bluuebunny/crossref_metadata_2025_split huggingface dataset:
Correlation of Film Quality and Hydrogen NMR Resonance Shifts in a-Si:D,H; a-Ge:D,H; and a-SiGe:D,H
Authors: Norberg R. E. , Kim Y. W. , Chan P. H. , Bodart J. R. , Kernan M. J. , Leopold D. J. , Fedders P. A. , Turner W. A. , Paul W. 
Published: April 2011

ABSTRACTA systematic study of both proton and deuteron NMR in hydrogenated amorphous silicon films has revealed significant resonance shifts among various resolved components. The shifts include both paramagnetic and diamagnetic displacements of resolved spectral features from trapped molecular hydrogens. The shifts depend on film quality and deposition conditions. Some of the shifts vary as 1/T and reflect Curie susceptibilities characteristic of local regions of differing dangling bond densities. Spectra from relatively immobile hydrogen molecules trapped in nanovoids are shifted diamagnetically and broadened as temperature decreases. Hydrogens tightly bound to Si do not show similar changes and thus are more remote from dangling bonds and other magnetic defects. Similar spectrally-resol ved shifts have been observed in a-Ge and a-SiGe films and are correlated with film photovoltaic quality as measured by mobility-lifetime products.
Light-Induced Degradation of a-Si:H - A Comparison of Short-Laser-Pulse and Steady Light Degradation
Authors: Tzanetakis P. , Kopidakis N. , Androulidakp M. , Kalpouzos C. , Stradins P. , Fritzsche H. 
Published: April 2011

ABSTRACTAn undoped and a compensated a-Si:H sample have been degraded by 17–34 ns laser pulses and by steady light (CW) at 78K and 300K. The light-induced defect concentration N is monitored by the increase in subgap absorption a. For the same change in a pulses degrade the photoconductivity σp more than CW light and more strongly for exposures at 78K than at 300K. The lack of correlation between σp and N suggests that light soaking causes additional damage besides an increase in N. This additional effect is more pronounced for pulse and low temperature exposures.
Examination of the Defect Pool Model by An Improved Analysis of the Constant Photocurrent Method
Authors: Stiebig Helmut , Siebke Frank 
Published: April 2011

ABSTRACTWe have developed an improved analysis of constant photocurrent method (CPM) data. It is based on a numerical simulation of CPM spectra taking into account the full set of optical transitions between localized and extended states, capture and emission processes as well as the position of the Fermi level. Comparing measured and simulated CPM spectra provides information about the density of localized states in a-Si:H, i.e. the valence band tail, the integrated defect density, the energy distribution and the charge state of defect states. Based on these results we examine the predictions of the defect-pool model. The defect distribution in undoped and doped a-Si:H can be described by the defect-pool model taking into account the doping level dependence of principal parameters including the valence band tail, the equilibration temperature, and the width of the defect-pool.
Evidence for Exchange Between Free and Deep Hydrogen (Deuterium) During Diffusion
Authors: Branz Howard M. , Asher Sally , Xu Yueqin , Kemp Mathieu 
Published: April 2011

ABSTRACTWe do not observe any immobile deuterium in secondary ion mass spectrometry D profiles taken after long anneals of hydrogenated amorphous silicon sandwich structures with a thin deuterated interior layer. This suggests that a single deep H level (∼1.4 eV deep) controls H diffusion. On its face, our result contradicts nuclear magnetic resonance and H effusion measurements that show about 30% of H in a-Si:H is “isolated” and deeply bound (∼ 2.1 eV deep). We reconcile our experimental results with the existence of isolated deep H by assuming there is a low-barrier (<< 1.4 eV) exchange process between free H and deep D. In tracer experiments, exchange has the effect of increasing the apparent emission rate of the deep D to nearly that of the shallowest trapped H. We solve for the D profiles and confirm that a deep-trapped D component is consistent with our D tracer profiles if and only if exchange processes are important. We also find that the mean distance D travels before retrapping (100–200Å) is determined by an exchange process of free D with trapped H.
High Electric Field Forming of a-Si:H P-I-N Diodes
Authors: Ilie A. , Equer B. , Pochet T. 
Published: April 2011

