bluuebunny/crossref_metadata_2025_split huggingface dataset:
Peculiarities of the quantisation of the energy spectrum of gapless semiconductors in a magnetic field under space confinement
Authors: Germanenko A. V. , Minkov G. M. , Rumyantsev E. L. , Rut O. E. 
Published: May 2005

AbstractAn exact solution for the zero boundary condition of the problem of carriers in spatially confined gapless semiconductors in a magnetic field is presented. Three cases are analysed: (i) the semiconductor occupies a half‐space and the magnetic field orientatin is H ⟂ n (n is the surface normal); (ii) and (iii) a film of a gapless semiconductor at two orientations of the magnetic field, i.e. H ⟂ n and H | n respectively. It is shown that since the energy spectrum of gapless semiconductors is formed by strong relativistic spin–orbit interaction, significant peculiarities of the quantisation of the electron energy spectrum occur in all cases considered. Experiments to check the results obtained are discussed.
Anisotropy of dissolution and microrelief of II–VI semiconductor compound surfaces
Authors: Yablonskii G. P. 
Published: May 2005

AbstractThe shape, crystallographic orientation and size of microrelief elements of various surfaces of CdS, ZnSe and ZnO monocrystals after chemical etching have been studied. When illuminated with a focused laser beam, the microrelief creates a symmetric light pattern, or light figures, on the opposite surface whose shape corresponds to the crystal symmetry.The effects of the dissoltion rate and etching time on the form, size and angles of the microrelief elements in the temperature interval from 263 to 333 K were investigated. During etching, laser light was also used to convert the process of selective etching into a polishing process. To elucidate the relationship between the crystallographic orientation of the microrelief elements and the dissolution anisotropy, mean etching rates were determined and polar diagrams of resistance to dissolution were constructed for {1120} and {0001} by the Gross method. The relation between the kinetics of dissolution and the structure of the chemical bonds is discussed.The light figures formed by the surface microrelief enabled us to carry out the approximate orientation of semiconductor planes and solid samples. In the early stages of dissolution one may determine the density and distribution of the microscopic etch pits. The microrelief created on the side surfaces and the ‘fully reflected’ mirrors of II–VI semiconductor lasers pumped by electron beam or optical radiation promote the multiple enhancement of laser power and efficiency.
Stimulated emission in ZnSxSe1 − x/ZnSe heterostructures grown by MOVPE
Authors: Nägele M. , Weckendrup D. , Neukirch U. , Gutowski J. , Geyzers K. P. , Heuken M. 
Published: May 2005

AbstractNon‐linear and stimulated emission of ZnSxSe1 − x/ZnSe multilayer structures grown by MOVPE on GaAs is investigated by means of high‐density excitation spectroscopy using a high‐resolution pulsed excimer‐dye laser system as well as a picosecond titanium–sapphire laser for time‐resolved measurements. Heterostructures with ZnSe layers or single and multiple quantum wells were grown in which the ZnSe layer widths were varied between 1 nm (strong quantum confinement) and 500 nm (quasi‐bulk situation). The sulphur concentration in the ZnSxSe1 − x buffer, barrier and cap layers was chosen between x = 0.045 and x = 0.74 in order to find the most promising compromise with regard to maximum band offset to ZnSe for most efficient carrier confinement and suitable waveguiding properties depending on variation in the refractive index, and to highest structural quality of the actively emitting ZnSe layers. Stimulated emission is found to occur in all samples, being brightest in the sample with the lowest sulphur concentration in the cap and barrier layers. Its dynamical properties point to a probable interpretation in terms of electron–hole plasma creation, which, however, may not be the basic process in narrow‐quantum wells or strongly structurally disturbed samples.
Experimental and theoretical aspects of electrical characteristics of Au/ZnSe/GaAs heterostructures
Authors: Martinez R. , Schmeits M. , Evrard R. 
Published: May 2005

AbstractWe present results of a theoretical and experimental study of AuZnSeGaAs heterostructures. In the theoretical part we report the band diagrams, charge densities and static I–V curves obtained from a detailed numerical analysis. In the experimental part we give the results for the static I–V curves and frequency‐dependent admittance and impedance at different bias voltages for an AuZnSeGaAs heterostructure with a ZnSe layer of 2.75 μm thickness. An explicit analysis of the data shows that the system can be represented by an equivalent circuit of two RC elements in series corresponding to the ZnSeGaAs and AuSe heterojunctions.
Luminescence dynamics of CdSe quantum dots
Authors: Wind O. , Kalt H. , Woggon U. , Klingshirn C. 
Published: May 2005

