bluuebunny/crossref_metadata_2025 huggingface dataset:
Electroluminescence and Transport in a-Si:H p-i-n Diodes at Room Temperature
Authors: Carius R. , Becker F. , Wagner H. , Zettler J.-Th.
Published: March 2011

The transport and recombination of injected electrons and holes in a-Si:H p-i-n-solar cells is studied by simultaneous detection of electroluminescence and forward current, both steady state and time resolved. We have calculated the spatial distribution of the radiative recombination in the layer using an optical model that takes into account all layers of the solar cell as well as the substrate and the back contact. The validity of the results has successfully been tested by photoluminescence measurements using different excitation energies (penetration depths). By comparison between measured EL spectra and calculated spectra it is found that in a 0.6μm thick cell at room temperature the radiative recombination occurs in a narrow region (90 nm) in the vicinity of the p-layer. Time resolved electroluminescence and forward current measurements show that at room temperature the forward current is first determined by the space charge limited current of the electrons subsequently followed by the much larger recombination current. The recombination current is determined by the injection of holes from the p-contact in agreement with results from device modelling. Radiative and non-radiative lifetimes of the injected carriers are determined.
Effect of C Impurities in a-Si:H as Measured by Drive-Level Capacitance, Photo Current, and Electron Spin Resonance
Authors: Hautala J. , Unold T. , Cohen J.D.
Published: March 2011

The effect of C impurities in a-Si:H in levels of 0.4 to 2.6 at. % were studied over a wide range of metastable defect densities. Three complimentary experimental techniques [electron spin resonance (ESR), drive-level capacitance (DLC) and photo-current] were employed to track the material's defect density with light soaking and annealing, as well as Urbach energies, midgap absorption and mobility gaps energies as a function of the C content. Our results show C impurities have a definite effect on the initial and saturated defect densities, as well as the midgap absorption and Urbach energies at levels 1 at. % and above. The results indicate that C acts mainly as a center for increased disorder in the material which results in an increase in the bandtail widths, and consequently an increase in intrinsic defects. Comparison to the ESR and drive-level data show an excellent agreement between these two techniques in determining the bulk defect densities in a-Si:H.
A Quasi-Exact Inverteble Equation for Absorption Coefficient from Reflectance and Transmittance Measurements
Authors: Summonte C.
Published: March 2011

Exact formulas describing reflectance and transmittance R and T of the system absorbing film%substrate%back ambient are examined. Basing on the consideration that, unlike R and T, the quantity T%(l-R) does not oscillate with wavelength, the entity of terms entering the full equation are evaluated, and some approximations are made. As a result, a non-oscillating analytical equation is obtained, that can be inverted and therefore utilized to compute the film absorption coefficient with an accuracy that is better than 3 %for α>103cm-1. The effect of further approximations, like fixing the refractive index of the film and the substrate, is also evaluated. A comparison with a normally used, simplified formula, as well as an example of application, are also reported.
Irregular Electron Transport Through a-Si:H Based Potential Barriers
Authors: Bernhard Norbert , Frank B. , Movaghar B. , Bauer G.H.
Published: March 2011

Irregularities in the current-voltage-characteristics of a-Si:H based potential barriers have been investigated experimentally, and are discussed theoretically with respect to different transport mechanisms. The investigated samples were different series of double and single barrier a-Si:H - a-Si1-xCx:H - heterostructures, as well as homogeneous samples without heterostructure barrier. Current-voltage-(I-V)-characteristics showing a wide variety of features, from complete smoothness of the curves, to bumps and even accidental step-like switching behaviour, as well as different forms of noise, were recorded at different temperatures. Resonant tunnelling as an explaining transport mechanism for the anomalies was excluded because of inconsistency between experiment and calculations partially including special amorphous features. Instead it is argued that all observed irregularities, i. e. bumps in I-V-curves, switching-like behaviour, and appearance of noise, are related to current transport via trap-assisted tunnelling through locally strongly confined transport paths, leading to the meta-stable formation, change and break-down of conductory filaments.
Photocarrier Transport and Recombination in Amorphous Silicon
Authors: Wronski C.R. , Dawson R.M. , Gunes M. , Li Y.M. , Collins R.W.
Published: March 2011

The effect of microstructure in undoped a-Si:H films on carrier transport, recombination, densities of midgap states and solar cell characteristics has been investigated. Extended state mobilities of electrons were obtained from photo and dark conductivity measurements between 40° C and 190° C and the gap states characterized using Dual Beam Photoconductivity. In these films the estimated room temperature electron mobilities increase from about 1 to 30 cm2/V sec as the dihydride concentrations and void volume fractions decrease. It is found that the carrier mobility-lifetime products are not solely determined by the dangling bond states. The effects of changes in the mobilities and midgap states on p-i-n homojunction solar cell characteristics are presented and discussed.
Recombination Process in the As-Deposited State of Hydrogenated Amorphous Silicon
Authors: Yoon Jong-Hwan
Published: March 2011

Intrinsic deep defect-related recombination process has been studied in a series of undoped hydrogenated amorphous silicon(a-Si:H) films grown under different deposition conditions. Steady-state photoconductivity (σph) was measured as a function of deep defect density Nd, Urbach energy Eu, and dark Fermi energy Ef. It was found that σph strongly depends on these parameters while Ef- stays at the energy levels lower than 0.82 eV below Ec, but it is nearly independent of those while Ef stays at above 0.82 eV. These behaviors were found to be independent of the sample deposition conditions. These results indicates that subgap defect states enclosed by E=0.82 eV and Ef are the dominant recombination centers.
The µτ Problem: New Results on Micro-Doped a-Si:H Films
Authors: BECK Natalie , WYRSCH Nicolas , SAUVAIN Evelyne , SHAH Arvind
Published: March 2011

