bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of the fractional interstitial component of boron diffusion and segregation coefficient of boron in Si0.8Ge0.2
Authors: Fang Tilden T. , Fang Wingra T. C. , Griffin Peter B. , Plummer James D.
Published: July 2002

Investigation of boron diffusion in strained silicon germanium buried layers reveals a fractional interstitial component of boron diffusion (fBI) in Se0.8Ge0.2 approximately equal to the fBI value in silicon. In conjunction with computer-simulated boron profiles, the results yield an absolute lower-bound of fBI in Si0.8Ge0.2 of ∼0.8. In addition, the experimental methodology provides a unique vehicle for measuring the segregation coefficient; oxidation-enhanced diffusion is used instead of an extended, inert anneal to rapidly diffuse the dopant to equilibrium levels across the interface, allowing the segregation coefficient to be measured more quickly.
Optical spectroscopic observation of spontaneous long range ordering in AlGaInP
Authors: Kowalski O. P. , Wegerer R. M. , Mowbray D. J. , Skolnick M. S. , Button C. C. , Roberts J. S. , Hopkinson M. , David J. P. R. , Hill G.
Published: July 2002

We report the unambiguous optical spectroscopic observation of spontaneous long-range crystal ordering in AlGaInP epitaxial layers grown by metalorganic vapor phase epitaxy. Polarized spectroscopy demonstrates the existence of an in-plane anisotropy for samples grown on substrates oriented close to (100). This anisotropy results from the order-induced splitting of the normally degenerate zone-center valence-band states. Our measurements allow the size of the valence-band splitting to be measured and also allow a determination of the order-induced band-gap reduction. Both of these quantities are found to decrease with increasing misorientation of the substrate away from (100), indicating that the degree of ordering also decreases with increasing misorientation.
Conduction band offsets in ordered-GaInP/GaAs heterostructures studied by ballistic-electron-emission microscopy
Authors: O’Shea J. J. , Reaves C. M. , DenBaars S. P. , Chin M. A. , Narayanamurti V.
Published: July 2002

Ordered-GaInP/GaAs heterostructures have been studied using ballistic-electron-emission microscopy (BEEM). The GaInP/GaAs conduction band offset was found to decrease with increasing order. Samples were grown simultaneously on different misoriented substrates to vary the degree of order in the GaInP. Concurrent scanning tunneling microscopy and BEEM images show ridge structures in the topography and contrast in the BEEM current that may correspond to ordered domains in the GaInP. Room temperature conduction band offsets of 137 and 86 meV were measured using BEEM spectroscopy for GaInP with 2 K band gaps of 1.97 and 1.89 eV, respectively.
Complementary circuits with organic transistors
Authors: Dodabalapur A. , Laquindanum J. , Katz H. E. , Bao Z.
Published: July 2002

The operating characteristics of complementary inverters with n-channel napthalenetetracarboxylic dianhydride thin-film transistors (TFTs) and p-channel transistors with hole transporting organic active materials are described. The n-channel TFTs have been used as the load in one circuit configuration and as the driver in the second configuration.
GaInP/GaP partially ordered layer type-I strained quantum well
Authors: Lee J.-W. , Schremer A. T. , Fekete D. , Ballantyne J. M.
Published: July 2002

Strong photoluminescence is observed in strained GaInP quantum wells (QW) grown on GaP. Variable temperature photoluminescence indicates that the pseudomorphic quantum well consists of type-I regions of ordered GaInP and type-II regions of disordered GaInP. Observation of photoluminescence at room temperature suggests that this QW may be useful as an active layer for laser structures grown on GaP.
Surfactant-mediated epitaxy of metastable SnGe alloys
Authors: Lyman P. F. , Bedzyk M. J.
Published: July 2002

An effective method for molecular beam epitaxial construction of metastable, pseudomorphic SnGe/Ge(001) heterostructures is presented. This method exploits a surfactant species, Bi, to alter Sn surface-segregation kinetics. Using the x-ray standing wave technique, we demonstrate not only that Bi segregates to the growth surface more strongly than Sn, but that it also dramatically suppresses the segregation mobility of Sn. The limited Sn diffusivity, which is believed to stem from the full coordination of subsurface Sn atoms, allows the epitaxy of well-ordered, metastable SnGe heterostructures.
Two-wave mixing in Stark geometry photorefractive quantum wells using moving gratings
Authors: Lahiri I. , Brubaker R. M. , Nolte D. D. , Melloch M. R.
Published: July 2002

Nonreciprocal energy transfer between two coherent laser beams during two-wave mixing requires a photorefractive phase shift between the interference pattern and the resulting space charge. The symmetry of the Stark geometry photorefractive quantum wells forbids a phase shift using either dc or ac fields. We present the first experimental demonstration of nonreciprocal energy transfer during two-wave mixing using moving gratings. Optical energy exchange is observed in photorefractive p-i-n quantum well diodes with photorefractive gains approaching 1000 cm−1 and exhibiting complex spatio-temporal dynamics.
Photoemission spectroscopy studies of the surface of GaN films grown by vapor phase epitaxy
Authors: Ma Jian , Garni B. , Perkins N. , O’Brien W. L. , Kuech T. F. , Lagally M. G.
Published: July 2002

Surfaces of GaN films have been investigated with photoemission spectroscopy. The measured valence band is in good agreement with band structure calculations and correlates well with tunneling luminescence measurements performed on the same samples. The effect of N depletion on band structure is explored, clarifying disagreements in previous photoemission measurements.
Novel (Pt/Co/Pt/Ni) multilayers for magneto-optical recording media
Authors: Srinivas G. , Shin Sung-Chul
Published: July 2002

