bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical and structural changes in the near surface of reactively ion etched InP
Authors: Pearton S. J. , Chakrabarti U. K. , Baiocchi F. A.
Published: July 2002

Near-surface (∼1000 Å) modification in the net carrier concentration in n-type InP (n=6×1015–1.5×1017 cm−3) was observed after reactive ion etching (RIE) in Cl-based (CCl2F2/O2) or organic-based (C2H6/H2) discharges. The carrier loss is slightly more pronounced in the latter case, due possibly to the creation of deep level, compensating acceptors at greater depths as a result of implantation of the light hydrogen ions. Near-complete recovery of the initial carrier density occurs after annealing at 500 °C for 30 s. Structural disorder is detected by ion channeling to depths of ∼400 Å after C2H6/H2 RIE with a self-bias of 380 V. This disorder shows significant recovery after 400 °C, 30 s annealing. Current-voltage measurements on Au Schottky diodes showed ohmic behavior after etching of the InP in a C2H6/H2 discharge, due to the nonstoichiometric surface remaining after RIE. Diodes fabricated on CCl2F2/O2 etched material show only a slight increase in reverse current compared to unetched control samples.
Lateral resonant tunneling in a double-barrier field-effect transistor
Authors: Ismail K. , Antoniadis D. A. , Smith Henry I.
Published: July 2002

We report on electron transport measurements in a planar resonant tunneling field-effect transistor (PRESTFET) on a modulation-doped GaAs/AlGaAs heterostructure. The PRESTFET is created by defining two independently biased, 60-nm-long Schottky gates separated by 60 nm, on top of the AlGaAs layer, which presents a tunable double-barrier potential modulation to the electrons traveling from source to drain. Current measurements 4.2 K, as a function of gate bias, with both gates connected, exhibit strong multiple negative transconductance swings at a fixed drain bias below 5 mV, providing evidence of resonant tunneling through quantized states between the two barriers. Fixing the bias on one of the gates and scanning the second, or fixing the bias on both and varying the light intensity of a light-emitting diode confirms this observation. In addition, a structure in the output conductance as a function of drain voltage at a fixed gate bias is clearly observed.
Shock wave induced changes in superconductivity in YBa2Cu3O7−δ
Authors: Murr L. E. , Niou C. S. , Jin S. , Tiefel T. H. , James A. C. W. P. , Sherwood R. C. , Siegrist T.
Published: July 2002

Shock wave loading produced significant changes in superconductivity in sintered YBa2Cu3O7−δ causing a broad transition with Tc(R=0)∼40 K. The normal-state resistivity increased by 20–50× with the ρ-T curve exhibiting a semiconducting behavior. Comparative thermogravimetric analysis, however, indicated no loss of oxygen (δ∼0.1) in the shock-loaded sample, and x-ray powder diffraction analysis showed no major changes except for slight line broadening. The observed semiconductive behavior and degredation in superconductivity is thus attributed to a rather subtle disturbance in crystal structure, the nature of which is not clearly understood at present. The lack of sufficient recovery in Tc by post-shock oxygen processing at temperatures as high as 750 °C and subsequent cooling implies that the atomic-scale disturbance may not necessarily be related to a simple oxygen disorder. Such defects, if controlled properly, may be advantageously turned into desirable flux-pinning sites for improved critical currents.
Surface layers on superconducting Y-Ba-Cu-O films studied with x-ray photoelectron spectroscopy
Authors: Chang C. C. , Hegde M. S. , Wu X. D. , Dutta B. , Inam A. , Venkatesan T. , Wilkens B. J. , Wachtman J. B.
Published: July 2002

The chemical compositions of surface and bulk regions of pulsed laser deposited YBa2Cu3O7−x films on SrTiO3(001) substrates were examined. From the relative intensities of the surface and bulk components of the Ba 3d and Ba 4d spectra taken at different take-off angles and different escape depths [using Al Kα (1486.6 eV) and Mg Kα (1253.6 eV) excitations], we have concluded that there is a nonsuperconducting surface layer of 1 nm thickness with a composition of BaCuO2. This layer contains oxygen with a photoelectron binding energy of 531 eV, and Cu2+ ions. A superconducting film which was only 8 nm thick also had a layer of 1 nm thickness. By detecting the substrate Ti signal through this film, and ruling out a high density of pinholes, we provide evidence that the x-ray photoelectron spectroscopy data contain information from the superconducting phase. A polycrystalline pellet scraped in vacuum had a similar surface layer, which was only 0.4 nm thick.
Deposition of epitaxial thin films of Nd1.85Ce0.15CuO4−y by laser ablation
Authors: Gupta A. , Koren G. , Tsuei C. C. , Segmüller A. , McGuire T. R.
Published: July 2002