Comparative µτ-product measurements performed on a series of slightly doped (micro- doped) a-Si:H films by steady-state photocarrier grating (SSPG), steady-state photoconductivity (SSPC) and time of flight (TOF) are presented. The observed discrepancy between transient and steady-state majority carriers µτ-products is discussed within the framework of a dangling bond recombination model. Furthermore, results on the variation of µτ with doping and light-soaking are reported and ratio of capture cross-sections of charged to neutral defects are deduced.
Creation of Staebler-Wronski Defects at Low Temperatures
Authors: Stradins Paul , Fritzsche H.
Published: March 2011

We extended the kinetics study of light-induced creation of metastable defects in undoped a-Si:H down to T =4.2K. Using band gap light with photocarrier generation rate G0 =3.8x1021cm-3s-1 we find that the change in metastable defect concentration ΔND depends on exposure time te as tme with m = 0.35 ±0.02 at 4.2K, 80K and 300K. The dependence of ΔND on generation rate is G0.44 at 4.2K. The relation between ND and photoconductivity at 300K is nonlinear and not single-valued.
Role of Photodegradation on the \x03C4;Product and Microstructure of the a-Si:H Pin Devices
Authors: Vieira M. , Fortunato E. , Lavareda G. , Carvalho C.N. , Martins R.
Published: March 2011

PIN solar cells were light soaked up to 60 hours. The cell characteristics, the optoelectronic properties and the microstructure parameter (R=I2100/I2100+I2000) as well as the hydrogen content (CH) and density of states (g(Ef)) of the active i-layer were monitored throughout the entire light induced degradation process and compared with the correspondents μτ product (for both carriers) inferred through steady photoconductivity and FST measurements.

Data show a strong correlation between the decrease of μτ product for electron and the increase of the fraction of hydrogen bonded on internal surfaces (R increases from 0.1 to 0.4) suggesting structural changes during the light induced defects' formation. For holes, the μτ product remains approximately constant and only dependent on the initial hydrogen content. As g(Ef) increases, μτ presents an asymmetrical decrease showing that electrons are more sensitive to defects' growth than holes.

We also observe that the rate of degradation is faster for samples having the lowest defect densities, R and CH, showing that the amount of degradation is not a simple function of the photon exposure (Gt product) but also depends on the material microstructure.
Thermal Annealing Recovery and Saturation of Light-Induced Degradation of Amorphous Silicon Alloy Solar Cells with Different Microvoid Density
Authors: Xu X. , Yang J. , Guha S.
Published: March 2011

We have studied the light-induced degradation and thermal annealing recovery of amorphous silicon alloy solar cells with different microvoid density in the intrinsic layer. The microvoid density was changed by altering the deposition rate. The experiments show that cells with higher microvoid density need longer annealing time to recover after prolonged light-soaking. As a consequence, cells with high density of microvoids do not seem to saturate even after long duration of light exposure. The cells with high microvoid density also show much lower degraded efficiency. A careful comparison between degradations caused by accelerated and one-sun light soaking and subsequent annealing recovery indicates that the defects created in the two cases have different nature.
The Relation Between Microstructure and Electronic Properties of Magnetron Sputtered a-Si1−x,Cx:H
Authors: Yang S.Y. , Maley N. , Abelson J.R.
Published: March 2011

We have grown a-Si1-x,Cx:H films by reactive magnetron sputtering, varying the H2 partial pressure from 0 to 6 mTorr and maintaining the substrate temperature at 275°C and argon and methane partial pressures at 1.70 and 0.10 mTorr, respectively.

We investigate the correlation between electronic properties and the fraction of H bonded in "microstructure," defined by the ratio of SiHx stretching mode absorptions in IR and the low temperature H2release in thermal evolution. Our results on sputtered films disprove the monotonic decrease in carrier transport with increasing microstructure fraction which is commonly observed for a-Si1-xCx:H grown by glow discharge of SiH4 and CH4. We find that the electronic properties and microstructure depend on film composition and growth technique, and that the electronic properties are not uniquely determined by the microstructure of hydrogen bonding.
Improvement in Performance of A-SiGe:H Solar Cells for Multi-Junction Cells
Authors: Maruyama E. , Yoshimine Y. , Terakawa A. , Sayama K. , Ninomiya K. , Hishikawa Y. , Tarui H. , Tsuda S. , Nakano S. , Kuwano Y.
Published: March 2011

The quality of a-SiGe:H film was improved by considering the effects of substrate temperature and deposition rate on film properties. Accurate measurement of the optical gap and the film composition of Si, Ge and H made it possible to formulate the optical gap using a linear function of bonded H content (CH) and Ge content (CGE). It was found for the first time that, when the optical gap is fixed to a certain value, the optimum compositions of CHAand CGe exist for high-quality a-SiGe:H. Based on these, we obtained the world's highest conversion efficiency of 3.7 % under red light (AM-1.5, 100mW/cm2 through an R65 filter which allows passage of longer wavelength (>650nm) light) for a 1cm2 a-SiGe single-junction cell. Long-term stability of the cell was also improved.
A New Thin Film Transistor Structure for Increasing Storage Capacitance in the Pixel Element
Authors: Min B.H. , Choi H.S. , Park J.S. , Han M.K.
Published: March 2011

In a high resolution TFT LCD, the ratio of a parasitic capacitance between a gate and a source electrode to the liquid crystal capacitance increase. Increase of the Cgs/Clcmakes the voltage shift of the pixel electrode large. This also results in degradation of the display quality such as image sticking or flicker. The voltage shift can be decreased by increasing the value of a storage capacitor, however, it decreases the aperture ratio.

