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1 Sep 2001

Volume 90, Issue 5, pp. 2057-2628

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Ultrathin (<4 nm) SiO2 and Si–O–N gate dielectric layers for silicon microelectronics: Understanding the processing, structure, and physical and electrical limits

M. L. Green, E. P. Gusev, R. Degraeve, and E. L. Garfunkel

J. Appl. Phys. 90, 2057 (2001); http://dx.doi.org/10.1063/1.1385803 (65 pages) | Cited 333 times

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The outstanding properties of SiO2, which include high resistivity, excellent dielectric strength, a large band gap, a high melting point, and a native, low defect density interface with Si, are in large part responsible for enabling the microelectronics revolution. The Si/SiO2 interface, which forms the heart of the modern metal–oxide–semiconductor field effect transistor, the building block of the integrated circuit, is arguably the worlds most economically and technologically important materials interface. This article summarizes recent progress and current scientific understanding of ultrathin (<4 nm) SiO2 and Si–O–N (silicon oxynitride) gate dielectrics on Si based devices. We will emphasize an understanding of the limits of these gate dielectrics, i.e., how their continuously shrinking thickness, dictated by integrated circuit device scaling, results in physical and electrical property changes that impose limits on their usefulness. We observe, in conclusion, that although Si microelectronic devices will be manufactured with SiO2 and Si–O–N for the foreseeable future, continued scaling of integrated circuit devices, essentially the continued adherence to Moore’s law, will necessitate the introduction of an alternate gate dielectric once the SiO2 gate dielectric thickness approaches ∼1.2 nm. It is hoped that this article will prove useful to members of the silicon microelectronics community, newcomers to the gate dielectrics field, practitioners in allied fields, and graduate students. Parts of this article have been adapted from earlier articles by the authors [L. Feldman, E. P. Gusev, and E. Garfunkel, in Fundamental Aspects of Ultrathin Dielectrics on Si-based Devices, edited by E. Garfunkel, E. P. Gusev, and A. Y. Vul’ (Kluwer, Dordrecht, 1998), p. 1 [Ref. 1]; E. P. Gusev, H. C. Lu, E. Garfunkel, T. Gustafsson, and M. Green, IBM J. Res. Dev. 43, 265 (1999) [Ref. 2]; R. Degraeve, B. Kaczer, and G. Groeseneken, Microelectron. Reliab. 39, 1445 (1999) [Ref. 3]. © 2001 American Institute of Physics.
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85.40.Sz Deposition technology
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
01.30.Rr Surveys and tutorial papers; resource letters
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
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Optimized active-matrix drives for liquid crystal displays

H. Nakamura, J. Crain, and K. Sekiya

J. Appl. Phys. 90, 2122 (2001); http://dx.doi.org/10.1063/1.1389078 (6 pages) | Cited 9 times

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A combination of computer simulation and experimental methods is used to provide a reliable and systematic means of optimizing the response time of active-matrix liquid crystal displays. Optical transients are measured and simulated (within a continuum elastic framework including hydrodynamic backflow) and are thereby related to director reorientation processes under various driving conditions. We find that an unconventional “overdrive” method, in which the device is briefly biased to a voltage exceeding the target voltage, leads to dramatic improvements in device response time which approach a factor of 6 in some cases. The computational model is capable of accurately predicting the optimum overdrive voltage. The physical origins of these findings and the importance of hydrodynamic backflow are discussed. © 2001 American Institute of Physics.
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85.60.Pg Display systems
42.79.Kr Display devices, liquid-crystal devices

Polymer light-emitting devices using ionomers as an electron injecting and hole blocking layer

