 p. K67-K70 Dielectric and Optical Properties XPS study of TbF3 and TbOF centres in ZnS J. van den Bossche, J. van den Bossche Vakgroep Elektronica en Informatiesystemen, Universität Gent Search for more papers by this authorK. A. Neyts, K. A. Neyts Vakgroep Elektronica en Informatiesystemen, Universität Gent Sponsored by the National Fund for Scientific Research, Belgium.Search for more papers by this authorP. de Visschere, P. de Visschere Vakgroep Elektronica en Informatiesystemen, Universität Gent Search for more papers by this authorD. Corlatan, D. Corlatan Vakgroep Elektronica en Informatiesystemen, Universität Gent Sponsored by the Belgian Ministry of Science IUAP/24.Search for more papers by this authorH. Pauwels, H. Pauwels Vakgroep Elektronica en Informatiesystemen, Universität Gent Search for more papers by this authorR. Vercaemst, R. Vercaemst Vakgroep Vaste-Stofwetenschappen, Gent Search for more papers by this authorL. Fiermans, L. Fiermans Vakgroep Vaste-Stofwetenschappen, Gent Search for more papers by this authorD. Poelman, D. Poelman Vakgroep Vaste-Stofwetenschappen, Gent Search for more papers by this authorR. L. van Meirhaeghe, R. L. van Meirhaeghe Vakgroep Vaste-Stofwetenschappen, Gent Search for more papers by this authorW. H. Laflére, W. H. Laflére Vakgroep Vaste-Stofwetenschappen, Gent Search for more papers by this authorF. Cardon, F. Cardon Vakgroep Vaste-Stofwetenschappen, Gent Search for more papers by this author J. van den Bossche, J. van den Bossche Vakgroep Elektronica en Informatiesystemen, Universität Gent Search for more papers by this authorK. A. Neyts, K. A. Neyts Vakgroep Elektronica en Informatiesystemen, Universität Gent Sponsored by the National Fund for Scientific Research, Belgium.Search for more papers by this authorP. de Visschere, P. de Visschere Vakgroep Elektronica en Informatiesystemen, Universität Gent Search for more papers by this authorD. Corlatan, D. Corlatan Vakgroep Elektronica en Informatiesystemen, Universität Gent Sponsored by the Belgian Ministry of Science IUAP/24.Search for more papers by this authorH. Pauwels, H. Pauwels Vakgroep Elektronica en Informatiesystemen, Universität Gent Search for more papers by this authorR. Vercaemst, R. Vercaemst Vakgroep Vaste-Stofwetenschappen, Gent Search for more papers by this authorL. Fiermans, L. Fiermans Vakgroep Vaste-Stofwetenschappen, Gent Search for more papers by this authorD. Poelman, D. Poelman Vakgroep Vaste-Stofwetenschappen, Gent Search for more papers by this authorR. L. van Meirhaeghe, R. L. van Meirhaeghe Vakgroep Vaste-Stofwetenschappen, Gent Search for more papers by this authorW. H. Laflére, W. H. Laflére Vakgroep Vaste-Stofwetenschappen, Gent Search for more papers by this authorF. Cardon, F. Cardon Vakgroep Vaste-Stofwetenschappen, Gent Search for more papers by this author First published: 16 December 1994 https://doi.org/10.1002/pssa.2211460248Citations: 12 Sint-Pictersnieuwstraat 41, B-9000 Gent, Belgium. Krijgslaan 281/S1, B-9000 Gent, Belgium. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume146, Issue216 December 1994Pages K67-K70 RelatedInformation

Effects of C incorporation on the luminescence properties of ZnSe grown by metalorganic chemical vapor deposition