We present a new thin film transistor structure to increase the storage capacitance without reducing the aperture ratio. In the simulation results, we have observed that the pixel voltage shift is remarkably reduced compared with the conventional one.
Considerations for High Frame Rate Operation of Two-Dimensional a-Si:H Imaging Arrays
Authors: Antonuk L.E. , Yorkston J. , Huang W. , Siewerdsen J. , Street R.A.
Published: March 2011

Large area, two-dimensional, amorphous silicon arrays are under development for x-ray imaging applications. Theoretical limits on frame rates imposed by array design and operational requirements are examined. Measurements of image lag as a function of frame rate are reported.
Page Sized a-Si:H 2-Dimensional Imaging Arrays
Authors: Street R.A. , Weisfield R. , Nelson S. , Nylen P. , Wu X.D.
Published: March 2011

The first page-sized a-Si:H sensor array intended for use as a contact imager is described. The array collects light very efficiently, making it well suited to high speed document input and medical x-ray imaging (by the addition of a phosphor). The array structure, control electronics and imaging properties are discussed. Data is presented from a 13" diagonal array with 512⋗560 pixels of size 0.45 mm, although the technology is capable of higher resolution. The image is read-out using 8 ICs containing 64 voltage sensitive amplifiers. The intrinsic dynamic range of the imaging array is about 105, but is limited to <1000 by the read-out amplifiers. The minimum read-out time of about 25 msec allows real time imaging.
MÖssbauer Studies of Ion Implanted Alloys
Authors: Longworth G.
Published: March 2011

A review is presented of the use of Mössbauer spectroscopy to study the mechanisms responsible for the improvements in wear resistance in ferrous alloys implanted with either light or heavy ions. The phases present in the near surface layers of iron and steel samples implanted with either nitrogen, carbon or tin ions are identified using Conversion Electron Mössbauer Scattering (CEMS) spectra. Samples of wear debris from tin-implanted iron wear discs are analysed in Mössbauer absorption measurements.
Hydrides Examined by Nuclear Magnetic Resonance
Authors: Barnes R. G.
Published: March 2011

Nuclear magnetic resonance (NMR) methods offer many opportunities for studying both crystal and electronic structure in hydrides, as well as the changes that occur in these at phase transitions. NMR also affords an almost uniquely powerful approach to the study of hydrogen diffusion in hydrides. The NMR of all three hydrogen isotopes can be utilized, as well as of a range of technolgically significant metals. Single crystals are not required, samples need not be single-phase, and measurements can be conveniently made over a wide range of temperatures.
Hyperfine Interaction Investigations of Helium Trapping in Metals
Authors: Waard H. De
Published: March 2011

Helium decorated vacancies may be trapped to a high degree and with a high activation enthalpy at impurities in metals. This effect is studied by means of the hyperfine interaction of the radio-active impurities 111In → 111Cd, 119Sb → 119Sn and 129mTe → 129I, implanted into a number of f.c.c. metals and into iron and cobalt. Large changes of the magnetic hyperfine field are caused at 119Sn impurities in Ni, Co and Fe and hiqh values of the electric quadrupole interaction strength are found at 111Cd impurities in Al, Cu, Ag, Ni and Pt when helium decorated vacancies are trapped at the impurities. These effects provide a new method for studying the trapping and desorption mechanism of helium in metals.
The Nature of Fluorine Modified Oxide Surfaces: An Nmr Study
Authors: SCHLUP John R. , Vaughan Robert W.
Published: March 2011

Fluorine modified oxide surfaces have received considerable attention both as research materials and as commercial catalysts. Pulsed NMR has been used to directly observe protons and fluorine on fluorine modified silica,alumina, and aluminosilicates. The center of mass of the 19F spectra is consistent with values reported for covalent siliconfluorine and aluminum-fluorine bonds. The proton and fluorine concentrations have been investigated as a function of sample preparation.
Electronic Structure of Iron Substituted Lithium Intercalated TaS2
Authors: Eibschütz M. , Murphy D. W. , DiSalvo F. J.
Published: March 2011

We have used the 57Fe Mössbauer effect to study the electronic spin configuration of Fe substituted in the layer compound LixTal-yFeyS2(0≤x≤l;0≤y≤0.1). The Mössbauer effect results show that the Fe is localized and in Fe2+ valence state but the electronic configuration depends on the lithium concentration. At room temperature the isomer shift of Fe2+ increases from 0.56 mm/s for x = 0 (no Li) to 0.77 mm/s for x = .86 (at y = 0.05). The isomer shift results reflect the changes in the electronic configuration of the host from Ta4+(5d1) to Ta3+(5d2) and an increase in ionicity as the lithium content increases from 0 to 1.
Silicide Formation at Fe-Si Interfaces Studied by Mössbauer Spectroscopy and Rutherford Backscattering
Authors: Cohen R. L. , Feldman L. C. , West K. W. , Silverman P. J.
Published: March 2011