Thin films of the electron-doped superconductor Nd1.85 Ce0.15 CuO4−y have been deposited on (100) SrTiO3 substrates at 780 °C using the laser ablation technique. The deposited films are very smooth and show epitaxial growth with the c axis normal to the substrate. The transport properties of the films are very sensitive to the concentration of oxygen vacancies. Films deposited and cooled in the presence of 150 mTorr O2 exhibit localization behavior with no evidence of superconductivity down to 5 K. Superconductivity is observed on vacuum annealing the films in situ after deposition. Films with optimum concentration of oxygen vacancies show a superconducting onset temperature of 21 K and Tc (R=0) of 20 K, with a critical current density of 2×105 A/cm2 at 5.5 K in zero magnetic field.
Thin stacked oxide/nitride/oxide dielectrics formation by i
n s
i
t
u multiple reactive rapid thermal processing
Authors: Ting W. , Lin S. N. , Kwong D. L.
Published: July 2002

Thin stacked SiO2/Si3N4/SiO2 (ONO) films have been fabricated for the first time using in situ multiple step rapid thermal processing chemical vapor deposition (RTP-CVD). Stacked Si3N4/SiO2 (NO) layers were deposited in situ by RTP-CVD. Some samples received an in situ rapid thermal oxidation immediately after stacked layer deposition to form oxide/nitride/oxide stacked layers. These films were characterized by ellipsometry, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and Auger electron spectroscopy. Results show that well-defined Si3N4/SiO2 and Six Ny Oz /Si3N4/SiO2 stacked layers have been formed.
Photorefractive gain and response time of Cr-doped strontium barium niobate
Authors: Sayano Koichi , Yariv Amnon , Neurgaonkar Ratnakar R.
Published: July 2002

We present experimental results on the photorefractive two-beam coupling constant and response time of two Cr-doped strontium barium niobate crystals with different dopant concentrations. Both showed significantly faster response times over Ce-doped SBN:60, but with corresponding decreases in their coupling constants.
Optically excited minority-electron velocity in selectively Be-doped AlGaAs/GaAs/AlGaAs single quantum wells
Authors: Shigekawa Naoteru , Furuta Tomofumi , Maezawa Koichi , Mizutani Takashi
Published: July 2002

The minority-electron velocity versus electric field (v-E) relationship was measured for selectively Be-doped Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As single quantum wells with different well-layer thicknesses by means of the time-of-flight (TOF) method at room temperature. It was found that the electron drift velocity for the 200-Å-thick quantum well is suppressed in comparison with those for the 600-Å-thick and 2000-Å-thick wells. This suppression is successfully explained by considering that the electron-hole interaction is enhanced in narrower wells due to a larger overlap of the wave functions of electrons and holes.
HgCdTe on GaAs/Si for mid-wavelength infrared focal plane arrays
Authors: Zanio Ken , Bean Ross , Mattson Reed , Vu Paul , Taylor Scott , McIntyre Dave , Ito Chris , Chu Muren
Published: July 2002

Mid-wavelength HgCdTe was grown by metalorganic chemical vapor deposition at 390 °C on CdTe/GaAs/Si substrates. Resistance-area products as high as 107 Ω cm2 were measured for 320×5 arrays of detectors having a λco of 4.6 μm at 77 K. Rudimentary thermal imaging was demonstrated for 1×32 hybrid HgCdTe/Si arrays having a λco of 2.8 μm. Temperature cycling of these arrays between room temperature and 77 K caused no significant degradation of the resistance-area products of the HgCdTe detectors.
Molecular beam epitaxy regrowth by use of ammonium sulfide chemical treatments
Authors: Melloch M. R. , Carpenter M. S. , Dungan T. E. , Li D. , Otsuka N.
Published: July 2002

