bluuebunny/crossref_metadata_2025_split huggingface dataset:
Si-Induced AlGaAs/GaAs Superlaitce Disordering Using a Grown-In Impurity Source and the Effects of Annealing Ambient
Authors: Olmsted B.L. , Houde-Walter S.N. 
Published: March 2011

ABSTRACTWe report on a study of the role of defect diffusion from the crystal surface in the disordering of a multiple quantum well structure that was Si-doped during MBE growth. The distribution of native defects was inferred from correlating the results of photoluminescence spectroscopy, secondary ion mass spectrometry, and electrochemical C-V profiling. No significant change was observed between the Al-Ga interdiffusion coefficients of Si-doped and undoped superlattices when annealed with excess Ga. This is attributed to the lack of a source of group III vacancies. Furthermore, only a small fraction of the enhancement predicted for the Si doping was observed when excess As was used instead. The largest Fermi-level enhancement was observed when no excess Ga or As was included in the evacuated ampoule. The results indicate that the crystal surface was the source and sink of the native defects known to mediate the Al-Ga interdiffusion. Furthermore, significant electrical compensation of the donors was observed after both As- and Ga-rich anneals. This is attributed to ionized group III vacancy generation in the former case, and Si atoms moving from group In to V sites in the later.
Investigation of Carbon Incorporation into GaAs by TEGa-AsH3 Based Low Pressure Metalorganic Chemical Vapor Deposition
Authors: Feng M. S. , Chen H. D. , Wu C. H. 
Published: March 2011

ABSTRACTHeavily Carbon doped GaAs(l×1018−1×1020cm−3 ) grown by low pressure metalorganic chemical vapor deposition(LPMOCVD) using triethylgallium(TEGa), arsine(AsH3) as sources and liquid carbon-tetrachoride(CCI4) as dopant has been investigated. The carrier concentration was verified at various growth temperatures, V/III ratios and CCI4 flow rates. Dopant concentration first increased from 550°C and reached a maxium at 570°C and then decreased monotonously. Carbon incorporation was strongly enhanced when V/III ratio was less than 30 at Tg=590°C or less than 40 at Tg=630°C. Hole concentration increased and then decreased as CCI4 increased. The doping efficiency of epitaxtial layers grown on(100) substrate was higher than that on 2° off toward <110> misoriented substrate. Carbon doped GaAs films had higher Hall mobility than zinc doped GaAs films at high doping level due to less self-compensation. The highest dopant concentration in this system was 2.3×1020cm−3 at Tg=580°C and V/III=10.
Capacitance-Voltage-Method Carrier Concentration Depth Profiles in Liquid-Encapsulated-Czochralski-Technique Grown GaAs Wafers from Near-Stoichiometric and Extremely-Composition Melts
Authors: Saito Yasuyijki , Nishio Jhoji 
Published: March 2011

ABSTRACTIt was observed that carrier concentration depth profiles under 200μm-diameter gold Schottky electrodes of deeply Si-implanted electrically active layers on undoped semi-insulating GaAs wafers depend on melt composition of liquid-glass encapsulation Czochralski technique (LEC) growth, Fourier-transformed infrared (FT-IR) measurement carbon content of LEC growth, and consecutive cooling thermal cycle of LEC growth. In the range of this experiment, for head position of boules and 2.5 × 10exp.12/cm2 Si dosage, peak carrier concentrations of As-rich melt LEC growth (initial: [As]/([As]+[Ga])≃0.526) were comparable to or slightly higher than those of near-stoichiometric melt LEC growth. For tail position and 3 × 10exp.12/cm2 Si dosage, a peak carrier concentration of a father As-rich melt LEC-growth was clearly higher than that of Ga-rich melt LEC-growth. LEC-grown melt composition effect depended on consecutive cooling thermal cycle. For peak carrier concentration dispersion of head position, there was anticorrelation between carbon content of FT-IR measurement and peak carrier concentration dispersion.
Junction Formation in Silicon by Rapid Thermal Annealing
Authors: Fair Richard B. 
Published: March 2011

