bluuebunny/crossref_metadata_2025 huggingface dataset:
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u x-ray diffraction measurement of Pd2Si transformation kinetics using a linear position-sensitive detector
Authors: Little T. W. , Chen Haydn
Published: July 2002

The x-ray diffraction technique described previously for measurement of growth kinetics of Pd2Si layers from their solid state reaction couples has been extended by the use of a one-dimensional position-sensitive detector (PSD). Additionally, the method has been extended to include measurement of the Pd layer. A detailed description of the experimental arrangement and analytical procedures is presented. The kinetics of epitaxial Pd2Si film growth were measured in situ over a range of 170–230 °C. The PSD results, using data obtained from both the Pd2Si and Pd layers, were able to confirm parabolic growth behavior for the Pd2Si film. The rate constants followed Arrhenius behavior and yielded an activation energy of E=1.32±0.07 eV with a prefactor k0=0.49 cm2/s for the Pd2Si layer analysis and E=1.34±0.17 eV with a prefactor of 0.72 cm2/s for the Pd layer analysis. The PSD technique significantly enhances data collection and provides extended analytical capabilities. The method has the potential for measuring rate kinetics of other solid state reactions/transformations such as surface oxidation and alloy decomposition.
Properties of ion-beam-sputtered Ni/Fe artificial lattice film
Authors: Nagai Yasuhiro , Senda Masakatsu , Toshima Tomoyuki
Published: July 2002

This paper reports the results of experimental and analytical investigations into the properties of ion-beam-sputtered Ni/Fe artificial lattice films. Through structure analysis, it is known that the Fe layer has poor crystallinity and the Ni layer has a face-centered-cubic structure with strong preferred orientation. Additionally, the Ni/Fe lattice film is found to possess good soft-magnetic properties with lower coercivity less than 1 Oe and uniaxial anisotropy as the lattice period is decreased. The saturation magnetization and magnetostriction are also confirmed to be controlled by changing the lattice period and the thickness of Ni and Fe layers. As a result of the simplest model analysis, the very small magnetostriction obtained in this experiment is thought to be realized by the balance in magnetostriction among Ni, Fe, and Ni-Fe interdiffusion layers. Furthermore, a good domain structure is observed in the Ni/Fe lattice film with very small magnetostriction.
Analysis of transmission electron microscopy images of hydrogen platelets in proton-bombarded GaAs
Authors: Neethling J. H. , Snyman H. C. , Ball C. A. B.
Published: July 2002

The technique of cross-sectional transmission electron microscopy has been applied to study the nature of the hydrogen platelets on {110} planes in proton-bombarded (5×1015 H+ cm−2 at 300 keV) and annealed (temperatures of 500 °C and above) GaAs samples. Models are presented to explain the absorption of hydrogen atoms at platelets and to calculate gas pressures in platelets. From a consideration of the radiation-induced damage and annealing processes, the absence of self-interstitial loops in these low-dose samples is explained.
An 18O study of oxygen exchange phenomena during microwave-discharge plasma oxidation of silicon
Authors: Kimura Shin-ichiro , Murakami Eiichi , Warabisako Terunori , Mitani Eisuke , Sunami Hideo
Published: July 2002

The mechanism of oxygen migration during microwave-discharge plasma oxidation of Si is investigated using secondary ion mass spectroscopy depth-profile analysis and 18O as a tracer. The exchange phenomenon between migrating oxygen and its counterpart in SiO2 is observed. When the plasma-grown oxide (Si16O2) is reoxidized in 18O plasma, the 18O is observed both at the Si/SiO2 interface and in the bulk of the Si16O2. In a reverse example, when Si18O2 is reoxidized in 16O plasma, the total amount of pre-existing 18O in Si18O2 decreases. The suppression of 18O is more distinct near the surface region. These oxygen distributions indicate that oxygen migrates toward the interface accompanied by oxygen exchange. Since the exchange phenomenon is not observed in dry thermal oxidation, in which oxygen molecules migrate, active oxygen atoms or atom ions should induce the exchange by breaking the Si–O bond during migration.
Isothermal anisotropy rotation in a Au-Fe spin-glass alloy
Authors: Ziq Kh. , Kouvel J. S.
Published: July 2002

Magnetization-vector measurements were made on a slowly rotating disk sample of Au85 Fe15 after cooling to 4.2 K from above Tg (=52 K) in a 15-kOe field that saturates the thermoremanence. For MT , the magnetization component transverse to the applied field H, results are shown as HMT vs θ, the sample-rotation angle relative to H, for θ cycled between 0° and 180° at each value of H. For H≲0.1 kOe, HMT varies nearly reversibly in simple accord with an anisotropy field HK (0.41 kOe in size) that rotates rigidly with the sample. At higher H, the rotational hysteresis grows rapidly until, for H≳0.4 kOe, another simple but highly irreversible behavior is observed. From this behavior, it is deduced that HK rotates relative to the sample isothermally when the torque on it exerted by the sample magnetization reaches the magnitude of a frictional torque. The frictional-torque coefficient is seen to decrease steadily with increasing H, as confirmed by direct measurements of the rotations of the remanence that result from sample rotations in various H at 4.2 K.
The application of sodium amalgam to prepare ferrofluids containing iron particles in mercury
Authors: Takács L.
Published: July 2002

