bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of A-SI Pin Solar Cells with Buffer
Authors: Pfleiderer H P.H
Published: March 2011

The buffer of standard solar cells restricts the "surface recombination" at the front side. Some typical cell properties linked to the buffer are exposed by numerical simulations: The "blue snake" appearing in small-signal photocharacteristics, the electron inversion layer, the reverse field peak and the satellite space-charge dipole layer. It is possible to base a simulation on the roots of an algebraic equation.
Design and Fabrication of Graded Bandgap Solar Cells in Amorphous Si and Alloys
Authors: Dalal Vikram L. , Baldwin Greg
Published: March 2011

In this paper, we discuss the appropriate design conditions and fabrication technology for graded bandgap solar cells in a-Si:H and a-(Si,Ge):H. In particular, we show that by carefully designing the buffer layers and the placement of the graded gap in the i layer of a p-i-n cell, one can fabricate a-Si:H solar cells which are more stable than standard design solar cells. Similarly, appropriate considerations of device physics and electric field profiles in devices made from a-(Si,Ge):H alloys can result in high performance a-(Si,Ge):H cells . We also show that using significant H dilution during growth of a-(Si,Ge):H layers and cells results in both films and devices of high quality and reproducibility.
Enhanced Light Absorption in a-Si:H Layers of Solar Cells by Applying Tco/Metal Back Contacts
Authors: Tao G. , Girwar B.S. , Landweer G.E.N. , Zeman M. , Metselaar J.W.
Published: March 2011

The optimization of the back contact reflectivity for thin film a-Si:H solar cells has been performed. The results of optical calculations show that a-Si:H/TCO/Metal interfaces with a proper TCO thickness reflect much more than their a-Si:H/Metal counterparts. We compared solar cells which were deposited on a flat substrate with different back contacts. The back contacts consisted of a metal layer (aluminum, silver/aluminum) or combined TCO/metal layers (TCO/Al, TCO/Ag/Al). The same was done with solar cells which were deposited on a textured substrate. The solar cells with a TCO/metal back contact showed not only a significantly increased short-circuit current density but also an increase in the spectral response. The cells with TCO/Ag/Al back contact showed the best result.
Use of a Field Effect Transistor to Study Phototransport Properties of a-Si:H
Authors: Grant A. R. , Persans P. D. , Kwasnick R. F. , Possin G. E.
Published: March 2011

We report new measurements of the diffusion length of minority photocarriers in thin film amorphous silicon field effect transistor structures. We are able to vary the majority carrier photoconductance by more than four orders of magnitude while monitoring the effective ambipolar diffusion length using the photocarrier grating technique.
Hydrogenation Effect of Amorphous Silicon Thin Film Transistors by Atmospheric Pressure CVD
Authors: Ahn Byung Chul , Kim Jeong Hyun , Kim Dong Gil , Moon Byeong Yeon , Kim Kwang Nam , Lee Chan Woo , Jang Jin
Published: March 2011

The hydrogenation effect was studied in the fabrication of amorphous silicon thin film transistor using APCVD technique. The inverse staggered type a-Si TFTs were fabricated with the deposited a-Si and SiO2 films by the atmospheric pressure (AP) CVD. The field effect mobility of the fabricated a-Si TFT is 0.79 cm2/Vs and threshold voltage is 5.4V after post hydrogenation. These results can be applied to make low cost a-Si TFT array using an in-line APCVD system.
Reduction of the Defect Density in a-Si:H Deposited at ≤250°C
Authors: Nishio Hitoshi , Ganguly Gautam , Matsuda Akihisa
Published: March 2011

We present a method to reduce the defect density in hydrogenated amorphous silicon (a-Si:H) deposited at low substrate temperatures similar to those used for device fabrication . Film-growth precursors are energized by a heated mesh to enhance their surface diffusion coefficient and this enables them to saturate more surface dangling bonds.
Addressable Photosensing Elements for 2-Dimensional Image Sensors Using a-Si Alloy P-I-N Diodes
Authors: Cesare G. De , Rosa P. Di , Monica S. La , Salotti R. , Rita R. , Schirone L.
Published: March 2011

We describe amorphous silicon alloy addressable photo-sensitive elements whose operation has been experimentally verified in 2-dimensional image sensors. The investigated structures consist of p-i-n photodiodes (PD) stacked and back-to-back connected to n-i-p blocking diodes (BD). A first developed device is based on a TCO-p+(Si)-i(Si)-n+(Si)- i(SiC)-p+(SiC)-Metal structure. Due to an optimization of the thickness and of the energy gap of the layers, we obtained a rectification ratio between the current levels in forward and reverse bias conditions If/Ir=106, under AM1.5 illumination, filtered at 500 nm. A better rectification ratio If/Ir>106, under white AM 1.5 light, has been achieved by introducing a metallic film inside the n+ layer, for light shielding; this further technological step allows both the independent optimization of BD’s and PD’s structures, and the increase of the operation speed.
2D Image Sensing Arrays with NIP Diodes
Authors: Berkel C Van , Bird N C , Curling C J , French I D
Published: March 2011

2D image sensor arrays made with a-Si devices on glass over large area are of considerable interest as document scanners and in medical applications. We have made a test array containing a-Si NIP diodes for both the sensors and the active matrix switching devices. The issues of vertical crosstalk and image lag are discussed in relation to the device performance of the switching diode. The vertical crosstalk is controlled by the diode capacitance and the image lag by the high transient current in the device. We speculate that the transient current is a trap filling current in the deep states of the switching diode.
Photoresponse Linearity of a-Si:H Imaging Pixels
Authors: Yorkston J. , Antonuk L.E. , Huang W. , Street R.A.
Published: March 2011