Tae-Woo Lee, O Ok Park, Lee-Mi Do, Taehyoung Zyung, Taek Ahn, and Hong-Ku Shim

J. Appl. Phys. 90, 2128 (2001); http://dx.doi.org/10.1063/1.1391215 (7 pages) | Cited 34 times

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The effect of ion concentration, neutralization level and counterions in ionomers was systematically studied to obtain the optimal electroluminescent (EL) characteristics in polymer light-emitting diodes using poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) for the emissive layer and sulfonated polystyrene (SPS) ionomers for the electron-injecting layer. The optimum ion concentration of NaSPS was determined to be at 6.7 mol %. Ionomers with a higher neutralization level make the EL device more efficient, with the highest efficiency being at 200% overneutralization. The ionomer with a smaller metal counter ion greatly enhances the efficiency of EL devices with the indium–tin–oxide/MEH-PPV/LiSPS/Al device having the highest EL quantum efficiency, 1.18% photons/electron. The dominant factor in enhancing the luminance is the number of ionic dipoles near the cathode irrespective of the type of metal counterions, while the hole blocking mostly depends on the restriction of chain segmental motion in ionomers. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics
78.60.Fi Electroluminescence

Dry laser cleaning of particles from solid substrates: Experiments and theory

Y. W. Zheng, B. S. Luk’yanchuk, Y. F. Lu, W. D. Song, and Z. H. Mai

J. Appl. Phys. 90, 2135 (2001); http://dx.doi.org/10.1063/1.1389477 (8 pages) | Cited 27 times

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The experimental analysis of dry laser cleaning efficiency is done for certified spherical particle (SiO2, 5.0, 2.5, 1.0, and 0.5 μm) from different substrates (Si, Ge, and NiP). The influence of different options (laser wavelength, incident angle, substrate properties, i.e., type of material, surface roughness, etc.) on the cleaning efficiency is presented in addition to commonly analyzed options (cleaning efficiency versus laser fluence and particle size). Found laser cleaning efficiency demonstrates a great sensitivity to some of these options (e.g., laser wavelength, angle of incidence, etc.). Partially these effects can be explained within the frame of the microelectronics engineering (MIE) theory of scattering. Other effects (e.g., influence of roughness) can be explained along the more complex line, related to examination of the problem “particle on the surface” beyond the MIE theory. The theory of dry laser cleaning, based on one-dimensional thermal expansion of the substrate, demonstrates a great sensitivity of the cleaning efficiency on laser pulse shape. For the reasonable pulse shape this theory yields the threshold fluence by the order of magnitude larger than the experimental one. At the same time the theory, which takes into account the near-field optical enhancement and three-dimensional thermal expansion effects, yields the correct values for threshold. © 2001 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors
79.20.Ds Laser-beam impact phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
52.77.Bn Etching and cleaning
52.38.Mf Laser ablation
61.82.Fk Semiconductors
68.35.Dv Composition, segregation; defects and impurities
65.40.De Thermal expansion; thermomechanical effects

Time domain analysis of a rational harmonic mode locked ring fiber laser

G. Zhu, H. Chen, and N. Dutta

J. Appl. Phys. 90, 2143 (2001); http://dx.doi.org/10.1063/1.1390304 (5 pages) | Cited 11 times

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In this article, we present a theory of the pulse train generated by a rational harmonic mode locked ring fiber laser. The pulse width is calculated as a function of the rational harmonic order and the optical transfer function of the modulator. The theoretical work is based on a time domain analysis, which predicts that the pulse width decreases when the rational harmonic order goes up. The pulse width as a function of the modulation amplitude and bias level of the modulator was measured, and the experimental results agree with the theory. © 2001 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Wd Fiber lasers
02.30.-f Function theory, analysis
42.30.Lr Modulation and optical transfer functions
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Impact of gas heating in inductively coupled plasmas

D. B. Hash, D. Bose, M. V. V. S. Rao, B. A. Cruden, M. Meyyappan, and S. P. Sharma

J. Appl. Phys. 90, 2148 (2001); http://dx.doi.org/10.1063/1.1390503 (10 pages) | Cited 26 times

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Recently it has been recognized that the neutral gas in inductively coupled plasma reactors heats up significantly during processing. The resulting gas density variations across the reactor affect reaction rates, radical densities, plasma characteristics, and uniformity within the reactor. A self-consistent model that couples the plasma generation and transport to the gas flow and heating has been developed and used to study CF4 discharges. A Langmuir probe has been used to measure radial profiles of electron density and temperature. The model predictions agree well with the experimental results. As a result of these comparisons along with the poorer performance of the model without the gas–plasma coupling, the importance of gas heating in plasma processing has been verified. © 2001 American Institute of Physics.
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52.77.-j Plasma applications
52.50.-b Plasma production and heating
52.25.Kn Thermodynamics of plasmas
52.70.Ds Electric and magnetic measurements