Mercury-based ferrofluids are prepared by using sodium amalgam to reduce iron into mercury while agitating mechanically and magnetically by an ordinary magnetic stirrer. The field dependence of the room-temperature magnetization is measured and used to determine the particle size distribution and its aging behavior. Samples prepared by the conventional method of electroplating into a mercury cathode are also studied for comparison. It is shown that the samples prepared by the two methods are very similar and the small amount of sodium remaining in the samples prepared from sodium amalgam can enhance the stability.
Induced magnetic anisotropy related to the local atomic order: A study in amorphous Co-Zr and Co-Zr-M thin films
Authors: Suran G. , Naili M. , Sztern J.
Published: July 2002

The in-plane uniaxial anisotropy Ku, induced by a magnetic field applied during the deposition, was investigated in amorphous thin films of Co1−xZrx and Co1−x−yZrx My (M=Ti, Nb, and Pt) obtained by rf sputtering. For a given concentration Ku presents a bell-shaped variation as a function of Ar pressure PAr. The critical pressure for which the maximum value of Ku is obtained and the absolute value of (Ku)max changes for the various alloys. These results and the high value of (Ku)max are explained by a model where (Ku)max is related to the local anisotropy via the local structure upon the nonmagnetic metal. (Ku)min is essentially related to a pseudodipolar short-range order.
High-pressure thermal oxidation of InP in steam
Authors: Gann R. G. , Geib K. M. , Wilmsen C. W. , Costello J. , Hrychowain G. , Zeto R. J.
Published: July 2002

The thermal oxidation of InP in dry oxygen has previously been shown to result in mixed oxide layers, even when grown at pressures as high as 500 atm. This appears to be caused by the slow diffusion of P and O2 through the oxide relative to In. This paper reports on the oxidation of InP in steam at one and 500 atm. Growth in one atm yields an oxide with a composition very similar to those grown in dry oxygen, indicating similar growth kinetics. However, at 500 atm of steam the growth kinetics are changed dramatically and result in a uniform InPO4 layer, suggesting that at high pressure, the H2O diffuses rapidly to the oxide-InP interface where the oxidation reaction occurs.
Reversible interaction of hydrogen with thin layers of thermally grown silicon dioxide
Authors: Fare T. , Spetz A. , Armgarth M. , Lundström I.
Published: July 2002

Some effects of hydrogen on the electrical properties of Pd-metal-thin (≊10 nm) oxide-silicon capacitors are reported. High-frequency (1 MHz) and quasistatic capacitance voltage curves are measured at 100 °C as a function of hydrogen partial pressure in a background atmosphere of 20% O2/Ar. Besides the standard hydrogen-induced shift of the capacitance-voltage characteristics we find: (1) an increase in the accumulation capacitance with increasing hydrogen partial pressure, and (2) a nonmonotonic increase in the quasistatic capacitance minimum with increasing hydrogen pressure. The relative increase in the accumulation capacitance is shown to be related to the square of the hydrogen-induced voltage shift (and hence to the square of the concentration of hydrogen atoms at the Pd-SiO2 interface). We discuss our findings, based on existing hydrogen-silicon dioxide models, to interpret the effects of hydrogen on the high-frequency and quasistatic capacitance characteristics.
The microstructure and electrical properties of contacts formed in the Ni/Al/Si system due to rapid thermal processing
Authors: Katz A. , Komem Y.
Published: July 2002

The microstructure and electrical properties of the contacts formed in the Ni(30 nm)/Al(10 nm)/〈100〉n-Si system due to rapid thermal processing were studied at temperatures between 300 and 900 °C. A melting at the intermediate Al layer was observed already at about 580 °C after 2-s heat treatments. This rapid eutectic melting, assumed to initiate at the Al-Si interface, resulted in the formation of a unique contact composed of the Ni(Al0.5Si0.5)/Al3Ni/NixSiy/n-Si structure with fairly smooth interfaces between the layers. The sheet resistance of the layers and the Schottky barrier height of the contact were measured as a function of the rapid thermal processing temperatures. As a result of the eutectic melting reaction at 580 °C the sheet resistance of the formed layers decreased from 3.2 to 2.6 Ω/⧠, the Schottky barrier height between the layers and Si increased from 0.61–0.76 eV, and the effective electrically active area of the contact increased. These electrical properties are discussed in correlation with the microstructure formed in the Ni/Al/Si system due to the rapid thermal processing.
A lithium-fluoride flashover ion source cleaned with a glow discharge and irradiated with vacuum-ultraviolet radiation
Authors: Burns E. J. T. , Woodworth J. R. , Bieg K. W. , Mehlhorn T. A. , Stygar W. A. , Sweeney M. A.
Published: July 2002

We have studied methods of varying the ion species generated by a lithium-fluoride overcoated anode in a 0.5-MV magnetically insulated ion diode. We found that cleaning the anode surface with a 13.6-MHz rf glow discharge or illuminating the anode with a pulsed soft x-ray, vacuum-ultraviolet (XUV) radiation source just before the accelerator pulse significantly altered the ion species of the ion beam produced by the diode. The glow-discharge plasma removed adsorbates (carbon, hydrogen, and oxygen) from the surface of the LiF flashover source. The ions seen were lithium and hydrogen. Unfortunately, the diode impedance with a lithium-fluoride anode was high and the ion efficiency was low; however, XUV irradiation of the surface dramatically lowered the impedance by desorbing neutrals from the ion source via photon-stimulated desorption. Current densities of ten times the Child–Langmuir space-charge limit were achieved under XUV irradiation. In particular, ion currents increased by over a factor of 3 when 12 mJ/cm2 of XUV radiation was used. However, with XUV irradiation the largest fraction of ions were fluorine, oxygen, carbon, and hydrogen, not lithium.
The domain and the domain wall structures of an Fe90Zr10 reentrant alloy
Authors: Senoussi S. , Hadjoudj S. , Jouret P. , Bilotte J. , Fourmeaux R.
Published: July 2002