Amorphous silicon imaging arrays with ∼3×105pixels have recently been developed and x-ray images of low contrast anatomical phantoms have been demonstrated. This paper reports on the linearity of response of these a-Si:H imaging pixels as a function of reverse bias voltage. The fraction of the imaging pixel's full signal range that maintains a linear response has been found to increase with increasing voltage.
Simulation of a-Si:H Color Sensors for Application in Intelligent Sensor Systems
Authors: Stiebig H. , BÖhm M.
Published: March 2011

Amorphous silicon based n-i-p-i-n structures may be used as color detectors. A simulation program has been developed which allows the examination of the spatial distribution of carrier concentrations, electric field and current densities under different illumination conditions. Furthermore current/voltage- and monochromatic response curves are presented. The results of the simulation point out that the defect density in the p-layer has a major influence on device performance.
Utilization of a-Si:H Switching Diodes for Signal Readout from a-Si:H Pixel Detectors
Authors: Cho Gyuseong , Drewery J.S. , Hong W.S. , Jing T. , Lee H. , Kaplan S.N. , Mireshghi A. , Perez-Mendez V. , Wildermuth D.
Published: March 2011

Two-dimensional arrays of amorphous silicon photodiodes can be used as position-sensitive radiation detectors when they are coupled to an appropriate phosphor. We have developed signal readout schemes from amorphous silicon photodiode arrays utilizing one or two switching diodes attached to each pixel photodiode. Individual cells and prototype arrays of amorphous silicon photodiodes with single- and double-diode switching readout were fabricated and tested. A charge storage time and a readout time were measured. The measurement results were analyzed by simple circuit theory.
Electron Transport and Conduction-Band-Tail States in a-Si:H Deposited with a Remote Hydrogen Plasma
Authors: Nebel C.E. , Street R.A. , Johnson N.M. , Walker J.
Published: March 2011

Electron transport properties of a-Si:H prepared in a remote hydrogen plasma deposition reactor (RHPD) at TD = 400°C were investigated in the temperature regime 110 K ≤ T ≤ 300 K by time-of-flight and post-transit spectroscopy experiments. Based on these data the conduction-band-tail state distribution was calculated. In the energy range 85 meV ≤ Ec- E ≤ 350 meV below the mobility edge Ec the tail is well described by an exponential distribution with a characteristic energy of ≃ 21 meV. Deeper in the mobility gap (Ec-E > 350 meV) the tail smoothly passes over into the defect density which is approximately six orders of magnitude smaller than at the mobility edge. Comparisons with data deduced on conventionally prepared a-Si:H (RF-, DC-glow discharge) at TD = 230 °C show that electron transport and the conduction band tail of the RHPD material are comparable.
An Asynchronous Image Subtracting Optically Addressed Spatial Light Modulator
Authors: Barbier Pierre R. , Moddel Garret
Published: March 2011

The operation of image-subtraction is useful in optical processing. We report the first asynchronous image-subtracting optically addressed spatial light modulator incorporating a ferroelectric liquid crystal and a color-sensitive a-Si:H p-i-n-i-p photodetector. We present experimental results characterizing the sensitivity of the photodetector current-voltage characteristics to wavelength, and demonstrate image subtraction. Finally, we propose a model that explains the operation of the image-subtracting OASLM.
Coal and the Moessbauer Effect
Authors: Montano Pedro A.
Published: March 2011

The presence of iron bearing minerals in coal makes the Moessbauer effect extremely useful as an analytical tool. In this paper we present a general review of the use of Moessbauer spectroscopy in coal research. We discuss a simple method to identify iron bearing minerals in coal. Several researchers have used the Moessbauer effect to study the transformations of iron minerals during coal processing. We have studied the stoichiometries of iron sulfides produced during coal liquefaction. We found drastic changes in the stoichiometry of the pyrrhotites as a function of the total sulfur content of the coal, and the reaction conditions. Some in situ experiments are reported in this paper. We have observed evidence of reactions between the coal components and the iron sulfides at high temperatures (400° C). The possibility of studying in situ reactions makes the Moessbauer effect a unique analytical tool.
NMR of Small Platinum Particles
Authors: Stokes Harold T. , Rhodes Howard E. , Wang Po-Kang , Slicuter Charles P. , Sinfelt J. H.
Published: March 2011

We present 195Pt NMR lineshapes as well as relaxation data in three different samples of platinum metal particles (46%, 26%, and 15% dispersion) supported on alumina. We show that the electronic properties of these particles are very much different from those of bulk Pt metal. A prominent peak in the lineshape has been identified as a “surface resonance” which arises from Pt nuclei on the surface of the Pt particles. We find that these surface Pt atoms are “nonmetallic” when coated with adsorbed molecules.
Motional Correlation Time of Dilute 111Cd Impurities in Se-Rich Liquid Se-Te Alloys
Authors: Gaskill D. K. , Gardner J. A. , Krane K. S. , Krusch K. , Rasera R. L.
Published: March 2011