Measurements of the electron energy distribution function in an Ar/CF4 inductively coupled plasma

M. D. Bowden, R. Tabata, P. Suanpoot, K. Uchino, K. Muraoka, and M. Noguchi

J. Appl. Phys. 90, 2158 (2001); http://dx.doi.org/10.1063/1.1398775 (4 pages) | Cited 8 times

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Measurements of the electron energy distribution function (eedf) of a low-pressure inductively coupled plasma operated in a mixture of Ar and CF4 are reported. The measurement method was laser Thomson scattering. Extensive test were performed in order to verify that any perturbations caused by the laser did not affect the measurements. The eedf was measured for different concentrations of CF4 gas, and the results indicated that it was non-Maxwellian when even small amounts of CF4 gas were present. This dependence was attributed partially to the effect of electron-molecule vibrational excitation collisions. © 2001 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Hc Glow; corona
52.20.-j Elementary processes in plasmas

Plasma expansion in the preshock region

K. T. A. L. Burm, W. J. Goedheer, and D. C. Schram

J. Appl. Phys. 90, 2162 (2001); http://dx.doi.org/10.1063/1.1390309 (7 pages) | Cited 8 times

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The supersonic expansion of an underexpanding argon plasma from a high density arc source with small dimensions into a low-pressure vessel with large dimensions is studied by an extended one-dimensional nonlocal thermal equilibrium fluid model, called SPIRIT. In an expanding plasma the velocity increases and the pressure, the density, and the temperatures decrease severely. In this article the virtual source model is discussed first, which is a model describing the expanding plasma as originating from a virtual source. The virtual source model includes some viscosity and heat transport in simplified form, but most of the viscosity and heat transport contributions are neglected. The SPIRIT code includes the full energy and momentum balances. The inclusion of viscosity and heat sources may lead to deviations from an adiabatic and/or isentropic expansion. The SPIRIT code can analyze the deviations. When deviations are small, the isentropic expressions from gas dynamics can be used to model expanding plasma too. Model outcomes are compared with experimental data. © 2001 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.25.Kn Thermodynamics of plasmas
52.65.-y Plasma simulation

Hybrid model for the calculation of ion distribution functions behind a direct current or radio frequency driven plasma boundary sheath

Matthias Kratzer, Ralf Peter Brinkmann, Winfried Sabisch, and Harald Schmidt

J. Appl. Phys. 90, 2169 (2001); http://dx.doi.org/10.1063/1.1389081 (11 pages) | Cited 23 times

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A hybrid fluid dynamic/kinetic model is presented which describes the sheath and the presheath regions of dc or rf driven low pressure gas discharges in a realistic and self-consistent way. The model assumes an infinite extended sheath parallel to the electrode, allowing a one-dimensional spatial description. It provides for the presence of multiple positive ion species and their collisional interactions with the neutral background, and takes into account the possibility of a nonharmonic modulation of the sheath potential and the application of an external dc bias; in this work, the model is applied to a two-species capacitively coupled argon and oxygen plasma. The input required by the model consists of the fluxes of the incoming ions, of the modulating current, and of the pressure, the composition, and the temperature of the background gas. On output, the model provides the values of the electric field and of the particle densities within the sheath and the presheath, the total voltage drop across the sheath, and also the energetically and angularly resolved distributions of the positive ions and the energetic neutrals which impinge the material substrate at the boundary. In general, the model is able to treat dc discharges as well as capacitively and/or inductively coupled rf discharges, it thus covers most of the plasmas used in very large scale integration microelectronics manufacturing and other surface modification techniques. Using the model, studies of the energy distributions of the incoming ions have been performed for a wide range of parameters, and the effects of varying process conditions have been investigated. At low and intermediate pressures (p<50 mTorr), the distribution functions of rf driven discharges exhibit a characteristic bimodal structure; this structure disappears with increasing pressure as ion-neutral collisions become significant. A comparison of calculated ion energy distributions with experimental measurements on capacitively coupled argon and oxygen discharges shows excellent quantitative agreement. In addition to the ion energy distribution, the angular distributions of the incident ions at various energies are also discussed as a function of the neutral gas pressure. It turns out that the details of the angular distribution not only depend on the field structure of the sheath itself but also on that of the presheath. The results of the presented model are therefore more reliable than those of previous models which restricted themselves to the sheath region. This high physical accuracy of the presented model, together with its flexibility and its high execution speed, allows its use as a tool for technology-oriented computer-aided design in the microelectronics industry. © 2001 American Institute of Physics.
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52.40.Kh Plasma sheaths
52.80.Dy Low-field and Townsend discharges
52.65.Ww Hybrid methods