The sputter deposited (Pt/Co/Pt/Ni) multilayer films were studied as possible alternative low Curie temperature multilayers for magneto-optical recording. The Curie temperatures of these multilayers were found to be between 150 and 300 °C, which are much lower than those of Co/Pt multilayers or (Co,Ni)/Pt multilayers. The coercivities of these multilayers were between 450 and 800 Oe. The Kerr spectra of these multilayers exhibited enhancement of the Kerr rotation at lower wavelengths. These multilayers were found to show comparable magnetic and magneto-optical properties to Co/Pt multilayers and have an added feature of low Curie temperature making them attractive for magneto-optical storage applications.
The compensation and depletion behavior of iron doped GaAs grown by molecular beam epitaxy
Authors: McInturff D. T. , Harmon E. S. , Chang J. C. P. , Pekarek T. M. , Woodall J. M.
Published: July 2002

We describe the growth and characterization of GaAs films in which a high concentration (1 at. %) of elemental iron is introduced during growth in a conventional molecular beam epitaxy system. For films grown at 600 °C, the iron incorporates as Fe3GaAs precipitates. Unlike the formation of As precipitates in low temperature grown (LTG) GaAs, iron precipitate formation does not require a postgrowth anneal. Hall measurements of the as-grown GaAs/Fe3GaAs composite intentionally doped with silicon indicate that Fe3GaAs precipitates will deplete carriers in the same manner as As precipitates deplete carriers in annealed LTG GaAs. The degree of depletion depends on the initial growth temperature and the intentional doping level. Electrical behavior of samples subjected to a postgrowth rapid thermal anneal indicate that the material is deep level compensated by iron acceptor doping via dissolution of the Fe3GaAs precipitates.
Photoluminescence study of initial interdiffusion of SiGe/Si quantum wells grown by ultrahigh vacuum-chemical vapor deposition
Authors: Lafontaine H. , Houghton D. C. , Rowell N. L. , Aers G. C.
Published: July 2002

SiGe quantum wells were grown at 525 °C using a commercially available, ultrahigh vacuum–chemical vapor deposition system, in which the purity of the material and quality of interfaces have already been demonstrated. Changes in photoluminescence line energies are monitored and the extent of interdiffusion in the wells during annealing is calculated. A strong initial enhancement of the diffusivity is observed in as-grown material. Material annealed using a two-step process in which strain and Ge peak concentrations are unchanged after the first (low temperature) step, shows a much lower interdiffusion during the second step. It is argued that strain alone cannot explain the enhanced interdiffusion, which is, thus, attributed to grown-in, nonequilibrium point defects.
Reversible transition between transparency and opacity for the porous silica host dispersed with silver nanometer particles within its pores
Authors: Cai Weiping , Tan Ming , Wang Guozhong , Zhang Lide
Published: July 2002

The porous silica dispersed with silver nanometer particles (about 3 nm) within its pores (cages) has been prepared by a new method. In the process of alternative exposure to the ambient air and annealing, this material assumes reversible transition between transparency and opacity. This can be explained by oxidation of the outer part of the Ag particles during exposure to the ambient air and dissociation of the oxide during annealing in air.
Polarization insensitive InGaAs/InGaAsP/InP amplifiers using quantum well intermixing
Authors: He J.-J. , Charbonneau S. , Poole P. J. , Aers G. C. , Feng Y. , Koteles E. S. , Goldberg R. D. , Mitchell I. V.
Published: July 2002

A polarization insensitive optical amplifier based on a lattice matched InGaAs/InGaAsP/InP multiple quantum well (MQW) laser structure operating at 1.5 μm has been fabricated through vacancy enhanced quantum well intermixing using broad area, high energy (1 MeV P+) ion implantation. A simple model shows that if the interdiffusion rate of the anions is larger than that of the cations, the blue shift in the ground state heavy hole transition energy after implantation and annealing is greater than the light hole state blue shift, bringing the two bands together. Current–voltage measurements indicate that junction characteristics are well maintained after implantation. This simple technique for fabricating polarization insensitive optical amplifiers is readily extended to the monolithical integration of such devices along with other passive and active optoelectronic devices and opens the door to practical photonic integrated circuits.
Coulomb scattering in strained-silicon inversion layers on Si1−xGex substrates
Authors: Gámiz F. , Roldán J. B. , López-Villanueva J. A. , Cartujo P.
Published: July 2002

Results of electron mobility in strained-Si inversion layers grown on Si1−xGex substrates are reported. Drift velocities are calculated by Monte Carlo simulations including electron quantization and Coulomb scattering, in addition to phonon and surface roughness scattering. The strain is shown to contribute as well to the enhancement of the Coulomb-limited mobility due to better screening of the interface centers by the mobile carriers. Even in the case of high-doped substrates, Coulomb scattering does not cancel the mobility enhancement provided by the reduction of both intervalley scattering and conduction effective mass.
Fabrication and characteristics of ZnS nanocrystals/polymer composite doped with tetraphenylbenzidine single layer structure light-emitting diode
Authors: Yang Yi , Xue Shanhua , Liu Shiyong , Huang Jinman , Shen Jiacong
Published: July 2002

The hexagonal ZnS nanocrystals were synthesized in polymer matrix. The ZnS polymer composite doped with tetraphenylbenzidine (TPB) as light-emitting layer was used to fabricate a single layer structure light-emitting diode which has a low turn on voltage such as 2.5 V. The electroluminescence spectrum was obtained at room temperature. Owing to the effect that TPB interacted with ZnS nanocrystal to form the luminescent center, the emission was peaking at 520 nm which shifts to the lower energy compared with that of ZnS, and the half-width of the emission was about 20 nm.
Cu enhanced oxidation of SiGe and SiGeC
Authors: Jaquez E. J. , Bair A. E. , Alford T. L.
Published: July 2002