The motional correlation time, τc, in liquid Se and Se-rich Se-Te alloys has been investigated between 500 and 900°C using time differential perturbed angular correlations of y-rays from dilute 111Cd impurities. In all alloys we find τc ∝ exp (E0/kT) at low T where E0 = 0.36 eV. τC deviates from this relation at high T. At low T, τCis tentatively identified as the lifetime of a Cd to host molecule bond, and at high T as the average lifetime of bonds in the host molecule.
Study of Internal Indium Oxidation in Silver by TDPAC
Authors: Pasquevich A. F. , Sánchez F. H. , Bibiloni A. G. , Massolo C. P. , López-García A.
Published: March 2011

Internal oxidation of indium in a silver matrix is studied by time-differential perturbed angular correlations. The oxidizer treatments were performed in air at 1 atm. Our results are consistent with the formation of different In-O complexes.
A Mössbauer Study of the Amorphous System (FexNi1−x)75P16B6Al3
Authors: Bjarman S. , Wäppling R. , Rao K.V.
Published: March 2011

In the system (FeXNi1−x)75P16B6Al3 an unusual magnetic behaviour is found in the composition range 0.2<x<0.3. The drastic changes seen at low temperature in the thermomagnetic measurements is found not to affect the Mössbauer spectra. From the width of the magnetic hyperfine field distribution as function of temperature there seems to be a distribution in Curie temperatures. Due to the absence of spin texture it was not possible to make a distinction between the two proposed low temperature phases although the general results favour the spin glass alternative.
Isotope Effect on The Electronic Structure of Hydrogen in Metals
Authors: Jena P. , Satterthwaite C. B.
Published: March 2011

The effect of the isotopic mass on the redistribution of electron charge and spin density around a light impurity such as hydrogen in metals has been studied. Considered in this review are: (a) the magnetic hyperfine coupling to the hydrogen nucleus and the effect of isotopic mass, (b) the isotope effect in hydrogen impurity resistivity, (c) the reverse isotope effect in superconducting PdH(D) and (d) the thermally induced detrapping of hydrogen from the vicinity of solute sites in metallic hosts.
Electron Spin Resonance Studies of Amorphous Silicon
Authors: Biegelsen David K.
Published: March 2011

Electron spin resonance and related spin dependent measurements have been used to make key contributions to the understanding of amorphous silicon, specifically as probes of the dominant states in the gap, recombination processes and doping. In this paper we give a cursory description of the techniques as they apply to this problem. We then review what has been learned in a-Si:H usually from coupled results of spin resonance and other complementary experimental techniques. The results lead us to a surprisingly simple picture of the equilibrium and non-equilibrium behavior of defects and carriers in this prototypical amorphous semiconductor.
Integration of a Quantum Well Laser with AlGaAs/GaAs-HEMT Electronics
Authors: Bronner W. , Hornung J. , Köhler K. , Olander E. , Wang Z.-G.
Published: March 2011

In this presentation the various technology steps for the monolithic integration of GaAs quantum well lasers with Double Pulse Doped AlGaAs/GaAs/AlGaAs Quantum Well (DPDQW) E/D HEMT electronics on a single substrate in one process run are described. All layers are grown by molecular beam epitaxy. The laser structure, consisting of three 74 Å GaAs quantum wells between two AlGaAs cladding layers, are grown on top of the electronic structure. The laser mesas and contact areas are defined by a combined wet and dry etch process. Apart from the transistor gates which are exposed by electron beam lithography, all lithography steps are performed using contact printing. A two layer metallization is used to interconnect the devices whereby air-bridges are used to connect the laser mesas to the electronics. First results showed laser action of laser diodes of area 3 x 300 μm2 at a threshold current of less than 60 mA, as well as the operation of different electronic devices on wafers which have been processed in this way. These include a laser diode driver, and an optoelectronic receiver with a MSM photo diode, both devices operating at a data rate of 5 Gbit/sec. These results indicate that the process sequence described is suitable for the integration of laser diodes and HEMT electronics.
Small Diameter Dry Etched Via Holes in GaAs
Authors: Pearton S. J. , Ren F. , Katz A. , Tseng B. , Lothian J. R. , Fullowan T. R.
Published: March 2011

Two techniques for fabricating through-wafer via holes in 2-4 mil thick GaAs substrates were examined. In the first, Ni or thick photoresist masks were used for patterning 30 μm diameter vias by ECR-rf dry etching using low pressure (10-20 mTorr), low bias (– 150V) BCI3/C12 discharges. Microwave enhancement of these discharges produced faster etch rates but a greater degree of isotropic material removal at a given pressure. Reducing the process pressure produces extremely anisotropic features with high aspect ratio. The BC13-to-C12 ratio must be kept to ≥5:1 to maintain the anisotropy. A novel laser drilling technique was also examined - in this case a Q-switched beam with high energy density was used to ablate material in each pass of the beam, producing a via in approximately 40 passes. This is a maskless procedure capable of producing any desired via hole pattern, but currently there is no selectivity for ablating GaAs over a front-side metal film.
Electron Cyclotron Resonance CVD of Silicon Oxynitride for Optoelectronic Applications
Authors: Boudreau M. , Boumerzoug M. , Kruzelecky R. V. , Mascher P. , Jessop P. E. , Thompson D.A.
Published: March 2011

Silicon oxynitrides with compositions varying from Si3N4 to SiO2 were deposited on silicon substrates by electron cyclotron resonance plasma enhanced chemical vapour deposition (ECRPECVD). The silicon source used is an organic liquid, Tris Dimethyl Amino Silane (trade name SiN – 1000TM). Optical emission spectroscopy is used to characterize the ECR plasma, this information then is correlated with the optical properties of the deposited film, as determined by in situ ellipsometry. Auger electron spectroscopy showed that only low levels of carbon (< 3 at%) are present. The SiO2 and Si3N4 films are close to stoichiometric, with low levels of bonded hydrogen as determined by infrared absorption spectroscopy.

