bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient and Stress Effects in Amorphous Silicon Thin-Film Transistors
Authors: Hack M. , Weisfield R. , Willums M.F. , Masterton G.H. , Lecomber P.G.
Published: March 2011

In this paper we present experimental and simulation results of the transient response of amorphous silicon (a-Si) thin film transistors (TFTs) over many orders of magnitude in time after the application of a voltage pulse to the gate. In general three regimes are observed by plotting drain current versus the logarithm of time. At times longer than the carrier transit time and extending up to 1 - 100 msecs, the current rapidly decreases due to trap filling, after which it then slowly decays up until defects are created in the silicon channel when it then finally decays more rapidly again. Our simulation results are in good agreement with the data for the short time trap filling regime, as a function of both gate bias and stress condition. Measurements at elevated temperatures show that the middle slow decay regime is caused by charge injection into interface states or the gate dielectric. Finally we also demonstrate that this slow decay regime does not occur in nin diodes, confirming that it is not caused by defect generation in the a-Si, and is instead related to the presence of the dielectric in a TFT.
Amorphous Silicon and Silicon-Germanium Thin-Film Transistors Formed by Ion Implantation
Authors: Sarcona G. , Hatalis M.K. , Catalano A.
Published: March 2011

Thin-film, n-channel transistors were fabricated in hydrogenated amorphous silicon and silicon- germanium thin films using ion implantation to form source and drain regions. The germanium alloy content in the films were: 0, 15, and 25 at % For each content of germanium, the annealing temperature and time necessary to activate the implant, without degrading device performance due to hydrogen effusion, was determined. The time necessary to anneal aluminum to form ohmic contacts at the optimal anneal temperature (260°C) was also determined. Thin-film transistors were characterized, and important device parameters such as: saturation mobility, threshold voltage, subthreshold swing, and ON-OFF current ratio were determined.
Extraction of Altered Localized-States in a-Si and poly-Si TFT’s Under Various Conditions
Authors: Hwang J.R. , Park J.S. , Jun M.C. , Jang J. , Han M.K.
Published: March 2011

We present results regarding to extraction of altered localized-states in both amorphous silicon and polycrystalline silicon thin film transistors under various conditions, such as electrical and light stress, crystallization, and hydrogenation. Both deep and tail states have been extracted by fitting calculated current-voltage curves to measured data. The density of deep states as well as tail states in a-Si are significantly increased by stress, which may be the predominant mechanism causing the degradation in a-Si TFT performances. Also, the correlations between trap distributions in poly-Si films and their device performances have been successfully identified by analyzing the effects of crystallization and hydrogenation on the current-voltage characteristics of poly-Si TFT’s.
Effects of Excimer Laser Irradiation on the Characteristics of a-Si:H TFT's
Authors: Lee S.K. , Oh C.H. , Kim Y.S. , Park J.S. , Han M.K.
Published: March 2011

We have investigated the annealing effects of ultraviolet (UV) irradiation on the characteristics of hydrogenated amorphous silicon (a-Si:H) thin films and hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFT's) using XeCl excimer laser. The pulse duration of laser was 30nsec/shot and its intensity was varied from 10mJ/cm2 to 80 mJ/cm2. By irradiating the excimer laser on the a-Si:H TFT's degraded by the electrical stress and/or the visible light illumination, the characteristics of TFT's, such as the on- current, threshold voltage, field-effect mobility and subthreshold sharpness, have been effectively restored to those of virgin sample, while the leakage current changed little. It should be noted that the a-Si:H channel layer was not crystallized by varying the laser intensity.
Current-Noise-Power-Spectra for Amorphous Silicon Photodiode Sensors
Authors: Boudry J.M. , Antonuk L.E.
Published: March 2011

Pixelated imaging arrays consisting of hydrogenated amorphous silicon (a-Si:H) photodiode sensors and field effect transistors are under development for x-ray imaging. For such arrays it is important to quantify the sensor noise characteristics as these may, in some cases, limit the array performance for certain applications. The current-noise-power-spectra of ∼1 nm thick a- Si:H p-i-n sensors of various areas are presented. The power spectra were measured for different reverse bias voltages over a frequency range of ∼0.01 to 1.0 Hz. The power spectra revealed the noise to be composed primarily of flicker noise. The flicker noise showed a l/fbdependence where b ranged from ∼1.1 to 1.2. The magnitude of the flicker noise as a function of the sensor leakage current and the sensor area has been investigated and is presented.
Large Area Position Sensitive Detector Based on Amorphous Silicon Technology
Authors: Fortunato E. , Vieira M. , Ferreira L. , Carvalho C.N. , Lavareda G. , Martins R.
Published: March 2011

We have developed a rectangular dual-axis large area Position Sensitive Detector (PSD), with 5 cm × 5 cm detection area, based on PIN hydrogenated amorphous silicon (a-Si:H) technology, produced by Plasma Enhanced Chemical Vapor Deposition (PECVD). The metal contacts are located in the four edges of the detected area, two of them located on the back side of the ITO/PIN/A1 structure and the others two located in the front side. The key factors of the detectors resolution and linearity are the thickness uniformity of the different layers, the geometry and the contacts location. Besides that, edge effects on the sensor's corner disturb the linearity of the detector. In this paper we present results concerning the linearity of the detector as well as its optoelectronic characteristics and the role of the i-layer thickness on the final sensor performances.
Mossbauer Spectroscopy Studies of Amorphous Metallic Solids
Authors: Chien C. L.
Published: March 2011