A study of the effects of C and Ge additions on the Cu catalyzed oxidation of Si has been performed. It was found that the addition of Ge alone resulted in a marked slowdown in the rate of oxygen incorporation; during the first three days of the experiment the rate of oxygen incorporation was 25 times higher in the Si reference sample. The Ge was incorporated into the oxide. Small amounts of C added to the SiGe compound have a more pronounced effect. Carbon concentrations of less than 2% prevent oxidation of SiGeC for periods of at least one month. Copper enhanced oxidation of Si(100) has produced oxides of several hundred nanometers in under one month.
High-resistance layers in n-type 4H-silicon carbide by hydrogen ion implantation
Authors: Nadella Ravi K. , Capano M. A.
Published: July 2002

The effect of hydrogen ion implantation damage on the resistivity of n-type 4H–silicon carbide is investigated. The variation of resistivity as a function of measurement temperature and postimplant annealing temperature is studied. Calculated resistivities obtained from resistance measurements are as high as 8×106 Ω cm when resistances are measured at room temperature. When measured at 250 °C, the resistivity of the implanted layer is 1×104 Ω cm. The resistivity is almost constant for annealings up to 1000 °C. The high-resistance behavior is believed to be related to implantation damage caused by 350 keV H+ implantation. The results of this study can be used to obtain high-resistance regions for device isolation.
Photorefractive multiple quantum well device using quantum dots as trapping zones
Authors: Le Corre A. , De Matos C. , L’Haridon H. , Gosselin S. , Lambert B.
Published: July 2002

Results on the optical properties of a GaInAs/GaInAsP multiple quantum well photorefractive device operating at 1.55 μm in the longitudinal quantum-confined Stark geometry are reported. Self-assembling quantum dots (SAQDs) have been used in this device to trap the photocarriers in two regions out of the multiple quantum well. An efficient screening of applied electric field and the possibility to reduce the lateral diffusion of carriers with SAQDs are demonstrated. Finally, degenerate four-wave mixing measurements were performed in this device.
Thermal stability in oligomeric triphenylamine/tris(8-quinolinolato) aluminum electroluminescent devices
Authors: Tokito Shizuo , Tanaka Hiromitsu , Noda Koji , Okada Akane , Taga Yasunori
Published: July 2002

Thermal stability of the electroluminescent (EL) devices using various hole-transporting materials based on triphenylamine, and a typical emitting material, tris(8-quinolinolato) aluminum has been systematically studied. The thermal stability of the EL devices is clearly seen to depend on the glass transition temperature (Tg) of the hole-transporting material. The highest thermal stability up to 155 °C is obtained in the device using the pentamer of triphenylamine. It has been found that the linear linkage of triphenylamine is useful to attain high Tg rather than the branch linkage.
Naturally formed ZnCdSe quantum dots on ZnSe (110) surfaces
Authors: Zhang B. P. , Yasuda T. , Segawa Y. , Yaguchi H. , Onabe K. , Edamatsu E. , Itoh T.
Published: July 2002

We successfully realized ZnCdSe quantum dots on a cleavage-induced ZnSe (110) surface by depositing a ZnSe/ZnCdSe/ZnSe heterostructure under growth conditions that cannot lead to layer-by-layer growth of ZnSe. This growth mode introduces surface roughness to the newly deposited ZnSe layer, and ZnCdSe quantum dots are then formed. Cathodoluminescence and microphotoluminescence measurements demonstrate the formation of quantum dots.
Transient enhanced diffusion of Sb and B due to MeV silicon implants
Authors: Eaglesham D. J. , Haynes T. E. , Gossmann H.-J. , Jacobson D. C. , Stolk P. A. , Poate J. M.
Published: July 2002

We measure the transient enhanced diffusion of shallow molecular-beam-epitaxy grown marker layers of Sb and B due to deep MeV Si+ ion implants at very high doses (≈1016 cm−2). We expect the near-surface region of these implants to be vacancy rich, and we observe transient enhanced diffusion of Sb (the classic vacancy diffuser). The large enhancements imply a significant vacancy supersaturation (≈700 at 740 °C). Double implantation of the high-dose MeV Si followed by a shallow (40 keV) Si implant and annealing produces a greatly reduced number of {311} defects compared to a 40 keV implant into virgin Si, again consistent with a vacancy-rich region in the near-surface region of an MeV implant. However, the shallow B marker layers also show transient enhanced diffusion for the same MeV implant under similar annealing conditions, implying that an interstitial supersaturation is present at the same time. We discuss possible mechanisms for a simultaneous supersaturation of both types of point defects.
Demonstration of 110 GHz electro-optic polymer modulators
Authors: Chen Datong , Fetterman Harold R. , Chen Antao , Steier William H. , Dalton Larry R. , Wang Wenshen , Shi Yongqiang
Published: July 2002

Electro-optic modulation up to 113 GHz has been demonstrated using traveling wave polymer modulators. The modulation signal was directly detected at 1.3 μm using a laser heterodyne system with an external-cavity tunable semiconductor laser. The device optical response variation, as a function of frequency over the whole W band, was within 3 dB. A well-matched coplanar probe was used to launch W band millimeter wave driving power into the microstrip line electrode on the device. Based upon these measurements, high speed electrodes with integrated millimeter wave transitions had been fabricated and tested.
Influence of interstitial copper on diffusion length and lifetime of minority carriers in p-type silicon
Authors: Istratov A. A. , Flink C. , Hieslmair H. , Heiser T. , Weber E. R.
Published: July 2002

