bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of ZnSe‐Based Layer Structures for Blue‐Green Laser Diodes
Authors: Pessa M. , Rakennus K. , Uusimaa P. , Savolainen P. , Salokatve A. 
Published: July 2007

AbstractThe possibilities of developing ZnSe blue‐green lasers with new materials and layer structures are studied. In particular, it is considered: (i) the use of an „inverted”︁ laser structure, n‐on‐p configuration, having p‐type barrier reduction layers of III–V compound semiconductors which are sandwiched between the substrate and the device and (ii) the use of ZnMnSSe as a cladding layer. Electronic band structures, current–voltage curves, and light–current curves are calculated for the lasers with inverted layer structures. Preliminary results of a study of ZnMnSSe layers grown by the molecular beam epitaxy method are also presented.
Semiconductor Modulators and Optical Switches
Authors: Cavenett B. C. , Wang S. Y. , Prior K. A. 
Published: July 2007

AbstractOptoelectronic devices are important for laser modulators and Q‐switches as well as in optical communication and network systems where all optical switching is required. The development of II–VI semiconductor devices fabricated by molecular beam epitaxy and based on the quantum confined Stark effect in p–i–n structures where the i‐region is a set of quantum wells is reviewed. In particular, the characterisation of ZnSe/ZnCdSe/ZnSe devices is discussed.
Recent Results on ZnSe‐Based Vertical‐Cavity Surface Emitting Lasers Operating in the Blue
Authors: Floyd P. D. , Furdyna J. K. , Luo H. , Merz J. L. , Yamada Y. , Yokogawa T. 
Published: July 2007

AbstractThe first successful operation of vertical‐cavity surface emitting lasers (VCSELs) operating in the blue is achieved using ZnSe/ZnCdSe multilayers. The vertical‐cavity resonators are constructed by depositing SiO2/SiN distributed Bragg reflectors on both sides of the active ZnSe/ZnCdSe region. Pulsed optical pumping is used to demonstrate the feasibility of this configuration. Although our first attempts at VCSEL operation required significant threshold excitation power densities (75 kW/cm2 at 2 K for lasing at 477 nm), even modest modifications in design and fabrication of subsequent structures already show substantial improvement in these figures.
Deep Etched ZnSe‐Based Nanostructures for Future Optoelectronic Applications
Authors: Bacher G. , Illing M. , Forchel A. , Hommel D. , Jobst B. , Landwehr G. 
Published: July 2007

AbstractBy electron beam lithography and a subsequent wet/dry etch process, optically active nanostructures are developed based on ZnSe with lateral extensions down to 35 nm. Dry etching using Ar+ ions is found to generate very smooth etch surfaces, while the photoluminescence efficiency of narrow wires is much higher in wet chemically etched structures. As a first application of deep etched nanostructures, index coupled distributed feedback laser structures of second order are realized with periods down to 185 nm on the base of (Cd, Zn)Se/ZnSe/(Mg, Zn) (Se, S) vertical waveguide heterostructures. A clear correlation between the resonator period and the emission wavelength is observed, indicating a high coupling coefficient of the structures. For optical pumping using a pulsed N2‐laser, the laser threshold at room temperature is about 100 kW/cm2.
Review of Compensation Centres in ZnSe:N
Authors: Prior K. A. 
Published: July 2007

AbstractOver the past few years nitrogen has been found to be by far the best dopant to use in the production of p‐type ZnSe, although it can be highly compensated. This review presents evidence for compensation within ZnSe:N due to the presence of selenium vacancy and dopant–vacancy clusters, followed by a comparison of the models which attempt to calculate the degree of compensation and then discuss evidence for the generation and motion of point defects within ZnSe:N at room temperature.
Doping Characteristics of N‐Doped p‐ZnSe and Cl‐Doped n‐ZnSe
Authors: Yao T. , Zhu Z. 
Published: July 2007

AbstractDoping characteristics of N‐doped p‐ZnSe and Cl‐doped n‐ZnSe are extensively studied by Hall measurements, CV, PL, DLTS, ICTS, and ion‐beam analysis. N forms both deep donors and acceptors in heavily N‐doped ZnSe. The lattice location of the N atoms in heavily N‐doped ZnSe is studied by ion beam channeling to get insight into the compensation mechanism. Free excitonic emission shifts to the lower energy side with N concentration, indicating a shrinkage of band gap. It is suggested that the carrier compensation mechanism in heavily Cl‐doped ZnSe is due to degradation of crystallinity. The maximum carrier concentration is greatly enhanced by selective doping of Cl.
p‐Type Doping of ZnSe. On the Properties of Nitrogen in ZnSe:N
Authors: Kurtz E. , Einfeldt S. , Nürnberger J. , Zerlauth S. , Hommel D. , Landwehr G. 
Published: July 2007