Planar waveguide structures were fabricated and tested using the prism coupling technique to determine the mode effective indices. These are compared to those expected from the ellipsometry measurements.
Vacuum Integrated Fabrication of Buried Heterostructure Edge Emitting Laser Diodes
Authors: Hong M. , Vahkshoori D. , Grober L. H. , Mannaerts J. P. , Chu S. N. G. , Wynn J. D. , Freund R. S.
Published: March 2011

We describe an in-situ fabrication process which combines electron cyclotron resonance (ECR) plasma H2 to clean native oxides, ECR SiCl4 to etch anisotropically, a brief Cl2 chemical etch to remove any near surface damage and contamination, and molecular beam epitaxial (MBE) regrowth. We report the first buried heterostructure (BH) AlGaAs/GaAs/InGaAs edge emitting laser diodes fabricated using this in-situ process. The lasers operate in continuous mode without noticeable degradation.
Influence of CH4/H2 Reactive Ion Etching on Deep Levels in Si-Doped AlxGa1−xAs (x=0.25)
Authors: Pereira R. , Van Hove M. , de Potter M. , Van Rossum K.
Published: March 2011

The effect of CH4/H2 reactive ion etching (RIE) on Si-doped AlxGa1−xAs (x=0.25) is studied by deep level transient spectroscopy (DLTS) and Hall measurements. After RIE exposure, the samples were annealed between 250 and 500°C in order to study the recovery kinetics of deep and shallow levels. Non-etched reference samples showed broad DLTS spectra which were deconvoluted in two different emission peaks. We assigned them to DX1 and DX2 centers. The different deep levels are characierized by different aluminium configurations, one or two aluminium atoms, surrounding the silicon donor which are responsible for the DX centers. After RIE exposure and subsequent thermal annealing, a third emission peak is observed. This emission is attributed to the DX3 center, which is characterized by three aluminium atoms neighbouring the silicon donor. The recovery activation energy is calculated based on first-order kinetics. The activation energies are found to be around 1.9 eV in all cases.

Complementary Hall measurements as a function of temperature (4-300 K) were used to characterize the electron capture of deep levels in Si-doped AlGaAs exposed to CH4/H2 RIE. We observed that the samples exposed to RIE and annealed at temperatures higher than 400°C exhibit electron capture in the 120-150 K temperature range. On the other hand, samples annealed at lower temperatures, showed additional capture features between 200 and 230 K.
Growth of Heterojunction Bipolar Transistors by Metalorganic Molecular Beam Epitaxy
Authors: Abernathy Cammy R.
Published: March 2011

Heterojunction bipolar transistors (HBTs) are becoming increasingly important for highspeed electronic applications. This paper will discuss how the unique growth chemistry of metalorganic molecular beam epitaxy (MOMBE) can be used to produce high performance HBTs. For example, it has been well documented that MOMBE's ability to grow heavily doped, well-confined layers of either n- or p-type is a significant advantage for this device. This feature arises primarily from the ability to use gaseous dopant sources in the absence of interfacial gas boundary layers. While this is an advantage for doping, it can be a disadvantage in other areas such as AlGaAs purity or InGaP lattice matching. This paper will discuss how these difficulties can be overcome through the use of novel Al or Ga precursors thus allowing deposition of high quality GaAs-based HBTs. By using trimethylamine alane (TMAA), background impurity concentrations can be reduced substantially. Further improvements in purity require cleaner Ga precursors or alternatively novel Ga substitutes. The resulting reduction in compensation allows for the use of lower dopant concentrations in the AlGaAs thus producing significant improvement in the leakage behavior of the base-emitter junction. Even further improvement can be achieved through the use of InGaP. Using novel Ga precursors, such as tri-isobutylgallium (TIBG), the problems associated with the sensitivity of composition to growth temperature are greatly reduced, allowing for the reproducible deposition of devices containing InGaP emitter layers.
Lattice Damage in Ion-Implanted Compound Semiconductors and Its Effect on Electrical Activation
Authors: Haynes T. E. , Morton R. , Lau S. S.
Published: March 2011

In recent years, a number of experimental observations have indicated that interactions between mobile point defects generated during ion implantation play an important role in the damage production in Ill-V compound semiconductors, and particularly GaAs. This paper reviews a set of such observations based on ion channeling measurements of the lattice damage in GaAs implanted with Si ions. Selected independent observations are also surveyed to illustrate the importance of point-defect interactions. Taken together, these show that at least two contributions to the lattice damage must often be considered: a “prompt” contribution attributed to direct-impact amorphization, and a “delayed” contribution attributed to point-defect clustering. New measurements are then described which show the different effects that these two damage components have on the electrical activation in annealed, Siimplanted GaAs. The aim is to indicate the potential to exploit the balance between these two damage contributions in order to improve the electrical performance and reproducibility of ion-implanted and annealed layers. Finally, the applicability of these concepts to other ion species and other compound semiconductors (GaP and InP) is briefly discussed.
Modeling Dopant Diffusion in Gallium Arsenide
Authors: Deal M. D. , Hu C. J. , Lee C. C. , Robinson H. G.
Published: March 2011