Though copper can be quenched interstitially in p-type silicon, it precipitates completely within 10–15 h at room temperature. The decay of concentration of interstitial copper in p-Si was monitored by capacitance–voltage characteristics (C–V) and surface photovoltage (SPV). It is shown that the time constant of change of minority carrier diffusion length, as measured by SPV, correlates well with the precipitation of interstitial copper. The capture cross section of interstitial copper is estimated to be in the range 10−15–10−17 cm2. It is shown that interstitial copper is far less deleterious than iron and can limit the diffusion length of commercial p-Si wafers only if its concentration is above 1013 cm−3. However, copper precipitates may be detrimental to lifetime even for much lower copper concentrations.
Electron field emission characteristics of planar diamond film array synthesized by chemical vapor deposition process
Authors: Lee J. S. , Liu K. S. , Lin I. N.
Published: July 2002

Selected area deposition of diamond films on silicon substrates was successfully achieved using the patterned Pt layer as a nucleation inhibitor in the chemical vapor deposition process. The planar diamond film array thus made possesses good electron field emission properties, that is, emission current density of (Je)Si=150 μA/cm2 (under 23.6 V/μm) and turn on field of (Eo)Si=10 V/μm. Precoating a thin Au layer (20 nm) on a Si surface further increased the emission current density to (Je)Au/Si=960 μA/cm2 (under 23.6 V/μm) with (Eo)Au/Si=10 V/μm. The effective work functions (φ) estimated by Fowler–Nordheim plots of the I–V characteristics are (φ)Si=0.059 eV and (φ)Au/Si=0.085 eV. The emission properties of both planar diamond film arrays satisfy the requirement for applying as the electron emitters in the flat panel displays.
Determination of interdiffusion coefficients of cations and anions in InGaAs/InP superlattice
Authors: Ryu Sang-Wan , Choe Byung-Doo , Jeong Weon Guk
Published: July 2002

The interdiffusion coefficients of cations and anions in InGaAs/InP superlattices (SLs) on their respective sublattices were analyzed quantitatively. Double crystal X-ray diffraction and simulation of the rocking curves based on dynamical diffraction theory were used to measure the interface strain that develops during rapid thermal annealing. Low temperature photoluminescence (PL) measurements were also done to assess the interdiffusion through the change in ground state transition energy of the SL. Simulation with the proper selection of the interdiffusion coefficients results in proper fitting of the interface strain profile and PL transition energies. Using this method, interdiffusion behaviors of InGaAs/InP SLs with and without SiO2:P capping were analyzed. Interdiffusion coefficients of 5.8×10−17 and 2.9×10−17 cm2/s were obtained for the anion and cation sublattices respectively, when the SL without SiO2:P was annealed at 800 °C.
Substitutional carbon incorporation in epitaxial Si1−yCy layers grown by chemical vapor deposition
Authors: Mitchell T. O. , Hoyt J. L. , Gibbons J. F.
Published: July 2002

The incorporation of carbon in Si1−yCy alloys grown using silane and methylsilane by low-pressure rapid thermal chemical vapor deposition is investigated. Substitutional carbon content determined by x-ray diffraction analysis is compared to total carbon concentration measured by secondary ion mass spectrometry. Lower growth temperatures (<600 °C) and higher silane partial pressures are observed to significantly improve substitutional carbon incorporation. At 550 °C, to within experimental error, fully substitutional carbon incorporation is observed over the range of compositions studied (0–1.8 at. % carbon). Fourier transform infrared spectroscopy is also used to verify the presence of substitutional carbon.
Diffusional narrowing of Ge on Si(100) coherent island quantum dot size distributions
Authors: Drucker Jeff , Chaparro Sergio
Published: July 2002

The normalized width=standard deviation of island radius/mean island radius (σr/〈r〉) of molecular beam epitaxy grown Ge on Si(100) coherent island quantum dot size distributions is analyzed for various deposition conditions. It is found that this width decreases as substrate temperature increases independent of deposition flux. This result is interpreted in the context of models which suppose that the energy barrier for edge atom detachment decreases with island size. The faster diffusion kinetics at higher growth temperatures allow these detached edge atoms to more rapidly find the smaller islands producing sharper island size distributions.
Monitoring of ion implantation in Si with carrier plasma waves using infrared photothermal radiometry
Authors: Salnick A. , Mandelis A. , Funak F. , Jean C.
Published: July 2002

Photothermal infrared radiometry was used for monitoring the ion implantation in Si wafers implanted with phosphorus to doses in the range of 5×1010–1×1016 ions/cm2 at different implantation energies. Quantitative results on the sensitivity of the carrier plasma-dominated radiometric signal to the implantation dose and energy are presented and compared to those obtained using a commercial implantation monitoring instrument.
Microstructures of phased-in Cr–Cu/Cu/Au bump-limiting metallization and its soldering behavior with high Pb content and eutectic PbSn solders
Authors: Pan G. Z. , Liu Ann A. , Kim H. K. , Tu K. N. , Totta Paul A.
Published: July 2002

The microstructure of phased-in Cr–Cu/Cu/Au multilayer thin films and their solderability with high Pb-content PbSn solder (95/5%) and eutectic PbSn solder (37/63%) were studied by using cross-sectional transmission electron microscopy and scanning electron microscopy. We found that the phased-in Cr–Cu layer is intermixed and grains of both Cr and Cu are elongated along the growth direction. This special compositionally graded or functionally graded microstructure presents a lock-in effect of the Cr and Cu grains. It has succeeded in preventing the spalling of Cu3Sn in solder joints formed using the 95/5% solder, but failed in preventing the spalling of Cu6Sn5 in those formed using the eutectic solder. We suggest that the difference may be due to the different dissolution rates of the two compounds in the solders.
Piezoeffect and gate current in AlGaN/GaN high electron mobility transistors
Authors: Gaska R. , Yang J. W. , Osinsky A. , Bykhovski A. D. , Shur M. S.
Published: July 2002