EXTENDED ABSTRACT

We have deposited the Mössbauer isotope Fe 57 on (111) Si surfaces at room temperature and measured the Mössbauer spectrum using conversion electron Mössbauer spectroscopy for enhanced surface sensitivity. Samples were examined as a function of substrate preparation and thermal anneal. Rutherford backscattering was used to monitor sample preparation. The Fe 57 layers have been coated with natural iron (2.2% Fe 57) or silver to prevent them from oxidizing when exposed to air. The known distinctive Mössbauer spectra of Fe, FeSi, FeSi 2 , Fe in Si, and Si in Fe allows the identification of these phases in the samples.
Laser Annealing of Te-Implanted III-V Semiconductors Studied by Mossbauer Spectroscopy
Authors: Van Rossum M. , Dezsi I. , Langouche G. , De Bruyn J. , Coussement R.
Published: March 2011

The laser annealing behaviour of Te-implanted GaAs, GaSb, GaP and InP has been studied by Mössbauer Spectroscopy. The spectra of the as-implanted samples are characterized by a quadrupole split multiplet, showing that the Te ions come to rest at non-substitutional lattice sites. The laser annealing is shown to shift the implanted impurities towards substitutional positions. The efficiency of the laser annealing procedure is very similar for all lattices under study.
A MÖssbauer Study of Microstructural and Chemical Changes in FE-9NI Steel During Two-Phase Tempering
Authors: Fultz B. , Morris J. W.
Published: March 2011

Two-phase tempering of martensitic Fe-9Ni steel serves to enhance the low temperature toughness and forms austenite precipitates in this material. Hyperfine field effects in Fe-Ni alloys were systematized so that tempering induced chemical composition changes in the martensite could be quantified by Mössbauer spectrometry. The kinetics of segregation of alloy elements from the martensite into the fresh austenite can be determined simultaneously with the amount of austenite which has formed.
Interstitial-Atom Trapping and Deuterium Localization at 57Co Impurities in Cu
Authors: Ma C.T. , Makowski B. , Marcuso M. , Boolchand P.
Published: March 2011

A high purity Cu target foil doped with 57Co and cooled to 80 K has been deuteron irradiated (E = 2 MeV to .5 MeV) using a Van de Graaff accelerator. In-situ Mössbauer spectra of the target were taken as a function of deuterium dose and post irradiation annealing. Two new 57Co sites are observed in addition to the original substitutional site. The new site ‘1’, populated at low temperature following the irradiations is identified with a 57Co impurity atom having Cu-interstitials trapped in its immediate vicinity. The new site ‘2’, populated on annealing the target above 360 K is believed to represent a 57Co impurity having deuterium localized in its vicinity.
Electron Paramagnetic Resonance of Material Properties and Processes
Authors: Brower K. L.
Published: March 2011

The purpose of this paper is to demonstrate, primarily for the non-specialist and within the context of new and recent achievements, the diagnostic value of electron paramagnetic resonance (EPR) in the study of material properties and processes. I have selected three EPR studies which demonstrate the elegance and uniqueness of EPR in atomic defect studies and exemplify unusual achievements through the use of new techniques for material measurement and preparation. A brief introduction into the origin, interaction, and detection of unpaired electrons is included.
Defects in III-V Semiconductors Studied Through EPR
Authors: Kennedy T. A.
Published: March 2011

EPR studies of Cr impurities in GaAs and intrinsic defects in GaP are reviewed to illustrate the contributions that EPR has made to the materials science and technology of III-V semiconductors. EPR has shown how the Cr impurity acts to compensate residual shallow donors or acceptors to produce semi–insulating GaAs which is used for device substrates. EPR work has identified two intrinsic defects, the PGa antisite and the VGa vacancy, and clarified their role in electrical and stoichiometric properties of GaP.
High Power Broad Area GaInAs/GaAs/GaInP Lasers Grown by CBE for Pumping Er Doped Glasses
Authors: Maurel Ph. , Garcia J.C. , Hirtz J.P. , Vassilakis E. , Baldy M. , Parent A. , Carriere C.
Published: March 2011

GaInAs/GaAs/GaInP multiquantum well laser structures have been grown by chemical beam epitaxy (CBE) using conventional sources (hydrides as group V element sources). Large area lasers were photolitographically defined and mounted for continuous wave (CW) measurements. CW output power levels of 600 mW at 25°C are reported from 100 μm wide, 300 μm long laser diodes without any facet treatment. At these levels, the delivered current is 2A, with an associated voltage of less than 1.7 V. The characteristic temperature of the structure is 95 K.