Mössbauer spectroscopy as applied to the studies of amorphous metallic, and often magnetic solids will be discussed. The advantages of using this microscopic technique will be compared with others in terms of obtaining information on electronic, magnetic, hyperfine, structural and other properties. Examples of magnetic ordering structures, concentration dependence of ordering temperature, hyperfine field distribution, spin-wave excitations, crystallization behavior, quadrupole interaction, isomer shift, etc., as obtained by Mössbauer spectroscopy will be presented.
Defects in Metals–Detected by Spin Precession Methods
Authors: Wichert TH. , Recknagel E.
Published: March 2011

Recent advances in the study of point defects and small defect clusters by nuclear methods will be reviewed. Suitable radioactive atoms which fulfill the requirements of spin precession techniques are introduced into solids, where they are used as microscopic probes to investigate their immediate surrounding. Trapping, detrapping or annealing of defects is reflected by changes of the hyperfine interaction between the nuclear moments of the probe atoms and the electromagnetic fields of the defects. The interaction is extracted from a time differential spin precession pattern or–more obviously–from the Fourier transform of it, which can be regarded as the resonance spectrum of the involved frequencies. It allows a distinct recognition of different defects and comprises detailed information about their structural properties. Experimental data on interstitials, vacancies and clusters in metals will be quoted as illustrations for the scope of information, which can be achieved by hyperfine interaction studies.
Muons as Light Hydrogen Probes–Diffusion and Trapping
Authors: Richter D.
Published: March 2011

Contributions of the muon spin rotation technique (μSR) to metal physics problems are surveyed. The similarity between the muon and the proton constitutes μSR as a new tool to investigate the physics of H–like interstitials on an atomic scale. Experiments on the lattice location and on local properties like the Knight shift as well as diffusion measurements are reviewed. In particular the extreme sensitivity of muons toward impurities and lattice defects is emphasized. Results on the trapping of muons by substitutional impurities or vacancies in the ppm range are displayed.
MÖssbauer Effect Study of the Absence of Fe Magnetism in Superconducting Sc2Fe3Si5 and Th7Fe3
Authors: Cashion J. D. , Shenoy G. K. , Niarchos D. , Viccaro P. J. , Falco Charles M.
Published: March 2011

There are only a few Fe-based compounds which are superconducting since the depairing of Cooper pairs is unavoidable in the presence of an Fe moment. In Sc2Fe3Si5 and Th7Fe3, Mössbauer measurements on 57Fe show that there is no magnetism at the Fe site in either compound. The isomer shift values indicate the reason behind this identical magnetic behavior to be quite different in its electronic origin.
Proton NMR Spin-Lattice Relaxation Time Characterization of a-Si(H) Structure
Authors: Lowry M. E. , Barnes R. G. , Torgeson D. R. , Jeffrey F. R.
Published: March 2011

NMR data are presented for reactively sputtered amorphous silicon-hydrogen alloys (a-Si(H)). Measured differences in two of the samples are attributed to two distinct morphologies: a mixed phase (monohydride and dihydride) and a purely monohydride composition. Features of the mixed phase morphology have been modeled. Room temperature, 35 MHz spin-lattice relaxation times are presented for a series of monohydride samples prepared with systematically varied sputtering parameters. A correlation of proton T1 with the density of ESR states tentatively is suggested.
Proton NMR Studies of Amorphous Plasma-Deposited Films
Authors: Reimer Jeffrey A. , Vaughan Robert W. , Knights John C.
Published: March 2011

Proton magnetic resonance data are presented for the hydrogen alloys of plasma-deposited amorphous boron, silicon, carbon, silicon carbide, and silicon nitride. Linewidth and lineshape analysis leads to the conclusion that hydrogen nuclei are clustered in a-Si/C:H, a-C:H, and a-Si/NiH. The a-Si/C:H and a-C:H data show that hydrogen exists in two phases. Modeling of linewidths in a-Si/C:H indicates that the two phases are heavily hydrogenated carbon clusters imbedded in a weakly hydrogenated silicon lattice. Evidence is also presented for the presence of motionally narrowed hydrogen spectra in a-B:H, a-Si/N:H and a-C:H. “B NMR spectra in a-B:H show no evidence of motional narrowing. It is suggested that the hydrogen nuclei giving rise to the motionally narrowed spectra are associated with disorder modes.
Tdpac-Studies of Electric Field Gradients in Amorphous Metallic Systems
Authors: Heubes P. , Korn D. , Schatz G. , Zibold G.
Published: March 2011

The time differential perturbed γ-γ angular correlation technique (TDPAC) is applied to the amorphous metallic systems Ga, Bi, In50Au50 and In80Ag20. The electric field gradient tensor probed by 111Cd nuclei shows a broad probability distribution with a relative width of 0.4 – 0.5 for all systems, as suggested by a continuous random structural model.
Radiation Damage Studies of USn
Authors: Mcguire T. K. , Herber R. H.
Published: March 2011