We report on a high positive turn-on voltage (close to 2.5 V) of the gate-source leakage current in AlGaN/GaN high electron mobility transistors (HEMTs). The piezoeffect, the barrier, and channel doping result in the electron sheet concentration as high as 1013 cm−2. A larger conduction band discontinuity and a larger electron effective mass (compared to AlGaAs/GaAs HEMTs) lead to a lower gate current and to a higher turn-on voltage. This means that AlGaN/GaN technology can be suitable for applications in digital and mixed-mode integrated circuits.
Strain relaxation of InGaAs/GaAs superlattices by wet oxidation of underlying AlAs layer
Authors: Seo Jin Ho , Seo Kwang Seok
Published: July 2002

The effects of AlAs wet oxidation on overlayers were investigated using InGaAs/GaAs strained-layer superlattice structures grown on an AlAs layer. The superlattice partially relaxes towards its equilibrium spacing as the result of the oxidation of the underlying AlAs layer. Double-crystal x-ray diffraction measurements were used to determine the degree of strain relaxation. Larger relaxation is observed for the sample with a higher indium composition and a thicker AlAs layer.
Two-color corrugated quantum-well infrared photodetector for remote temperature sensing
Authors: Chen C. J. , Choi K. K. , Chang W. H. , Tsui D. C.
Published: July 2002

A quantum-well infrared photodetector (QWIP) based on the corrugated light-coupling scheme has been fabricated and tested for remote temperature sensing. The QWIP consists of two stacks of multiple quantum wells (MQWs), each sensitive in one of the atmospheric infrared transmission windows and each with a separate readout circuit. High optical coupling efficiency is obtained in both wavelength ranges, demonstrating the use of the corrugated structure for two-color detection. By monitoring the ratio of the photocurrent generated simultaneously in each MQW stack, the temperature of the object emitting the radiation can be determined, regardless of its emissivity and the geometrical factors. This temperature sensing ability is tested by using a blackbody radiator with precision temperature control as the target. The agreement between the measured and the preset temperatures indicates that the corrugated QWIP is capable of precision thermometric measurements.
Ultraviolet GaN light-emitting diodes grown by molecular beam epitaxy using NH3
Authors: Grandjean N. , Massies J. , Leroux M. , Lorenzini P.
Published: July 2002

Si- and Mg-doped GaN layers were grown on c-plane sapphire substrates by molecular beam epitaxy with NH3 as the nitrogen precursor. Their optical and electrical properties were investigated by photoluminescence experiments and Hall measurements, respectively. P-type conductivity, with a net acceptor concentration of 3×1017 cm−3 and a mobility of 8 cm2/V s, was obtained. Mesa-etched light-emitting diodes were processed from p–n junctions. The turn-on voltage is 3 V and the forward current reaches 20 mA at 3.5 V. The room-temperature electroluminescence exhibits a strong emission at 390 nm.
Electrical and magnetic phases of the layered perovskite Ca4−xLaxMn3O10
Authors: Witte N. S. , Goodman P. , Lincoln F. J. , March R. H. , Kennedy S. J.
Published: July 2002

We analyze magnetic susceptibility, resistivity and neutron diffraction measurements of the electron doped triple layered perovskite, or Ruddlesden–Popper class of manganates Ca4−xLaxMn3O10. Near the undoped region a paramagnetic insulator to antiferromagnetic insulator transition is observed with decreasing temperature and a concomitant change in the conduction process from thermal activation to Mott-type hopping. For larger doping, with a Mn valence of 3.97, there is a transition from the paramagnetic insulator to a canted antiferromagnetic insulator which exhibits a more dramatic change in the conduction mechanism.
Quantitative imaging of sheet resistance with a scanning near-field microwave microscope
Authors: Steinhauer D. E. , Vlahacos C. P. , Dutta S. K. , Feenstra B. J. , Wellstood F. C. , Anlage Steven M.
Published: July 2002

We describe quantitative imaging of the sheet resistance of metallic thin films by monitoring frequency shift and quality factor in a resonant scanning near-field microwave microscope. This technique allows fast acquisition of images at approximately 10 ms per pixel over a frequency range from 0.1 to 50 GHz. In its current configuration, the system can resolve changes in sheet resistance as small as 0.6 Ω/□ for 100 Ω/□ films. We demonstrate its use at 7.5 GHz by generating a quantitative sheet resistance image of a YBa2Cu3O7−δ thin film on a 5 cm diam sapphire wafer.
Local channel temperature measurements on pseudomorphic high electron mobility transistors by photoluminescence spectroscopy
Authors: Landesman J. P. , Depret B. , Fily A. , Nagle J. , Braun P.
Published: July 2002

Spatially resolved photoluminescence (PL) measurements have been performed on GaAs/GaInAs/GaAlAs pseudomorphic high electron mobility transistors to determine the local temperature on both sides of the gate with spatial resolution of about 1 μm and temperature resolution better than 1 °C. This local temperature is deduced from the energy shift of one of the peaks in the PL spectra. Asymmetry in the temperature distribution between the drain and source sides is observed. The experimental temperature values have also been compared with predictions from an analytical model to determine the thermal resistance in these devices.
The larger polar Kerr rotation of Fe-Si alloy films and their magnetic properties
Authors: Zhou Tie-Jun , Yang W. , Yu Z. , Zhang H. H. , Shen J. C. , Du Y. W.
Published: July 2002