The same structures were then grown using tertiarybutylarsine (TBAs) and tertiarybutylphosphine (TBP). The large area laser diodes were characterized under pulsed conditions. For a 300 μm long cavity, threshold current density of 390 A/cm2 and external quantum efficiency of 0.6 W/A (2 facets) were obtained, demonstrating the suitability of TBP and TBAs as substitutes of arsine and phosphine in chemical beam epitaxy for laser fabrication.
Recombination at Heterojunction Interfaces
Authors: Müllenborn M. , Haegel N. M.
Published: March 2011

Generation and recombination mechanisms at heterojunction interfaces are quantitatively discussed for lattice-matched (AlGaAs/GaAs) and lattice-mismatched (InGaAs/InP) systems. The effect of increased interface recombination on photon recycling and carrier diffusion through the interface region are estimated through a calculation based on the ambipolar diffusion equation. Experimental photoluminescence power dependencies, revealing information about generation and recombination mechanisms, fit well with calculated photoluminescence intensities. Lifetimes and interface extent can be determined by these fits.
In-Situ Dry Etching of InP Using Phosphorus Tri-Chloride and Re-Growth Inside a Chemical Beam Epitaxial Growth Chamber
Authors: Kapre K M. , Tsang W. T. , Sciortino P. F.
Published: March 2011

We have extended the capability and versatility of a chemical beam epitaxial (CBE) system by demonstrating reactive chemical beam etching (RCBE) of InP using phosphorus tri chloride (PCl3)as the gaseous etching beam injected directly into the growth chamber. This permits instant switching from etching to growth (and vice versa) in the same run for the first time in CBE. We investigated RCBE of InP at various substrate temperatures between 400 °C and 580°C, under different PCl3 fluences, and etching conditions. Excellent surface morphology was obtained at high temperatures (> 530°C - 570°C) and under an etching rate of < 6 Å/sec. We also found that upon addition of trimethylindium flow equivalent to a growth rate of 1 Å/sec during RCBE a dramatic improvement in surface morphology was obtained even at a high net etching rate of 10 Å/sec. The surface morphology obtained under such conditions is indistinguishable from that of the original substrate surface. Using Si02 as a mask, in-situ etching of laser mesas followed immediately by regrowth of blocking layers with excellent wetting characteristics was obtained.
Modification of AmBv Semiconductor Layers by Ion Implantation
Authors: Wesch W.
Published: March 2011

The damage production in GaAs, InAs, GaP and InP implanted with different mass ions in the temperature region 80K to 450K has been investigated by means of the RBS/channeling technique at 300K and 100K as well as by optical transmission and reflection measurements. The influence of the implantation parameters on the damage production as well as the differences observed for the various materials are discussed. Further, results concerning the electrical activation after rapid thermal annealing of GaAs and InP implanted at different temperatures are presented.
Defects and Diffusion in Si+ Implanted GaAs
Authors: Jones K.S. , Robinson H.G. , Haynes T.E. , Deal M.D. , Lee C.C. , Allen E.L.
Published: March 2011

The effect of extended defects on the diffusion of ion implanted species is an area of concern in the development of process simulators for GaAs. This study explores the effect of type I extended defects including voids and dislocation loops on the diffusion of Si implanted into GaAs. <100> Semi-insulating GaAs wafers were implanted with 1 × 1014/cm2 Si+ at implant temperatures between -51°C and 80°C and at energies ranging from 20 keV to 200 keV. SIMS results show that the diffusivity of Si decreases with both increasing implant temperature and increasing implant energy. At the same time extrinsic dislocation loop concentrations also increased. For the implant conditions studied, no voids were observed. The diffusion results can only be reconciled with the TEM results if the dislocation loops are behaving in a reactive rather than proactive manner. In other words, the changes in vacancy concentration that are affecting the diffusivity are also affecting the loop concentration. This model is supported by evidence that Si diffusivity is enhanced over the same time interval the dislocation loops are dissolving which is consistent with the loops having a reactive role. It remains unclear whether the existence of loops significantly affects the total concentration of vacancies and thus diffusion by acting as a competing sink.
Rapid Thermal Annealing of InP Implanted with Group IV Eleients
Authors: Ridgway M.C. , Kringhoj P
Published: March 2011

Electrical activation and carrier mobility have been studied as a function of ion dose and annealing temperature for InP implanted with Group IV elements (Si, Ge and Sn). In general, electrical activation increases with decreasing ion dose and/or increasing annealing temperature. Si and Sn exhibit comparable activation and mobility, superior to that of Ge, over the ion dose and temperature range examined. The relative influences of implantation-induced non-stoichiometry and the amphoteric behaviour of the group IV elements have been investigated. For the latter, the amphoteric behavior of Ge > Si > Sn.
Optical Characterization of 100 eV C+ Ion Doped GaAs
Authors: Iida Tsutomu , Makita Yunosuke , Kimura Shinji , Winter Stefan , Yamada Akimasa , Shibata Hajime , Obara Akira , Niki Shigeru , Fons Paul , Tsai Yushin , Uekusa Shin-ichiro
Published: March 2011

Low energy (100 eV) impinging of carbon (C+) ions was made during molecular beam epitaxy (MBE) of GaAs using combined ion beam and molecular beam epitaxy (CIBMBE) technologies for the growth temperature ( Tg ) between 500 °C and 590 °C. 2 K photoluminescence (PL), Raman scattering and Hall effect measurements were made for the samples. In the PL spectra two specific emissions, “g” and [g-g], were observed which are closely associated with acceptor impurities. PL and Hall effect measurements indicate that C atoms were very efficiently introduced during MBE growth by CIBMBE and were both optically and electrically well activated as acceptors even at Tg=500 °C. The results reveal that defect-free impurity doping without subsequent annealing can be achieved by CIBMBE method.
Pseudomorphic HEMT Devices for Microwave and Millimeter Wave Applications
Authors: Wu C.S. , Lan G.L. , Pao C.K. , Bar S.X. , Hu M.
Published: March 2011