ABSTRACTThe feasibility of using isothermal RTA in annealing ion implanted layers for forming junctions has been investigated for the past 10 years. While many of the scientific details surrounding defect formation, transient diffusion and dopant activation remain to be clarified, RTA intrinsically is a viable annealing process which is essential for fabricating advanced silicon devices.
Rapid Thermal Processing for Strained-Layer Semiconductor Devices
Authors: Zolper John C. , Myers David R. 
Published: March 2011

ABSTRACTStrained-layer semiconductors have revolutionized modern heterostructure devices by exploiting the modification of semiconductor band structure associated with the coherent strain of lattice-mismatched heteroepitaxy. The modified band structure improves transport of holes in heterostructures and enhances the operation of semiconductor lasers. Strainedlayer epitaxy also can create materials whose band gaps match wavelengths (e. g. 1.06 μm and 1.32 μm) not attainable in ternary epitaxial systems lattice matched to binary substrates. Other benefits arise from metallurgical effects of modulated strain fields on dislocations.Lattice mismatched epitaxial layers that exceed the limits of equilibrium thermodynamics will degrade under sufficient thermal processing by converting the as-grown coherent epitaxy into a network of strain-relieving dislocations. After presenting the effects of strain on band structure, we describe the stability criterion for rapid-thermal processing of strained-layer structures and the effects of exceeding the thermodynamic limits. Finally, device results are reviewed for structures that benefit from high temperature processing of strained-layer superlattices.
Fabrication/Characterization of a Pseudomorphic Ga0.1In0.9P/InP MESFET
Authors: Feng M. S. , Hsin Y. M. , Wu C. H. 
Published: March 2011

ABSTRACTA pseudomorphic Ga0.1In0.9P/InP MESFET grown by low pressure metalorganic chemical vapor deposition(LP-MOCVD) has been fabricated and characterized. The results indicated a transconductance of 66.7 ms/mm and a saturation drain current (Idss) of 55.6 mA have been achieved; furthermore, the Schottky barrier on InGaP as high as 0.67eV can be obtained using Pt2Si as the gate material. For comparison, a conventional InP MESFET with 5μm gate length has also been fabricated on InP epitaxial layer grown by low pressure metalorganic chemical vapor deposition on Fe-doped semi-insulating InP substrate. The transconductance and Idss were found to be 46.7 mS/mm and 43.1 mA at zero gate, respectively, for the depletion mode n-channel MESFET with Au as the gate metal; whereas, for the MESFET using Pt2Si as the gate metal, a transconductance of 40.3 mS/mm and a saturation drain current of 41.1 mA at zero gate bias have been obtained. The results indicated that Ga0.1In0.9P/lnP MESFET has better performance than InP MESFET because of higher energy gap of Ga0.1In0.9P.
Evaluation of Electrical Contact Material Stability on Mercuric Iodide
Authors: Cheng A. Y. 
Published: March 2011

ABSTRACTMercuric iodide detectors are leading candidates for room-temperature radiation detection applications. The inherently reactive nature of mercuric iodide limits the number of materials suitable for fabrication of electrical contacts. The theoretical stabilities of elemental contact materials on mercuric iodide were evaluated at 25°C. Additionally, the stabilities of transparent conductive compounds, for photodetector applications, were studied. Calculations were based on Gibbs free energy data, estimates and a series of hypothesized reactions with mercuric iodide. Leading candidate materials were identified and compared to experimental results.
Investigation of Deep Levels In X-Ray Detector Material With Photo Induced Current Transient Spectroscopy (Picts)
Authors: Eiche C , Fiederle M , Weese J , Maier D , Ebling D , Benz K W 
Published: March 2011

ABSTRACTDeep 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.
Electrical Properties of Natural Iia Diamonds Using Photo- and Particle Excitation
Authors: Pan L. S. , Han S. , Kania D. R. , Gan K. K. , Zhao S. , Kagan H. , Kassa R. , Malchow R. , Morrow F. , Palmer W. F. , White C. , Kim S. K. , Sannes F. , Schnetzer S. , Stone R. , Thomson G. B. , Sugimoto Y. , Fry A. , Kanda S. , Olsen S. , Franklin M. , Ager J. W. , Pianetta P. 
Published: March 2011