AbstractWe present results of time‐resolved luminescence measurements of CdSe quantum dots embedded in glass with radii around 20 Å using intense picosecond excitation resonant into the first excited hole state of a photodarkened sample. Distinct luminescence bands with different spectral widths and positions are found. Their decay on nano‐ and subnanosecond time scales reflects three different relaxation processes. The fastest luminescence component is discussed in terms of the direct recombination of the excited electron–hole pair, the slower components as being due to the recombination from surface‐related states.
Origin of the stokes shift in semiconductor quantum wells
Authors: Hagston W. E. , Harrison P. , Stirner T. 
Published: May 2005

AbstractExcitonic energy levels have been calculated in CdTe quantum wells with Cd1−xMnxTe barriers. It has been shown that the introduction of small‐scale (relative to the exciton Bohr radius) interface disorder, which either preserves or breaks the inversion symmetry, can produce appreciable Stokes shifts between optical absorption and emission and that the associated line‐widths can remain narrow. A criterion for the existence of high‐quality interfaces, based on optical spectra, is described.
Laser processes in wide gap II–VI semiconductors
Authors: Klingshirn C. 
Published: May 2005

AbstractAfter a brief historical remark about the evolution of scientific interest in wide gap II–VI compounds, we review the various laser processes which have been identified in bulk materials and thin layers during the last 25 years. We then proceed to quantum wells and superlattices and stress the differences from III–V compounds. We finish by considering the exploitation of specific properties of widegap II–VI compounds for light‐emitting and laser diodes.
The role of ZnS in ZnS/SrS:Ce,Cl multilayered TFEL devices
Authors: Velthaus K. O. , Mauch R. H. , Schock H. W. 
Published: May 2005

AbstractDifferent ZnS/SrS:Ce,Cl multilayered electroluminescent devices have been prepared by a multisource deposition method. The highest luminance achieved in this investigation is 1540 cd m−2 at 1 kHz using a stack of nine alternating layers of ZnS and SrS:Ce,Cl; the highest luminance in the blue exceeds 14 cd m−2 at 60 Hz, 50 μs pulse excitation. The influence of the ZnS thickness on device performance and stability has been investigated. The electrical and optical behaviour of standard and multilayered devices in time‐resolved measurements is compared.
Dynamical aspects of free exciton–magnetic polaron formation in CdTe–Cd1 − xMnxTe quantum wells
Authors: Goodwin J. P. , Hagston W. E. , Harrison P. , Stirner T. 
Published: May 2005

AbstractCalculations of the energies of magnetic polarons formed by free excitons localised in non‐magnetic CdTe wells next to magnetic Cd1 − xMnxTe barriers are presented. A comparison with recent time‐resolved spectroscopy results allows insight to the physical aspects governing the dynamics of the formation of the polarons. It is shown that the experimentally measured energy shift is not the polaron energy itself but the difference between this and the change in the exciton binding energy. The latter is calculated within the envelope function approximation and by employing a variational technique. The polaron energy calculation uses a modified version of an approach described by Wolff.The results show that static polaron calculations are not generally reliable and that the exciton–magnetic polaron has to be viewed as a dynamically evolving complex. It is initially energetically favourable for the exciton–magnetic polaron complex to increase its spatial localisation, since the gains in polarisation energy exceed the loss in exciton binding energy. However, thermodynamic considerations suggest that in general saturation of the magnetic ions will not occur.
Spin‐polarised tunnelling current in metal–insulator–gapless semiconductor structures in a magnetic field
Authors: Germanenko A. V. , Kruzhaev V. V. , Minkov G. M. , Rumyantsev E. L. , Rut O. E. 
Published: May 2005

AbstractExperimental investigations of tunnelling conductivity oscillations of metal–insulator–gapless semiconductor structures are performed. For the orientation of the magnetic field H | n (n is normal to the structure plane) a splitting of the oscillation maxima of the tunnelling conductivity due to the spin splitting of the Landau levels is observed. It is revealed that when the magnetic field turns away from this direction the amplitudes of the low‐bias maxima decrease monotonously, and at H ⟂ n oscillations corresponding to tunnelling into one spin state only are observed. A theoretical analysis shows that this is caused by an unusual behaviour of the electron wavefunctions near the surface of gapless semiconductors in an applied magnetic field.
Photoluminescence and efficiency of Ce3+ in SrS powders
Authors: Hüttl B. , Müller G. O. , Mach R. , Fouassier C. , Benalloul P. 
Published: May 2005