On-line monitoring of perfluoro compounds in exhaust gases during semiconductor manufacture: Use of Li+ ion attachment mass spectrometry

Toshihiro Fujii and Megumi Nakamura

J. Appl. Phys. 90, 2180 (2001); http://dx.doi.org/10.1063/1.1384857 (5 pages) | Cited 12 times

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Li+ ion attachment mass spectrometry was used to continuously measure trace amounts of perfluoro compounds (PFCs) and byproducts in exhaust gas during semiconductor manufacture. Effluents were characterized to assess the environmental impact of dry-etching processes and operations. The feasibility of performing real-time measurements of PFCs in exhaust gas at the parts per billion level by direct introduction of the Li+ ion attachment source was demonstrated. © 2001 American Institute of Physics.
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07.88.+y Instruments for environmental pollution measurements
89.60.-k Environmental studies
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
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Electroluminescence thermal quenching in alternating-current thin-film electroluminescent devices

B. A. Baukol, J. C. Hitt, J. F. Wager, and S.-S. Sun

J. Appl. Phys. 90, 2185 (2001); http://dx.doi.org/10.1063/1.1385570 (6 pages) | Cited 2 times

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Electroluminescence (EL) thermal quenching in alternating-current thin-film electroluminescent (ACTFEL) devices refers to a reduction in the luminance with increasing temperature, which is in excess to that of normal thermal quenching and is concomitant with a reduction in the transferred charge. A comparison of thermal quenching trends for ZnS:Mn, SrS:Ce, SrS:Cu,Ag, and multilayer SrS:Cu,Ag/SrS:Ce ACTFEL devices is presented. Respectively, ZnS:Mn; SrS:Cu and SrS:Cu,Ag; and SrS:Ce and multilayer SrS:Cu,Ag/SrS:Ce ACTFEL devices exhibit very little (normal), a large amount (of primarily EL), or a small amount (of primarily normal) thermal quenching. Insertion of one or more interface layers of SrS:Ce significantly reduces the extent of EL thermal quenching in a SrS:Cu,Ag ACTFEL device. Simulation suggests that SrS:Ce interface layers decrease the rate and displace the location of hole creation by band-to-band impact ionization away from the SrS:Cu,Ag layer, where hole trapping at Cu or Ag acceptor sites leads to EL thermal quenching via thermally activated annihilation of positive space charge due to thermionic emission of holes from Cu or Ag acceptor traps. © 2001 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
71.55.Gs II-VI semiconductors
73.50.Fq High-field and nonlinear effects
73.61.Ga II-VI semiconductors
77.22.Jp Dielectric breakdown and space-charge effects
79.40.+z Thermionic emission
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

In-plane tensile-strained interfacial structure in a GaN nucleation layer on sapphire(0001)

C. C. Kim, J. H. Je, M. S. Yi, D. Y. Noh, and P. Ruterana

J. Appl. Phys. 90, 2191 (2001); http://dx.doi.org/10.1063/1.1388859 (4 pages) | Cited 2 times

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Interfacial microstructure in GaN nucleation layers was investigated using synchrotron x-ray scattering and transmission electron microscopy. We find that tensile-strained, aligned, interfacial domains coexist with misaligned domains in an as-grown nucleation layer of mostly cubic stacking. The tensile strain originates in a 6/7 matched interfacial structure, wherein 6-Ga atomic distances in GaN match to 7-Al atomic distances in sapphire. The tensile state of the aligned, interfacial domains is preserved during annealing to 1100 °C, while the stacking sequence changes from cubic to hexagonal order. The correlation length of the stacking order is rather short, ∼9 Å in the hexagonal phase, compared to that of the cubic phase in the as-grown nucleation layer, ∼25 Å, due to stacking faults generated during the kinetically limited transformation. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
68.60.Bs Mechanical and acoustical properties
68.35.Ct Interface structure and roughness
61.72.Nn Stacking faults and other planar or extended defects
62.20.-x Mechanical properties of solids