We have been developing models for our process simulators, SUPREM 3.5 and SUPREM-IV, for processes used in the fabrication of GaAs devices. Our initial experiments led to relatively simple models for diffusion of common dopants in GaAs, usually dependent only on temperature and the local dopant or carrier concentration. These models were incorporated into our first GaAs simulator, SUPREM 3.5. While these simple models were adequate for some process conditions, there are many cases where anomalous diffusion occurs and these models break down. The generally accepted diffusion mechanisms for n- and p-type dopants in GaAs have been shown to be the same as, or indistinguishable from, the models used for diffusion in silicon, and are therefore compatible with the diffusion algorithms used in SUPREM-IV. These algorithms include the effects of point defects. GaAs and eight of its dopants have recently been incorporated into SUPREM-IV and we have modeled, or are attempting to model, many of the anomalous diffusion phenomena using this simulator. These phenomena include uphill diffusion of implanted dopants, time dependent diffusion, implant energy dependent diffusion, and abnormal diffusion of grown-in dopants in MBE and MOCVD material.
Application of the Amphoteric Native Defect Model to Diffusion and Activation of Shallow Impurities in III-V Semiconductors
Authors: Walukiewicz W.
Published: March 2011

The effects of heavy doping on the formation of charged point defects are considered. It is shown that the Fermi level dependent part of the formation energy of highly localized defects can be determined using a universal energy reference, common to all III-V compound semiconductors. The concept is used to analyze the electrical activity and diffusion of dopant impurities in these compounds. We present model calculations which explain the correlation between the maximum hole concentrations and the acceptor impurity diffusion in InP and in InGaAs alloys, doped with group II acceptors. The calculations account for the redistribution of the impurity atoms at the lattice matched InP/InGaAs interface. It is also demonstrated that an abrupt enhancement of the Fermi level induced defect formation is observed at the onset of highly degenerate statistics in heavily doped semiconductors.
Arbitrary Composition Profiles by MBE Using Desorption Mass Spectrometry
Authors: Evans K.R. , Kaspi R. , Cooley W.T. , Jones C.R. , Solomon J.S.
Published: March 2011

The ability to produce semiconductor structures with arbitrary vertical composition profiles offers the device physicist new freedom in device structure design. We report on the incorporation of the in-situ sensor technique of desorption mass spectrometry (DMS) in a realtime feedback loop for the continuous control of desorption rates. Assuming previous knowledge of relevant incident fluxes, this technique provides for continuous determination of the composition of the outermost layer of the growing crystal. Using AlGaAs growth as an example, the Ga desorption rate Fd(Ga) is monitored continuously during growth, providing an accurate measure of Al-fraction in the topmost layer of the growing film. By comparing the measured and desired Fd(Ga), an error signal is generated and minimized by varying an appropriate growth parameter. Structures which are vertically graded in composition are produced by programming a varying Fd(Ga) versus time profile. Both substrate temperature Ts and incident arsenic flux Fi(As2) affect Fd(Ga) in a controllable way. Thus, two distinct control loops are constructed based on variable Ts and Fi(As2), respectively. As demonstration vehicles, graded AlGaAs structures with linear, parabolic, sawtooth, and sinusoidal compositional profiles have been produced and characterized. Additionally, we discuss some of the limitations of this technique and its applicability to other materials.
Electrical Characterization of Passivation Processes in Si-GaAs by Isothermal Photoinduced Transient Measurements
Authors: Dkiouak R. , Macia J. , Perez-Rodriguez A. , Gual J. , Morante J.R.
Published: March 2011

The analysis of SI-GaAs passivated with different plasma treatments by isothermal PITS measurements shows the ability of this technique for the characterization of the electrical effects of the surface treatments. PITS spectra show, in addition to a midgap level assigned to EL2, a non exponential peak which strongly depends on the passivation process. This is related to the generation of defects during the surface processing, likely through the presence of interaction processes involving mid-gap related levels. The comparison between the spectra with different passivation conditions suggests the presence of ionized species in the plasma treatment and the fast growth rate of the passivation layer to determine a higher generation of these process related defects.
In Situ Flux Transient Monitoring and Correction During MBE Growth of Quantum Well Structures
Authors: Celii F. G. , Kao Y.-C. , Katz A. J.
Published: March 2011

Shutter closure during MBE deposition causes source overheating and results in flux transients. These transients are particularly detrimental to the thickness and compositional accuracy of thin quantum well layers. In this paper, we document the effects of flux transients on growth of multiple quantum well (MQW) and resonant tunneling diode (RTD) structures, and demonstrate rudimentary transient correction by employing real-time flux detection.

Reflection mass spectrometry (REMS) provides a convenient in situ method for MBE flux monitoring. The Group III partial pressures can be detected in the presence of Group V overpressure, and REMS is compatible with wafer rotation. We used REMS to characterize In, Al and Ga flux transients as a function of shutter closed time, cell flux and substrate temperature. Overshoot magnitudes up to 30% were observed. We verified the correspondence of REMS signal transients and effusion cell flux transients using GaAs/AlGaAs and InGaAs/lnAlAs MQW and test structures. We also successfully demonstrated flux transient correction by cell temperature ramping during MQW and RTD growth.
Creation of In-Plane Anisotropic Strain in GaAs/A1xGa1−xAs Multiple Quantum Well Structures
Authors: Lu Y. , Kuo H.C. , Shen H. , Taysing-Lara M. , Wraback M. , Pamulapati J. , Dutta M. , Kosinski J. , Sacks R.
Published: March 2011