Lorentz electron transmission microscopy investigations of the magnetization structure as a function of temperature (6 K≲T≲290 K) in amorphous films of Fe90Zr10 are reported. Magnetic domains as large as ∼50 μm are observed. It is found that the domain configuration stays essentially unchanged upon cooling through the so-called reentrant spin-glass phase. However, direct magnetic measurements on the same sputtered films show that the degree of spin-glass order which sets in below∼30 K is rather low, whereas the Curie temperature exceeds 290 K.
Corrosion-resistant-rare-earth–transition-metal amorphous films with high recording sensitivity for magneto-optical disks
Authors: Kawamoto A. , Nagato K. , Kuzuo R. , Yorozu T.
Published: July 2002

This study provides a method for improving the corrosion resistance of rare-earth–transition-metal films used for magneto-optical recording without depressing the recording sensitivity. This was attained by increasing Co content and substituting Dy for Tb and TbFeCo amorphous films. Potentiostatic polarization measurements indicate that the pitting potential of the film increases with the increase of Co content up to y=0.17 for (Tb0.5Dy0.5)0.21Fe0.79−yCoy. Attempts are made to explain the results using Auger electron spectroscopy and x-ray photoelectron spectroscopy. For the above-noted composition, both the Kerr rotation angle and coercivity observed through the substrate retain their initial values after the accelerated aging test. Results indicate that the (Tb0.5Dy0.5)0.21Fe0.62Co0.17 film offers superior characteristics for corrosion resistance without disturbing the magnetic properties.
Analysis of high-field magnetization measurements on R2Fe14B single crystals (R=Tb, Dy, Ho, Er, and Tm)
Authors: Givord D. , Li H. S. , Cadogan J. M. , Coey J. M. D. , Gavigan J. P. , Yamada O. , Maruyama H. , Sagawa M. , Hirosawa S.
Published: July 2002

Single crystals of the compounds R2Fe14B some 1–4 mm in size have been grown for a study of the anisotropy of the magnetization curves. These curves for crystals with R=Tb, Dy, Ho, Er, and Tm were measured at the Service National des Champs Intenses, Grenoble, between 4.2 and 275 K, with fields of 0–18 T being applied along the [100], [110], and [001] directions. Magnetization curves for all five compounds are analyzed in terms of the exchange and crystal field interactions (including terms up to sixth order, which may differ at 4 f and 4g sites) following the analysis previously developed for Nd2Fe14B. Molecular field coefficients representing the exchange interactions between R and Fe spins decrease from light to heavy R compounds as previously deduced from analysis of Curie temperatures. The CEF parameters are approximately the same across the series. In particular, the A20 terms are constant to within 10%.
Magnetic and structural properties of Mn(SCN)2(ROH)2 compounds
Authors: DeFotis G. C. , McGhee E. M. , Echols K. R. , Wiese R. S.
Published: July 2002

Three new members of the title series, where R=CH3, C2H5, i-C3H7 or n-C3H7, have been studied in addition to the previously examined ethanol homologue. A crystal structure for the methanol compound reveals a two-dimensional network of manganese ions bridged by thiocyanate groups with methanols separating they layers. The situation is somewhat similar to that occurring for the ethanol compound, in which magnetic quasi-two-dimensionality was apparent. On the other hand, for the isopropanol compound a crystal structure suggests more nearly one-dimensional magnetic character. Weiss constants in Curie–Weiss fits to high-temperature data are −22.4, −20.9, −20.5, and −37.2 K for the methanol, ethanol, n-propanol, and isopropanol systems, respectively. The susceptibilities exhibit broad maxima at about 12.7 K for the methanol and n-propanol systems and about 16.0 K for the isopropanol system. All but the isopropanol exhibit a phase transition at about 10 K. For the methanol and ethanol systems weak ferromagnetism occurs below the ordering temperature; this appears not to occur for the n-propanol system. Susceptibility data are analyzed on the basis of two-dimensional (methanol, n-propanol) or one-dimensional (isopropanol) S=5/2 antiferromagnetic Heisenberg models. The exchange interaction is substantially stronger in the isopropanol than in the other members of the series.
Micromagnetic predictions for barium ferrite particles (invited)
Authors: Victora R. H.
Published: July 2002

The quantitative application of micromagnetic theory to barium ferrite particulate media is reported. The theory includes magnetostatic, anisotropic crystalline, and exchange interactions. It is found that neither packing, stacking, thermal fluctuations, nor curling can account for the discrepancy between the predictions of noninteracting coherent rotation theory and experimental observations. Induced domain nucleation can reduce the coercivity sufficiently: however, ignorance of the nucleation mechanism prevents first principles predictions. Important practical consequences of the calculation include a demonstration that stacked particles switch together, which implies increased recording noise, and quantitative predictions for the effect of thermal fluctuations on barium ferrite coercivity.
Magnetization reversal in Ba-ferrite particulate media
Authors: Speliotis D. E.
Published: July 2002