AbstractThe luminescence efficiency of SrS: Ce powders in the doping range from 0.01 to 1.0 at.% was investigated by photoluminescence decay studies. The radiative decay time of Ce3+ in SrS was determined to be 27 ns. The onset of concentration quenching at concentrations higher than about 0.7 at.% has been obtained. The photoluminescence spectrum of Ce3+ exhibits two emission bands as a consequence of the ground state splitting. The Huang–Rhys factor of the 5d‐4f transition was estimated to be about 6. The inhomogeneous broadening of the emission band of samples with higher doping level has been investigated by site‐selective and time‐resolved spectroscopy.
Free exciton absorption in zinc selenide
Authors: Zheng Jia‐Zhen , Allen J. W. 
Published: May 2005

AbstractWe have measured the absorption spectrum of the n = 1 free exciton in ZnSe from 4.2 to 190 K. By fitting to a Lorentzian, we have found the exciton peak energy, width and oscillator strength. The values are compared with published ones, which were mainly obtained by less direct methods. The importance of the electron–hole interaction in radiative processes in ZnSe is emphasised.
Homogeneious linewidth and relaxation of excited hole states in II–VI quantum dots
Authors: Woggon U. , Gaponenko S. V. , Uhrig A. , Langbein W. , Klingshirn C. 
Published: May 2005

AbstractBy use of differential absorption spectroscopy at different temperatures we investigate the homogeneous line broadening of small CdSxSe1 − x quantum dots embedded in glass. Our experiments show the strong correlation between the precipitation stages and characteristics optical parameters such as the saturation intensity and the longitudinal and transverse relaxation times. In samples grown in the diffusion‐controlled regime to avoid coalescence, we find after strong laser excitation for the first time spectrally narrow holes in the non‐linear differential absorption spectra. These sharp non‐linear resonances with a halfwidth Γ of only 10 meV at T = 20 K allow us to investigate the energetic distance of the lowest hole levels and the temperature dependence of the line broadening. The different contributions of LO phonon coupling and temperature‐independent scattering to the homogeneous linewidth will be analysed. The relaxation from the excited hole states has been investigated by exciting in the higher‐energy hole states and measuring the resulting change in the ground state absorption.
Tackling problems in the growth of ZnS/Se through precursor design
Authors: Foster Douglas F. , Patterson Ian L. J. , James Linda D. , Cole‐Hamilton David J. , Armitage David N. , Yates Heather M. , Wright Andrew C. , Williams John O. 
Published: May 2005

AbstractA variety of problems in the growth of wide band gap II/VI materials by MOVPE has been addressed by the use of alternative precursors. The quality of grown layers of ZnSe has been greatly improved by adduct purification of Me2Zn. Using 4,4′‐bipyridyl, the recovery of Me2Zn is variable because of the insolubility of 4,4′‐bipyridyl in diethylether. Higher yields can be obtained using the ether‐soluble base 1,3‐bis(4‐pyridyl)propane.tBuSH has been introduced for the growth of ZnS. Being a liquid, this compound is easy to handle and it allows growth of high‐quality ZnS at temperatures down to 325°C with very little gas phase pre‐reaction with Me2Zn. Growth of ZnSxSe1 − x at atmospheric pressure using H2S and Et2Se as the group 16 precursors allows excellent stoichiometric control, since the ratio of S : Se in the grown solid is similar to that of H2S : Et2Se in the gas phase for all compositions. Finally, multilayer structures have been grown at low pressure with excellent interface abruptness and goodquality material. However, the ternary layers are all much higher in sulphur than expected from the gas phase composition and the composition of the ternary appears to be influenced by the nature of the surface on which it is growing.
Mixed alkyl zinc or cadmium complexes with dialkyl thio‐ or selenocarbamates: Precursors for cadmium chalcogenides
Authors: Malik M. Azad , O'Brien Paul 
Published: May 2005