Uranium stannide, the most stable intermetallic compound in the Uranium/Sn system, has the Cu3Au(LI2 ) structure, and is paramagnetic to liquid He temperature. The magnetic susceptibility data are consistent with 5f band states rather than a localized electronic structure. Samples of this compound have been prepared both with depleted and 235U enriched, as well as 119Sn enriched starting material. Detailed 119mSn Mössbauer effect studies have been carried out over the temperature range 78≤T≤300 K on 60Co gamma ray irradiated, thermal neutron irradiated (depleted), and thermal neutron irradiated (enriched) samples, using the V 10 position of the Brookhaven HFR facility for the neutron irradiations (thermal/fast >3.6×102). The Mössbauer hyperfine parameters are: IS(78) = 2.45 mm/sec, Q.S.(78) 1.38 mm/sec for the unirradiated samples, consistent with the metallic nature of Sn in the USn3 structure. No anomalous charge states have been identified in the Mössbauer spectra of the gamma or neutron irradiated samples. The free-atom lattice temperature is ∼250 K for the unirradiated sample, and shows only minor changes with 60Co–γ radiation to a total dose of 1000 Megarad. Thermal neutron radiation (nvt ∼5×1016 ) of the depleted sample results in a lowering of the lattice temperature to ∼240 K. Two hours heating at 800°C are sufficient to anneal the radiation damage as judged by lattice dynamical data. A sample enriched to 99.94% 235U and irradiated to a fluence of ∼5×1015 slow neutrons/cm2 showed an increase in the freeatom lattice temperature to ∼275 K. A two hour anneal at 800°C restored this parameter to its original value. Resistivity data for these samples and their relationship to spin fluctuation temperatures will also be discussed.
Epr of Mn2+ in Ni(CH3COO)2 4H2O and K2 Ni(SO4)2 6H2O
Authors: Misra Sushil K. , Jalochowski M.
Published: March 2011

The technique of electron paramagnetic resonance has been applied to study the magnetic properties of nickel acetate and nickel potassium tutton salt single crystals, using Mn2+ ion as probe. From the values of spin Hamiltonian parameters and linewidths at room, liquid nitrogen and liquid helium temperatures it is concluded that these crystals do not become magnetically ordered as the temperature is lowered to 3.2K, and thus the transition temperature, below which the crystal would order either ferromagnetically, or antiferromagnetically, for these crystals, should be below 3.2K.
Study of Internal Motion in Materials by Means of Direct Observation of Relaxation Resonances in NMR (NMRRR)
Authors: Van Gerven L. , Coppens P. , Van Hecke P.
Published: March 2011

A method, different from the classical ones, for studying internal motions - in particular reorientational and tunneling modulation of rotations - via NMR is described. Instead of looking for matching or resonance maxima in NMR T1−1 vs. T - curves [ where o (↗)≅ωo,with ρ the correlation rate and ωo: the Larmor frequency] we look for such maxima in NMR T1−1 vs. ωo - curves [where ω =↗o, with ω: the (tunneling)frequency]. These method, Nuclear Magnetic Resonance Relaxation Resonance (NMRRR), has marked advantages, which are discussed. A field cycling technique is presented. Typical results, for solid silane, are given.
Fully Planar Ion-Implanted 0.98 μm Strained Quantum Well Laser
Authors: Hobson W. S. , Pearton S. J. , Ren F. , Chu S. N. G. , Bylsma R. , Elliman R. G.
Published: March 2011

GaAs-InGaAs quantum well laser structures were fabricated using a 5 MeV O+ implant (∼1015 cm−2 dose) to disorder the quantum well for optical isolation upon post-implant annealing. End-of-range disorder is placed in the underlying substrate, and consisted of small dislocation loops. Electrical isolation was provided by a subsequent multiple energy (40-300 keV) O+ implant scheme. Masking for both implant steps was obtained using a lift-off Au deposition. This fully planar process is considerably simpler than the Si diffusion process for quantum well disordering that is commonly employed for 0.98 gim laser fabrication. A discussion will be given of the relative advantages and disadvantages of the two processes, with particular emphasis on reliability issues.
C-V and DLTS Investigations of GaAs/InGaAs/GaAs Strained Quantum Well Structures
Authors: Subramanian S. , Arora B. M. , Srivastava A. K. , Banerjee S. , Fernandes G.
Published: March 2011

In this paper we report a modified Kroemer's analysis for the determination of the band offset (ΔEc) of single quantum well (SQW) structures from simple C-V measurements. The experimental carrier profile from an MOVPE grown pseudomorphic GaAs/InGaAs/GaAs strained SQW structure shows a sharp accumulation peak bounded by depletion regions on either side. The full width at half maximum of the accumulation peak is comparable to the width of the quantum well. The value of ΔEC obtained from C-V measurement is in good agreement with the values determined by simulation and photoluminescence measurements. DLTS measurements on our SQW samples do not show any peaks which is contrary to the published reports. We believe that it is necessary to carefully isolate the role of interface states, before assigning a DLTS peak to emission from the quantum well.
Low Temperature SiNx as a Sacrificial Layer in Novel Device Fabrication
Authors: Lothian J. R. , Ren F. , Pearton S. J. , Abernathy C. R. , Tseng B. , Hobson W. S.
Published: March 2011

In this paper we will describe applications of a low temperature SiNx for the novel fabrication of lasers and FET's. Sidewall roughness which appears on dry etched semiconductor laser mesas is a common problem in laser fabrication. Protecting the sidewall with a low temperature PECVD SiNx can greatly reduce laser mesa roughness that occurs during dry etching of the mesa. Another application uses low temperature SiNx to extend the resolution of standard optical replication. Submicron gate fingers in field effect transistors can be fabricated by using this low-temperature SiNx deposition. By depositing SiNx on the photoresist gate pattern and etching back the SiNx leaving a sidewall, this will reduce the opening of gate features. Submicron gate length MESFETs have been demonstrated with this technique which showed comparable results to conventional submicron MESFETs fabricated with E-beam direct writing.
Stable Pt/Ge/Au Ohmic Contact to N-GaAs with a Ta-Si-N Barrier
Authors: Chen J. S. , Kolawa E. , Ruiz R. P. , Nicolet M-A.
Published: March 2011

A Pt/Ge/Au contact of the structure: /Pt(17nm)/Ge(25nm)/Au(43nm), overlaid with a Ta-Si-N barrier layer and a Au metallization layer has a contact resistivity, ρc, of 3.7×10−6 Ωcm2 after annealing at 450°C for 15 min. After aging at 450°C for 60 h, ρc slightly degrades to 5.5×10−6 Ωcm2 while the surface keeps smooth. When alloyed at 550°C for 15 min, ρc is 1.8×10−6 Ωcm2 and stays about the same value after annealing at 550°C for 1 h. Without the Ta-Si-N barrier and the Au overlayer, the Pt/Ge/Au contact alone is also ohmic after annealing at 450°C for 15 min but with a ρc of ∼10−5 Ωcm2 while the surface morphology deteriorates significantly after aging at 450°C for 20 h.