AbstractGrowth and optical properties of MBE grown ZnSe:N are investigated. Doping levels between NA – ND = 1 × 1015 to 1 × 1018 cm−3 are achieved by using either a rf or ECR plasma source for nitrogen activation. The different behaviour of the photoluminescence for both doping methods is discussed. It is shown that during the operation of the rf plasma in the high brightness mode about 5 to 8% atomic nitrogen is present in the growth chamber. Results for different optical methods are presented. This includes direct observation of the Zeeman splitting of the acceptor bound exciton and the determination of the degree of compensation by poly‐and monochromatic transmission.
Exciton Dynamics and Gain Mechanisms in Optically Pumped ZnSe‐Based Laser Structures
Authors: Gutowski J. , Diessel A. , Neukirch U. , Weckendrup D. , Behr T. , Jobst B. , Hommel D. 
Published: July 2007

AbstractAlthough lasing is meanwhile achieved in various ZnSe‐based heterostructures, the underlying mechanisms are still seriously under debate. The gain spectra of various MBE‐grown samples are measured using the variable‐stripe‐length method. A description of the gain spectra for low particle densities is possible in terms of the model of Ding et al. The responsible gain mechanism is assumed to be an induced recombination of strongly exchange‐interacting localized excitons, which, however, may be a questionable precondition. By means of time‐dependent measurements the localizing character of the active material is demonstrated. However, several indications are given that under certain circumstances more than one process contribute to lasing, in particular biexciton recombination seems to be involved in the gain mechanism.
Current Activity in CNRS‐Sophia Antipolis Regarding Wide‐Gap II–VI Materials
Authors: Faurie J. P. , Brunet P. , Morhain C. , Ongaretto C. , Tournié E. 
Published: July 2007

AbstractPreliminary results about MBE growth and characterization of ZnSe‐based alloys and multi‐quantum wells (MQW) are presented. Undoped ZnSe and Zn1−xCdxSe compounds exhibiting structural and optical properties, comparable to the best results previously published, are grown. RHEED intensity oscillations are observed during ZnSe and Zn1−xCdxSe growth. Several Zn1−xCdxSe/ZnSe MQWs are grown. RHEED intensity analysis is used to accurately control the well thicknesses. The MQWs produce very intense and sharp photoluminescence peaks. The sharpness of interfaces is confirmed by X‐ray analysis. Cl‐doped ZnSe epilayers with doping levels at 77 K ranging from 6 × 1015 to 6 × 1018 cm−3 are obtained.
On the Structure of Micro‐ and Nano‐Crystalline Semiconductors and Semimetals
Authors: Gerlach E. 
Published: July 2007

AbstractIt is shown that the size distribution of the grains of micro‐ and nanocrystalline semiconductors and semimetals can be determined from a measurement of the dynamical conductivity Re σ(Ω). Here Ω has to be larger than the plasma resonance frequency, and the average grain size must be smaller than λF/2 (λF Fermi wavelength) which is about 100 nm for an electron concentration of 1015 cm−3.
On the Pressure and Volume Dependence of the Grüneisen Parameter and Debye Temperature for NaCl Crystals
Authors: Dixit S. , Shanker J. 
Published: July 2007

AbstractAn analysis of the pressure and volume dependence of the Grüneisen parameter γ and the Debye temperature θ is presented for NaCl crystals using the model developed by Kumari and Dass. It is pointed out that the parameter q = d l γ/d ln V should be taken nearly equal to unity for predicting γ and θ at different pressures. Various thermodynamic approximations implied in the analysis are discussed.
Effect of Interface Energy Anisotropy on Thermal Stability and Transformation of Lamellar Structures. I. Behaviour of Two‐Phase Systems under Annealing as Related to Particle Shape Equilibrium
Authors: Mazurski M. I. , Salishchev G. A. 
Published: July 2007

AbstractThermodynamical regularities determining the occurrence of this or that shape of a particle and its stability at high temperatures are analyzed on the basis of a comparison of the calculated values of interface energies of sphere and disk. The thermodynamical stability of lamellar and spherical shapes is found to be determined by the level of interface energy anisotropy. Peculiarities of phase morphology changes in two‐phase systems during annealing, predicted on this basis, agree with the experimental data.
On the Effective Electron Mass in Quantum Wires of Non‐Parabolic Semiconductors under a Parallel Magnetic Field
Authors: Bhattacharyya D. , Ghatak K. P. 
Published: July 2007