The application of ammonium sulfide chemical treatments for molecular beam epitaxy regrowth is examined. Reflection high-energy electron diffraction, transmission electron microscopy, and capacitance-voltage profiling techniques are used to investigate the regrown interface. A slight enhancement of the electron concentration is seen at the regrown interface due to the incorporation of residual sulfur atoms as donors. The amount of residual sulfur donors is a strong function of the substrate temperature at which regrowth is initiated.
Deposition of superconducting YBaCuO thin films by pseudospark ablation
Authors: Höbel M. , Geerk J. , Linker G. , Schultheiss C.
Published: July 2002

Thin YBaCuO films have been deposited on ZrO2(Y) and SrTiO3 substrates by a novel ablation method, using a pulsed intense electron beam generated by a pseudospark source. Films with zero resistance around 85 K were grown at substrate temperatures of 820 °C with high reproducibility. X-ray analysis indicates highly textured growth on both substrates. Jc values were 6×106 A/cm2 at 4.2 K and 1.1×105 A/cm2 at 77 K. Because of the high simplicity of the deposition system and the variety of changeable parameters it represents an interesting alternative to existing laser ablation methods.
Suppression of emitter size effect on the current-voltage characteristics of AlGaAs/GaAs heterojunction bipolar transistors
Authors: Mohammad S. Noor , Chen J. , Chyi J.-I. , Morkoç H.
Published: July 2002

The effect of emitter periphery-to-area ratio on the current-voltage characteristics of Npn AlGaAs/GaAs heterojunction bipolar transistors has been studied. It is shown that an electric field generated by a properly controlled nonuniform doping of the base region can very significantly suppress the reduction in current gain when the emitter area-to-periphery ratio is decreased, as is the case in high-speed devices. The superiority of doping-induced grading to compositional grading is discussed.
Reactive ion beam etching of ZnSe and ZnS epitaxial films using Cl2 electron cyclotron resonance plasma
Authors: Saitoh Tohru , Yokogawa Toshiya , Narusawa Tadashi
Published: July 2002

Reactive ion beam etching of ZnSe and ZnS epitaxial films was carried out using pure Cl2 as an etching gas. Electron cyclotron resonance plasma was excited at pressures of 2.5×10−4 –2.5×10−3 Torr. Chlorine ions were extracted with voltages of 0–400 V. Sputtering yields were strongly dependent on the extraction voltage and the gas pressure. The etching mechanism starts with the generation of chloride compounds, mainly ZnClx, by the chemical reaction of the surface and chlorine radicals, mainly Cl atoms. The chloride compounds are subsequently sputtered off by the accelerated ion beam. The crystalline quality of etched ZnSe films was characterized by photoluminescence measurements. We found that high quality etched films, which have almost no damage and no Cl contamination, can be obtained at an extraction voltage of about 300 V.
Self-induced transparency soliton digital switch
Authors: Guzmàn A. , Romagnoli M. , Wabnitz S.
Published: July 2002

We investigate self-induced transparency soliton switching in a nonlinear two-level resonant dual-waveguide directional coupler. The soliton transfer properties of the coupler depend on the input pulse area; for areas larger than π, an integer number of 2π solitons is transmitted from the output ports. Tapered coupling provides digital transmission characteristics. A specific example of application to impurity bound excitons in semiconductors is discussed.
Mobility-lifetime product of photoexcited electrons in GaAs
Authors: Valley George C. , Rajbenbach H. , von Bardeleben H. J.
Published: July 2002

We show that photorefractive beam coupling gain as a function of grating period measured in semi-insulating GaAs with an external ac electric field or with a dc field and moving fringes can be explained theoretically by a mobility-lifetime product about four orders of magnitude smaller than that obtained in low-field conditions. This reduction is caused by enhanced occupation of the L band at high fields coupled with the low L band mobility and by the increase in recombination due to the cascade capture process that occurs for electric fields above a few kV/cm.
Optical nonlinearities due to subband structures in Al0.08In0.92Sb/InSb superlattices
Authors: Walrod D. , Auyang S. Y. , Wolff P. A. , Tsang Won
Published: July 2002

We report the first observation of optical nonlinearities due to subband structures in the growth direction of an n-type superlattice by four-wave mixing in an end-firing configuration. We observe a nearly eightfold increase in the third-order optical susceptibility when the electric fields of the CO2 laser are changed from a parallel to a perpendicular orientation to the plane of an Al0.08In0.92Sb/InSb superlattice. No change is observed in a control InSb epilayer under similar conditions.
Optical detection of growth oscillations in high vacuum metalorganic vapor phase epitaxy
Authors: Jönsson J. , Deppert K. , Jeppesen S. , Paulsson G. , Samuelson L. , Schmidt P.
Published: July 2002