In this paper, we investigated the mechanism of magnetization reversal in Ba-ferrite particulate media by measuring and analyzing the angular dependence of the coercivity, the remanence coercivity, and the hysteresis losses, and also by investigating the rotational hysteresis properties. The measurements were performed in longitudinally oriented and in nonoriented media in order to avoid demagnetization effects. The angular dependence of the magnetic properties was found to vary widely depending on the degree of orientation and the particle-to-binder loading of the media. Our conclusion is that the mechanism of magnetization reversal is one of incoherent rotation, and most probably fanning, but closely resembling curling in the closely coupled arrays of the platelet-shaped particles of Ba ferrite. Comparisons with the predictions of theoretical models agree well with our experimental results. The large increase of the remanence coercivity with angle for oriented media represents one of the most important and fundamental characteristics of these media and has a profound effect in reducing the recording demagnetization and enhancing their short wavelength response.
The mechanism of nucleation in uniaxial ferromagnets
Authors: Chang Ching-Ray , Fredkin D. R.
Published: July 2002

The nucleation of the uniform rotation mode for uniaxial ferromagnets is rigorously determined including the second anisotropy constant K2. The results show that the value of K2 will affect both the hysteresis loop and nucleation field significantly. For example, the square loops, for the easy axis direction, are rounded for certain values of K2. The relation Hk=2K1/MS needs to be modified when K2 is taken into account. Modified astroids are used to analyze the angular dependence of hysteresis loop. The calculated angular variation of Hc show bell-, M-, and W-type dependence. For certain values of second anisotropy the easy axis may be oblique to the c axis.
Diluted magnetic semiconductor superlattices for magnetic studies of dimensional crossover (invited)
Authors: Hong J. M. , Awschalom D. D. , Chang L. L. , Segmüller Armin
Published: July 2002

Diluted magnetic semiconductor Cd1−xMnxTe-CdTe superlattices with x=0.069, 0.13, 0.15, and 0.20 and various layer thicknesses were grown by molecular-beam epitaxy for optical and magnetic studies of dimensional crossover. X-ray diffraction patterns, low-temperature photoluminescence spectra, and ac magnetic susceptibility measurements were used to verify the integrity of these structures. In particular, the magnetic studies showed the spin-glass transition present in the thicker magnetic layers to broaden and eventually disappear with decreasing thickness, suggesting the inability of the two-dimensional system to support long-range spin-glass order.
Sealed-ampoule diffusion of zinc into Ga1−xAlxAs at 650 °C
Authors: Quintana V. , Clemencon J. J. , Chin A. K.
Published: July 2002

The diffusivity of the zinc Ga1−xAlxAs at 650 °C was studied using sealed-ampoule diffusion. Whereas Ageno, Roedel, Mellen, and Escher [Appl. Phys. Lett. 47, 1193 (1985)] found dramatic decreases in the zinc diffusivity at xAl≊0.05 and xAl≊0.20 using open-tube diffusion, the results of the present study show that the sealed-ampoule technique results in a more uniform dependence of the zinc diffusivity on aluminum concentration.
Electron energy distributions, transport parameters, and rate coefficients in GaAs
Authors: Cheng M. , Kunhardt E. E.
Published: July 2002

Monte Carlo methods have been used to obtain the electron energy distributions, transport parameters, and rate coefficients for electrons in a three-valley model of GaAs with nonparabolic energy bands in the presence of an external electric field. A technique has been developed which reduces the computation time when using self-scattering algorithm. Consequently, for a given computation time, more test particles can be used in the simulation. This results in a reduction in the fluctuation of the calculated quantities. In this paper, the Monte Carlo technique is presented for two generic time variations of the applied field: (a) dc and (b) a step change. The results shown are for the steady-state behavior of electrons in GaAs, for dc electric fields with values up to 70 kV/cm.
Depletion zone limited transport in Si-TaSi2 eutectic composites
Authors: Ditchek B. M. , Yacobi B. G. , Levinson M.
Published: July 2002

Depletion zones surrounding aligned, cylindrical, metal-semiconductor junctions formed during the directional solidification of a eutectic mixture are shown to influence the transport properties of the composite. Hall-effect and direct depletion zone width measurements made using the electron beam induced current technique of the scanning electron microscope have demonstrated that a relatively small total volume fraction (∼10%) of depleted material can lead to a significant increase in resistivity. The sensitivity of the resistivity of the composite to the depleted zone volume is attributed to a cellular distribution of the TaSi2 rods which causes substantial current streamlining. An analysis of the dopant segregation that occurs in the Si matrix of the composite boule during solidification supports the depletion zone limited transport model. The dependence of the resistivity on the depleted zone volume fraction of the composite indicates that the switching action in this novel material is achievable by increasing the volume fraction of depleted material between a source and drain contact.
Processing of La1.8Sr0.2CuO4 and YBa2Cu3O7 superconducting thin films by dual-ion-beam sputtering
Authors: Madakson P. , Cuomo J. J. , Yee D. S. , Roy R. A. , Scilla G.
Published: July 2002

High quality La1.8Sr0.2CuO4 and YBa2Cu3O7 superconducting thin films, with zero resistance at 88 K, have been made by dual-ion-beam sputtering of metal and oxide targets at elevated temperatures. The films are about 1.0 μm thick and are single phase after annealing. The substrates investigated are Nd-YAP, MgO, SrF2, Si, CaF2, ZrO2-9% Y2O3, BaF2, Al2O3, and SrTiO3. Characterization of the films was carried out using Rutherford backscattering spectroscopy, resistivity measurements, transmission electron microscopy, x-ray diffraction, and secondary ion mass spectroscopy. Substrate/film interaction was observed in every case. This generally involves diffusion of the substrate into the film, which is accompanied by, for example, the replacement of Ba by Sr in the YBa2Cu2O7 structure, in the case of SrTiO3 substrate. The best substrates were those that did not significantly diffuse into the film and which did not react chemically with the film. In general, the superconducting transition temperature is found to depend on substrate temperature and ion beam energy, film composition, annealing conditions, and the nature and the magnitude of the substrate/film interaction.
Picosecond time-resolved photoluminescence using picosecond excitation correlation spectroscopy
Authors: Johnson M. B. , McGill T. C. , Hunter A. T.
Published: July 2002