Pseudomorphic HEMT (PHEMT) devices have demonstrated superior performance at microwave and millimeter wave frequency ranges. They exhibit multi-functional characteristics such as high power, high efficiency and low noise over a broad frequency range (C-band through W-band). Because of their important, broad range of applications, the microwave industry has recently begun developing the PHEMT manufacturing technology in order to cope with the increasing demand for PHEMT insertion into microwave products. In this paper we will discuss the advantages of using PHEMT devices for microwave and millimeter wave applications and provide an overview of the published state-ofthe-art performance of PHEMT devices and monolithic microwave integrated circuits (MMICs) at microwave and millimeter wave frequencies. We will also present recent progress in Hughes PHEMT technology development including device epitaxial design and process enhancements. Finally, we will present recent data on PHEMT reliability.
Gas-Phase Generation of Nanometer-Sized Metal Particles for Fabrication of Zero-Dimensional Quantum Structures
Authors: Pluym Tammy C. , Kodas T.T. , Wang L.M. , Wiedensohler A. , Hansson H.C. , Maximov L. , Samuelson L.
Published: March 2011

Nanometer-sized particles of Mo, Ta, Nb, and Pd were formed by gas-phase reactions of metal halides and β-diketonates in the presence of hydrogen. Particle diameters ranged from 5-100 nm depending on the reaction temperature (500-950 βC) and precursor characteristics. Gasphase particle concentrations reached 108/cm3. These particles are suitable as etching masks on semiconductor substrates for generation of zero-dimensional quantum structures.
Effect of Doping on the Growth of InGaP by Low Pressure Metalorganic Chemical Vapor Deposition
Authors: Wu C.H. , Feng M.S. , Wu C.C.
Published: March 2011

A study of the effect of dopant incorporation on the growth of InGaP by low pressure metalorganic chemical vapor deposition has been performed, in which diethylzinc (DEZn) and H2Se are used as p and n-type doping sources, respectively. The enhancement of interdiffusion, i.e., the disordering of a InGaP layer has been observed due to the introduction of Zn into the growth layer, as indicated by the decrease of intensity of the extra spots on TEM diffraction results. In addition, streaky and wavy diffraction pattern for Se-doped layer reveals the formation of anti-phase domains on a growth layer. According to PL measurement, the emission energy of the grown layer is a function of doping concentration, for which the energy shift as high as 141 meV has been obtained at heavily zinc doping concentration. Therefore, by varying the doping concentration, energy shift can be controlled, providing a potential for its application in optical devices.
Determination of the Valence Band Offset in GaAs/(Ga,Al)As Superlattices by Hot Electron Excitation Spectroscopy
Authors: Weinert H. , Zukauskas A. , Latinis V. , Stepankevicius V.
Published: March 2011

A GaAs/Ga1−xA1xAs-superlattice was investigated using quasi-cw PL measurements at T=2 K. The relevant sample parameters were determined by X-ray diffraction: barrier thickness - 5 nm, qw-thickness - 5 nm, x = 0.41. A series of PL-spectra at medium, but constant excitation intensity for different excitation energy (from 1.64 eV to 2.1 eV) was measured. From the high-energy slope of the PL-spectra the electron-temperature Te was determined. A clearly structured dependence of Te on hvexc (excitation energy) was found. We assumed the pronounced structures of the Te - hvexc - hvexc - “spectrum” to be the onset-energies of new, for lower excitation energies not possible relaxation processes. Calculating the excess energy for each kind of carriers (heavy and light holes and electrons) separately, we found δEv=( 0.18 ± 0.05) ∆Eg for the investigated sample. Using this new experimental method one also is able to obtain the energies of higher electronic states (for example Γ → L -transitions) of GaAs/(Ga,Al)Assuperlattices.
DX Centers in AlGaAs and Pressurised GaAs
Authors: Anand S. , Subramanian S. , Arora B. M. , Lu Y. C. , Bauser E.
Published: March 2011

In this paper, we present results of our investigations on some aspects of the DX centers. It is shown from the low temperature Hall mobility measurements that the charge state of the DX center is neutral supporting the positive U model for the DX center. Hall and DLTS measurements on Al-rich Al0.8Ga0.2As:Te sample show a reversal in the ordering of the energies of the hydrogenic and deep states of the Te donor, with the DX state lying higher than the X valley related effective mass state. Thermal emission properties of the pressure induced DX states of Ge and Se donors in neutron transmutation doped (NTD) GaAs are discussed.
Low Dislocation-Density and Vacancy-Rich Glassy-Pinning Quasi GaAs Crystal by Liquid-Encapsulated Czochralski Growth
Authors: Saito Yasutuki , Fujii Takashi
Published: March 2011

Not all threshold voltage (Vth) scattering of Si-implanted metal-semiconductor field- effect- transistors (MESFETs) on low dislocation density and semi-insulating (S.I.) liquid- glass encapsulation Czochralski (LEC) GaAs crystals grown at relatively high pull-speed were small. By comparison with the Lang x-ray topographs of the wafers, it was found that x-ray topograph contrast variations reflected on the films did not correspond with Vth variations of the wafers at all. Especially, in low dislocation density regions, which are in white regions on the films of the x-ray topographs, very large Vth turbulences were observed. We believe that dislocation-less in LEC GaAs crystals causes large Vth turbulences of Si-implanted MESFETs and that frozen cell-lattice-structure large turbulences by pinning centers associated with vacancies like glass cause large Vth turbulences.
Electronic and Optical Properties of HgI2
Authors: Chang Yia-Chung , Sim Hock-Kee , James R. B.
Published: March 2011