The thermal reactions of this Pt/Ge/Au contact on GaAs, with or without a Ta-Si-N barrier layer, are investigated by backscattering spectrometry, x-ray diffraction, and transmission electron microscopy in conjunction with energy dispersive analyses of x-rays. For all samples, the main reaction products after annealing at 450°C for 15 min are Au7Ga2, and PtGe:As, a PtGe phase that also contains arsenic. The product phases are randomly distributed within a laterally uniform reacted layer when the Pt/Ge/Au contact is covered by a Ta-Si-N layer. Without the Ta-Si-N barrier layer, a small arsenic loss and a Ga-rich phase (probably Gaoxides) on the contact surface are observed after annealing at 450°C. In this case, the surface and contact-semiconductor interface are more faceted than with a Ta-Si-N barrier layer.
The Study of TiWN Schottky Contacts on n-Ga0.51 In0.49P
Authors: Chang Edward Y. , Lai Yeong-Lin , Lin Kuen-Chyuan , Chang Chun-Yen , Juang F. Y.
Published: March 2011

The first study of the TiW nitrides (TiWNx) as the Schottky contact metals to the n type Ga0.51In0 49P has been made. The Ga0.51 In0.49P epitaxial layer was successfully grown on the GaAs substrate by LP-MOCVD to form a lattice-matched heterostructure. The RF-magnetron sputtering system was utilized for the nitride deposition. The thermal stability of the nitride films were studied using rapid thermal annealing (RTA) method. Both the electrical characteristics and the materials characteristics were investigated. The materials properties of the nitride films were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), and Auger electron spectroscopy (AES). The TiWNx Schottky contacts demonstrate excellent electrical and physical characteristics, even after high temperature annealing. The barrier heights range from 0.81 to 1.05 eV depending on the content of the nitrogen and the annealing conditions. The XRD and AES results show no indication of interaction at the TiWNX/GaInP interface of both as-deposited and annealed samples. The outstanding characteristics of the contact were attributed to the high bandgap nature of the Ga0.51In0.49P and the incorporation of nitrogen into the TiW films.
Metallurgical and Electrical Properties of Capped Au-based Metallizations on GaAs
Authors: Lin X. W. , Piotrowska A. , Kaminska E. , Liliental-Weber Z. , Washburn J.
Published: March 2011

Gold-based contacts on GaAs, i.e., Au(Te)/n-GaAs, Au(Ge)/n-GaAs, and Au(Zn)/p- GaAs, were annealed with or without an Al2O3 cap, in order to examine the effects of capping on their metallurgical and electrical properties. Current-voltage measurements showed that ohmic contact can be formed for all the metallizations, except capped Au(Te) which remained nonohmic even after annealing up to 480°C. Transmission electron microscopy and x-ray diffraction observations showed that the reactions between a contact and GaAs can be strongly affected by a capping layer. For all uncapped contacts, annealing generally resulted in growth of Au-Ga compounds and nonuniform contact morphology, whereas capped Au(Ge) and Au(Zn) contacts were stable and retained flat interface with GaAs. Capped Au(Te) was found to be unstable, reacting extensively with GaAs, due to the presence of Te. Electrical data are explained in terms of the doping model for ohmic contact formation.
Layer Disordering and Carrier Concentration in Heavily Carbon-Doped AlGaAs/GaAs Superlattices
Authors: You H. M. , Tan T. Y. , Gösele U. M. , Höfler G. E. , Hsieh K. C. , Holonyak N. , Lee S.-T.
Published: March 2011

Al-Ga interdiffusion, carbon acceptor diffusion, and hole reduction were studied in carbondoped Al0.4Ga0.6As/GaAs superlattices (SL). Al-Ga interdiffusion was found to be most prominent for Ga-rich annealing, with the hole concentrations in the SL almost intact during annealing. For As-rich annealing, the interdiffusivity values, DAI.Ga, are in approximate agreement with those predicted by the Fermi-level effect model, and the hole concentrations in the SL decreased dramatically after annealing. By analyzing the measured hole concentration profiles, it was found that both carbon acceptor diffusion and reduction have occurred during annealing, with both depending on As4 pressure values to the one quarter power. These As4 pressure dependencies indicate that carbon diffuses via the interstitial-substitutional mechanism while hole reduction is governed by a precipitation mechanism.
Sulfur Passivation of InP and GaAs
Authors: Kapila A. , Si X. , Malhotra V.
Published: March 2011

Passivation of electronic defect states at the SiNx/InP and the SiNx/GaAs interfaces has been achieved using both ‘wet’ (ammonium and phosphorous polysulfide solutions) and ‘dry’ (H2S gas) sulfur treatments. The passivated surfaces are encapsulated by depositing SiNx overlayers at ∼ 200 °C using the electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) technique. The capacitance-voltage (C-V) characteristics of metal-insulatorsemiconductor (MIS) capacitors indicate substantial reduction in the density of interface defects. Schottky diodes, fabricated in sulfur-treated n-GaAs, also exhibit significant improvements. The H2S-treatment provides better reproducibility and uniformity when compared with the ‘wet’ sulfide treatment of the surfaces.
Deposition of Tin by Electron Cyclotron Resonance - Metal Organic Molecular Beam Epitaxy
Authors: Wisk P. W. , Abernathy C. R. , Pearton S. J. , Ren F. , Katz A. , Bohling D. A.
Published: March 2011