AbstractA series of new compounds [RME2CNR′2]2 (R and R′ are various alkyl groups, e.g. M  Zn or Cd, R  Me, R′  Et) have been synthesised and characterised. The compounds can be used as single molecular precursors for the deposition of the corresponding binary chalcogenides. In the present paper the range of compounds synthesised and their uses are reviewed. Preliminary observations on the deposition of thin films on glass and GaAs(100) substrates are reported.
Effects of rapid thermal annealing on the electrical properties of Hg1 − xCdxTe bulk crystals
Authors: Rubio J. A. López , Sangrador J. , Rodríguez T. 
Published: May 2005

AbstractThis paper reports the change in the bulk transport properties of p‐type MCT samples induced by a rapid thermal annealing (RTA) process. This change is produced homogeneously within the crystal without interchange of mercury with the surrounding atmosphere. The carrier concentration varies towards an equilibrium value that depends only on the annealing temperature. For the material and temperatures investigated (250–420°C) the equilibrium carrier concentration depends exponentially on the inverse of the temperature, its value ranges between 1 × 1017 and 4 × 1017 cm−3. The time needed to reach equilibrium is a function of the temperature, varying from 10 s at 420°C to 200 s at 250°C. The hole mobility is also affected by the RTA process, its evolution being a function of the process temperature and time. A model is proposed to explain these modifications based on a reaction of generation‐annhilitation of mercury vacancies and interstitials that would take place within the crystal with no external interaction.
High‐resolution scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) of ZnSxSe1 − x/ZnSe Quantum Wells
Authors: Bollig B. , Geyzers K. P. , Heuken M. 
Published: May 2005

AbstractEpitaxial growth techniques for ZnSxSe1 − x/ZnSe heterostructures have already achieved a high degree of development. Further improvements strongly require characterisation techniques with high compositional sensitivity and high spatial resolution. Therefore in this work high‐resolution Z‐contrast, which provides compositional information down to the atomic scale, has been used for the first time to characterise ZnSxSe1 − x/ZnSe quantum well structures. The influence of structural defects on Z‐contrast is demonstrated by comparison of scanning transmission electron microscopy (STEM) bright field images and STEM Z‐contrast micrographs of planar defects and dislocations. The compositional abruptness of ZnSxSe1 − x/ZnSe interfaces in MOVPE‐grown quantum well (QW) structures is judged from high‐resolution Z‐contrast micrographs. Electron energy loss spectroscopy (EELS) measurements were performed for the first time in ZnSxSe1 − x/ZnSe QW structures in order to obtain quantitative compositional information with nanometre spatial resolution. From EELS line scans, which monitor the selenium concentration across ZnSe QWs, the obtainable spatial resolution is estimated to be about 1–2 nm. The problems that have prevented quantitative analysis of the selenium concentration up to now are discussed.
Radiative efficiencies and deep levels in zinc selenide
Authors: Allen J. W. 
Published: May 2005

AbstractAlthough zinc selenide and related materials are promising for blue light‐emitting diodes and lasers, present performance is unsatisfactory. The blue radiative efficiency at room temperature is low and the decay time of luminescence is correspondingly short. It is argued that the problem is non‐radiative recombination by the Hall–Shockley–Read mechanism at deep levels and that the concentration of these levels must be high. Experimental evidence for the existence of such levels is presented. Characterisation and control of deep levels will be essential for progress in this area.
Plasma‐enhanced MOVPE and nitrogen doping of ZnSe
Authors: Taudt W. , Hermans J. , Schneider A. , Woitok J. , Geurts J. , Heuken M. 
Published: May 2005

AbstractIn order to obtain high quality Znse epilayers on GaAs which can be intentionally P‐ and n‐type doped growth at a reduced temperature is highly desirable. Therefore in this work the suitability of diallylselenide and the influrnce of plasma precracking have ben investigated. Photoluminesscence, Raman spectroscopy, scanning electron microscopy, X‐ray, SIMS and Hall measurements were used to anaylse the samples. The selenium precursor was fully decomposed at temperatures above 360°C if it was precracked by a plasma. Bound excitions could be resolved with negligible donor–acceptor pair (DAP) and copper green emission in the PL spectra form films which were grown with a plasma at temperatures beyond 530°C. Clearly the hpe for reduction in the deposition temperature was not achieved. Raman spectra also revealed strong crystalline quality variations. For the doping experiments nitrogen was used as the carrier gasa instead of hydrogen. Plasma cracking of the selenium precursor was still necessary. Thye substitution of the H2 carrier gas by nitrogen reduced the growth rate by a factor of 2.6 but enhanced the crystalline properties of the samples as shown by the Raman measurements. Strong DAP emission at 2.7eV in the (PL) spectra was observed. SIMS measurements showed a nitrogend concertration of about 3 × 1017 cm−3. An additional nirtogen plasama (0–7W) had a begligible effect on the nitrogen concentration in the sample. The samples were semi‐insulating, whichmight be a conswquence of the crystalline quality of ZnSe grown with DASe as selenium precursor.
A comparison of the diffusion of copper, gallium and cadmium in cadmium telluride
Authors: Jones E. D. , Stewart N. M. , Mullin J. B. 
Published: May 2005