Thin film of GaAs/AlGaAs multiple quantum well (MQW) structure have been bonded to the lithium tantalate (LiTaO3) or calcium carbonate (CaCO3) substrates cut such that one of the linear thermal expansion coefficients almost matches that of the MQW while its orthogonal counterpart does not. By choosing the proper bonding and operating temperatures, in-plane anisotropic strain up to 0.3% has been achieved. The transmission spectrum shows an anisotropy in excitonic absorption which results in a polarization rotation of a light beam at normal incidence to the structure. The theoretical calculation is in agreement with the experimental results. Using the polarization rotation, we have demonstrated a novel MQW light modulator with an exceedingly high contrast ratio of 330:1.
Rapid Thermal Low Pressure Metalorganic Chemical Vapor Deposition of InP and Related Materials
Authors: Katz A. , Feingold A.
Published: March 2011

High quality InP and In0.53Ga0.67As undoped and Zn-doped layers were grown by means of rapid thermal low pressure metalorganic chemical vapor deposition (RTLPMOCVD) technique, using tertiarybutylphosphine (TBP) and tertiarybutylarsine (TBA), as the phosphorus and arsenic sources. The InP films were grown at a P:In ratios of about 75 and the InGaAs films were grown at a As:In ration of about 2, low temperatures at the range of 450-550°C, pressures it the range of 1-4 tons, and growth rates of 2-3 nm/sec. All the film growth conditions were optimized to yield defect-free layers with featureless morphology, which reflected at a minimum backscattering yield (Xmin) as low as 3.1% for the InP and 3.6% for the InGaAs. These films presented a good electrical properties, as well, with hole mobility of 4200 cm2/Vs for the undoped-InP layers and 75 cm2/Vs for the undoped-InGaAs layers.
Investigation of an Alternative Chemical Etchant for Mercuric Iodide Detectors
Authors: David Dominique C , Scyoc J. Van , Khudatyan Mardik , James R. B. , Anderson R. J. , Schlesingfer T. E.
Published: March 2011

At present a 10% KI solution is commonly used as an etchant for HgI2 crystals. Recent photoluminescence (PL) spectra from such etched samples show that impurities contained in the KI solution dope the HgI2 during the etching process. Some of these dopants are known to cause carrier trapping in the detectors fabricated from the material. Thus, it is desirable to find an alternative etchant that does not create new defects in HgI2. Etchants studied here include deionized water, 10% potassium iodide (KI), methanol, and acetone. The results of acetone as an etchant reveal only small changes in the PL spectra after etching. Methanol etching causes the incorporation of a deep radiative recombination center in HgI2.
Recent Progress in The CdTe γ-Rays Detector Simulation
Authors: Manfredotti C. , Fizzotti F. , Ongaro C. , Vittone E. , Nastasi U.
Published: March 2011

Recently, we reported a simulation of spectroscopic performances of CdTe detectors by a Monte Carlo program ‘ISIDE’. The program was demonstrated to be extremely useful both for an exact simulation of the spectral response of CdTe to γy-rays and for a detailed understanding of the effect of physical and electronic parameters on the experimental performances. In the present work, the attention is focused on the various aspects of CdTe response to 57Co γ-rays, in an energy interval which is extremely interesting for practical applications of CdTe spectroscopy. Spectra are presented for different experimental conditions, particularly as far as electronics set up is concerned, in correlation with the relevant rise time distributions and with spatial distribution of interaction points in the detector. It is proved that in order to account for the rise times distributions as compared with the experimental ones, one must assume the presence of a dead region on the front of the detector. Moreover, a clear indication of what is needed in order to reach the best energy resolution in realistic conditions is given.
Use of Room Temperature Semiconductor Detectors for the Verification of Nuclear Material in International Safeguards Recent Advances
Authors: Arlt R. , Rundquist D.E. , Bot D. , Siffert P. , Richter M. , Khusainov A. , Ivanov V. , Chrunov A. , Petuchov Y. , Levai F. , Desi S. , Tarvainen M. , Ahmed I.
Published: March 2011

In the paper the development and usage of radiation detection systems based on room temperature semiconductors are described. The detection systems are intended for use by safeguards inspectors to verify nuclear material. Because of their high intrinsic efficiency, these detectors have advantages compared to classical germanium or Nal detectors. Several measurement tasks which cannot be handled in an optimum manner by using standard detectors have been solved. The main problem in the application of room temperature semiconductor detectors is the limitation in the availability of large detector volumes.
Pulse Processing for Planar Cadmium Telluride Detectors
Authors: Richter M. , Hage-Ali M. , Kuznicki Z.T. , Siffert P.
Published: March 2011

Planar CdTe detectors with different performances for gamma radiation detection have been investigated. The detector internal electric field was analyzed by means of time-of-flight experiments. The correlation of the results with the current-voltage characteristics of the samples, their risetime distribution for different gamma irradiation and, eventually, the shape of detected gamma spectra led us to a detector model based on the theory of space charge limited current.

Using this model, we try to explain operation and failure of trapping loss correction methods for the different detector groups.
Mathematical Model for the Simulation of Crystallization of CdTe in a vertical Bridgman Furnace.
Authors: Steer Ch. , Hage-Ali M. , Siffert P.
Published: March 2011

Temperature measurements in a crystal growth ampoule of CdTe (Cadmium Telluride) are very difficult. Mathematical simulation is a very powerful tool to predict the behavior and temperature distribution during crystal growth. We applied this technique to the bulk growth of large single crystals of CdTe. The simulation revealed that for CdTe, it is possible to create a convex interface shape during growth, necessary for single crystal growth. The controlling parameter is the temperature profile along the ampoule. The temperature gradient is rather meaningless, as we can show with our simulations.