AbstractThe effective electron mass at the Fermi level in quantum wires of non‐parabolic semiconductors in the presence of a parallel magnetic field is studied on the basis of a newly derived 1D‐electron dispersion law. It is found, taking n‐Hg1−xCdxTe and In1−xGaxAsyP1‐y lattice matched to InP as examples, that the effective Fermi level mass depends on the size quantum numbers in addition to the Fermi energy due to the presence of a magnetic field. The effective masses corresponding to different subbands increase with increasing electron concentration and decreasing film thickness in various ways. In addition, the corresponding well‐known results of quantum wires of wide gap materials in absence of a magnetic field are also obtained as special cases of a generalized formulation under certain limiting conditions.
Evidence for Photoinduced Hole Coupling in BaTiO3:Co
Authors: Chanussot G. 
Published: July 2007

AbstractA possible photoinduced correlation mechanism in BaTiO3:Co is described. The underlying microscopic process is a local hole photoinjection at a Co3+ site close to a preexisting metastable hole. The Jahn‐Teller field at the Co2+ site transfers this pair of holes in the next cell along the rhombic direction [111] before normal polaronic or band conduction. The spatial extension of this correlation depends on a characteristic „delocalization”︁ length. This unstable conductive state appears to be possibly frozen in a permanent way below Tc.
Apical Oxygen and Frustration Effects in CuO2 Lattice
Authors: Eid Kh. , Matlak M. , Zieliński J. 
Published: July 2007

AbstractA microscopic model for the CuO2 lattice which takes into account two orbitals of copper (3d, 3d and three orbitals of oxygen (2px, y, z) is considered. Applying the canonical transformation to eliminate the d–p hybridizations, the effective spin‐dependent Hamiltonian is derived describing superexchange interaction (SX) and Ruderman‐Kittel‐Kasuya‐Yosida (RKKY)‐type interaction. The possible role of apical oxygen degrees of freedom (β (2pz − 2px(y) hopping integral), Δ (2pz − 3d hybridization), and ε (apical oxygen energy)) for antiferromagnetic frustration effects in the CuO2 plane due to SX is investigated. The presence of an apical orbital coupled to the in‐plane copper and oxygen orbitals can effectively enhance these effects. Therefore, both these interactions (SX and RKKY) can cooperate in destroying the antiferromagnetic order in the sublattice of copper spins upon doping. It is shown that the increase of the frustration due to doping favours the formation of the superconducting state. The RKKY interaction is of ferromagnetic character. For small hole concentrations SX and RKKY integrals are of the same order of magnitude but different in sign.
Nonlinear Dynamics of Optical Switching Fronts in CdS
Authors: Schmolke R. , Schöll E. , Nägele M. , Gutowski J. 
Published: July 2007

AbstractA two‐level model for impurity‐related optical switching in lightly doped CdS crystals is developed which explains dynamical switching between a low and a high transmissivity state by a bleaching front traversing the crystal with a velocity of several 108 cm/s and offers detailed insight into the internal nonlinear spatio–temporal dynamics of the process. The predicted front is detected experimentally by a 90° pump‐and‐probe configuration. The front velocity in the experiment agrees well with the theoretical prediction.
Excitonic radiative dynamics in multiple quantum wells
Authors: Citrin D. S. 
Published: July 2007

AbstractThe fundamental intrinsic radiative process associated with excitons in semiconductor multiple quantum wells is discussed within the context of exciton polaritons. Multiple quantum wells in which each well is randomly displaced from its ideal periodic position are discussed in order to investigate the effect of disorder on excitonic radiative widths. The coherent transpori of excitons in multiple quantum wells is discussed.
Polaritons in PbI‐based self‐organized superlattices
Authors: Gippius N. A. , Mulyarov E. A. , Tikhodeev S. G. 
Published: July 2007

AbstractThe polariton reflection spectra in PbI‐based compounds – self‐organized semiconductor/insulator superlattices – for different polarizations of incoming light and within a nonlocal model for the exciton response are calculated.
On the existence of quasi‐1D quantum exciton crystals
Authors: Ivanov A. L. , Haug H. 
Published: July 2007