The structure, magnetic properties and polar Kerr effects of Fe100−xSix (0⩽x⩽70) alloy films prepared by ion-beam co-sputtering were studied. We find that the saturation magnetization of these films decreases with increasing x, and a plateau of constant magnetization occurs as 22⩽x⩽28. Their polar Kerr rotation θk decreases with increasing x as x⩽16.2 and x⩾30, but increases with increasing x as 20⩽x⩽28. In the measuring wavelength range of 400–800 nm, the θk of Fe72Si28 film is 40% to 50% larger than that of pure Fe film. We think that amorphization may play an important role in enlarging the polar Kerr rotation of these films.
Annealing kinetics and reversibility of stress-induced leakage current in thin oxides
Authors: Riess P. , Ghibaudo G. , Pananakakis G. , Brini J.
Published: July 2002

The annealing kinetics of stress-induced leakage current in ultrathin SiO2 has been quantitatively investigated after high temperature bakes. We have found that the defects at the origin of the stress induced-leakage current can be fully annihilated and that it is possible to generate and anneal them several times without deterioration of the oxide quality. Moreover, the activation energy and diffusion coefficient deduced from the recovery time constant of the annealing kinetics are found nearly independent of the oxide thickness.
Model of leakage characteristics of (Ba, Sr)TiO3 thin films
Authors: Maruno S. , Kuroiwa T. , Mikami N. , Sato K. , Ohmura S. , Kaida M. , Yasue T. , Koshikawa T.
Published: July 2002

We have investigated the dependence of leakage current and capacitance of Pt/Ba0.5Sr0.5TiO3/Pt capacitors on annealing temperature under high vacuum conditions. It is observed that leakage currents increase asymmetrically for negative and positive bias voltage with increasing annealing temperature. A model of leakage current and capacitance characteristics has been proposed on the assumption of generation of oxygen vacancies by annealing at the interfaces of the dielectric film adjacent to the Pt electrodes. The model predicts the oxygen vacancies of about 1020 cm−3.
Noise gain and detectivity of n-type GaAs/AlAs/AlGaAs quantum well infrared photodetectors
Authors: Schönbein C. , Schneider H. , Rehm R. , Walther M.
Published: July 2002

We have investigated noise currents in GaAs/AlAs/AlGaAs quantum well infrared photodetectors (QWIPs). The specific design of these detectors implies a carrier mean-free path of exactly one period of the superlattice with N=20 periods, leading to a carrier capture probability pc≈1 associated with a noise gain gn=1/N at sufficiently small applied bias voltages. The gain values obtained from our measurements are analyzed using three different noise gain models, which predict different dependencies of the detectivity on the capture probability. Our results indicate that a photoconductive QWIP with pc≈1 should have a higher detectivity than a conventional GaAs/AlGaAs QWIP.
Transient enhanced diffusion from decaborane molecular ion implantation
Authors: Agarwal Aditya , Gossmann H.-J. , Jacobson D. C. , Eaglesham D. J. , Sosnowski M. , Poate J. M. , Yamada I. , Matsuo J. , Haynes T. E.
Published: July 2002

Transient enhanced diffusion (TED) from implantation of 5 keV B10H14 and 0.5 keV B ions has been quantified and compared for nominal boron doses of 1014 and 1015 cm−2. Boron diffusivity during annealing was extracted from secondary ion mass spectroscopy depth profiles of diffused marker layers in boron doping-superlattices and the actual implanted B dose was independently measured by nuclear reaction analysis. Comparable enhancements were observed from both ions. Transmission electron microscopy analysis revealed that both boron- and decaborane-implanted samples were amorphized at a nominal 1015 cm−2 B dose. A comparison with data from low energy Si implants revealed a similar dependence of diffusivity enhancement on implant dose. These findings are consistent with the understanding that TED is caused by the interstitial supersaturation resulting from a number of excess interstitials approximately equal to the number of implanted atoms which can become substitutional in the silicon lattice. Accordingly, no contribution to TED is expected from the hydrogen in the B10H14 ions and none is observed. Furthermore, there is no detectable effect in the diffusion profiles which can be attributed to a difference in the ion damage produced by the decaborane molecule and the boron atom. In both cases the reduction in diffusivity enhancement is due only to proximity of the implantation-induced excess interstitials to the wafer surface.
Injection level dependence of the defect-related carrier lifetime in light-degraded boron-doped Czochralski silicon
Authors: Schmidt Jan , Berge Christopher , Aberle Armin G.
Published: July 2002

The carrier recombination lifetime in light-degraded boron-doped 1 Ω cm Czochralski-grown silicon wafers is measured as a function of the bulk excess carrier concentration Δn. The measurements are performed with the quasi-steady state photoconductance method and cover a large injection level range between 1013 and 1.5×1017 cm−3. We observe a very strong increase of the carrier lifetime in the Δn range between 1014 and 2×1016 cm−3, which is attributed to boron–oxygen (BiOi) defect pairs. The observed strong increase of the defect-related carrier lifetime allows us to determine the previously unknown hole capture cross section σp of the BiOi pair. Our analysis gives a σp value of (0.45–1.2)×10−15 cm2, which is 2–3 orders of magnitude smaller than the corresponding electron capture cross section.
Tunneling-like magnetoresistance in bicrystal La0.8Sr0.2MnO3−δ thin films
Authors: Steenbeck K. , Eick T. , Kirsch K. , Schmidt H.-G. , Steinbeiß E.
Published: July 2002

