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The Sun’s activity has been evolving in the ascending phase of Solar Cycle 23 since 1996. Similarly, the research on solar activity is also in the ascending phase of a new active period. Numerous new results have been obtained from a large amount of space and ground observations covering a wide spectral range. In particular, observations with YOHKOH, SOHO, and TRACE have revealed a multitude of phenomena and processes in the solar atmosphere which provide us a new picture of the Sun.
Within the Herschel key project “The Warm And Dense ISM” (WADI) we systematically observe
a number of prominent photon-dominated regions (PDRs) to measure the impact of varying UV
fields on the energy balance, the chemical and dynamical structure of heated molecular
Spatially resolved resistivity measurements of CdTe crystals doped with Titanium (Ti) and Vanadium (V) were performed. From the temperature dependence of the resistivity the spatial variation of the thermal activation energy was deduced. Variations in axial as well as radial direction were observed and qualitatively explained by a combined segregation and compensation model. It is based on the deep donor levels of Ti and V at 0.95 eV below the conduction band.
Cd1-xZnxTe ZriTe crystals grown by the travelling heater methode (THM) have been investigated by low temperature photoluminescence (PL). The excitonic energy gap as a function of the alloy composition was determined for the complete range of x - 0 to x - 1. The composition dependent broadening of the neutral acceptor bound exciton (A°X) line was measured and compared to theoretical calculations. The Donor - Acceptor pair luminescence in the crystals is a superposition of recombinations due to residual Cu acceptors and A - centers (anion vacancy - donor pairs ).
An overview of SiGe-based, modulation doped heterostructures is given. Strained layer handling, a prerequisite for realizing both n- and p-type devices, Is treated in terms of band engineering. The main emphasis is put on recent results obtained with high-electron mobility n-type Si/SiGe structures. Hall, Shubnikov-deHaas, and cyclotron resonance measurements are presented. The thermal stability of the heterostructures and the dopant distribution are treated with respect to device applications. Room temperature and 77K dc-measurements on very recent modulation doped field effect transistor (MODFET) implementations using implanted source/drain contacts are discussed. Device concepts with n- and p-type MODFETs combined in a superior complementary layout (CMODFET) are proposed.
Deep levels have a great influence on the recombination behavior of the free carriers in semiconductors. For several years PICTS has been used to investigate the deep levels in high resistivity material such as GaAs or CdTe used in detector applications. An important feature of the PICTS measurements is the analysis of the current transients after pulse excitation. We propose using a new method based on Tikhonov regularization. This method was implemented in the program FTIKREG (Fast Tikhonov Regularization) by one of the authors. The superior resolution of the regularization method in comparison to conventional techniques is shown using simulated data. Moreover, the method is applied to investigate deep levels in CdTe:Cl, SI-GaAs and GaAs:Cr samples used for room temperature radiation detectors. A relation between deep level properties and detector performance is proposed.
Impedance or admittance spectroscopy has been shown to be a very convenient tool for the investigation of deep levels in semiconductor junctions. At constant temperature a frequency sweep is performed. After that the impedance signal is analysed by a regularization method based on Tikhonov regularization in order to obtain the thermal relaxation times of the deep levels present in the junction. The high resolution of the regularization method in comparison to conventional techniques is demonstrated using simulated data. The temperature dependence of the thermal relaxation times provides information about the properties of the deep levels such as activation energy or capture cross section. Two donor levels with activation energies dE1 =0.58 eV and dE2 =0.68 eV are observed in our detector diodes. It can be shown that the concentration of level 2 is increased after irradiation.
A pressure controlled vapor source was developed for the gas source doping of (Hg,Cd)Te alloys. The dopant source has been subjected to extensive tests, and the flow characteristics determined. The dopant source was used to control the flow rates of ethyliodide for the n-type doping of CdTe. Highly conductive CdTe:l films were grown by molecular beam epitaxy.
In this paper we present a short review of statistical properties
of extrasolar planets, and of the core-accretion model and some of its
extensions. We also present results of population synthesis models
based on extended core-accretion planet formation models
(taking into account disk structure and evolution and migration
of the protoplanet, see Alibert et al. 2005a).
The population synthesis is carried out by calculating
the evolution of many disk-protoplanet
systems, assuming initial conditions (in particular
disk mass, disk lifetime and metallicity of the system)
taken from observations. Taking into account the
observational bias introduced by radial velocity surveys,
we statistically compare the results of our
models and the population of known extrasolar
planets. We show that our models are able to quantitatively reproduce the
mass and semimajor axes
of extrasolar planets around solar type
stars. Finally, we discuss the effect of the mass of the central star on the planet
formation process and on the final planetary population.
Observations using the HIFI and PACS instruments aboard the Herschel
satellite provide a unique way to study the chemical inventory,
the dynamics, and the energy balance in dense interstellar clouds heated by
UV radiation. We propose a comprehensive observing program to reveal
the details of the interaction of massive young stars with their
parental molecular clouds.
CdTe:Zn:V crystals grown by the seeded Bridgman method in microgravity conditions during the STS95-Spacelab-AGHF-1 mission and in the ground laboratory (l-g) were analyzed and compared. The results obtained clearly show that the structural quality of the space crystal is better. Density of inclusions, concentration of dislocations, and presence of stresses are lower in the microgravity-grown (μ-g) crystal. The l-g crystal contains twins and grains from the beginning of the growth process, that is, from the near-seed region. In general, the concentration of inclusions and amount of segregated impurities on the l-g crystal are larger than in the μ-g crystal. X-ray rocking curves and low-temperature photoluminescence spectra demonstrate the relatively high quality of both crystals on a microscale at the beginning of the growth and show that the l-g conditions were worse at the end. The results of this investigation demonstrate a positive role of contactless growth and μ-g conditions in the melt in suppressing the creation of inclusions and dislocations.
Morphology and analysis of composition of inclusions were done by secondary electron microscopy and spatially resolved energy-dispersive analysis of x-ray on semiintrinsic CdTe:Cl and CdTe:Zn:Cl crystals grown from the vapor phase by the modified Markov technique and on undoped CdTe crystals grown from the melt by the Bridgman method. In CdTe:Cl and CdTe:Zn:Cl crystals nonstoichiometric inclusions of about 10–20 μm were found, which contain high concentrations of Cl and Na impurities. The Cl is concentrated in small precipitates of 1–2 μm inside these inclusions. After short-time low-temperature annealing (600 °C), the inclusions mostly disappeared.
A reinvestigation of the phase diagram of the Cu–In–Se system along the quasi-binary
cut In2Se3–Cu2Se reveals an existence range of the chalcopyrite
α-phase that is much narrower than commonly accepted. The presence of 0.1% of
Na or replacement of In by Ga at the at.% level widens the existence range of the
α-phase, towards In- and Ga-rich compositions. We also investigate the
interplay between phase segregation and junction formation in polycrystalline
Cu(In, Ga)Se2 films. Here, we attribute the band bending observed at bare surfaces
of the films to a positively charged surface acting as a driving force for the
formation of a Cu-poor surface defect layer via Cu-electromigration. The
electrical properties of this defect layer are different from those found for the
bulk β-phase. We suggest that Cu-depletion is self-limited at the observed
In/(In+Cu) surface composition of 0.75 because further Cu-depletion would require a
structural transformation. Capacitance measurements reveal two types of junction
metastabilities: one resulting from local defect relaxation, invoked to explain a
light-induced increase of the open-circuit voltage of Cu(In, Ga)Se2 solar cells,
and one due to Cu-electromigration.
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