AbstractThe rates of diffusion of both Ga and Cu in CdTe have been measured over the temperature ranges 350–820 and 200–400°C respectively and the results are compared with the self‐diffusion of Cd (350–920°C).In the case of the Cd self‐diffusion the Arrhenius graph showed two active diffusion mechanisms, one dominating above 500°C and the other below. It suggested that in the temperature range 500–800°C the main defect responsible for diffusion was Cd, with a significant contribution at lower temperatures from the associated defect of the form (CdiVcd)x Below 500°C another mechanism predominated which was possibly due to residual impurities.The results for the diffusions were in close agreement with those obtained by other workers. The Ga diffusions showed a complex behaviour which suggested that two mechanisms were active simultaneously, one independent of Cd partial pressure and the other decreasing with increasing Cd partial pressure.It was concluded that CdTe would be suitable as a diffusion barrier to protect HgxCd1 − xTe devices from Ga contamination from GaAs substrates but would not be efficient at reducing Cu contamination from the substrate in the device.
Recombination dynamics of dense elctron–hole plasma in CdS‐doped glasses
Authors: Juršėnas S. , Žukauskas A. , Strumskis M. , Ekimov A. I. 
Published: May 2005

AbstractTime‐resolved luminescence spectra of highly excited CdS‐microcrystallites are studied at room temperature in relation to the hot electron–hole plasma (EHP) effect. When the EHP thermalization is complete the luminescence kinetics shows a steady increase in the recombination rate with decreasing microcrystallite average radius (from 1000 Å to 54 Å). The obtained size dpendence is attributed to surface recombination.
Electrical and optical properties of the transition metal iron in ZnTe and CdTe
Authors: Lechner H. , Hofmann D. M. , Meyer B. K. , Azoulay M. , Krambrock K. , Spaeth J.‐M. , Döornen A. , Kaufmann B. , Omling P. , Salk M. , Benz K. W. 
Published: May 2005

AbstractWe present results of electron paramagnetic resonance (EPR) and optical spectroscopy on different charge states of the transition metal impurity iron in ZnTe and CdTe. We identify the energy level position of the Fe+ acceptor in ZnTe at Ev + 1.7eV and estimate its position in CdTe. Ionisation transitions from Fe+to the conduction and valence bands ar found in both absorption spectroscopy and photo‐EPR. Optical intra‐defect tracsitions from Fe+ to crystalfield‐split excited states ar resolved for the first time. This assignment to Fe2+ is based on optically detected EPR. Application of both far‐infrared Fourier transform and EPR spectroscopy allows the determination of the total iron concentration in all charge states.
Comparison of two approaches to forced convection in crystal growth of II–VI compounds by THM
Authors: Bloedner R. U. , Presia M. , Gille P. 
Published: May 2005

AbstractHg1 − xCdxTe and Cd1 − xZnxTe single crystals were grown by the tracwelling heater method (THM), applying two different techniques of artificially stirring the solution zone. Accelerated crucible rotation (ACRT) was used in a vertical growth arrangement and compared a technique with constant rotation around the horizontal axis of the ampoule. The dominant hydrodynamic mechanisms of noth methods are discribed by the rotating disc model and are suggested to be almost identical with respect to the growth conditions at the interface. Convective flow is effectively enhanced adhacent to the growing crystal, where the matter transport is regarded as the rate‐limiting step of solution growth. Inclusion density analysis by IR microscopy was used to characterise the crystals of Cd1 − xZnxTe grown at different rates. It was shown that forced convection allows an increase in the crystal growth rate from a few mm day−1 with ACRT or horizontally rotating THM.