We present a study of the temporal decay of photoluminescence (PL) as detected by picosecond excitation correlation spectroscopy (PECS). We analyze the correlation signal that is obtained from two simple models; one where radiative recombination dominates, the other where trapping processes dominate. It is found that radiative recombination alone does not lead to a correlation signal. Parallel trapping type processes are found to be required to see a signal. To illustrate this technique, we examine the temporal decay of the PL signal for In-alloyed, semi-insulating GaAs substrates. We find that the PL signal indicates a carrier lifetime of roughly 100 ps, for excitation densities of 1×1016–5×1017 cm−3. PECS is shown to be an easy technique to measure the ultrafast temporal behavior of PL processes because it requires no ultrafast photon detection. It is particularly well suited to measuring carrier lifetimes.
Abrasive wear resistance of ion-deposited hard-carbon films as a function of deposition energy
Authors: Koskinen J.
Published: July 2002

Hard-carbon layers were deposited on WC-Co hard-metal substrates using mass-separated 12C+-ion beams with ion energies varying between 10 eV and 2 keV. The abrasive wear resistance, hardness, density, and dc resistance of these films were measured as a function of ion energy. Coatings deposited at ion energies between 100 eV and 2 keV possessed the highest hardness, best wear resistance, and good adhesion to the substrate, whereas coatings prepared at ion energies Ei ≤50 eV suffered from poor adhesion. The resistance of the hard-carbon coating against the abrasive wear was found to be about 300 times better than that of a typical ceramic Al2O3. In addition, Vickers hardness 120±20 GPa, density 3.3±0.3 g/cm3, and dc resistance 2×109 Ω cm were obtained. The hardness was found to remain unchanged after the thermal annealing up to 600 °C.
Evolution of the electron acoustic signal as function of doping level in III-V semiconductors
Authors: Bresse J. F. , Papadopoulo A. C.
Published: July 2002

The evolution of the electron acoustic signal has been measured for Be- and Si-doped GaAs and Ga0.28Al0.19In0.53As layers with doping levels from1017 to 1020 at. cm−3. The samples have also been analyzed by cathodoluminescence spectroscopy for near-band-edge transition and deep level emission. The results are explained by the reduction of the mean free path of phonons, giving rise to a lattice thermal conductivity decrease. Meanwhile, the electronic part of the thermal conductivity of these compounds is found to be nearly negligible.
Relativistic free-electron wave generator with finite axial magnetic field
Authors: Willett Joseph E. , Hwang Un-Hak
Published: July 2002

An analysis of the parametric excitation of fast and slow space-charge waves in a cylindrical metallic waveguide filled with relativistic beam electrons is presented. The pump wave in the laboratory reference frame consists of a static, spatially periodic axial electric field. Formulas are derived for the temporal growth rate and frequency of the backscattered fast space-charge wave in both the laboratory and beam frames. The effects of a uniform axial magnetic field of arbitrary magnitude on the amplitude gain and frequency enhancement are studied.
Hydrogenated amorphous carbon dielectric coatings for magneto-optic data storage media
Authors: Robinson C. J. , Payne R. N. , Bell A. E.
Published: July 2002

Thin films of hydrogenated amorphous carbon (a-C:H) have been evaluated as quarter-wave, antireflection dielectric coatings for application in magneto-optic data storage media. The films, which are produced by plasma deposition from methane, have low optical absorption at 830 nm wavelength, high refractive index (n≊2.1), and provide enhancement of the polar Kerr rotation (θk) when used in conjunction with rare-earth–transition-metal (RE–TM), TbFe, or TbFeCo alloys. The chemical stability, inertness, and homogeneity of the carbon films makes them effective diffusion barriers to oxygen or water vapor and thus provides excellent protection against environmental oxidation of the RE–TM layer. Dynamic disk performance data show improved write sensitivity of the media when used with a-C:H dielectric layers.
Piezoreflectance as a supplement to photoreflectance for nondestructive characterization of GaAs/AlxGa1−xAs multiple quantum wells
Authors: Tober R. L. , Smirl Arthur L. , Boggess Thomas F. , Schulman J. N.
Published: July 2002

Piezoreflectance is used to identify allowed and forbidden transitions in the spectra of as-grown 100 and 50 Å GaAs/AlxGa1−xAs multiple quantum well samples from which no photoreflectance spectra suitable for characterization could be obtained. Features in the piezoreflectance spectra are shown to result from excitonic transition by direct comparison with the absorbance measurements made on semitransparent regions of these samples. Transition energies are extracted from the piezoreflectance spectra using a form of the Aspnes equation appropriate for the first derivative of a Lorentzian.
Optical and electrical characterization of high-resistivity liquid-phase-epitaxial In0.53Ga0.47As:Fe
Authors: Chen Z. , Wolf T. , Korb W. , Bimberg D.
Published: July 2002