Epitaxial ferromagnetic La0.8Sr0.2MnO3−δ films have been sputtered on SrTiO3 bicrystal substrates. Etched patterns crossing the bicrystal grain boundary are compared with identical patterns not crossing it. The films were annealed at different conditions and their magnetoresistance measured as a function of temperature T and of in plane magnetic field H strength and direction. Annealing at 900 °C was found to modify the grain boundary and to increase its magnetoresistance. For H=±80 Oe parallel to the grain boundary and T=32 K narrow magnetoresistance peaks of 60% height are measured. They are interpreted in the frame of an in plane magnetotunneling structure.
Trends in residual stress for GaN/AlN/6H–SiC heterostructures
Authors: Edwards N. V. , Bremser M. D. , Davis R. F. , Batchelor A. D. , Yoo S. D. , Karan C. F. , Aspnes D. E.
Published: July 2002

We discuss trends in residual stress as a function of film thickness, growth temperature, and substrate orientation for GaN/AlN/6H–SiC heterostructures. Films are mostly compressive for samples less than about 0.7 μm thick, are tensile up to about 2 μm, then abruptly become less tensile with stress values near 1 kbar thereafter. We interpret this as a successive relief of lattice mismatch and thermal stresses culminating in a catastrophic relief by unknown mechanisms at moderate thicknesses. These data indicate that relaxation processes in these heterostructures are not as well understood as previously supposed.
Nonconservative Ostwald ripening of dislocation loops in silicon
Authors: Huang Y. L. , Seibt M. , Plikat B.
Published: July 2002

We have investigated the effects of the proximity of the surface on the ripening behavior of dislocation loops in preamorphized silicon. Starting from well-defined initial conditions, we have varied the location depth of the loops by successive chemical removal of surface layers and measured changes of the size–distribution function during subsequent annealing by means of transmission electron microscopy. Our results show that the amount of Si atoms bound in the loops is not conserved during annealing and that the loop location depth has a prominent effect on the ripening kinetics. Both these observations prove the nonconservative nature of Ostwald ripening of dislocation loops near wafer surfaces. In addition, we observed different ripening kinetics for annealing in vacuum and in Ar which show that different boundary conditions at the surface are established during annealing in these two ambients.
Micromagnetics and magnetoresistance of a Permalloy point contact
Authors: van Gorkom R. P. , Caro J. , Theeuwen S. J. C. H. , Wellock K. P. , Gribov N. N. , Radelaar S.
Published: July 2002

We performed micromagnetic calculations for a Permalloy point contact. The magnetization configurations show the formation of a Néel wall in the constriction. The occurrence of a Néel wall instead of a Bloch wall results from the dipole–dipole energy in this region. The evolution of the magnetization with field differs strongly for fields parallel and perpendicular to the electrodes. In the former case, the pattern evolves abruptly and in a narrow range, while in the latter case it evolves smoothly and in a rather wide range. From the magnetization patterns, we estimate the domain-wall magnetoresistance and the anisotropic magnetoresistance, which we compare with experimental data.
Demonstration of microwave generation by a ferroelectric-cathode tube
Authors: Drori R. , Einat M. , Shur D. , Jerby E. , Rosenman G. , Advani R. , Temkin R. J. , Pralong C.
Published: July 2002

A ferroelectric cathode is employed in a cyclotron-resonance maser (CRM). The CRM oscillator device operates at ∼7 GHz, near the cutoff frequency of a hollow cylindrical cavity. The cathode is made of a PLZT 12/65/35 ceramic with high-dielectric constant (εr∼4000). Electrons are extracted from the plasma excited on the cathode surface by ∼1 kV short rise-time pulses. The use of ferroelectric cathodes may advance the microwave tube technology for various applications.
Schottky energy barriers and charge injection in metal/Alq/metal structures
Authors: Campbell I. H. , Smith D. L.
Published: July 2002

We present internal photoemission, photocurrent versus bias voltage, and current–voltage measurements of metal/tris-(8-hydroxyquinoline) aluminum [Alq]/metal structures. Internal photoemission and photocurrent versus bias measurements were used to determine metal/Alq Schottky energy barriers for a range of contact metals with work functions from 2.7 eV (Sm) to 5.6 eV (Pt). The electron Schottky barrier for low work-function metals ( about 3.6 eV) the ideal Schottky model is generally accurate. A previously established device model was used to describe the current–voltage characteristics using the measured Schottky barriers. The results imply comparable electron and hole mobilities of about 2×10−5 cm2/V s at an electric field of 106 V/cm.
Ultrathin silicon oxynitride film formation by plasma immersion nitrogen implantation
Authors: Baumvol I. J. R. , Krug C. , Stedile F. C. , Green M. L. , Jacobson D. C. , Eaglesham D. , Bernstein J. D. , Shao J. , Denholm A. S. , Kellerman P. L.
Published: July 2002

A method is proposed to prepare ultrathin silicon oxynitride films for gate dielectrics used in deep submicron metal–oxide–semiconductor field effect transistor device structures, namely plasma immersion N implantation into SiO2 films. Plasma immersion implantation pulse voltages in the range 200–1000 V, and fluences from 1016 to 1017 N cm−2 were implanted into thermally grown SiO2 films, with thicknesses between 3 and 6 nm. The areal densities of N and O in the resulting oxynitride films were determined by nuclear reaction analysis, before and after annealing in high-vacuum. N, O, and Si profiles in the films were determined with subnanometric depth resolution by medium energy ion scattering. The results indicate that plasma immersion ion implantation allows for shallow and controlled deposition of significant amounts of nitrogen (up to 3.8 nm of equivalent Si3N4 thickness). Implantation is accompanied by moderate damage at the oxynitride/Si interface which can be recovered by thermal annealing.
Influence of 6H–SiC(0001) substrate surface morphology on the growth of AlN epitaxial layers
Authors: Torres V. M. , Edwards J. L. , Wilkens B. J. , Smith David J. , Doak R. B. , Tsong I. S. T.
Published: July 2002