Surface morphology and structural changes in insulators induced by high-current 60 keV Cu− implantation

C. G. Lee, Y. Takeda, N. Kishimoto, and N. Umeda

J. Appl. Phys. 90, 2195 (2001); http://dx.doi.org/10.1063/1.1388599 (5 pages) | Cited 3 times

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Surface morphology and structural changes of amorphous (a-), crystalline (c-) SiO2 and MgAl2O4 spinel, implanted with high-current Cu− of 60 keV, were studied using atomic force microscopy. Kinetic variation of the surface morphology was evaluated by changing dose rate from 1 to 100 μA/cm2. In the cases of a-SiO2 and c-SiO2, the surface morphology significantly varied with dose rate: dome-type textures in the lower dose-rate region caused radiation-induced roughening, while net-type ones in the higher region occurred with radiation-induced smoothing. Step-height measurements showed radiation-induced expansion and compaction for c-SiO2 and a-SiO2, respectively. Radiation-induced amorphization is responsible for the expansion processes of c-SiO2. Contrarily, no amorphization was observed in the spinel up to dose rates of about 100 μA/cm2, although radiation-induced swelling, due to defect accumulation, was discernible by the step-height measurement. The surface morphology and the roughness of the spinel were not very dependent on dose rate. The results of c-SiO2 and a-SiO2 indicate that both of them are subjected to enhanced changes in surface morphology and microstructures and that high-current implantation causes highly dynamic states in the near-surface region. On the other hand, the results for the spinel show pronounced stability and that the spinel may be used as an effective substrate for optical modification, even for high-current ion implantation. © 2001 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
61.80.Jh Ion radiation effects
61.82.Ms Insulators
61.72.up Other materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.43.Er Other amorphous solids

Energy migration of the local excitation at the Eu3+ site in a Eu–O chemical cluster in sol-gel derived SiO2:Eu3+ glasses

Tomokatsu Hayakawa and Masayuki Nogami

J. Appl. Phys. 90, 2200 (2001); http://dx.doi.org/10.1063/1.1384491 (6 pages) | Cited 13 times

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By using the fluorescence line-narrowing technique, we observed a broad fluorescence band in the vicinity of a resonant line of the 5D0→7F0 transition in an Eu3+-doped SiO2 glass synthesized by a sol-gel process. The comparison with a similar line in an Al2O3–SiO2:Eu3+ sol-gel glass revealed the existence of a chemical cluster of Eu3+ and O2− in the tetrahedral SiO4 network. The broad fluorescence band was attributable to an energy migration among the Eu3+ ions for the site-selectively received excitation energy. Also, based on Yokota–Tanimoto’s energy diffusion model, the fluorescence decay curves for the 5D0→7F2 transition were closely correlated with the energy migration and gel–glass transformation. The gel-shrinkage and reduced interatomic distance between Eu3+ ions due to a thermal treatment at higher temperature definitely resulted in a decrease in the associated lifetime of the initial decay. © 2001 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
42.70.Ce Glasses, quartz
81.05.Kf Glasses (including metallic glasses)
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.43.Fs Glasses
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions

Refractive index change caused by electron irradiation in amorphous As–S and As–Se thin films coated with different metals