Semi-insulating In0.53Ga0.47As with carrier concentration n=1.2×1012 cm−3, resistivity up to 1090 Ω cm, and mobility up to 9500 cm2/V s at 300 K is grown by liquid-phase epitaxy and doping with Fe. The influence of Fe doping on the photoluminescence of In0.53Ga0.47As is systematically investigated. An acceptor level at Ev+150 meV, tentatively assigned to Fe by some of us earlier, is definitively identified as an Fe-related complex. This acceptor level, however, is not responsible for the semi-insulating behavior of In0.53Ga0.47As as shown by statistical calculations. High-resolution deep-level transient spectroscopy experiments show two deep acceptors at EC−ET=0.44 and 0.30 eV, respectively. The first one, which dominates, is identified as being caused by the Fe3+/Fe2+ acceptor level. The second, somewhat weaker one, might be caused by the O-related trap recently discovered by Loualiche et al. [Appl. Phys. Lett. 51, 1361 (1987).] Combining the Fe acceptor energy position in In0.53Ga0.47As with its known value in InP and the known conduction-band discontinuity of the InP/In0.53Ga0.47As heterointerface we find that the vacuum referred binding energy model is approximately but not strictly valid. In this model the transition-metal impurity levels are aligned with respect to the vacuum level across interfaces regardless of the surrounding host crystal environment.
Photoluminescence study of strain relaxation in Ga1−xInxAs/GaAs single heterostructures
Authors: Morris D. , Roth A. P. , Masut R. A. , Lacelle C. , Brebner J. L.
Published: July 2002

Low-temperature photoluminescence (PL) spectra of Ga1−xInxAs/GaAs single heterostructures with 0.07≤x≤0.19 and thicknesses ranging from 10 nm to 5 μm have been analyzed to study strain relaxation. Two series of samples were grown simultaneously on GaAs substrates oriented exactly on (100) and misoriented by 2° towards 〈110〉. In both kinds of samples, the strain induced exciton shift decreases first slowly with increasing thickness and then drops abruptly. This variation is analyzed in terms of the equilibrium critical thickness where misfit dislocations are generated and the kinetics of these dislocations in the relaxation process. The decrease of the exciton energy shift is accompanied by a large reduction of the PL intensity and broadening of the emission. In thicker layers, however, the behavior of the two series of samples is strikingly different. While the layers grown on misoriented substrates have all the characteristics of high-quality unstrained crystals, those grown on (100) substrates have PL spectra dominated by a low-energy emission. These results show that the critical thickness for the generation of misfit dislocations is the same for layers grown on both kinds of substrates but that the relaxation process is different and results in inhomogeneous layers on (100) substrates.
Effects of i
n s
i
t
u plasma supply in undoped and boron-doped polycrystalline silicon by low-pressure chemical vapor deposition at 500–840 °C
Authors: Hasegawa S. , Morita M. , Kurata Y.
Published: July 2002

Undoped and boron-doped polycrystalline silicon films were prepared on a fused quartz at 500–840 °C by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) from a SiH4+B2H6+H2 mixture, using the same fabrication system. The effects of plasma (rf power) supply on the structural and electrical properties were investigated. Below 700 °C, all films show a 〈110〉 preferential orientation (P.O.), increasing with an increase in rf power. Particularly between 650 and 700 °C, an extremely stronger 〈110〉 P.O. is found at a rf power >15 W. Above 730 °C, undoped LPCVD and PECVD films and boron-doped LPCVD films represent a nearly random orientation. On the other hand, for boron-doped PECVD films, a strong 〈111〉 texture is observed in the intermediate doping range. The 〈110〉 texture increasing with rf power in undoped PECVD films is interpreted as indicating enhanced nucleation at the surface in contact with the gas phase. The plasma supply also has essential effects for smoothing the surface and improving the boron-doping efficiency. The effects of plasma supply are discussed in terms of increased surface diffusion of adsorbates, sputtering effect, and a contribution of hydrogen covering the surface. PECVD films are more stable for foreign contamination after fabrication than LPCVD films.
Hot-electron conduction in Hg0.8Cd0.2Te in the extreme magnetic quantum limit at low temperatures
Authors: Basu Partha Pratim , Sarkar C. K. , Chattopadhyay D.
Published: July 2002

A theoretical analysis of hot-electron transport in narrow-gap semiconductors under a large magnetic field is developed at low temperatures. The energy relaxation time and the electric-field dependence of the drift velocity of hot electrons in Hg0.8Cd0.2Te at 1.5 K in the extreme quantum limit, i.e., when all the electrons occupy the lowest Landau subband, are calculated. The model includes scattering by the acoustic phonons and other complexities such as the band nonparabolicity, free-carrier screening, nonequipartition of phonons, and the level broadening due to electron-impurity interactions. The theoretical results are compared with the experimental data on the energy relaxation time in Hg0.8Cd0.2Te for magnetic flux densities of 4 and 6 T. When the equilibrium phonon distribution is considered, the theoretical values are found to be several times less than the experimental values. The discrepancy is attributed to the nonequilibrium phonons or ‘‘hot phonons’’ that exist under hot-electron conditions. Including the hot-phonon effects, the theoretical results are in satisfactory agreement with the experimental data, giving a reasonable estimate of the phonon life time. The model has been applied to calculate the electric field dependence of the drift velocity of hot electrons in Hg0.8Cd0.2Te at 1.5 K in the extreme quantum limit by assuming scattering by the nonequilibrium acoustic phonons and ionized impurities, and a satisfactory agreement with the experimental results is obtained.
Dual-species ion implantation in AlxGa1−xAs
Authors: Adachi Sadao , Yamahata Shoji
Published: July 2002