We have investigated the feasibility of depositing TiN from nitrogen plasmas by Electron Cyclotron Resonance – Metal Organic Molecular Beam Epitaxy (ECR-MOMBE). Growth rate, index of refraction and resistivity were evaluated as a function of growth temperature and group V flow. It was found that TiN could be deposited at reasonable growth rates on either GaAs or Si substrates. However, the resistivity of the materia is quite high, >1700 µΩ-cm, probably because of significant carbon uptake into the layers.
Chemical Beam Epitaxy Grown Indium Gallium Arsenide Tunnel Junctions
Authors: Medelci N. , Bensaoula A. , Vilela M. F. , Freundlich A.
Published: March 2011

p+/n+ In0.53Ga0.47As tunnel junctions with room temperature peak to valley ratio of 9:1 are demonstrated. The device structures were grown on both InP and GaAs (4% lattice mismatch) using Chemical Beam Epitaxy (CBE). Be and Si were used as dopants. The devices grown on InP exhibit room temperature peak current in excess of 1000 A/cm2. The peak current of 452 A/cm2 achieved on lattice mismatched material (GaAs) is comparable to the highest results previously reported on lattice matched material (InP). Finally, The device characteristics and the influence of different fabrication steps on the performance of these devices are discussed based on temperature dependent I-V measurements.
High Gain, Low Noise InP Heut for Millimeter-Wave Application
Authors: Yuen C. , Pao Y. C. , Chiang N. , Bechtel N. G.
Published: March 2011

Lattice matched InP HEMT has demonstrated superior gain and noise figure performance compared to the AlGaAs HEMT and PHEMT. The gain and noise figure advantages of the InP HEMT have been transferred to the excellent MMIC performance in the millimeter-wave region.
Fabrication of High Quality MOS Devices for Application in Hazardous Environments Based on RTP Gate Dielectrics with In Situ RTCVD of Polysilicon Gates
Authors: Fröschle B. , Bruemmer H.P. , Lang W. , Neumeier K. , Ramm P.
Published: March 2011

Process modules for MOS gate fabrication were developed which can be completed subsequently in one RTP reactor: atmospheric process sequences for gate oxides and oxynitrides as well as low pressure chemical vapor deposition of polysilicon (RTCVD). Prior to the Rapid Thermal Oxidation (RTO), the wafers were treated with a Rapid Thermal Cleaning process (RTC) in H2/Ar ambient. After the desoxidation step the RTO was done in O2/H2/Ar followed by an anneal (RTA) for the gate oxide or a nitridation in NH3 (RTN) and reoxidation for the oxynitrides, respectively. The polysilicon gate electrode was fabricated either by RTCVD in situ or in a conventional furnace reactor. The two-step RTCVD process resulted in a very good thickness uniformity for the polysilicon layers of 3% (3mm from the edge). The influence of the process variations on breakdown field, fixed oxide charge, interface state density, flatband voltage, and threshold voltage of the different types of gate dielectrics was investigated. The charges and voltages were determined by LF-HF CV measurements. In order to characterize the radiation tolerance of electronic devices, radiation induced flatband and threshold voltage shifts as well as the build up of interface charges were determined. The irradiation was performed at a Co - 60 gamma source. Breakdown fields in the range of 19 MV/cm, interface state densities of less than 109 eV−1cm−2, and radiation induced threshold voltage shifts below 0.1 V after 1.5 Mrad(Si) were obtained.
Reliability of Carbon Doped Base AlGaAs/GaAs HBTs as a Function of Collector Current
Authors: Prasad S.J. , Hultine E.
Published: March 2011

The HBTs used in this study were grown by OMVPE. The base was carbon doped to 3×1019 cm−3 and the base thickness was 500Å. Several 3μ ×10μ HBTs were biased at Ic =2,4 and 10mA (VCE=2V) and maintained at TA=125°C. Based on 1000 hours of operation at 125°C, Ic =2mA is safe, Ic =4mA is marginal and Ic =10mA is fatal.
Epitaxial Growth, Fabrication, and Performance of Ingaas Strained Quantum Well Laser Structures
Authors: Hobson W. S.
Published: March 2011

There is considerable interest in InGaAs/GaAs strained quantum well lasers for applications within the 0.9 to 1.1 μm wavelength range, such as high power lasers for Efdoped fiber amplifiers and rare-earth-ion solid state lasers, obtaining blue-green laser emission by frequency doubling, and optoelectronic integrated circuits. Epitaxial growth of these structures by organometallic vapor phase epitaxy, molecular beam epitaxy, and gas source molecular beam epitaxy will be discussed. The relative merits of AlGaAs and InGaP cladding layers will be examined with respect to growth challenges, laser processing and performance, and device reliability. Several device structures which provide transverse and lateral confinement will be reviewed. Reduction of the transverse far-field angle, which improves fiber coupling efficiency, can be accomplished through the use of periodic index separate confinement and depressed index cladding heterostructures. The performance of ridge waveguide lasers, which require accurate control of the ridge height, can be improved through the incorporation of etch-stop layers, either InGaP or AlAs, in the AlGaAs cladding layer. Nonplanar growth over mesas etched into the substrate is a convenient method to obtain buried heterostructure lasers. Carbon-doped planar InGaAs/AlGaAs lasers, using CC14 as an extrinsic dopant, have been fabricated with an impurity-induced layer disordering process. Microcylinder lasers have been fabricated out of InGaAs/InGaP layer structures.
Defects in Silver-Doped Mercuric Iodide Crystals and their Effect on X-Ray and Gamma-Ray Detector Performance
Authors: James R. B. , Bao X. J. , Schlesinger T. E. , Cheng A. Y. , Gerrish V. M.
Published: March 2011