Nina Nordman and Olli Nordman

J. Appl. Phys. 90, 2206 (2001); http://dx.doi.org/10.1063/1.1388862 (5 pages) | Cited 1 time

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The refractive index change caused by electron irradiation was measured in amorphous As–S and As–Se thin films coated with different metals. Metal atoms/ions diffused into the films during irradiation. The diffusion was dependent on the metal and influenced the refractive index. The influence was smallest in As40S60 films although these films possessed the highest overall refractive index changes. Au atoms/ions were almost immobile in all films while Ag atoms/ions had the highest mobility. Their high mobility allowed them to diffuse laterally within the film. © 2001 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Jg Amorphous semiconductors; glasses
61.80.Fe Electron and positron radiation effects
61.82.Fk Semiconductors
66.30.J- Diffusion of impurities

Temperature dependence of growth morphology of sputtered (FePt/Pt) films on MgO (100) substrate

Mu-Gyeom Kim and Sung-Chul Shin

J. Appl. Phys. 90, 2211 (2001); http://dx.doi.org/10.1063/1.1389527 (5 pages) | Cited 10 times

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We have investigated growth morphology of FePt/Pt films prepared by sputtering on a MgO (100) substrate in a temperature range of 100–600 °C. The L10 ordered structure appeared at a low substrate temperature of 200 °C and became a dominant phase via a second-order type transformation. A transition of FePt film growth morphology from continuous two-dimensional (2D) layer-by-layer mode into 3D island growth mode was observed at a substrate temperature of about 400 °C. When the film grew in continuous mode the stress from lattice misfit played an important role in governing the growth morphology; while growing in island mode the thermal stress increasingly influenced it. The island structure revealed eightfold symmetry following the preferred process of elongating the channel length to broadening its width. © 2001 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Cd Deposition by sputtering
68.60.Bs Mechanical and acoustical properties
81.05.Bx Metals, semimetals, and alloys
68.35.B- Structure of clean surfaces (and surface reconstruction)

Visible electroluminescence in hydrogenated amorphous silicon oxynitride

Hiromitsu Kato, Akira Masuzawa, Hidefumi Sato, Takashi Noma, Kwang Soo Seol, Makoto Fujimaki, and Yoshimichi Ohki

J. Appl. Phys. 90, 2216 (2001); http://dx.doi.org/10.1063/1.1388864 (5 pages) | Cited 5 times

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The mechanism of electroluminescence in hydrogenated amorphous silicon oxynitride was investigated. The luminescence can be observed only in the samples with high nitrogen content and annealed at high temperatures. It depends on the direction of the applied electric field, and its peak photon energy decreases from 2.3 to 1.8 eV as the nitrogen content increases. From the measurements of conduction current and Fourier transform infrared absorption spectroscopy, it was found that the electrical conduction in the electric field region where the luminescence was observed is governed by the Poole–Frenkel process at the defect centers induced by the high temperature annealing. The electroluminescence is considered to be caused by electronic transition between the band-tail states, at least one of which is related to N or Si–N bonds. © 2001 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.60.Fi Electroluminescence
73.50.Fq High-field and nonlinear effects
73.61.Ng Insulators
61.72.Cc Kinetics of defect formation and annealing
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Shock-induced α–ω transition in titanium

C. W. Greeff, D. R. Trinkle, and R. C. Albers

J. Appl. Phys. 90, 2221 (2001); http://dx.doi.org/10.1063/1.1389334 (6 pages) | Cited 40 times

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Equilibrium free energies for the α and ω phases of Ti are constructed. The result is a consistent picture of the ambient pressure, static high pressure, and shock data, as well as first-principles electronic structure calculations. The Hugoniot consists of three segments: a metastable α-phase region, a transition region, and an ω-phase branch. All the Hugoniot data are consistent with a transition occurring at ∼12 GPa. An early identification [R. G. McQueen et al., in High Velocity Impact Phenomena, edited by R. Kinslow (Academic, New York, 1970)] of a phase transition at 17.5 GPa appears to have been an artifact. The shock Hugoniot extends further into the metastable region than static data, indicating the existence of a relaxation process occurring on a time scale intermediate between those of the static and dynamic measurements. © 2001 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
81.05.Bx Metals, semimetals, and alloys
64.70.K- Solid-solid transitions
64.30.-t Equations of state of specific substances
65.40.G- Other thermodynamical quantities
71.15.-m Methods of electronic structure calculations
71.20.Be Transition metals and alloys