Dual implantations of Be+/N+, Be+/Ar+, and Be+/O+ in AlxGa1−xAs are performed and studied by means of Hall-effect measurements. Dual implantation of Be+/N+ leads to significantly less Be redistribution and considerably higher electrical activity of the Be implant, compared with those of Be+ single implantation. Furthermore, while Be+/Ar+ coimplantation does not lead to Be redistribution, it neither distinctly improves electrical activity. Similar behavior is observed with both Be+/Ar+ and Be+/O+ coimplants. These results provide confirmation that the activation improvement observed in the (group II/group V) coimplanted AlxGa1−xAs arises mainly from chemical effects.
Magnetophotoluminescence characterization of residual donors in GaAs grown by metalorganic chemical vapor deposition
Authors: Watkins S. P. , Haacke G. , Burkhard H. , Thewalt M. L. W. , Charbonneau S.
Published: July 2002

The residual donor species in undoped GaAs epilayers grown by metalorganic chemical vapor deposition have been characterized by magnetophotoluminescence (MPL) measurements at high magnetic fields (7 T). Most samples were grown using trimethylgallium and arsine, but samples grown using the liquid group-V source t-butylarsine were also studied. The results show good agreement with identifications previously made in high-purity samples (NA+ND≤5×1014 cm−3) at zero magnetic field, but with greatly improved spectral resolution and signal levels. With the MPL technique, residual donor species were resolved even in relatively impure samples (NA+ND=1×1016) for which no information was obtained at zero magnetic field. For the samples grown with arsine, Ge donors were observed to predominate in the high-purity samples, but Si was the dominant donor in the lower-purity samples. The Si impurity was traced to contamination from a quartz baffle in the growth chamber. Lower levels of sulfur donors were observed in many samples. Sulfur was found to be the second most predominant donor after Ge in samples grown with t-butylarsine.
Thermal behavior and stability of room-temperature continuous AlxGa1−xAs-GaAs quantum well heterostructure lasers grown on Si
Authors: Hall D. C. , Deppe D. G. , Holonyak N. , Matyi R. J. , Shichijo H. , Epler J. E.
Published: July 2002

Data are presented on the thermal characteristics of p-n AlxGa1−xAs-GaAs quantum well heterostructure (QWH) diode lasers grown on Si substrates. Continuous 300-K operation for over 10 h is demonstrated for lasers mounted with the junction side away from the heat sink (‘‘junction-up’’) and the heat dissipated through the Si substrate. ‘‘Junction-up’’ diodes that are grown on Si substrates have measured thermal impedances that are 38% lower than those grown on GaAs substrates, with further reductions possible. Thermal impedance data on ‘‘junction-down’’ diodes are presented for comparison. Measured values are consistent with calculated values for these structures. Low sensitivity of the lasing threshold current to temperature is also observed, as is typical for QWH lasers, with T0 values as high as 338 °C.
Extended moment equations for electron transport in semiconducting submicron structures
Authors: Bringer Andreas , Schön Gerd
Published: July 2002

We present an extended set of moment equations which allow us to investigate hot-electron effects and ballistic transport in semiconducting devices with inhomogeneities in the submicron range. This model extends the familiar drift-diffusion description but nevertheless is computationally not much more involved. In contrast to full solutions of the Boltzmann transport equation, which can be obtained only in very simple limits, our model can describe realistic geometries and general collision processes. We find reasonably good agreement with rigorous solutions where these exist.
Arrival time measurements of films formed by pulsed laser evaporation of polycarbonate and selenium
Authors: Hansen S. G. , Robitaille T. E.
Published: July 2002

By measuring the rapid change in reflectivity of a substrate during film growth induced by pulsed laser evaporation, the time-of-arrival profiles of material emanating from polycarbonate and selenium targets were determined. Results for both targets are reasonably well described by Maxwell–Boltzmann velocity distributions. Selenium evaporation appears to be atomic while for polycarbonate a range of masses are involved. The high velocity of the material leaving polycarbonate strongly suggests that small polymers are not transported directly. The mechanism for polymer film formation must involve repolymerization on the substrate of species not weighing more than a few hundred amu. For both polycarbonate and selenium the time-of-arrival profiles were affected very little by changing the excitation wavelength from 248 to 1064 nm.
Low- and high-field transport properties of pseudomorphic InxGa1−xAs/In0.52Al0.48As (0.53≤x≤0.65) modulation-doped heterostructures
Authors: Hong W.-P. , Ng G. I. , Bhattacharya P. K. , Pavlidis D. , Willing S. , Das B.
Published: July 2002

We have grown pseudomorphic InxGa1−xAs/In0.52Al0.48As modulation-doped heterostructures by molecular-beam epitaxy under carefully controlled growth conditions. Mobilities as high as 13 900, 74 000, and 134 000 cm2/V s are measured at 300, 77, and 4.2 K in a heterostructure with x=0.65. Shubnikov–de Haas measurements indicate that the change in the effective mass with increasing In is not significant and is not responsible for the enhancement in mobilities. We believe that the improvement results from reduced alloy scattering, reduced intersubband scattering, and reduced impurity scattering, all of which result from a higher conduction-band offset and increased carrier confinement in the two-dimensional electron gas. The high-field electron velocities have been measured in these samples using pulsed current-voltage and pulsed Hall measurements. A monotonic increase in velocities is observed both at 300 and 77 K with an increase of In content in the channel. Velocities of 1.55×107 and 1.87×107 cm/s are measured at 300 and 77 K, respectively, in a In0.65Ga0.35As/In0.52Al0.48As modulation-doped heterostructure.
Thermally stable ohmic contacts to n-type GaAs. III. GeInW and NiInW contact metals
Authors: Murakami Masanori , Shih Yih-Cheng , Price W. H. , Wilkie E. L. , Childs K. D. , Parks C. C.
Published: July 2002