We present theoretical studies of electronic structures, optical responses, and phonon modes of undoped HgI2 in its red tetragonal form. The electronic band structure is studied via an empirical nonlocal pseudopotential model, including the spin-orbit interaction. The electron and hole effective masses, optical matrix elements for interband transitions, and complex dielectric function are computed. Excitonic effects on the absorption coefficient near the fundamental band gap are included within the effectivemass approximation. The resulting absorption spectra and their polarization dependence are compared with experiment with favorable agreement. The phonon modes of HgI2 are studied with a microscopic model and a good fit to the neutron scattering data is obtained.
Electrical Properties in Cvd Diamond Films
Authors: Zhao S. , Gan K.K. , Kagan H. , Kass R. , Malchow R. , Morrow F. , Palmer W. , White C. , Pan L.S. , Han S. , Kania D. , Plano M. , Landstrass M. , Lee M. , Kim S. , Sannes F. , Schnetzer S. , Stone R. , Thomson G. , Sugimoto Y. , Fry A. , Kanda S. , Olsen S.
Published: March 2011

The electrical properties associated with carrier mobility, μ, and lifetime, τ, have been investigated for the chemical vapor deposited (CVD) diamond films using charged particle-induced conductivity and time resolved transient photo-induced conductivity. The collection distance, d, the average distance which electron and hole depart when driven by an applied electric field E, was measured by both methods. The collection distance is related to the carrier mobility and lifetime by d = μEτ Our measurements show that the collection distance increases linearly with sample thickness for CVD diamond films. The collection distance at the growth side of the CVD diamond film is comparable to that of single crystal natural type IIa diamond; at the substrate side of the film, the collection distance is near zero. No saturation of the collection distance is observed for film thickness up to 500 microns.
Radiation Dosimetry Via the Radio-Photoluminescence of Synthetic Diamond
Authors: Keddy Rex J. , Nam Tom L. , Araikum Shawn
Published: March 2011

A method of radiation dosimetry based upon the radiophotoluminescence (RPL) of synthetic diamond crystals is presented. When the RPL is generated by a stimulation wavelength of 296 nm a linear response vs radiation dose of up to 20 kGy can be obtained with selected crystals. The response is very dependent on the chemistry of the synthesized specimen.
Electrical Mobility and Carrier Lifetime in Single-Crystal, Isotopically Pure Type IIa Synthetic Diamond
Authors: Pan L. S. , Han S. , Kania D. R. , Banholzer W.
Published: March 2011

Single-crystal type IIa diamonds were synthesized by applying high temperatures (1200°;C) and high pressures (52000 atm) to powdered polycrystalline diamond grown using conventional CVD techniques. These samples were isotopically pure, consisting of approximately 99.93% 12C, compared to roughly 98.96% in natural IIa diamonds. In addition, the dislocation density of the synthetic samples is significantly lower than in natural IIa diamonds, as indicated by birefringence measurements. Electrical properties of these samples were measured using transient photoconductivity, where a 3 ps pulse of ultraviolet light (6.1 eV) was used to excite free electron-hole pairs. Compared to natural IIa diamonds, the lifetime at low fields (200 V/cm) and low excitation densities (1015 cm-3) in the synthetic sample was significantly longer (1 ns in the synthetic sample vs. 200 to 300 ps in natural diamond). At higher fields, a much longer decay component, exceeding 10 ns, was observed in the synthetic sample. Combined electron and hole mobilities were around 2500 cm2/V-s in the synthetic diamond, compared to 3000 to 4000 cm2/V-s in the best natural samples. At a field of 2 kV/cm, the drift distance in the synthetic sample was over 50 μm, considerably longer than that of natural diamond (10 μm). This is due primarily to the much longer carrier lifetimes. The longer lifetimes in the synthetic sample demonstrate that the properties of the best natural diamonds can be exceeded and are encouraging for the development of sensitive diamond radiation detectors. These longer lifetimes are likely due to the higher quality and lower defect density in the synthetic samples, rather than the isotopic purity.
Fundamentals of Semiconductor Detectors for Ionizing Radiation
Authors: Knoll G.F. , Mcgregor D.S.
Published: March 2011

The modes of operation of semiconductor detectors are reviewed, together with the influence of charge carrier collection in developing a signal pulse for spectroscopic applications. Because of the importance of charge trapping in many semiconductors of interest in the fabrication of room temperature radiation detectors, the effects of incomplete charge collection are quantified. Calculated results are presented for the expected pulse height and energy resolution under a variety of charge collection conditions.
Sub-Nanosecond Detection of Heavy Ions Using Single-Crystal, Natural Type IIA Diamond
Authors: Han Sung , Prussin Stanley G. , Pan Lawrence S. , Lane Stephen M. , Kania Don R. , Wagner Ronald S. , Evans Caleb R.
Published: March 2011

The sub-nanosecond electrical transients induced by 5-MeV He+ and 10-MeV Si3+ ions have been measured in single-crystal, natural type Ila diamonds. The detectors were fabricated into conductivity modulated devices and were incorporated into 50-Ω high bandwidth transmission line structures. The electrical signals were recorded with a system based on a 70 GHz random sampling oscilloscope with the total recording rise time of 18.6 ±:0.6 ps.