The processing steps associated with purification of source material, crystal growth, and attachment of electrical contacts can introduce defects into mercuric iodide (HgI2) that degrade the performance of detectors. We have employed low-temperature photoluminescence (PL) spectroscopy to study radiative recombination centers in the interfacial region between a thin semitransparent film of silver and mercuric iodide. The Ag film was found to introduce a new broad emission band centered at 5490 Å in the photoluminescence spectrum of HgI2. This PL feature can be used as a signature to identify the existence of Ag as a contaminant in HgI2crystals and detectors. Experiments were also conducted on mercuric iodide surfaces that had been doped with silver, and the results showed that Ag is a rapid diffuser in bulk HgI2. Detectors with silver electrodes were also fabricated and tested using an americium-241 gamma-ray source. Large increases in the leakage currents were observed for the Ag-doped HgI2devices, indicated that Ag impurities are electrically active in HgI2. These measurements show that silver is unacceptable as an electrode material for mercuric iodide x-ray and gamma-ray detector applications. In addition, they reveal that caution must be taken during handling of mercuric iodide source material, crystals, and detectors to avoid contact with silver, silver compounds, or with any material that contains silver as a contaminant.
Incorporation of Extrinsic Defects in HgI2 During Detector Fabrication
Authors: Van Scyoc J.M. , Schlesinger T.E. , James R.B. , Cheng A.Y. , Ortale C. , van den Berg L.
Published: March 2011

The incorporation of extrinsic defects into mercuric iodide substrates during detector fabrication can be extremely detrimental to device performance. In particular, extrinsic defects can act as trapping and recombination centers, and they can reduce charge collection efficiencies, decrease gt product, or contribute to polarization effects in nuclear detectors. In this paper we present results of processing, photoluminescence, and electromigration experiments that clearly show that extrinsic defects can be incorporated in mercuric iodide during detector fabrication. By observing the luminescence features characteristic of Cu and Ag in mercuric iodide, we show that both these materials are taken up by mercuric iodide crystals during etching with KI if the etching solution is contaminated with these elements. The migration of material from contacts into the crystal, as shown by resistance measurements, is also presented. We infer from this work that other defects which are detrimental to device performance may also be incorporated in mercuric iodide if insufficient care is taken during device fabrication. Suggestions are therefore made as to some of the precautions that must be taken in order to realize the highest quality detectors.
X-Ray Analysis of Alpha Mercuric Iodide Crystal Structure and Processing Effects
Authors: Keller L. , Wang E.X. , Cheng A.Y.
Published: March 2011

X-ray topography and rocking curve experiments were performed on α-mercuric iodide samples. As-grown crystals were examined for intrinsic defects and crystallinity. Orientation of certain defects depends on the direction of crystal growth. The propagation of as-grown crystalline features was documented. The extent of crystal damage introduced during various steps of device fabrication such as sawing, polishing, etching and contact deposition was explored. Coefficients of linear thermal expansion of α33 = 54 ± 5 (10−6/°C) along the tetragonal c-axis, \001] direction and ±ll = 11 ± 4 (10−6/°C) in the \100] direction were measured.
CdTe:Cl and CdTeSe:Cl Single Crystals Application for Radiation Detectors
Authors: Meyer B.K. , Hofmann D.M. , Stadler W. , Salk M. , Eiche C. , Benz K.W.
Published: March 2011

We report on electrical and optical properties of vertical Bridgman grown Cl-doped CdTe including the ternary compositions Cd0.9Zn0.1Te and CdTe0 9Se0.1 with respect to application as a radiation detector. Based on Hall effect measurements, photoinduced current spectroscopy (PICTS) and photoluminescence we infer that high resistive material with good performance is controlled by deep level defects. The resistivity is calculated as a function of the shallow acceptor concentration (Cl-A-centers) with the conclusion that a deep donor state at mid gap must be present.
An Ultra Low Noise Preamplifier for Room Temperature X-Ray Detectors
Authors: Bertuccio G. , Rehak P. , Xi D.M.
Published: March 2011

A new circuital configuration for the charge amplifier is presented. By means of a double feedback loop, the input field-effect transistor can operate with its gate junction sligtly forward biased, collecting the detector current and discharging the feedback capacitor. The feedback resistor is so avoided and no resetting device or circuit is required for the preamplifier operation. The noise is limited by the input transistor, an equivalent noise charge of 19.5 r.m.s. electrons has been measured at room temperature by employing a commercial JFET.
Current-voltage characteristics of high resistivity CdTe
Authors: Iwase Y. , Ohno R. , Ohmori M.
Published: March 2011

Current-voltage characteristics of high resistivity CdTe, with consideration to Schottky barrier height at the contact and defect levels in the band gap were investigated by experimental and numerical simulation methods. From the electron injection investigation, the density of electron traps corresponded to the doped Cl concentration in the crystal. Numerical simulation of current-voltage characteristics was made based on Schockley Read Hall (SRH) statistics. In the low bias region, calculated characteristics were in fairly close agreement with the experimental results for Pt/CdTe/Pt diode. The electric field was not uniform along the biased direction and an almost neutral region was present in the vicinity of anode contact even when the bias was applied.
Characterization of Cvd Diamond Films by Optical Spectroscopies
Authors: Ager Joel W. , Han Sung , Wagner Ron S. , Pan Lawrence S. , Kania D.R. , Lane Stephen M.
Published: March 2011