ABSTRACTTwo complementary techniques are used to study the electrical transport properties related to the use of diamonds as materials for ionizing radiation detectors. Transient photoconductivity using soft x-rays is used to probe the first few microns of the material, while ionizing particle-excited conductivity is used to probe the entire bulk of the material (1 millimeter). Both techniques measure the mean drift distance of free carriers, or the collection distance d. In addition, transient photoconductivity is able to extract the lifetimes and mobilities of the excited carriers. The collection distance measured by the two methods are in agreement, suggesting the material is homogeneous. At an applied field of 10 kV/cm, d is 25 to 30 microns, and, up to a field of 25 kV/cm, d has not saturated. The lifetime varies between 100 and 600 ps, and the mobility varies between 1000 and 4000 cm2/V-s, the range due to natural variations from sample to sample. The primary defects limiting the lifetime are believed to be nitrogen impurities and dislocations.
Diamond Doping by Low Energy Ion Implantation During Growth
Authors: Jamison K.D. , Schmidt H.K. , Eisenmann D. , Hellmer R.P. 
Published: March 2011

ABSTRACTA novel method of implanting dopant material in diamond using low energy ions during growth is described. In this method, relatively low energy (∼10 KeV) dopant ions are directed through an aperture into a hot filament chemical vapor deposition growth chamber and onto the growing diamond sample. Collisions with the gas molecules in the growth chamber (∼10 Torr of a 99.5% H2 - 0.5% CH4 gas mixture) partially neutralize the ion beam and slow the dopant atoms down to a few hundred electron volts before striking the growing diamond crystal. The residual energy is large enough to embed the dopant atoms a few layers deep in the crystal but not large enough to cause significant lattice damage. Continued doping during growth yields uniformly doped material throughout the implanted region. Results for sodium, rubidium, and phosphorus atom doping are presented with sodium found to be a p-type dopant and phosphorus a deep n-type dopant.
Experimental Results in Picosecond and Subpicosecond Range of IIa Type Diamond Detector in X-UV, Visible and Ir Fields
Authors: Nail M , Gibert Ph. , Miquel J.L. , Cuzin M. 
Published: March 2011

ABSTRACTType IIa diamonds present photoconductive properties as well in X-ray detection range, as in near UV, visible, IR light range, in spite of the large bandgap of the material. Experimental results in these four fields, time measurements in picosecond and subpicosecond ranges are presented.
X-Ray Studies of Synthetic Radiation-Counting Diamonds
Authors: Yacoot Andrew , Moore Moreton , Makepeace Anthony 
Published: March 2011

ABSTRACTSynthetic diamonds with a nitrogen content less than 100ppm may be used as radiation dosimeters in a conduction counting mode, and are especially useful in medical applications. Crystal imperfections, revealed by X-ray diffraction topography, were found to affect counting performance. The best quality diamond gave the highest photocurrent (500nA at 50 V mm−1 and 2.75 Gy min−l). Diamonds containing dislocations had lower photocurrents but had the advantage of shorter settling times (seconds rather than minutes). Placing contacts on two opposite cube {100} faces gave a higher photocurrent than on a pair of octahedral {111} faces. Higher photocurrents were also achieved when the majority of dislocations were perpendicular rather than parallel to the electric field. Some recommendations for selecting synthetic diamonds for dosimeters are given.
New Compound Semiconductor Materials for Nuclear Detectors
Authors: Squillante Michael R. , Zhang John , Zhou Chuxin , Bennett Paul , Moy Larry 
Published: March 2011

ABSTRACTIn many instances, the ability of scientists and engineers to make nuclear radiation measurements is only limited by the properties of available radiation detectors. Because of this, research into new semiconductor materials for radiation detection has been, and continues to be, a very active field. This article reviews recent research on several promising “new” materials.
Variable Angle Spectroscopic Ellipsometry Studies of HgI2
Authors: Yao Huade , Johs Blaine 
Published: March 2011

ABSTRACTVariable angle spectroscopic ellipsometry (VASE) measurements were employed to study the optical properties of HgI2. The bulk crystal HgI2 surface was subjected to a 10% KI etching prior to the VASE measurements. SE measurements were performed at room temperature, in air with several different angles of incidence. The uniaxial anisotropic nature of the HgI2 crystal was treated in the VASE analysis. Anisotropic dielectric functions of single crystal HgI2, ε||(wo) and ε⊥(ω), for optical electric field vector oriented parallel and perpendicular to the c axis, respectively, were obtained in the range of ∼2.0 - 5.0 eV. Surface aging effects of the HgI2 crystal, after the 10% KI etching, were characterized by VASE.
Physical-Chemical Considerations for Semiconductor Room-Temperature Radiation Detectors
Authors: Schieber M. , Hermon H. , Roth M. 
Published: March 2011