Improvement in thermally stable, low-resistance ohmic contacts to n-type GaAs is reported for GeInW and NiInW contact metals. Coevaporation of In with Ge or In with Ni reduced the contact resistances by a factor of about 2 compared with those of the layered structures. The reduction is believed to be due to a uniform In distribution in the contact metals in the as-deposited state which resulted in an increased area of InxGa1−xAs phases in direct contact with the GaAs substrate. Annealing the coevaporated GeInW contacts for a short time at temperatures between 900 and 980 °C resulted in a mean contact resistance of 0.5 Ω mm. Similar annealing of the coevaporated NiInW contacts at temperatures between 800 and 1000 °C resulted in a contact resistance of 0.3 Ω mm. Additionally, the thermal stability of these ohmic contacts at 400 °C after contact formation, which is required by subsequent integrated circuit process steps, was studied. Although a slight increase in the contact resistances was observed after annealing for 100 h at 400 °C for the GeInW contacts, no change in the contact resistances was observed for the NiInW contacts after annealing for 100 h at 400 °C and for 10 h at 500 °C. This excellent thermal stability of the NiInW contacts is believed to be due to the formation of Ni3In intermetallic compounds which have high melting points. The present study suggests that in order to prepare thermally stable, low-resistance contacts it is desirable to deposit a metal which forms high melting point intermetallic compounds with In and which promotes formation of uniform InxGa1−xAs phases at the metal/GaAs interfaces. Further reduction in the measured contact resistances was achieved by reducing the sheet resistance of the contact metals.
Cubic zirconia as a high-quality facet coating for semiconductor lasers
Authors: Chin A. K. , Satyanarayan A. , Zarrabi J. H. , Vetterling W.
Published: July 2002

In this paper we describe the properties of high-quality, semiconductor laser facet coatings based on yttria-stabilizied cubic zirconia (90-m% ZrO2/10-m% Y2O3). We have found that cubic zirconia films can be reproducibly deposited by electron-beam evaporation with an index of refraction of 1.98 at 6328 Å, almost ideal for use as a single-layer antireflection coating for GaAs/GaAlAs-based lasers. ZrO2 has a monoclinic crystal structure at room temperature, but changes to tetragonal, hexagonal, and cubic phases upon heating to higher temperatures. However, the addition of the Y2O3 stabilizes ZrO2 in the cubic form, thus allowing electron-beam deposition of thin films of this material to be more controllable and reproducible without the usual addition of oxygen into the vacuum chamber during deposition. Preliminary aging tests of high-power GaAs/GaAlAs lasers show that cubic zirconia films suppress the photo-enhanced oxidation of laser facets that degrades device performance.
Numerical simulations of Czochralski silicon growth
Authors: Chan Y. T. , Gibeling H. J. , Grubin H. L.
Published: July 2002

The present study involves the development and application of a numerical technique to the most common method of growing silicon crystals—the Czochralski process. The equations solved for the melt phase are the conservation equations for the mass, momentum, and energy. For the crystal phase, the energy balance equation is solved. The governing equations are formulated using primitive variables and are not thereby restricted to two-dimensional symmetry. The crystal and melt phases are coupled through thermal conditions applied along the melt–crystal interface. The shape of the melt–crystal interface and meniscus are determined through solutions to differential equations that govern the kinematic conditions at the specific interfaces, and are not assumed a priori. The numerical procedures are obtained by a well-documented procedure known as the consistently split linearized block implicit (LBI) scheme. Calculations, including one three-dimensional case, are performed for various growth conditions suitable for silicon crystal growth. The present study has successfully demonstrated the numerical capabilities for Czochralski crystal growth simulations.
The role of crystal-growth properties on silicon implant activation processes for GaAs
Authors: Gray M. L. , Parsey J. M. , Pearton S. J. , Short K. T. , Ahrens R. E. , Sargent L. , Blakemore J. S.
Published: July 2002

Crystal properties such as bulk resistivity, mobility, and dislocation density which influence ion-implantation activation are reported for liquid-encapsulated Czochralski, horizontal gradient freeze, and vertical gradient freeze semi-insulating GaAs crystals. The liquid-encapsulated Czochralski crystals used in this study include as-grown, boule-annealed, and indium-alloyed GaAs. Wafer maps displaying the concentration and spatial distribution of neutral EL2 are presented for each crystal. Wafers from the various crystals were implanted with 29Si at a dose of 3×1012 ions/cm2 and an energy of 60 keV. Macroscopic variations in the donor distribution and peak carrier density demonstrate that point defects impact significantly the donor implant activation processes.
Preferentially oriented epitaxial Y-Ba-Cu-O films prepared by the ion beam sputtering method
Authors: Fujita J. , Yoshitake T. , Kamijo A. , Satoh T. , Igarashi H.
Published: July 2002

Preferentially oriented epitaxial Y-Ba-Cu-O films were prepared on (100) SrTiO3 substrates by oxygen reactive ion beam sputtering. The epitaxial orientations were varied by controlling both substrate temperature and oxygen parital pressure. c-axis oriented films tended to be formed at higher substrate temperatures (>620 °C) and lower oxygen pressures (<3×10−3 Torr). In contrast, a/c- and a-axis oriented films were formed at lower substrate temperatures (<600 °C) and higher oxygen pressures (>3×10−3 Torr). The best Tc (end) of 82 K was observed in one of the c-axis oriented film without post-annealing. The tendency for preferential orientation can be well understood in terms of the lattice mismatch between the substrate and the film, the lattice constants of which depend on oxygen deficiency.