ABSTRACTAmorphous hydrogenated p-i-n diodes submitted to a high reverse bias for a long period of time undergo a metastable evolution which tends to improve their properties. A forming procedure based on this effect has been developed and leads to a significant decrease of the reverse current and increase of the breakdown voltage. In this paper, the mechanisms underlying this forming process have been investigated using the Constant Photocurrent Method (CPM), (I-V) characteristics and Spectral Response under reverse bias. The effects of annealing and current induced defect creation have been studied. The forming process is found to be most consistent with a metastable increase in the dopant activation of the p-layer and a small decrease of the density of states in the i-layer.
Transient Photocurrent Measurements on Current-Stressed a-Si:H Schottky Diodes
Authors: Buykx Andreas A. , Zeman M. , Spiekerman A. J. G. , Metselaar J. W. 
Published: April 2011

ABSTRACTThe characteristics of a-Si:H based switches, as used in liquid crystal displays, degrade as a result of current injection. To assess this degradation we investigated the effects of current injection on the electron mobility, lifetime and the built-in electric field profile in a-Si:H Schottky diodes.We present steady-state current-voltage and transient photocurrent (TP) measurements on Mo and Pd a-Si:H Schottky diodes. The mobility, lifetime and electric field profile were determined from TP measurements. The electric field profile was calculated by fitting simulations from a non-linear model of the measurement to the measured TP currents.The electron drift mobility is not affected by current stressing, the electron lifetime reduces slightly, the built-in voltage decreases significantly. The widths of the built-in fields of Schottky and ohmic back contact are reduced with approximately the same factor, corresponding with a spatially homogeneous increase of the defect density.
AC Theory of Constant Photocurrent Measurement
Authors: Conte G. , Eray A. , Nobile G. , Palma F. 
Published: April 2011

ABSTRACTIn this paper we present a study of ac the Constant Photocurrent Measurement (CPM) with the aim to assess the precision of this method compared to the de CPM. In particular, we introduce a small signal theory of the ac photoconductivity, we relate the sub-bandgap absorption to the density of defects, and we assume a combination of a constant plus a sinusoidal generation rate. The method allows to calculate the variation occurring in defect occupation as a function of the wavelength and intensity of the light, and of the ac test frequency. We show that, in ac condition, carriers lifetime is a complicated function of the chosen parameter, and it is affected by the delay due to charge accumulation of free and trapped carrier densities. Large influence on the lifetime is played not only by recombination, which takes place all along the gap defects included between the two quasi-Fermi levels, but also by the process of carrier trapping and emission by defects located close to the quasi-Fermi levels. Both processes introduce large phase delay. Further information can thus be obtained from CPM by evaluating the phase behavior. Our analysis leads to a new method of evaluation of the dangling bond capture cross section and of their charged-to-neutral capture cross section ratio.
VHF-Deposited a-SiC:H Alloys for High-Bandgap Solar Cells: Combining High Voc and Reasonable Stability
Authors: Platz R. , Fischer D. , Shah A. 
Published: April 2011

ABSTRACTThe material properties of a-SiC:H alloys deposited by VHFGD are studied, with a special emphasis on the effect of hydrogen dilution of the plasma on layer quality. By incorporating these layers into p-i-n solar cells the authors compare layer properties and cell performance. Special attention is paid to the stability of the solar cells against light soaking. Furthermore, the authors show that the insertion of a buffer layer can, also in the case of entirely a-SiC:H cells, lead to a substantial increase of Voc. A reasonable stability of these cells is maintained by an appropriate doping of the buffer layers.
Organic Thin-Film-Transistors with High on/off Ratios
Authors: Torsi L. , Dodabalapur A. , Katz H. E. , Lovinger A. J. , Ruel R. 
Published: April 2011

ABSTRACTIn this article a new procedure to obtain alpha-hexathienylene (α-6T) thin-film-transistors (TFTs) with on/off ratios in excess of one million is reported. This procedure involves subjecting the TFTs to rapid thermal annealing. Previously, high on/off ratios have been achieved with improved device design and better chemical synthesis of α-6T oligomers. High on/off ratios, along with a switching time of ∼ 10 μs, render α-6T TFTs potential candidates as switching devices in active matrix displays. The experimental current-voltage (I-V) characteristics of oc-6T TFTs with channel length L = 4μm are also presented and a measured field effect mobility of 0.02 cm2/V-s is extracted from these characteristics using an analytical model which we have developed for short-channel α-6T TFTs.
Passivation of InGaAs/GaAs Vertical-Cavity Surface-Emitting Lasers by Amorphous GaAs Deposition
Authors: Park Hyo-Hoon , Yoo Byueng-Su , Park Min Soo , Lee Jaejin , Lee Hae Gwon , Lee El-Hang , Shin Jae-Heon , Lee Yong Hee 
Published: April 2011