Formation of diluted III–V nitride thin films by N ion implantation

K. M. Yu, W. Walukiewicz, J. Wu, J. W. Beeman, J. W. Ager, E. E. Haller, W. Shan, H. P. Xin, C. W. Tu, and M. C. Ridgway

J. Appl. Phys. 90, 2227 (2001); http://dx.doi.org/10.1063/1.1388860 (8 pages) | Cited 23 times

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Diluted III–Nx–V1−x alloys were successfully synthesized by nitrogen implantation into GaAs, InP, and AlyGa1−yAs. In all three cases the fundamental band-gap energy for the ion beam synthesized III–Nx–V1−x alloys was found to decrease with increasing N implantation dose in a manner similar to that observed in epitaxially grown GaNxAs1−x and InNxP1−x alloys. In GaNxAs1−x the highest value of x (fraction of “active” substitutional N on As sublattice) achieved was 0.006. It was observed that NAs is thermally unstable at temperatures higher than 850 °C. The highest value of x achieved in InNxP1−x was higher, 0.012, and the NP was found to be stable to at least 850 °C. In addition, the N activation efficiency in implanted InNxP1−x was at least a factor of 2 higher than that in GaNxAs1−x under similar processing conditions. AlyGa1−yNxAs1−x had not been made previously by epitaxial techniques. N implantation was successful in producing AlyGa1−yNxAs1−x alloys. Notably, the band gap of these alloys remains direct, even above the value of y (y>0.44) where the band gap of the host material is indirect. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Electrical and optical properties of TiO2 in accumulation and of lithium titanate Li0.5TiO2

Roel van de Krol, Albert Goossens, and Eric A. Meulenkamp

J. Appl. Phys. 90, 2235 (2001); http://dx.doi.org/10.1063/1.1388165 (8 pages) | Cited 16 times

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Changes in the optical absorption and electrical conductivity of dense and mesoporous anatase TiO2 films were measured in situ as a function of electrode potential during electrochemical lithium intercalation. A special two-electrode geometry was used for the conductivity measurements, in which the contacts were separated by a small gap bridged by the TiO2. When electrons are injected, an accumulation layer is formed and the conductivity increases several orders of magnitude. A monotonic increase of the optical absorption with wavelength confirms the presence of (partially) delocalized electrons. Insertion of lithium ions results in the formation of the Li0.5TiO2 phase and a decrease of the overall conductance. The specific conductivity of the Li0.5TiO2 phase is (9.1±0.2) S/cm, significantly lower than that of Li-doped anatase TiO2. This is corroborated by the absorption spectrum of Li0.5TiO2, which shows two pronounced peaks around 440 and 725 nm and no characteristic free-electron features. At potentials below 1.7 V vs Li additional lithium could be inserted into Li0.5TiO2, and the conductance was found to increase again. The results are discussed in terms of possible changes in the electronic structure that are induced by the insertion of lithium ions. © 2001 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
82.45.Fk Electrodes
72.80.Sk Insulators
73.61.Ng Insulators
78.66.Nk Insulators
71.20.Tx Fullerenes and related materials; intercalation compounds
82.30.Nr Association, addition, insertion, cluster formation

Effect of carrier trapping time on performance of alternating-current thin-film electroluminescent devices

Alex N. Krasnov and Peter G. Hofstra

J. Appl. Phys. 90, 2243 (2001); http://dx.doi.org/10.1063/1.1391219 (4 pages)

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In spite of a significant number of studies on memory effect in alternating-current thin-film electroluminescent devices, the phenomenon is still unclear. In the present work we investigate some peculiarities of memory behavior of the devices from the viewpoint of the nonequilibrium carrier trapping time. Applying a combination of unique voltage staircase waveforms, we demonstrate that the degree of memory of the device is determined by the trapping time of the carriers at the insulator–semiconductor interface and the sulfur vacancy (Vs) concentration in the bulk of the active layer. We also show that separating electrons and holes before the pulse arrival can increase the effective field across the phosphor layer. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
61.72.J- Point defects and defect clusters