Raman and photoluminescence spectroscopy was used to investigate radiation damage by 5 MeV He+ ions at room temperature in prototype CVD-diamond detector material. Amorphization of the diamond is not observed at fluences up to 8×1015 cm-2. A threshold behavior is seen in the formation of the H3 vacancy-dinitrogen color center. The defect is not observed for fluences in the range 1.6×1012 to 1.6×1013 cm-2; a linear behavior increase in H3 intensity is observed over the range 1.6×1014 to 1.6×1015 cm-2. The formation mechanism of the H3 color center under He+ irradiation involves a self-annealing effect that allows vacancies to diffuse to, and complex with, nitrogen complexes.
High-Purity Germanium Technology for Gamma-Ray and X-Ray Spectroscopy
Authors: Darken L.S. , Cox C. E.
Published: March 2011

High-purity germanium (HPGe) for gamma-ray spectroscopy is a mature technology that continues to evolve. Detector size is continually increasing, allowing efficient detection of higher energy gamma rays and improving the count rate and minimum detectable activity for lower energy gamma rays. For low-energy X rays, entrance window thicknesses have been reduced to where they are comparable to those in Si(Li) detectors. While some limits to HPGe technology are set by intrinsic properties, the frontiers have historically been determined by the level of control over extrinsic properties. The point defects responsible for hole trapping are considered in terms of the “standard level” model for hole capture. This model originates in the observation that the magnitude and temperature dependence of the cross section for hole capture at many acceptors in germanium is exactly that obtained if all incident s-wave holes were captured. That is, the capture rate is apparently limited by the arrival rate of holes that can make an angular-momentum-conserving transition to a s ground state. This model can also be generalized to other materials, where it may serve as an upper limit for direct capture into the ground state for either electrons or holes. The capture cross section for standard levels σS.L. is given by

where g is the degeneracy of the ground state of the center after capture, divided by the degeneracy before capture. Mc is the number of equivalent extrema in the band structure for the carrier being captured, mo is the electronic mass, m* is the effective mass, and T is the temperature in degrees Kelvin.
Investigation of Lead Iodide Crystals for Use as High Energy Solid State Radiation Detectors
Authors: David Dominique C. , James R. B. , Feemster H. , Anderson R. , Antolak A. J. , Morse D.H. , Pontau A. E. , Jayatirtha H. , Burger A. , Bao X. J. , Sch-Lesinger T. E. , Bench G. S. , Heikkinen D. W.
Published: March 2011

Significant developments have occurred in the technology of room-temperature PbI2 nuclear sensors which lead to some improvements in the detection of high energy gamma-rays. Discussion of crystal growth, purification, monitoring purification, and detector processing are reviewed as they relate to device performance.
Processing and Characterization of HgBrxI2−x Radiation Detectors
Authors: Zhou C. , Squillante M. R. , Moy L. P. , Bennett P.
Published: March 2011

This paper reports our recent work on the crystal processing, structural and optical characterization of HgBrxI2−x nuclear radiation detectors. To understand the electrical and optical properties of the detectors, we measured the energy gap of HgBrxI2−x as a function of the Br/I ratio. The energy band of this ternary semiconductor compound can be modulated from 2. 1eV (HgI2) to 3.4eV (HgBr2) by adjusting its chemical composition. This energy scope covers a wavelength spectrum between 365nm and 596nm, much of the visible spectrum. Nuclear and photoconductive detectors were fabricated from HgBrxI2−x single crystals and the responses of these devices were investigated with different radiation sources (241Am, 137Cs).
Excess Carrier Lifetimes in (HgCd)Te Grown by Mocvd Interdiftused Multilayer Process
Authors: Mitra P. , Schimert T. R. , Tyan Y. L. , Brouns A. J. , Case F. C.
Published: March 2011

Transient lifetime measurements on p- and n-type Hg1-xCdxTe epitaxial films, grown by the MOCVD-interdiffused multilayer process (IMP) on CdTe and CdZnTe, are reported. Lifetimes have been measured on undoped n-type, vacancy and arsenic doped p-type (HgCd)Te for x-values of 0.20-0.28 over the 25K-300K temperature range. Lifetime characterization has been carried out primarily by non-contact transient millimeter wave reflectance as well as by standard photoconductive decay. It is shown that Auger limited lifetimes are achievable in undoped n-type material. N-type lifetime results are analyzed within the framework of a multilevel Shockley-Read model which provide insight into the nature and density of defect states in the material. In p-type (HgCd)Te, for the same carrier concentration, longer lifetimes are obtained by As-doping than in vacancy doped material.
Twinning Effects in Hg1−xCdxTe (x∼0.2) Grown by Thm in The <111> Direction
Authors: Weiss Eliezer , Kedar Ehud , Mainzer Nili
Published: March 2011

Hg1−xCdxTe crystals with x∼0.2 were grown by the traveling heater method (THM), in either the [111]A or [111]B directions, using oriented CdTe seeds. Twins are sometimes formed during the growth of these crystals. In crystals grown in the [11]A direction the twins, of orientation [511]B, are constantly growing at the expense of the original [111]A oriented grain. Growth in the [111]B direction, on the other hand, suppresses the growth of the twin domain. Photodiodes and capacitors realized on the (111)A plane are markedly superior to those on the twin plane, (511)B. The difference is due to higher fixed charge and larger fast surface state densities in the case of the (511)B plane. These effects are explained by the lattice structures in the {111} and {511} planes and their possible influence on surface reactivity.
Silicon Detectors Highly Compensated by Neutron Induced Deep Levels for Low Energy X-RAY Detection
Authors: Li Zheng , Kraner H. W.
Published: March 2011