Signal rise times are less than 70 ps and fall times are less than 200 ps for electric fields in the range 3.8x104 - 1×105 V/cm. The plasma time appears to play a key role in defining the initial stages of the charge transport because signal rise times are much greater than the recording system rise time, especially with the Si-ion excitation. Furthermore, incomplete charge collection is quite severe even at the highest applied electric fields due to the dominance of carrier trapping/recombination at the defect sites.
Band-Edge Photoresponse Characteristics of Diamond Msm's
Authors: Marchywka Mike , Binari Steven C. , Koolbeck Deborah A. , Moses Daniel
Published: March 2011

Band-edge photoresponse measurements on simple diamond metal-semiconductor-metal (MSM) devices can give information about the quality of the diamond material and its utility as a detector. We have fabricated several such devices on a variety of substrates and measured their response between 700 and 120nm with special emphasis around the band edge near 220nm. Steady state and transient response have been measured as a function of bias conditions. Transient response in this case refers to initial overshoot, undershoot, and increased dark current in response to a chopped vacuum ultraviolet (VUV) light signal for times on the order of seconds. We compare steady state quantum efficiency results to a simple model, discuss the characteristics of response versus applied voltage, and examine relationships between response and substrate properties.
Fast GaAs Photoconductor Responses to Subnanosecond Proton Pulses
Authors: Brullot B. , Galli R. , Lecat X. , Rubbelynck C. , Pochet T.
Published: March 2011

GaAs photoconductors -have been tailored to detect ultrafast proton pulses having energies ranging between 4 and 9 MeV. The sensitivity, the linearity and the speed of response of the devices are analyzed as a function of their neutron pre-irradiation treatment. The dependence of the sensitivity on the proton energy and the applied polarization is also studied. Finally, the experimental results are compared with a simple theoretical model.
Multi-Element Mercuric Iodide Detector Systems for X-Ray and Gamma-Ray Imaging
Authors: Patt Bradley E.
Published: March 2011

The advancement of room-temperature mercuric iodide detector technology to the point of spectroscopy-grade energy resolution coupled with the advancement in long-term stability and the high efficiency of these detectors now make it's use in large scale array systems for x- and gamma-ray imaging applications viable. Camera design criterion differ depending upon the application. A HgI2 gamma-ray camera developed at EG&G Energy Measurements has been used for imaging with various apertures, and the energy dispersive imaging aspects have been examined. Concepts for applications such as medical diagnostic imaging and a satellite based telescopes for x- and gamma-ray mapping have been objectified.
Characterization of Growth Defects in ZnTe Single Crystals
Authors: Zhou W. , Wu J. , Dudley M. , Su C.H. , Volz M.P. , Gillies D.C. , Szofran F.R. , Lehoczky S.L.
Published: March 2011

(111) wafers sliced from a boule of ZnTe grown by horizontal physical vapor transport (PVT) have been characterized using synchrotron white beam X-ray topography. The growth axis was about 6° off [311]. The presence of dislocation slip bands, subgrain structures and [111] axis 180° rotational twins were revealed. The slip bands were observed to break up the ordered dislocation cell structures comprising the subgrain boundaries. The initiation of slip at regions of stress concentration at the junctions of subgrain boundaries and twin boundaries was observed. The asymmetric distribution of slip bands either side of the twinned region of crystal suggests that twin boundaries can act as barriers for slip. Several types of detailed twin boundary configuration were determined from the topographs. Using a combination of white beam X-ray topography and Nomarski interference microscopy, the three dimensional shapes of the twin boundaries were determined. Approximate atomic structures at these boundaries are presented.
An Array of CdTe Detectors for Imaging Applications
Authors: Eisen Y. , Polak E.
Published: March 2011

The performance characteristics of a linear array composed of several hundred miniature spectroscopy grade CdTe detectors are described. The linear array is utilized in a X-ray security imaging system. It operates either in an energy dispersive mode to highlight certain atomic elements in the luggage or in a regular mode for obtaining only the transmission image of the luggage. The array functions in the photon counting mode and tolerates count rates as high as 106 counts/sec. The array has high quantum efficiency and good spatial resolution which result in excellent image quality. The dynamic range, the electronic noise, the energy resolution, the homogeneity of response among detectors and the image quality are presented.
Elemental Impurity Analysis of Mercuric Iodide by Icp/Ms
Authors: Cros Eilene S. , Mroz Eugene , Olivares José A.
Published: March 2011

A method has been developed to analyze mercuric iodide (HgI2) for elemental contamination using Inductively Coupled Plasma/Mass Spectroscopy (ICP/MS). This paper will discuss the ICP/MS method, the effectiveness of purification schemes for removing impurities from Hgl2, as well as preliminary correlations between HgI2 detectorperformance and elemental contamination levels.
A HgI2 Microstrip Detector Based on Resistive Charge Division Readout
Authors: Grassi D. , Murolo F. , Perillo E. , Spadaccini G. , Vigilante M. , Amann M. , Koebel J.M. , Siffert P. , Dusi W.
Published: March 2011

A HgI2 linear array detector with a surface resistive layer between the readout strips has been constructed with the aim of achieving the maximum possible active detection area and a spatial resolution of ≈ 50 µm, by using an analog readout of the strip outputs and a centroid finding algorithm.

This device has been developed as a high efficiency position-sensitive detector for use in a Bragg X-ray spectrometer, designed for detecting X-ray photons with energies up to ≈ 30 keV.

Calculations performed by taking into account the various sources of electronic noise have allowed the optimization of the interstrip distance and resistance.

Fabrication techniques and preliminary results on energy and spatial resolution are reported and discussed.