ABSTRACTPhysical properties of large band gap semiconductors such as: HgI2, CdTe, Cd0.8Zn0.2Te, CdSe, Cd0.7Zn0.3Se, GaAs, PbI2 and TlBr are briefly reviewed and discussed in terms of their use as room temperature operating x-ray and gamma ray radiation detectors. It is shown that HgI2 which has the largest drift length for holes, λ=μτE i.e., the product of the mobility μh, life time τh and the electrical field E, is at present the leading material, being followed by the newly developed Cd0.8Zn0.2Te. Chemical defects in HgI2 were enhanced by doping the material with aliphatic, aromatic and oxyhydrocarbons as well as with excess Hg and I2 and the increase in unit cell parameter was studied as a function of the amount of dopant. The value of τ was measured as a function of dopant concentration and it was found that Hg doping causes the most severe trapping defects. Low temperature studies of τh down to 170K allowed the identification of the trapping energy levels and concentration of electrically active defects. Shallow traps of 0.13-0.18 eV stemming from deviation from stoichiometry of H-gI2 were found to be in the ppm level whereas deeper traps of 0.4-0.5 eV stemming from hydrocarbons were found to be in the ppb level. It is concluded that only extensive research on the physical, chemical and structural defects correlated with improved crystal growth and device fabrication methods, would lead, in the future, to improvements in λh also of the other large Eg semiconductor detector materials.
Analysis of Deep Levels in GaAs Detector Diodes Using Impedance Spectroscopy
Authors: Eiche C , Fiederle M , Weese J , Maier D , Ebling D , Ludwig J , Benz K W 
Published: March 2011

ABSTRACTImpedance 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.
Experimental Results from γ-irradiated GaAs Crystals Grown with Different Techniques
Authors: Bencivelli W. , Bertolucci E. , Bottigli U. , Cavallini A. , D'Auria S. , Via C. Da , Papa C. Del , Fantacci M.E. , Rosso V. , Stefanini A. , Stefanini G. 
Published: March 2011

ABSTRACTGallium Arsenide crystals are among the most efficient detectors of X-rays at room temperature. Different GaAs crystals have been irradiated with photons from radioactive sources, to compare their response in view of a possible application for Digital Radiology. The detectors have been obtained by various manufacturers and with different techniques (LEC and LPE crystals). Experimental results include I-V curves, charge collection efficiency and detection efficiency as a function of bias. A comparison is made with a simulation program.
Defect Reduction in Cd1−xZnxTe Epilayers on GaAs Substrates
Authors: Chadda Saket , Malloy Kevin , Reno John 
Published: March 2011

ABSTRACTCd0.91Zn0.09Te/CdTe multilayers of various period thicknesses were inserted into Cd0.955Zn0.045Te bulk alloys grown on (001) GaAs. The net strain of the multilayer on the underlying Cd0.955Zn0.045Te was designed to be zero. X-ray diffraction full width at half maximum (FWHM) was used as a means to optimize the period thickness of the multilayer. Transmission electron microscopy of the optimum period thickness samples demonstrated four orders of magnitude decrease in the threading dislocation density. Mechanism of bending by equi-strained multilayers is discussed.
Direct Heteroepitaxial Growth of ZnTe(100) and CdZnTe(100)/ZnTe(100) on Si(100) Substrates by MBE
Authors: Lyon T. J. de , Johnson S. M. , Cockrum C. A. , Wu O. K. , Roth J. A. 
Published: March 2011