The effects of C incorporation in heteroepitaxial ZnSe grown on GaAs by metalorganic chemical vapor deposition (MOCVD) with methylallylselenide (MASe), diethylselenide (DESe), and hydrogen selenide (H 2Se) selenium precursors together with dimethylzinc (DMZn) are investigated. The effects of growth temperature and VI/II ratio are determined. In material grown at 480°C and above, all of the low temperature photoluminescence (PL) peaks are generally shifted several meV lower in energy than in material grown in the 300–425°C range. In particular, the light hole component of the neutral donor-bound exciton shifts down to around 2.792 eV, where it was incorrectly identified in previous work as an exciton bound to a complex involving C. Detailed PL and reflectance measurements give conclusive evidence for this interpretation. The peak shifts are attributed to increased thermal mismatch strain resulting from the higher growth temperature used with MASe and DESe. However, the VI/II ratio strongly affects the strain in samples grown at 500°C using DESe, suggesting that heavy C incorporation at the ZnSe/GaAs interface may stimulate the thermal relaxation. The mechanism might involve the formation of C-related microprecipitates near the interface, which then nucleate misfit dislocations. We conclude that C from the growth precursors does not produce any new PL peaks above 1.4 eV in MOCVD ZnSe. Moreover, the room temperature PL efficiency is not degraded in C-contaminated material, suggesting that C is not an important non-radiative recombination center in ZnSe. The incorporation of moderate C levels is found to have little effect on the optoelectronic properties of MOCVD ZnSe.

Excitation and deexcitation of ac-driven thin-film ZnS electroluminescent devices

Theoretical formulas accounting for the excitation and deexcitation processes of the alternating current-driven thin-film electroluminescent devices have been obtained, which include both the impact excitation and the energy-transfer mechanisms. The empirical equations for the conduction current duration time and the luminescent decay time related to the tunneling emission of electrons at the interface, the capture of holes in traps, and the light emission of luminescent centers lead to the analytical formulas for the transferred charge ΔQ, the luminance L, and other quantities of physical interest as a function of the electric field. The estimates for ΔQ and L in ZnS:Mn and ZnS:TbF3 devices have been made on the basis of Wolff’s distribution function and found to be in good agreement with the experimental data. From the estimated results, it is found that the energy-transfer mechanism depends on various material parameters and drive conditions, and that it plays a role in improvement of the luminance in the low-electric-field region. In the high-electric-field region of interest, the energy transfer from Cu-related sensitizers to luminescent centers in ZnS:Mn and ZnS:TbF3 devices yields an increase of luminance by a factor of about 1.5 and 3, respectively.

Photoionization spectra of deep centers in semiconductors showing a narrow peak near the threshold.

A class of deep centers in semiconductors is identified by their photoionization spectra, which have a narrow peak near the threshold energy and a broader peak at higher energy. The M center in ZnSe is an example. An explanation of the spectral shape is given in terms of a wave function with a radial node. Such wave functions can occur when a substantial contribution to the function comes from nearest-neighbor atoms.

On the Tunneling Among Shallow and Deep Centers in ZnS

Radiative tunneling among randomly dstributed donors (D) and acceptors (A) is one of the most efficient processes responsible for the visible luminescence (VL) in many semiconductors (SCs). However, the quantum yield of these transitions may be strongly affected by presence of the other, usually deep, centers. The best known deactivators (killers) of VL in ZnS are transition metal (TM) impurities. In the previous papers [1, 2] two deactivation mechanisms were identified. Recently O,Donnel et al. [3] proposed a new one which can limit the donor—acceptor pair (DAP) luminescence in ZnSe:Fe. During this process an electron tunnels from a donor (D) to iron instead of acceptor (Α) (Fig. 1). In this paper we present the results of photoESR studies of recharging process in ZnS crystals. By selecting the experimental temperature and conditions we could obtain the metastably occupied D, A, Fe and Cr centers with their depopulation monitored via the studies of Fe 3+ and Cr+ ESR signal intensities. At low temperature this depopulation occurs only due to tunneling transitions of e.g. A Cr type. Hence, the decay kinetics of the Fe3+ and Cr+ ESR signals enables us to estimate the tunneling efficiencies among activator and killer centers. The effIciency of the DAP luminescence is usually characterized by two parameters: W0 and α. This comes from the fact that the tunneling rate W(r) between given donor and an acceptor located at a distance r is taken in the form:

