Multiple Mn2+ spin-flip Raman scattering (SFRS) in Voigt geometry was observed in self-organized disk-shaped quantum dots (QDs) of CdSe/Zn0.99Mn0.01Se, where magnetic ions and QD carriers are spatially separated and therefore the exchange interaction between them is expected to be weak. Many lines (about ten) were observed in SFRS spectra, yet the overlapping of the hole wave function with Mn2+ ions is very small, in agreement with both the absence of observable Zeeman splitting of the photoluminescence line and the calculation. Interesting polarization properties of SFRS spectra were observed which could be affected by tilting the sample out of normal alignment and changing the temperature. These polarization properties were attributed to the selection rules in SFRS in Voigt geometry. It has been found that the theoretical model suggested by Stuhler et al. [J. Cryst. Growth 159, 1001 (1996)] does not describe the SFRS spectra in systems with weak exchange interaction between charge carriers and magnetic ions. A qualitative model is suggested here for description of SFRS in such systems.

Wurtzite structure ZnMgO layers have been grown using radical-source molecular beam epitaxy on high-quality ZnO buffer layers grown on (000 1) sapphire substrates. The thickness of the ZnO buffer layers is 300 nm, with full width at half maxim of the HR-XRD (0002) rocking curves as low as 25 arcsec. In-situ Reflection High-Energy Electron Diffraction (RHEED) was employed for the optimization of the ZnMgO growth. RHEED and X-Ray Diffractometry measurements did not reveal any phase change from the wurzite structure to the rocksalt structure. The C-lattice parameter of Zn1-xMgxO films decreased from 5.209 to 5.176 angstrom with increasing x to 0.2. The surface morphology of the samples was studied with atomic force microscopy. The root mean square roughness values of 200 nm thick ZnMgO (x = 0.2) was less than 1 nm. The main photoluminescence peak of Zn1-xMgxO shifted to as high as 3.77 eV owing to the increasing Mg composition of up to x = 0.2.(c) 2007 Elsevier Ltd. All rights reserved.

Optical properties of ZnO doped with Mn and V were studied. Zn(Mn)O layers were grown by peroxide MBE, and Zn(V)O was prepared by high-dose ion implantation of bulk ZnO prepared by hydrothermal technique. The Zn(Mn)O layers containing up to 50% of Mn were characterized by high-resolution x-ray diffraction, photoluminescence, and optical absorption. A blue shift of the band edge revealed from optical absorption measurements points to the incorporation of at least a part of Mn atoms on the lattice sites. An increase in the Zn(Mn)O band gap and an enhancement of the broad below band gap absorption associated with Mn ions were observed with increasing Mn composition. Correlating structural and optical transmission data, we suggest that the band edge of Zn(Mn)O rises linearly with the amount of Mn ions substituting Zn on the lattice sites. Photoluminescence of ZnO moderately doped with Mn shows several emission lines (the strongest ones are located at 3.34 and 3.36 eV). Surprisingly, no shift in the near-band-edge emission (3.36 eV) was detected in the photo luminescence data. Photo luminescence excitation studies revealed that the near-band-edge peak and the peak centered around 3.34 eV have different origin. Most probably, the second line is due to Mn intracenter transitions. Photoluminescence studies of ZnO bulk samples implanted with V have revealed that thermal annealing at 800 degrees C restores to a large extent the optical quality of the material. A new emission line centered at 3.307 eV has been found in the photoluminescence spectrum of the highly conductive samples implanted with a V dose of 1 x 10(16) cm(-2).