We will present some crystals grown under good and bad thermal conditions.
Fast Diamond Photoconductors
Authors: Pochet T. , Brullot B. , Galli R. , Rubbelynck C.
Published: March 2011

Preliminary results on the response of type Ib and IIa diamond photodetectors to fast laser pulse exposures at 265 and 530 nm are presented. The influence of the applied bias, the laser wavelengths and the light intensity on the detector sensitivity is studied. Also, recent measurements with 1.25 MeV gamma ray pulses are reported.
Improvements in Thallium Bromoiodide Photodetectors for Scintillation Spectrometers
Authors: Zhang J.G. , Cirignano L. , Daley K. , Squillante M.R.
Published: March 2011

Thallium bromoiodide, a tuneable band gap semiconductor system, was investigated as a photodetector for scintillation spectrometers. Extensive zone refining of starting materials, based on numerical simulations, considerably enhanced the electrical resistivity to 1011 Ωcm. In addition, accelerated crucible rotation technique (ACRT) crystal growth and after-growth annealing have improved the charge carrier mobility-lifetime product. However, a relatively low signal-to-noise ratio due to a high dielectric constant and relatively low quantum efficiency continues to be an obstacle to achieving high performance, large area T1BrxI1−xphotodetectors.
Studies of Charge Collection in GaAs Radiation Detectors
Authors: Berwick K , Brozel M R , Butiar C M , Cowperthwaite M , Hou Y
Published: March 2011

The behaviour of the charge collection efficiency of particle detectors fabricated from Semi-Insulating (SI) Liquid Encapsulated Czochralski (LEC) GaAs as a function of applied bias is investigated for alpha particles and it is shown that it cannot be explained by simple models that assume a uniform electric field across the detector. To investigate this the electric field within the SI GaAs has been studied. We have attempted to correlate the measured charge collection efficiency with the observed field distributions. Some correlation is found but other effects may also be present.
Improved Quality of Bulk II-VI Substrates for HgCdTe and HgZnTe Epitaxy
Authors: Sen Sanghamitra , Stannard John E.
Published: March 2011

Single crystals of CdTe or dilute alloys of Cdl−y ZnyTe (y ≤ 0.04) and CdTel−zSez (z ≤ 0.04) with low defect density, high purity and large single-crystal area (>30 cm2) are required as substrates for high-quality epitaxial Hgl−xCdxTe thin films in the infrared (IR) detector industry. Bridgman or gradient freeze is the most common technique used for commercial production of these materials because of its success in producing large area substrates of good quality and reproducibility. For epitaxial growth of Hg1−xZnxTe, which has been of considerable interest in recent years as an IR detector material, the substrate of choice has been Cd0.80Zn0.20Te, for lattice matching with long wavelength Hg1−xZnxTe epitaxial layers (x = 0.13–0.14). The primary focus of this paper is on CdZnTe which is currently the preferred substrate material and most widely used for both HgCdTe and HgZnTe epitaxy. This paper reviews the current status of bulk substrate technology for IR detector applications, highlighting critical issues and essential research areas for further improvement of these materials.
Mapping of Defects in Metal-Semiconductor-Metal (MSM) Detectors in Hg1−xCdxTe by Nuclear Microprobe
Authors: Leech Patrick W. , Dooley Sean P. , Jamieson David N.
Published: March 2011

The incidence of compositional and structural inhomogenieties in MSM detectors based on Hg1−xCdxTe/GaAs and Hg1−xCdxTe/GaAs/Si has been examined by nuclear microprobe. With a 2 MeV He+ beam focussed to ≥5 μm, the microprobe has demonstrated the capability for RBS channelling in the active region of a Hg1−xCdxTe device and the imaging of defects by Channelling Contrast Microscopy (CCM). A series of linear growth defects in some Hg1−xCdxTe devices were identified using CCM. The channelling RBS spectra from these regions have shown an increase in χmin compared with the surrounding high quality crystal. The occurence of these defects was associated with a degradation in the performance of affected devices in an array. RBS spectra have also revealed the presence of an anomalous CdTe layer, correlating with a significant reduction in dark current and increase in breakdown voltage of these devices. RBS channelling of individual devices has identified differences in χmin between arrays which were prepared under equivalent conditions of growth and processing.
Quality of Bulk Cdte Substrates and Its Relation to Intrinsic Defects
Authors: Meyer B. K. , Hofmann D. M. , Stadler W. , Emanuelsson P. , Omling P. , Weigel E. , MÜller-Vogt G. , Wienecke F. , Schenk M.
Published: March 2011

Both the cadmium vacancy (Vcd) and the tellurium vacancy (VTe) in CdTe are identified by means of electron paramagnetic resonance (EPR). The VCd is a double acceptor and the EPR spectrum is observed in its single negative charge state. The symmetry is found to be trigonal, which can be explained in a model in which the hole occupies a dangling bond t2 orbital and the orbital degeneracy is removed by a static Jahn-Teller distortion. The hyperfine interaction shows that the hole is localised on one of the four Te neighbours. The EPR spectrum of VTe+ reveals cubic (unperturbed) symmetry and the hyperfine structure shows that the unpaired electron is equally spread over the four Cd neighbours.