AbstractWe report for the first time a successful application of semi-insulating amorphous GaAs layer for surface passivation of index-guided vertical-cavity surface-emitting lasers. The amorphous GaAs layers on ion-beam-etched active region and mirror layers provide a significant improvement, more than 20%, in the threshold current density and differential quantum efficiency. The improvement of these performances is attributed to low defect density at the surface of active layers induced by amorphous GaAs.
Extraction of Elastic Parameters of Heavily Boron-Doped Silicon Layer by Elimination of Misfit Dislocations
Authors: Lee HO-JUN , Han Chul-Hi , Kim Choong-Ki 
Published: April 2011

AbstractIn this paper, various elastic parameters of heavily boron-doped silicon layer have been extracted by eliminating the misfit dislocations in the layer. The dislocation-free silicon membranes doped with the boron concentration of 1.3 × 1020 atoms/cm3 have been fabricated and the Young’s modulus of 1.45 × 1012 dyn/cm2 and residual tensile stress of 2.7 × 109 dyn/cm2 have been extracted by blister method. From the Young’s modulus and residual stress, the residual tensile strain of 1.34 × 10−3, lattice constant of 5.424 Å, and misfit coefficient of 1.03 × 10−23 cm3/atom have been calculated. These parameters are very similar to those obtained from X-ray diffraction analysis and theory.
Surfaces and Crystal Defects of Silicon
Authors: Wagner P. , Brohl M. , Gräf D. , Lambert U. 
Published: April 2011

AbstractBulk crystal defects are accessible for investigation when silicon crystals are sliced and the defects occur close to or at the surface of wafers. Such near-surface defects can then be delineated by modifying some processes used for preparing clean, polished wafers. The delineated defects usually occur as pits the shape of which depends on the delineation process used. The different shapes of the pits has consequences for their detection by light scattering techniques (laser scanners or surface inspection systems). The density of the such generated surface defects is related to the defect density in the crystal bulk and is influenced by the growth parameters. These surface defects therefore provide a means for studying and for characterizing the bulk defect density.
Magnetic Circular Dichroism of Low-Temperature-Grown AlxGa1-xAs
Authors: Prasad A. , Liu X. , Stallinga P. , Weber E. R. , Verma A. K. , Smith J. S. 
Published: April 2011

AbstractWe study magnetic circular dichroism of absorption (MCDA) of LT AlxGa1−xAs as a function of aluminum content. The MCDA spectrum of LT AlxGa1−xAs is distinctly different from the MCDA spectrum of LT GaAs, which has one paramagnetic and one diamagnetic peak at 0.95 eV and 1.18 eV, respectively. As the aluminum content increases, the spectrum of LT AlxGa1−xAs is dominated by a diamagnetic peak similar to the 1.18eV peak of the EL20-like defects in LT GaAs. However, the peak shifts to higher energies as x increases. The photoquenching and temperature dependence of this peak indicates an association with the EL2 defect. The paramagnetic peak observed in LT GaAs also shifts to higher energies but faster and eventually merges with the diamagnetic peak as the Al content increases. The study of the MCDA spectrum of LT AlxGa1−xAs as a function of aluminum content allows a better understanding of the MCDA phenomena of LT AlxGa1−xAs and LT GaAs, as well as the EL2-related transitions in bulk semi-insulating GaAs.
Uniformity of Arsenic Dimer and Tetramer Fluxes from a Valved Arsenic Cracking Source in MBE
Authors: Patterson George A. , Chang James S.C. , Kellert Forrest G. 
Published: April 2011

AbstractWe have studied the uniformity of the arsenic flux from a commercially available valved arsenic cracker source for MBE. There are many epitaxial structures that require a uniform arsenic flux distribution for rotated epitaxial growth and, in the non-rotated case, for RHEED. For non-stoichiometric GaAs growth at low substrate temperatures, which results in arsenic precipitates being formed during the in-situ anneal process, a specific As/Ga ratio must be used to maintain high crystalline quality and to achieve the desired electrical properties. Also, in the growth of InGaAsP the As/P ratio is equally important for lattice match and quality device results. We report on the uniformity of amorphous arsenic (a-As) films condensed on the surface of 3" diameter sapphire wafers slightly below room temperature. Sapphire substrates were used in place of GaAs wafers to facilitate the use of x-ray fluorescence for the measurement of the arsenic film uniformity. Uniformity maps will be presented for rotated and non-rotated a-As depositions of As2 and As4. Results indicate the uniformity of a-As, As4, films to have a standard deviation of < 2.5% across a 3" diameter substrate for the rotated case. Characteristics of the non-rotated case will be presented.
Dopant-Defect Interactions in II-VI Semiconductors Studied by PAC
Authors: Wichert Thomas 
Published: April 2011