physica status solidi (c)Volume 0, Issue 5 p. 1544-1547 Original Paper Exciton states and energy relaxation in ZnCdSe nano-islands A. Reznitsky, Corresponding Author A. Reznitsky alexander.reznitsky@physik.uni-karlsruhe.de Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, Germany A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaPhone: +49-721 608-7479, Fax: +49-721 608-8480Search for more papers by this authorA. Klochikhin, A. Klochikhin Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, Germany Petersburg Nuclear Physics Institute, 188350 St. Petersburg, RussiaSearch for more papers by this authorH. Priller, H. Priller Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, GermanySearch for more papers by this authorB. Dal Don, B. Dal Don Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, GermanySearch for more papers by this authorG. Schwartz, G. Schwartz Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, GermanySearch for more papers by this authorH. Zhao, H. Zhao Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, GermanySearch for more papers by this authorH. Kalt, H. Kalt Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, GermanySearch for more papers by this authorC. Klingshirn, C. Klingshirn Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, GermanySearch for more papers by this authorS. Permogorov, S. Permogorov A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaSearch for more papers by this authorL. Tenishev, L. Tenishev A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaSearch for more papers by this authorI. Sedova, I. Sedova A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaSearch for more papers by this authorS. Sorokin, S. Sorokin A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaSearch for more papers by this authorS. Ivanov, S. Ivanov A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaSearch for more papers by this author A. Reznitsky, Corresponding Author A. Reznitsky alexander.reznitsky@physik.uni-karlsruhe.de Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, Germany A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaPhone: +49-721 608-7479, Fax: +49-721 608-8480Search for more papers by this authorA. Klochikhin, A. Klochikhin Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, Germany Petersburg Nuclear Physics Institute, 188350 St. Petersburg, RussiaSearch for more papers by this authorH. Priller, H. Priller Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, GermanySearch for more papers by this authorB. Dal Don, B. Dal Don Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, GermanySearch for more papers by this authorG. Schwartz, G. Schwartz Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, GermanySearch for more papers by this authorH. Zhao, H. Zhao Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, GermanySearch for more papers by this authorH. Kalt, H. Kalt Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, GermanySearch for more papers by this authorC. Klingshirn, C. Klingshirn Institut für Angewandte Physik, Universität Karlsruhe, 76128 Karlsruhe, GermanySearch for more papers by this authorS. Permogorov, S. Permogorov A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaSearch for more papers by this authorL. Tenishev, L. Tenishev A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaSearch for more papers by this authorI. Sedova, I. Sedova A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaSearch for more papers by this authorS. Sorokin, S. Sorokin A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaSearch for more papers by this authorS. Ivanov, S. Ivanov A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaSearch for more papers by this author First published: 04 August 2003 https://doi.org/10.1002/pssc.200303227Citations: 6AboutPDF 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 Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract We suggest a new concept of exciton states in nano-islands based on the study of optical spectra, namely the temperature dependence of cw photoluminescence (PL) and PL excitation (PLE), as well as PL spectra and kinetics under ps pulsed excitation. The scheme of the exciton states in nano-islands is as follows: (I) deep spatially isolated ground states, (II) excited meta-stable states the energy relaxation rate of which strongly depends on the temperature, and (III) the states extending over the whole island size. We show that a redistribution of the population between meta-stable and ground states is responsible for the anomalous temperature shift of the PL band in QWs with islands. Citing Literature Volume0, Issue5August 2003Pages 1544-1547 RelatedInformation

We report on the photoluminescence (PL) properties of thin BeTe/ZnSe/BeTe type II quantum wells (QW's), where the Gamma electron level in ZnSe is close to the resonance with the X electron level in BeTe. The Gamma-X levels crossover modifies the nature of the interband optical transitions which are indirect in real space but direct in k space for the thick enough QW's and direct in real space but indirect in k space for the QW's thinner than 2-3 monolayers. Approaching the crossover condition from the side of thicker QW's leads to a thresholdlike quenching and spectral narrowing of the PL band. The latter effect can be explained taking into account the inhomogeneous broadening of the Gamma electron level.

We have studied photoluminescence (PL), PL excitation (PLE), and micro-PL spectra of single quantum wells (QWs) formed by CdSe insertions in ZnSe matrix with different nominal Cd thickness (1-3 monolayers (ML)). The PL spectra are considerably red-shifted with respect to the position expected for homogeneous Cd distribution over the QW and can be attributed to the luminescence of CdSe-ricli islands. It has been found that PLE spectra of different points of the PL band show a characteristic divergence at excitation below some characteristic energy E-ME. This energy is identified with the percolation threshold above which the exciton is able to move over the whole lateral plane of QW whereas below the EME only a resonant excitation of island related states is possible.

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Parameters of a microrelief of poly(ethyleneterephthalate) (PET) 0.7 mm thick and poly(methylmethacrylate) (PMMA) 1.0 min thick films with a hard platinum covering are studied. The technology of manufacturing the PET substrates with the microrelief is optimized. The birefringence and transmission of the substrates in dependence on their elongation are measured. The possibility of their use as diffraction gratings, scattering and other optical elements for displays is discussed.

We have studied the localization of two-dimensional exciton states in II–VI heterostructures by compositional fluctuations of solid solution, forming the quantum well. It is shown that due to the two-dimensional character of exciton motion in quantum wells, the effect of compositional fluctuation on exciton states is much stronger than in three-dimensional solutions of the same composition. The method for calculation of the density of fluctuation states below the edge of two-dimensional exciton band and the spectral density of exciton transitions is developed. The classification of states with respect to its migration properties and contribution to the luminescence processes has been carried out using the continuum percolation theory. As a result, the shape of emission band, its relative shift with respect to absorption band and the position of mobility edge are calculated. The results of calculations are in good agreement with the experimental PL and PLE spectra of ZnSe superlattices with submonolayer insertions of CdSe.

Absorption and luminescence of the quantum wells formed by the (Zn-Cd)Se and (Ga-In)As solid solutions are studied in the range of exciton size-quantization ground state. The spectra observed are described by a model assuming the two-dimensional character of fluctuation states in quantum wells and the presence of a percolation threshold within the absorption contour.

We focus on several aspects of our recent optimization of Beryllium-containing ZnSe-based laser diodes. By passivating the GaAs surface with a BeTe buffer, defect densities below 104cm−2 can be achieved. Structures with BeZnSe–ZnSe-strained layer superlattices in the waveguide regions show T0 values of 366K at room temperature and, consequently, laser operation up to 140°C due to an efficient electrical confinement by the superlattice waveguide. In order to circumvent the limitation concerning the band gap (<2.85eV) of the p-type claddings, the p-type doping of BeMgZnSe/BeTe short period superlattices has been investigated. The insertion of BeTe fractional monolayers is shown to increase the p-type doping beyond the limits usually set by compensation in high band gap BeMgZnSe. Theoretical calculations indicate that an asymmetric design of the band gap of the cladding layers can reduce current overflow and also enable blue emission with the Beryllium-based material system.