Epitaxial AlN films were grown on 6H–SiC(0001) substrates using an ammonia supersonic seeded beam. The films grown on substrates etched in hydrogen at high temperatures were shown by ion beam channeling to exhibit a higher degree of order relative to those grown on the as-received substrates. Cross-sectional electron microscopy revealed sharper SiC–AlN interfaces with extended flat terraces. In particular, very few stacking mismatch boundaries were observed to originate from the 1.5 nm steps which correspond to the 6H stacking sequence of the substrate.
Measuring the gigahertz response of recording heads with the magnetic force microscope
Authors: Proksch Roger , Neilson Peter , Austvold Shane , Schmidt J. J.
Published: July 2002

We compare two different techniques for measuring the high frequency response of recording heads using a magnetic force microscope. The first technique is based on driving the recording head with a high frequency current. We separated the high and low frequency response of the recording head by making two measurements, one with the current on, one with the current off. The second technique is based on amplitude modulation of the high frequency current driving the recording head. This technique has the advantage of separating the low and high frequency response in a single measurement. We used both of these techniques to study the spatially dependent response of recording heads operating up to and beyond 1 GHz.
Exciton resonances in ultrathin InAs/InP quantum wells
Authors: Paki P. , Leonelli R. , Isnard L. , Masut R. A.
Published: July 2002

We have performed detailed optical measurements of ultrathin InAs/InP quantum wells grown by metal organic vapor phase epitaxy. Photoluminescence excitation spectra reveal the excitonic resonances associated with two- and three-monolayer thick InAs layers while polarization-dependent measurements clearly show the heavy- or light-hole nature of the resonances. These resonances, together with their emission bands, can be detected on the same sample, indicating the presence of well defined regions of different InAs layer thickness. We find that the energy position of the excitonic resonances cannot be reproduced by effective mass calculations based on the envelope function approximation.
Dynamic scaling of magnetic hysteresis in micron-sized Ni80Fe20 disks
Authors: Lee W. Y. , Choi B.-Ch. , Lee J. , Yao C. C. , Xu Y. B. , Hasko D. G. , Bland J. A. C.
Published: July 2002

The scaling of the magnetic hysteresis loop area of permalloy disks (20–400 μm diam) has been studied as a function of applied field amplitude H0 and frequency Ω using scanning Kerr microscopy. An increase in the dynamic coercivity with reduced size is observed for d<100 μm in the frequency range studied (0.1–800 Hz). However, the loop area A follows the scaling relation A∝H0αΩβ, with α≈0.14 and β≈0.50 throughout the entire size range studied. Our results demonstrate that the dynamic scaling behavior is universal even though the lateral size influences the domain structure and magnetic reversal behavior.
Ab-initio calculation of excited state absorption of Cr4+ in Y3Al5O12
Authors: Ching W. Y. , Xu Yong-Nian , Brickeen B. K.
Published: July 2002

The Cr3+ and Cr4+ impurity states in Y3Al5O12 (YAG) crystal are studied by ab-initio supercell calculations using the density-functional theory. Calculations are carried out with Cr substitutions at the octahedral and tetrahedral Al sites including the effect of Ca co-doping. Optical transitions between various levels and to conduction band states are also calculated. A model for excited state absorption for Cr4+ in YAG is proposed.
Light emission during fracture of a Zr–Ti–Ni–Cu–Be bulk metallic glass
Authors: Gilbert C. J. , Ager J. W. , Schroeder V. , Ritchie R. O. , Lloyd J. P. , Graham J. R.
Published: July 2002

A light emission phenomenon observed during dynamic fracture of a bulk metallic glass, Zr41.2Ti13.8Cu12.5Ni10Be22.5 (at. %), has been investigated using Charpy V-notch impact specimens. Unlike more conventional crystalline metals, these Zr-based amorphous alloys emit intense flashes of visible light when ruptured. The mechanisms for this surprising behavior are unknown and the phenomenon remains uncharacterized. Here we report spectroscopic measurements of the light emitted from specimens fractured in both room air and nitrogen gas. Spectra acquired from specimens ruptured in air exhibited a single broad peak, which could be fit to a blackbody temperature of ∼3175 K. Emission from specimens fractured in nitrogen, however, was at least four orders of magnitude less intense. The spectrum was shifted to the red with an effective blackbody temperature of ∼1400 K. Fracture surfaces of specimens ruptured in both air and nitrogen exhibited local melting, providing further evidence of intense heating during fracture. Based on these observations we argue that the intense light emission in air is associated with pyrolysis of fresh material exposed during rupture.
Thermally activated demagnetization in Co/Ni multilayers involving discrete identifiable stages
Authors: González J. M. , Salcedo A. , Cebollada F. , Freijo J. J. , Muñoz J. L. , Hernando A.
Published: July 2002

We present data, obtained from measured Co/Ni multilayers, that indicate that the magnetic relaxation processes take place through a nucleation-coalescence sequence, and thus crucially implicates the existance of exchange and dipolar interactions. Depending on the layer thickness the relaxation proceeds either through a single global stage or through several partial ones. In both cases the relaxation stages involve a time lapse during which the macroscopic state of the system evolves very slowly, followed by a sharp variation of the total moment of the sample. Such behavior clearly implies a significant departure from the conventionally accepted Arrhenius relaxation kinetics.