AbstractThe application of the perturbed γγ angular correlation technique (PAC) as an analytical tool for the characterisation of atomic defect configurations is discussed, using recent results on donor-acceptor pairs, which were observed in CdTe and other II-VI semiconductors by the radioactive donor 111In. For bulk CdTe crystals and MOCVD grown CdTe films, the role of the cation vacancy, group I and group V elements is discussed.
Hydrogen Passivation of Defects in Electron Irradiated Polycrystalline Silicon Solar Cells
Authors: Bilyalov R.R. , Abdurakhmanov B.M. 
Published: April 2011

AbstractThe effect of hydrogen passivation on photovoltaic performance of 1 MeV electron irradiated polycrystalline cast silicon solar cells is described. These cells were processed on cast p-type boron doped polycrystalline silicon substrates using standard technology. Passivation was made by low-energy hydrogen ion implantation on the front side. Cells performance was measured as a function of fluence, and it was found that the hydrogenated cell had the higher radiation resistance.Defect behavior were studied using deep level transient spectroscopy and infra-red spectroscopy. It was shown that the concentration of vacancies (Ec −0,09 eV), divacancies (Ec −0,23 eV) and A-centers (Ec −0,18 eV) is significantly lower in hydrogenated samples. This consistency strengthens the belief that hydrogen interacts with vacancy-type defects to prevent formation of the secondary radiation defects. It is confirmed by IR-measurements.
Hydrogen Diffusion in n-GaAs:Si Under Hydrostatic Pressure
Authors: Machayekhi B. , Chevallier J. , Theys B. , Besson J. M. , Weill G. , Syfosse G. 
Published: April 2011

ABSTRACTIt has recently been shown that deuterium diffusion experiments can provide information on the deepening of the hydrogen acceptor level in the band gap of AlxGa1-xAs alloys with increasing x. In the present work, we report on the influence of hydrostatic pressure on deuterium diffusion in n-GaAs:Si. SIMS analysis reveals that the deuterium profiles in n-GaAs:Si are sensitive to hydrostatic pressure: the diffusion depth decreases and a plateau appears in the diffusion profile as the pressure is applied. The results are interpreted in terms of an increasing amount of the H- species as pressure is applied. This increase is mainly attributed to a deepening of the H acceptor level with respect to the bottom of the Γ conduction band of GaAs. Qualitatively, this effect is similar to the deepening of the H acceptor level in AlxGa1-xAs alloys as x increases.
Native Defects in Low Temperature GaAs and the Effect of Hydrogenation
Authors: Pritchard R. E. , McQuaid S. A. , Newman R. C. , MÊkinen J. , Von Bardeleben H. J. , Missous M. 
Published: April 2011

AbstractGaAs grown at low temperatures by MBE has been doped with shallow impurities to ∼1019 cm−3. A layer doped with Be acceptors was completely compensated and the simultaneous detection of AsGa0 and AsGa+ confirmed that the Fermi level was close to midgap and that compensation was partly related to AsGa defects. There was no evidence for the incorporation of VGa in this layer. For Si-doped samples, more than 80 % of the donors were compensated and the detection of SiGa-VGa pairs by infrared localized vibrational mode (LVM) spectroscopy indicated that VGa were at least partly responsible. Increasing the Si concentration suppressed the incorporation of AsGa. Exposure of the Be-doped layer to a hydrogen plasma, generated a LVM near 2000 cm−1 which may be the stretch mode of a AsGa-H-VAs defect complex. For Si-doped layers, two stretch modes at 1764 cm−1 and 1773 cm−1 and a wag mode at 779 cm−1 relating to a H-defect complex were detected and we argue that the complex could be a passivated As antisite. The detection of characteristic hydrogen-native defect LVMs may provide a new method for the identification of intrinsic defects.
Time Resolved Photoluminescence Spectroscopy on GaN Epitaxial Layers
Authors: Meyer B. K. , Volm D. , Wetzel C. , Eckey L. , Holst J.-Ch. , Maxim P. , Heitz R. , Hoffmann A. , Broser I. , Mokhov E. N. , Baranov P. G. , Qiu C. , Pankove J. I. 
Published: April 2011