ABSTRACTEpitaxial films of ZnTe(100) and CdZnTe(100)/ZnTe(100) have been deposited by molecular-beam epitaxy onto Si(100) substrates misoriented from 0-8 degrees towards the [011] direction. The films were characterized with x ray diffraction, photoluminescence spectroscopy, optical microscopy, and stylus profilometry. Through use of ZnTe buffer layers, single crystal CdZnTe(100) films have been demonstrated on both 4° and 8° misoriented Si with structural quality comparable to that obtained with GaAs/Si composite substrates. X ray rocking curves for ZnTe(400) with FWHM less than 300 arcseconds and for CdZnTe(400) with FWHM less than 160 arcseconds have been obtained for as-grown films. The observed surface morphologies are superior to those obtained on GaAs/Si composite substrates. HgCdTe(100) films with x ray FWHM as low as 55 arcseconds and average etch pit densities of 5 x 106 cm−2 have been deposited by liquid phase epitaxy on these MBE CdZnTe/ZnTe/Si substrates.
Study of different Cadmium Telluride Materials doped with V, Zn and Cl grown by vertical Bridgman Furnace and by THM.
Authors: Steer Ch. , Chibani L. , Koebel J.M. , Hage-Ali M. , Siffert P. 
Published: March 2011

ABSTRACTThe properties of Cadmium Telluride are very sensitive to impurities. The growth method has also a strong impact on the material characteristics. Crystals grown by THM have good X-ray detector properties, while normal undoped Bridgman grown crystals do not detect. We have grown pure and doped samples by Bridgman and THM methods. As doping materials we used V, Zn and Cl, also in different combinations. The samples were characterized by several methods, including resistivity, TSC and nuclear detection measurements.
Progress in Cdl-xZnxTe (CZT) Radiation Detectors
Authors: Butler J. F. , Doty F. P. , Apotovsky B. , Friesenhahn S. J. , Lingren C. 
Published: March 2011

ABSTRACTResults of a program to improve the performance of Cd1-xZnxTe detectors by adjusting growth parameters to achieve low-strain, high purity low defect crystals, investigating surface effect phenomena and contacting methods, and establishing reproducible manufacturing methods are reviewed and discussed. Processing and fabrication methods were developed which are applicable throughout the composition range. Energy spectra for room temperature Cdl-xZnxTe detectors exhibit resolutions (FWHM) from 2.16 keV at 14 keV to 6.9 keV at 122 keV. An energy resolution of 910 eV at 5.9 keV was achieved at −25 C. Stable ohmic contacts and gamma ray detection for ZnTe are reported for the first time. Applications of Cdl-xZnxTe to nuclear medicine and X-ray fluorescence are discussed. New gamma ray imagers using Cd1-xZnxTe detector arrays are described, and imaging data for a 32 × 32 monolithic array of 1 mm2 elements on a 42mm × 42mm substrate are presented.
Fast Avalanche Photodiode Detectors for the Superconducting Super Collider
Authors: Vasile Stefan , Gordon Jeffrey S. , Farrell Richard , Squillante Michael R. 
Published: March 2011

ABSTRACTThe tracking of high energy, secondary products in the Superconducting Super Collider (SSC) presents challenging sensitivity and timing requirements for the scintillating fiber converters and the optical radiation detectors planned for use as signal readouts. Silicon Avalanche Photodiodes (APD) are very promising detectors which may ultimately meet these requirements.We have designed and manufactured 1 mm2APDs, to be operated in Geiger mode as single photon detectors for the SSC. The progress on decreasing the APD response time by platinum doping, device thinning and external avalanche quenching is reported.
Improvements of a-Si:H/CsI(TI) X-RAY Detectors for Radiation Monitoring
Authors: Manfredotti C. , Fizzotti F. , Boero M. , Cannistraci F. , Vittone E. , Torti A. , Turnaturi M. 
Published: March 2011

ABSTRACTPhotosensitive a-Si:H p-i-n diodes, working in photovoltaic mode, have been coupled to CsI(T1) scintillators for dosimetry applications to X-ray monitoring in the energy range from 50 keV up to 15 MeV. A “mesa” approach for p-i-n diodes has been adopted both in order to better define the geometry and to obtain very low dark current. In order to optimize the geometry, a computer program has been created which simulates light generation in the scintillator, the collection by the detector and the photovoltaic current obtained as a function of exposure rate.Measurements have been carried out in the X-rays energy ranges 50-240 keV, at 6MeV and at 15 MeV. Detectors are linear in response and shows a good sensitivity, with the capability of measuring dose rates as low as 60 mR/h.The agreement between experimental data and simulation outputs can be considered good.