AbstractThe development of a ground state of the squeezed quasi‐1D system of Wannier‐Mott excitons (x) into a quantum exciton crystal (EC) is examined. This quantum EC is due to repulsive interactions between singlet x (or biexcitons). Spatial squeezing of the x‐system can be realized by the surface and interface potentials of a quasi‐1D quantum wire. Stability and melting of the quantum EC are studied both within the Lindemann and Mott criteria. The phase diagram of the squeezed quasi‐1D x‐system is proposed. According to the estimates within the Heitler‐London approximation, the quantum EC can exist for moderate x densities (1 < rs ≦ 5.5). The expected short condensation times (ps) will allow an EC formation in, e.g., GaAs/Ga1−xAlxAs quantum‐well wires with relatively short x lifetimes. At low temperatures the quantum EC favors collective, coherent emission in the form of superradiance instead of incoherent luminescence.
Physics of gain and stimulated emission in ZnSe‐based quantum well lasers
Authors: Ding J. , Kozlov V. , Kelkar P. , Salokatve A. , Nurmikko A. V. 
Published: July 2007

AbstractSpectroscopic work is reviewed which focuses on the microscopic mechanism of gain in ZnSe‐based quantum well (QW) lasers, under optical and electrical injection, respectively. In particular, the lasing process in optically pumped ZnCdSe/ZnSe QW lasers at cryogenic temperatures is shown to be entirely an excitonic process. This conclusion is supported by results from resonant pumping experiments and femtosecond pump–probe measurements. A phenomenological model is presented, which can explain the experimental observation rather well. More strikingly for this strong quasi‐two‐dimensional (2D) exciton system, recent studies on room temperature ZnCdSe/ZnSSe/ZnMgSSe diode lasers show that pairwise electron–hole Coulomb correlation remains relevant in this case as well.
Transient response of a short‐cavity semiconductor laser
Authors: Pompe G. , Rappen T. , Wehner M. , Knop F. , Wegener M. 
Published: July 2007

AbstractThe transient response of short‐cavity semiconductor lasers excited by 250 fs optical pulses is investigated. The emission is time‐ and spectrally‐resolved by an up‐conversion technique. The experimental evidence is compared with simulations employing a simple resonator model, which allow for a comparison of the energetic position, width, and intensity of the laser emission as a function of time. The time scale of the lasing process is governed by heating due to stimulated emission. Caused by the changing carrier distribution functions, inducing changes of the refractive index, the resonance frequency of the cavity experiences a rapid red shift in time, which cannot be followed adiabatically by stimulated emission. This transient mismatch qualitatively explains the observed temporal evolution of the linewidth.
Carrier dynamics and lasing in epitaxial ZnTe layers on GaAs
Authors: Majumder F. A. , Kalt H. , Klingshirn C. , Stanzl H. , Gebhardt W. 
Published: July 2007

AbstractBy means of ps‐time resolved luminescence measurements the carrier dynamics in ZnTe/GaAs epitaxial layers of different thicknesses are investigated. A linear decay process corresponding to exciton recombination at low and a quadratic process corresponding to the recombination in an electron–hole plasma (EHP) at high excitation, respectively, are observed. The decay processes are dominated by the carrier diffusion into the substrate. The lifetime, binding energy, and temperature of the plasma are extracted from the time‐resolved luminescence spectra. The carrier density found from the luminescence fit is used to describe the band‐gap renormalization effect in ZnTe/GaAs epilayers at high excitation. Laser emission from all samples is observed at low and even up to room temperatures.
Lateral quantization effects in the Luminescence of InGaAs/InP quantum wires
Authors: Forchel A. , Kieseling F. , Braun W. , Ils P. , Wang K. H. 
Published: July 2007

AbstractCw and time‐resolved luminescence spectra of InGaAs/InP quantum wires with lateral extensions down to 10 nm are investigated. The luminescence of the wires shows shift to higher energy as well as features due to transitions of up to four lateral subbands when the wire widht is reduced to less than 50nm. Time‐resolved studies with subpicosecond time resolution indicate that the typical relaxation times for resonantly excited carriers in the wires are below 10 ps. If the laser is polarized perpendicular to the wires the direct absorption in the wires is suppressed. This is used to study the population of the wires by carrier capture from the unpatterned InP sections of the wires due to lateral quantization.
Time and frequency resolved luminescence from excitonic nanostructures
Authors: Chernyak V. , Wang N. , Mukamel S. 
Published: July 2007

AbstractTime and frequency resolved luminescence spectroscopy of molecular and semiconductor nanostructures provides a direct probe for exciton transport and relaxation. A microscopic Green function theory which incorporates effects of inelastic scattering induced by exciton–phonon interactions, and elastic scattering due to static disorder is developed.
Interferometric cross‐correlation measurements of interband polarization decay in GaAs
Authors: Böhne G. , Freundt S. , Arlt S. , Pfister D. , Nácke C. , Nagerl J. S. , Ulbrich R. G. 
Published: July 2007