Long range Mn Ion pairs and other Mn related centers in ZnS detected by site-selected spectroscopy

In ZnS : Mn crystals with pure cubic zinc-blende structure, two groups of zero phonon lines have been detected close to the zero phonon line originating from the single Mn ion center. Group I centers are attributed to pairs of Mn ions with distances ranging from third to sixth nearest neighbor. For group II centers a tentative assignment to a (V ZnMn Zn) associate will be given.

Isolated iron and chromium as recombination centers in ZnS

Free-carrier capture cross sections of isolated iron and chromium centers in ZnS are estimated. It is found that the Fe and Cr electron capture cross sections are comparable to those for shallow donors active in photoluminescence processes. The cross sections for hole capture are up to 103 times larger than those for the main ZnS acceptors. Our results allow us to explain the photoluminescence quantum yield of ZnS:Cu,Fe.

Anisotropy of the cross-section of impact excitation in electroluminescence

Taking into account the structure of conduction band, we deduced a formula which showed the anisotropy of the impact cross-section. We carried out the numerical calculations for that of the luminescent centers in ZnS and found the favourable orientation, along which the probability of excitation would be greatly increased.

Theoretical analysis of orbital and correlation effects on the electronic absorption spectrum of the MnS4 center in zinc-blende crystals.

Optical excitation energies ascribed to the ${\mathrm{Mn}}^{2+}$ center in ZnS:Mn are calculated from Gaussian-based self-consistent-field (SCF) molecular orbitals (MO's) obtained for the tetrahedral ${\mathrm{MnS}}_{4}^{6\mathrm{\ensuremath{-}}}$ cluster at three Mn-S distances in a static external potential, followed by a detailed investigation of two levels of electron correlation effects. The first level includes only configuration interaction (CI) among the ligand field (LF) ${d}^{5}$ states plus other intra-d-shell contributions by the empirical correlation-energy-correction method (CEC), which is formally equivalent to the intermediate-crystal-field (CF) model. The second level extends the CI to include a large manifold of cluster S\ensuremath{\rightarrow}Mn relaxed charge-transfer (RCT) states. At the LF-CI+CEC level, the relative separations among, and the overall width of, the six lowest quartets agree closely with the four bands observed in the spectrum. However, contrary to usual assignments, b $^{4}T_{1}$${(}^{4}$P) is found below b $^{4}T_{2}$${(}^{4}$D), and all quartets are obtained about 0.5 eV too high relative to $^{6}\mathrm{A}_{1}$. The delocalization effects in the MO's are noticeably smaller than obtained from empirical CF fits to the spectrum. At the second level, CI mixing with the RCT states introduces important changes and interactions not properly encompassed by the orbital-based LF parametrization schemes. This CI depresses the quartet levels almost uniformly down by 0.2 eV relative to $^{6}\mathrm{A}_{1}$. The order of b $^{4}T_{2}$ and b $^{4}T_{2}$ and ${b}^{4}$${T}_{1}$ is reversed and now agrees with the usual assignments. Finally these various results are discussed in comparison to less quantitative models in which extended interactions with the host are considered. A degree of similarity between the two formulations is established which gives further justification to the model as used herein.

Investigation of intrinsic defect-related deep centers in ZnSe

We have studied deep centers in highly resistive (ρτ ∼ 1012 Ω·cm) ZnSe, containing intrinsic impurities and defects, by means of nonequilibrium photoconductivity, photoluminescence, and wavelength-modulated transmission spectroscopy. We have determined the energy positions of photosensitive deep acceptors with ionization energies of 0.10, 0.18, 0.23, 0.27, 0.34, and 0.47 eV, as well as of radiative and nonradiative recombination centers.