Heating rate dependence of melting of silicon: An in situ x-ray topography study

Yuren Wang and Koichi Kakimoto

J. Appl. Phys. 90, 2247 (2001); http://dx.doi.org/10.1063/1.1389481 (5 pages) | Cited 1 time

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In situ observations of the melting processes of dislocation-free silicon crystals were carried out using x-ray topography technique. Heating procedures with various heating rates were used in the experiments. Dot contrasts were observed during the melting process at a high heating rate, while they could not be found at a low heating rate. It was found that the melting process at a high heating rate is spatially inhomogeneous, while that at a low heating rate is homogeneous. It was also found that the oxygen concentration in the sample plays an important role in the formation of dot contrasts during the melting process. The dot contrasts were assumed to originate from the dislocation loops around the oxygen precipitates. © 2001 American Institute of Physics.
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64.70.D- Solid-liquid transitions
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations

Deep-level transient spectroscopy of dislocation-related defects in epitaxial multilayer structures

E. Thor, M. Mühlberger, L. Palmetshofer, and F. Schäffler

J. Appl. Phys. 90, 2252 (2001); http://dx.doi.org/10.1063/1.1389762 (5 pages) | Cited 10 times

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Dislocated Si, SiGe, SiC, and SiGeC n-type heterostructures, grown by molecular beam epitaxy, were characterized by capacitance–voltage profiling and deep-level transient spectroscopy. Exclusively dislocation-related defects were found in the different layers, which correspond to the well-known defects found in plastically deformed silicon. © 2001 American Institute of Physics.
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81.05.Cy Elemental semiconductors
68.65.Ac Multilayers
81.05.Hd Other semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Creation of long lasting luminescence in transparent aluminas

T. Ishizaka and Y. Kurokawa

J. Appl. Phys. 90, 2257 (2001); http://dx.doi.org/10.1063/1.1391221 (5 pages) | Cited 16 times

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We have examined long lasting luminescence of transparent alumna and Tb3+–Zn2+(Ca2+)-codoped alumina films prepared by the aqueous sol-gel method. A strong luminescence of 300–500 nm was observed for nondoped alumina, and was shown to depend on the treat temperature of gel. The luminescence was not observed for alumina treated at temperatures higher than 600 °C. The luminescence band was composed of plural components due to oxygen defect sites in alumina. The lasting luminescence of Tb3+–Zn2+(Ca2+)-codoped alumina were observed after irradiation for several seconds using a UV lamp (15 W). The results indicated that the oxygen defect sites of alumina serve as a photoelectron trap center and that the AlV site serves as a hole trap center, which can be thermally released at room temperature. © 2001 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
42.79.Wc Optical coatings
78.66.Nk Insulators
78.47.-p Spectroscopy of solid state dynamics
81.40.Gh Other heat and thermomechanical treatments
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.40.Tv Optical and dielectric properties related to treatment conditions

Deactivation kinetics of supersaturated boron:silicon alloys

Weiwei Luo, Shenzhi Yang, Paulette Clancy, and Michael O. Thompson

J. Appl. Phys. 90, 2262 (2001); http://dx.doi.org/10.1063/1.1385360 (7 pages) | Cited 10 times

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The effect of laser annealing on the electrical activity of boron-doped silicon wafers has been investigated as a function of boron concentration, annealing time, and annealing temperature (from 600 °C to 1050 °C). Metastable supersaturated alloys were produced by the laser annealing of ion-implanted Si 〈100〉 wafers using an excimer laser with a pulse duration of 30 ns. The extent of dopant activation, deactivation, and tendency towards precipitation were subsequently studied following rapid thermal annealing in an argon ambient using a four-point probe of the sample resistance. Sheet resistances as low as 15 Ω/□ were achieved in 200 nm layers. Following laser anneals, boron atoms remained active at concentrations of 7.5×1020/cm3 up to 800 °C for 210 s. A two-mode relaxation model including defect association and precipitation was proposed to describe the annealing behavior. These results show that laser processing can produce metastable B-doping levels, stable to moderate thermal processing, at concentrations adequate for all anticipated device structures. © 2001 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
64.75.-g Phase equilibria
61.72.uf Ge and Si
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Cw Elemental semiconductors
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