AbstractFree and bound exciton luminescences as well as donor-acceptor pair recombination of GaN epitaxial layers on 6H-SiC and sapphire substrates were investigated using time integrated and time resolved photoluminescence measurements at low temperatures. Lifetimes are determined for the donor bound exciton at 3.4722eV and for two acceptor bound excitons with energies of 3.4672eV and 3.459eV. Luminescences between 3.29eV and 3.37eV are identified as due to excitons deeply bound to centers located near the substrate-epilayer interface.
Contactless Evaluation of the Surface Recombination Property of Silicon with an Ion-Implanted Layer
Authors: Usami Akira , Makino Takanori , Yoshida Hideaki , Morita Etsuro 
Published: April 2011

AbstractThe surface properties of silicon are investigated by the noncontact laser (λ=774nm)/microwave method. The effective surface recombination velocity (Seff) at an n+n high-low junction interface is estimated by fitting the experimental decay curve for excess carriers with the theoretical decay curve. The results show that Seg decreases as the dopant concentration increases and that Seff at the n+n high-low junction formed with a dose of 1×l015 ions/cm2 has values lower than 1 cm/s. And it is shown that Scff is inversely proportional to the potential barrier height of the n+n high-low junction. Similar results are obtained using an N2 laser (λ=337.1nm) instead of a laser diode (λ=774nm, 904nm) as a carrier excitation pulse source.
Ultrasound Defect Engineering of Transition Metals Via Metal-Acceptor Pairs in Silicon
Authors: Bell Ronald E. , Ostapenko Serguei , Lagowski Jacek 
Published: April 2011

AbstractExperimental evidence is provided for ultrasound stimulated dissociation of metal-acceptor pairs in silicon, and also for enhanced diffusion of metal interstitials which may lead to enhanced pairing. The first effect is found dominant in Fe-doped p-type silicon where ultrasound causes low temperature dissociation of Fe-B pairs. This is in contrast to Cr-doped p-type silicon where ultrasound enhances the formation of Cr-B pairs due to enhanced diffusivity of Cr by as much as two orders of magnitude.In this study, the metal-acceptor reaction was monitored in situ via corresponding changes of the minority carrier diffusion length measured by non-contact surface photovoltage. Ultrasound-stimulated pair reaction can be utilized for metal diagnostics for the silicon IC industry. Thus, with ultrasound, Cr-B pairing can be reduced from months to hours, making possible the identification of Cr via pairing kinetics in a reasonable period of time.
Room Temperature Infrared Electroluminescence from Thin-Film Polycrystalline Chalcopyrite Cu(In,Ga)Se2-Based Diodes
Authors: Contreras Miguel A. , Webb John , Tennant Andrew , Noufi Rommel 
Published: April 2011

AbstractEvidence of room-temperature infrared electroluminescence from thin-film polycrystalline CuInxGa1-xSe2-based diodes (0<×<0.4) has been observed by Fourier transform spectroscopy using a FT-Raman spectrophotometer that operates in the near-infrared spectral region. Electroluminescence spectra from ternary CuInSe2 and quaternary Cu(In,Ga)Se2 device structures are reported. In all electroluminescence cases we observe an approximate linear relationship of intensity to forward junction current. Film fabrication process determines to a great extent the optoelectronic properties of the emitters, and consequently, the characteristics of their luminescence spectra. Using a Gaussian multi-peak curve-fit routine to analyze electroluminescence spectra, we can deduce the position, width and relative intensity of the dominant optical transitions. Our purpose in this contribution is two-fold: (1) To report the room-temperature electroluminescence phenomena from chalcopyrite Cu(In,Ga)Se2 polycrystalline thin-films, and (2) to demonstrate electroluminescence as a viable technique to optically characterize Cu(In,Ga)Se2 materials using diode structures at RT.
Studies of Defects in ZnO by Positron Annihilation
Authors: Puff Werner , Brunner Sebastian , Mascher Peter , Balogh Adam G. 
Published: April 2011

AbstractIn order to investigate the basic properties of radiation-induced defects in ZnO crystals, positron annihilation lifetime and Doppler-broadening measurements were performed on crystals sinterd for 18 hours at 1200 °C and irradiated with 3 MeV protons at 223 K. The irradiation induced a colour change of the specimens from the original yellowish-white to dark orange or even brown. Isochronal annealing experiments showed three annealing stages, centred at about 150 °C, 500 – 550 °C, and 750 °C, respectively. These stages are related to the annealing of variously sized vacancy complexes.