Fast neutron radiation damage in silicon results in defect levels which are predominantly acceptor-like at low fluences and may be used to compensate high resistivity ntype material to create very high effective resisitivity material. Compensated material to the order of Neff below 1011/cm3 enables depletion of diode thicknesses ≥ 1mm at reasonable biases (<100V), yielding diodes of reasonable area and capacitance<1 pF which are suitable for low noise applications such as X-ray spectrometry. Although exposure to fluences of this order will greatly increase the generation current and require cooling, most high resolution X-ray spectrometry systems are routinely operated at reduced temperature to achieve low noise operation of the front end electronics. Silicon p+ /n− /n+ implanted devices (area ≤0.25 cm2) made on high resistivity FZ silicon have been irradiated by 1 MeV neutrons to fluences of a few times 1012 n/cm2. Thick n− substrates (d=630 μm and 1000 μm) were used to achieve detector capacitances εεo/d in the range of 1 pF. After a neutron fluence of ϕn=2.9×1012 n/cm2, the total depletion of a p+/n−/n+ detector, 1040 μm thick and an area of 0.1 cm2, is reached at about V=50 Volts, with a Cd of 1 pF and a neutron induced leakage current of about 300 nA at room temperature. A total depletion of an 680 μm thick detector was reached after the fluence of 2-5×1012 n/cm2 at a voltage of 20 volts, and the capacitance of a 0.25 cm2 diode is 4.5 pF The resistivities of the compensated detector substrates are in the range of 100 K Ω-cm, and are not inverted to “p” type. The trapping of collected charge by neutron induced deep levels is modeled and simulated, and is found to be less than a few percent; with no obvious effect on peak shape. Using a resistive feedback preamplifier of modest noise contribution (225 eV), resolution of the Mn K∝ X-ray was 255 eV (FWHM) with 3 μsec shaping time constants. Other effects of uncollected charge will be discussed and comparisons between this type of detectors and Li-drift silicon detectors will be made.
A Robotic Method for Creating Radiation Maps Using Mercuric Iodide Sensor
Authors: Kume Masao , Khosla Pradeep K.
Published: March 2011

In this paper we describe the development of a robotic system that uses Mercuric Iodide (HgI2) sensors to create a map of radiation intensity in the environment. The sensors are mounted at the end-effector of a PUMA 560 manipulator. Data from these sensors is used to compute the radiation intensity. A control system is developed that moves the end-effector along constant intensity contours. The experiments use light sources (instead of radiation sources) and demonstrate the efficacy of such a system to create radiation maps.
M.O.S. Transistors with > 1 μm Thick Gate Oxide for Ionizing Radiation Dosimetry
Authors: Gessinn F. , Sarrabayrouse G.
Published: March 2011

The effects of ionizing radiation on MOS transistors with gate oxide thickness up to 2 μm have been investigated. The major focus of workers in this area has been on the hardening techniques of technologies. On the other side, our goal is to use MOS devices to reach higher sensitivities in order to detect small amounts of dose. Therefore, sensitivity as well as temperature response in the mil-std range and stability of the dosimeters have been studied.
Characteristics of Silicon Photodetector Using Epitaxial Wafer with High Resistivity and Long Recombination Lifetime
Authors: Fujii Yoshimaro , Usami Akira , Kaneko Keisuke , Wada Takao
Published: March 2011

For the high quality Si Photodetector, the high resistivity epitaxial wafer using the low resistivity substrate were studied. The buffer layer was introduced in the interface, and it was very effective on the crystal quality of the epitaxial layer. Recombination lifetime in the epitaxial layer became very uniform and long even in the interface region which was confirmed by measuring the lifetime depth profiles. Then Si PIN Photodiode was fabricated on the above high quality epitaxial wafer and its optoelectric characteristics was evaluated.
Microscopic Noncontact Electrical Evaluation for the Silicon-on-Insulator Layer with Voids
Authors: Usami A. , Nakai T. , Ishigami S. , Wada T. , Matsuki K. , Takeuchi T.
Published: March 2011

We evaluate the electrical properties of the silicon-on-insulator (SOI) layer made by the wafer bonding using a noncontact laser beam induced conductivity/current (LBIC) method. Since the thickness of the SOl layer used in this study is about 40μm, the He-Ne laser, whose penetration depth for Si is small (about 3μm), is used as the carrier-injection light source.

We use the SOI wafer with some voids which are revealed by the X-ray topography. We have reported that the LBIC signal intensity decreases in the void region. In this study, we measure the microscopic signal variation near the edge of the void. It is observed that the LBIC signal intensity decreases in the outside region within a distance of about 700μm from the void edge. The diffusion length of the injected carrier (100-150μm) is shorter than the width of the region where the signal intensity decreases. Thus the decrease is not due to the carrier diffusion to the void. These results show that the formation of the void degrades the electrical properties not only in the void region but also outside the void.
Effects of Electron Radiation on the Optical Constants of P-Type Silicon
Authors: Russo Onofrio L. , Dumas Katherine A.
Published: March 2011

The optical constants n and k are determined for p-type silicon at the Eo and El and critical point energies for one MeV electron irradiated samples. The value for fluences of 1014 and 1016 e−/cm2 are compared to samples before irradiation. The real, ε1 and imaginary,ε2 components of the dielectric function, ε, used to find n and k, were obtained by measurement of tanψ and δ using spectroscopic ellipsometry (SE). The data show that changes in δ, in particular, are greater in the region about Eo than of E1. This is consistent with electrolyte electroreflectance (EER) results in which the Lorentz line shape is narrower for Eo than for E1. The value of n is found to increase and k to decrease with e- radiation at the critical points, although, neither does so monotonically. The change in n at the Eo critical point is greater than at the higher energy main structure E1 whereas, k is a slower varying function in this region.