Peculiarities of migration-enhanced epitaxy of CdSe fractional monolayers in a ZnSe matrix are studied using photoluminescence (PL) and transmission electron microscopy (TEM) techniques. Dependencies of Cd incorporation coefficient on Se/Cd flux ratio as well as on the temperature are discussed. The critical Cd coverage of growth surface per cycle is established by PL to be of 0.5ML at 280°C and depends on substrate temperature. The excess of Cd deposited is suggested to accumulate in CdSe-based nanoscale islands (∼30nm in diameter) formed at sites of the growth surface imperfections like point and extended defects, which is confirmed by plan-view TEM measurements.

We report on a GaAs/AlAs, wide-miniband, superlattice autocorrelator for picosecond THz radiation pulses (operated at room temperature); the autocorrelator is based on the THz radiation-induced reduction of current through the superlattice. THz radiation (frequency 7.2 THz) from the FELIX (free-electron laser for infrared experiments) was coupled into the superlattice with an antenna system. We measured the current reduction for two time-delayed pulses and found that the signal decreased when the time delay was smaller than the pulse duration. With this superlattice autocorrelator we were able to resolve laser pulses that had a duration of a few picoseconds.

Room-temperature optically pumped (Zn,Mg) (S,Se)/(Zn,Cd)Se laser structures have been grown by molecular beam epitaxy. Using of alternatively-strained short-period superlattice waveguide results in low threshold power density values over the whole blue-green (470-520 nm)wavelength range. Incorporation of CdSe fractional monolayer active region provides more than fourfold further decrease in threshold with respect to quantum well laser structure. Optical and structural properties of laser structure with 2.8 monolayer CdSe are discussed in detail.

We report on millimeter wave generation with a superlattice electronic device (SLED) operated at room temperature. The SLED, containing a wide-miniband GaAs/AlAs superlattice, had a quasi planar structure with two terminals lying in one plane. The device showed a negative differential conductance, due to Bloch oscillations of the miniband electrons. The SLED, mounted into a waveguide, delivered radiation in the 50 to 60GHz range, with a maximum power (400μW) corresponding to an efficiency of 1%. Additionally, harmonic radiation up to frequencies above 200GHz was observed. We associate the generation of radiation with current oscillation caused by traveling dipole domains. We also present an analysis, taking elastic and inelastic scattering into account, of the miniband electrons, indicating that our SLED should, in principle, be suitable for generation of radiation up to 1THz.

Three main stages of the intrinsic morphology transformation of MBE grown CdSe fractional monolayers in ZnSe with increase in their nominal thickness w in the 0.1-3.0 monolayer range were found using both structural and optical characterization techniques. Emergence of the extended (15-30 nm) CdSe-enriched quantum-dot-like pseudomorphic islands at w > 0.7 monolayer with the density increasing up to 2.5 x 10(10) cm(-2) at w = 2.8 monolayer is clearly displayed in the optical properties of CdSe fractional monolayer nanostructures. The below critical thickness CdSe fractional monolayers having extremely high quantum efficiency can be very perspective as an active region of ZnSe-based blue-green lasers.

The main stages of the intrinsic morphology transformation of MBE and MEE grown CdSe/ZnSe fractional monolayers (FMs) have been investigated by transmission electron microscopy (TEM). The FM morphology evolution is studied as a function of the FM nominal thickness in the range of 0.1-2.8 hit. Emergence of self-organized extended (15-30 nm) CdSe-based pseudomorphic islands is observed in the plan-view TEM images of FMs with a nominal thickness above 0.7 ML. A comparative analysis of the MEE and MBE grown structures has shown that in the case of MEE mode the FM morphology is more homogeneous, (C) 1998 Elsevier Science S.A. All rights reserved.

We report on a semiconductor superlattice oscillator for generation of millimeter waves (frequency 65 GHz). The main element of the oscillator is a doped short-period GaAs/AlAs superlattice with negative differential conductance. The oscillator is due to current oscillations caused by charge density domains. The oscillator delivered, at an efficiency of 0.2% for the conversion of electrical power to radiation power, a power of 100 μW in a bandwidth of the order of 200 kHz.

We report on experimental study of relative incorporation behaviour of Cd and Zn in MBE of ZnCdSe at different VI/II flux ratio conditions. Their incorporation coefficient (IC) values at VI/II = 1 : 1 (αCd0 and αZn0) are derived. Effect of Mg flux on sulphur IC in ZnMgSSe alloys, grown at different Mg flux intensities and substrate temperatures (Ts) under VI/II = 1 : 1 stoichiometric conditions is also investigated. The higher Mg flux is shown to increase efficiently the S IC in ZnMgSSe up to 30% with respect to that for ZnSSe growth due to a high binding energy between S and Mg, whereas no influence of Ts on the MgS interaction is observed.