Photo-EPR measurements locate the 0/+ state of VTe at Ev + 0.2 eV and the 2−/− acceptor level of VCd to be situated less than 0.47 eV above the valence band.
Recent Developments in High Resistivity Detector-Grade CdTe
Authors: Hage-Ali M. , Siffert P.
Published: March 2011

We present a brief review of results concerning the doping or compensation of CdTe by different elements like halogen, group IV, hydrogen and 3d transition elements for high resistivity materials. Comparison with theoretical models and discussion of results under this light is provided.
Bulk Defects and Radiation Damage in Detector Grade Silicon
Authors: Walter J. , Garber W. , Wunstorf R. , Bugg W. , Harvey J. , Casson W.
Published: March 2011

The importance of bulk defects in Si to the performance of Si radiation detectors is discussed and the current state of knowledge about deep level defects, including those induced by radiation damage, is briefly reviewed. The importance and origins of the fluctuations in the spatial distribution of the shallow point defects which determine the uncompensated net impurity density are discussed and information on this problem in FZ silicon, multipass FZ silicon, neutron transmutation doped Si, and radiation damaged Si is presented and compared to what should be expected on the basis of simple modeling. A new model for radiation damage induced changes in the net uncompensated impurity density is reviewed and compared to experimental data on fast neutron damage in Si.
Charge Collection Processes in a-Si:H p-i-n Detectors
Authors: Pochet T.
Published: March 2011

Charge induced as a function of time in a-Si:H p-i-n detectors by protons having energies ranging between 5 and 12 MeV have been studied. A multiple trapping transport model is developed in order to explain the non saturation of the collected charge with bias and evidence of a bias dependent recombination process is shown. The dependence of the total induced charge (the detector efficiency) with bias can be expressed by an Onsager function with a thermalization distance of 34 Å.
TiSi2 Formation on Submicron Polysilicon Lines: Role of Line Width and Dopant Concentration
Authors: Ganin E. , Wind S. , Ronsheim P. , Yapsir A. , Barmak K. , Bucchignano J. , Assenza R.
Published: March 2011

We report on a study of the effects of dopant concentration and linewidth on the formation of TiSi2 on polysilicon. The transformation from the C49 phase to the C54 phase is inhibited by a high concentration of either phosphorus or arsenic in blanket polysilicon films. For sub-half-micron lines, patterned in polysilicon doped with As or P, agglomeration is the key factor in the inability to produce low resistance silicide. The result is a critically shrinking process window for the attainment of low resistance VLSI interconnects.
Optical Fiber Pyrometry with in-Situ Detection of Wafer Radiance and Emittance—Accufiber's Ripple Method
Authors: Fiory A. T. , Schietinger C. , Adams B. , Tinsley F. G.
Published: March 2011

A two-channel optical-fiber pyrometry technique for simultaneous measurement of thermal radiance and emittance was used to measure and control the temperature of silicon wafers heated by quartz-halogen-tungsten lamps in various rapid-thermal processors, including an A.G. Associates Heatpulse. The ripple method dynamically determines emittances by sensing time-dependent components in radiation from the lamps and radiation reflected by the wafer surface. Wafers were coated with films of various textures and patterns to test the technique over a range of surface emittances spanning about an order of magnitude. Temperature accuracies of at least ±5°C are achievable from 650°C to 1050°C, and above, for pyrometry at lμm wavelength.
To the Influence of the Wafer Edge in RTP
Authors: Zöllner Jens-Peter , Patzschke I. , Pietzuch V. , Pezoldt J. , Eichhorn G.
Published: March 2011

The goal in Rapid Thermal Processing is the realization of homogeneous and stable temperature distribution across the wafer.

Due to the wafer edge an additional heat loss occurs, which leads to temperature decrease near the wafer boundary. This can be the origin for layer thickness inhomogenities and defect generation. For successful compensation it is necessary to know why such a temperature gradient exists.

The heat transfer at the wafer edge was investigated by using computer simulation.

The results confirmed by experimental data in the pressure range of 1.. 760 Torr are discussed and criteria for the compensation of the temperature gradient near the wafer edge are developed.
Stress and Warpage Studies of Silicon Based Plain and Patterned Films During Rapid Thermal Processing (RTP)
Authors: Thakur R.P.S. , Martin A. , Fackrell W.T. , Barbour R. , Kawski J. L. , Perroots L.
Published: March 2011

Single wafer rapid thermal processing (RTP) is emerging as a key player in the processing of advanced sub-half micron memory devices. The high temperature processing of large diameter silicon wafers can create sufficient thermal stress for generation of dislocation, slip, and gross mechanical instability of the wafer. The aforementioned factors may lead to loss of device yield, dielectric defects, and reduced photolithographic yield due to degradation of virtual wafer flatness. Moreover, the loss of geometrical planarity of wafer due to warpage can make it impossible to process a wafer or can lead to self-fracture of the wafer.

In this paper we present the warpage and stress results of our study on plain and patterned structures that were subjected to RTP at different stages of the CMOS process flow. Experimental results have been gathered with full wafer scanning technology using non-contact capacitive probes to measure more accurate global stress values. The stress and warpage values on the patterned wafers could be measured accurately without any light scattering effects and destructive interference. It is reported that the thermal processing creates significant variations in shape change around the wafer which could be identified using the full wafer data set acquired using this evaluation technique. We have successfully tracked variations in film stress for both plain and patterned structures as a cumulative effect and correlated it with the overall wafer warpage. The effects of incoming wafer warpage, ramp rate in RTP, and high stress nitride films on the overall wafer warpage are also reported.