AbstractThe method of interferometric cross‐correlation is used to obtain precise information about the phase and amplitude of the laser pulse induced interband polarization in semiconductors. With this technique it is possible to study the linear as well as nonlinear response of a sample. The light transmitted through a thin GaAs crystal after excitation with femtosecond pulses near the band gap is measured. The phase shift between the driving laser pulses and the induced polarization is measured in the time domain. The influence of additional pump pulses on the decay of the polarization is studied. The instantaneous frequency of the polarization depends on the laser center frequency, on the pump pulse delay time, and on the relative polarization of the pump pulse with respect to the test pulse.
Non‐markovian polarization decay in semiconductor quantum wells studied by three‐beam four‐wave mixing
Authors: Löser F. , Klatt D. , Pantke K.‐H. , Leo K. , Bakker H. , Shah J. , Köhler K. 
Published: July 2007

AbstractThe polarization and population dynamics of resonantly generated excitons in GaAs/AlGaAs quantum well structures are investigated using transient three‐pulse four‐wave mixing. The decay dynamics show strongly nonexponential behavior for both variation of the delay between the first two pulses reflecting the polarization dynamics and variation of the delay between the second two pulses, which reflects the population dynamics. A comparison with a theoretical model shows that the dynamics of both polarization and population are mainly determined by frequency fluctuations and not by scattering processes or by recombination. The characteristic time of the fluctuations TC has to be energy‐dependent to fully describe the results.
Four‐wave mixing in modulation‐doped GaAs quantum wells under strong magnetic fields
Authors: Bar‐Joseph I. , Finkelstein G. , Bar‐Ad S. , Shtrikman H. , Levinson Y. 
Published: July 2007

AbstractTime‐resolved four‐wave mixing is used to study electron scattering in modulation‐doped GaAs quantum wells in high magnetic fields up to 8T. A strong increase in dephasing times in strong magnetic fields is observed and attributed to a decrease in the scattering rates relative to zero field. An early time signal in high magnetic field is found, which is due to a polarization interaction process. A strong enhancement of the signal at the absorption edge is measured which is attributed to the Fermi edge singularity.
Phase relaxation of excitons in Zn1−xCdxSe/ZnSe multiple quantum well structures
Authors: Weckendrup D. , Saschek M. , Neukirch U. , Gutowski J. , Ferreira S. O. , Sitter H. 
Published: July 2007

AbstractThe coherent dynamics of excitons in Zn1−xCdx,Se/ZnSe multiple quantum wells measured by means of spectrally integrated as well as spectrally resolved transient degenerate four‐wave mixing are reported. When simultaneously exciting the heavy‐hole and light‐hole excitons by spectrally broad femtosecond pulses a quantum beating between heavy‐ and light‐hole excitons is observed. In spectrally resolved measurements an additional contribution from the 2s heavy‐hole exciton to the four‐wave‐mixing signal occurs which dephases very rapidly. By use of narrow‐band ps pulses the energy dependence of the dephasing rate in localized heavy‐hole exciton states is investigated. The dephasing times deduced from the experimental data increase for decreasing energy up to 4 ps in deeply localized states.
Renormalization effects in dense neutral magnetoplasma photoexcited in CdTe/CdMnTe quantum wells
Authors: Tyashlov M. , Lebedev M. V. , Kulakovskii V. D. , Forchel A. , Yakovlev D. R. , Waag A. , Landwehr G. 
Published: July 2007

AbstractAn optical study of the dense neutral electron‐hole magnetoplasma is carried out in an undoped CdTe/Cd0.88Mn0.12Te quantum well in magnetic fields up to 14 T at 2 K. The renormalization of the Landau‐level transition energies is found to be qualitatively similar to that in magnetoplasmas photoexcited in the InGaAs/GaAs quantum wells, but to differ quantitatively. The difference appears due to the enhanced Coulomb interaction and electron‐phonon coupling in CdTe quantum wells.
Negative differential gap renormalization in type‐II superlattices
Authors: Langbein W. , Hallstein S. , Kalt H. , Schönherr H. P. , Nötzel R. , Ploog K. 
Published: July 2007

AbstractA quantitative determination of the band gap renormalization in type‐II GaAs/AlAs superlattices under high excitation is reported. The time‐resolved photoluminescence after intense picosecondexcitation is analyzed using a detailed luminescence lineshape fit. The renormalization of the type‐I transition is found to be comparable to that in type‐I superlat tices, whereas the type‐II transition reveals a negative differential renormalization. This is attributed by a quantitative calculation to the space‐charge effects caused by the carrier separation.