We report the first measurements of growth oscillations in high vacuum metalorganic vapor phase epitaxy (MOVPE). The reflection difference response of the surface is used for real-time monitoring of the layer-by-layer growth of GaAs from triethylgallium (TEG) and arsine. The frequency of the optically detected growth oscillations is found to be proportional to the flux of TEG and to the growth rate. We expect our results to extend the more limited ranges of applicability offered by reflection high-energy electron diffraction to allow the study of growth oscillations also in other MOVPE-related growth techniques.
Room-temperature operation of three-terminal quantum-confined field-effect light emitters
Authors: Kan Y. , Okuda M. , Yamanishi M. , Ohnishi T. , Mukaiyama K. , Suemune I.
Published: July 2002

The field control of the luminescent characteristics is investigated with three-terminal field-effect light-emitting devices with superlattice buffer layers, showing a high-speed switching (∼0.8 ns) of emission intensity, free from lifetime limitation at room temperature and a high quantum yield of the emission intensity, i.e., an external efficiency ηex≥1%. It is demonstrated that a combination of the field control of radiative lifetime with carrier leakage results in a high-speed modulation of luminescence intensity under a fixed carrier population in the active layer, unchanged with and without electric fields.
Development of a second cyclotron harmonic gyrotron operating at 0.8 mm wavelength
Authors: Idehara T. , Tatsukawa T. , Ogawa I. , Tanabe H. , Mori T. , Wada S. , Kanemaki T.
Published: July 2002

This letter describes the development of a submillimeter wave gyrotron operating at the second harmonic of the cyclotron frequency. The observed frequency is 383 GHz, which corresponds to the wavelength of 0.79 mm, and the output power is about 1 kW. We believe that the frequency is a world record for a stable, long pulse gyrotron operation at the second cyclotron harmonic, without a competition with the operation at the fundamental. Comparisons with the simulation results are represented.
Two pseudobinary semiconducting silicides: RexMo1−xSi2 and CrxV1−xSi2
Authors: Long Robert G. , Mahan John E.
Published: July 2002

Two groups of thin-film samples were grown on silicon wafer substrates of compositions spanning the entire range of the ternary disilicides: RexMo1−xSi2 and CrxV1−xSi2. In each case, the lattice parameters vary smoothly with composition. The optical and electrical properties of the films suggest that when molybdenum is added to semiconducting ReSi2 and when vanadium is added to semiconducting CrSi2, the forbidden energy gap in each case decreases smoothly to zero.
Ion beam deposition of i
n s
i
t
u superconducting Y-Ba-Cu-O films
Authors: Klein J. D. , Yen A. , Clauson S. L.
Published: July 2002

Oriented superconducting YBa2Cu3O7 thin films were deposited on yttria-stabilized zirconia substrates by ion beam sputtering of a nonstoichiometric oxide target. The films exhibited zero-resistance critical temperatures as high as 80.5 K without post-deposition anneals. Both the deposition rate and the c lattice parameter data displayed two distinct regimes of dependence on the beam power of the ion source. Low-power sputtering yielded films with large c dimensions and low Tc’s. Higher power sputtering produced a continuous decrease in the c lattice parameter and an increase in critical temperatures.
Evidence for As-H bonds in H-implanted GaAs
Authors: Stein H. J.
Published: July 2002

A new absorption band at 2029 cm−1 has been observed in GaAs following implantation with hydrogen at 80 K. Association of the band with a vibrational mode of hydrogen is confirmed by substitution of deuterium. Tentative assignment is made to As-H bonds. The new band is unstable below room temperature and a previously identified Ga-H absorption band forms as the new band is removed by annealing near 200 K.
In-plane anisotropy in batch-produced Langmuir–Blodgett films: Side-by-side and face-to-face arrays
Authors: Tabe Yuka , Ikegami Keiichi , Kuroda Shin-ichi , Saito Kazuhiro , Saito Mitsuyoshi , Sugi Michio
Published: July 2002

In-plane anisotropy of Langmuir–Blodgett (LB) films is affected by the arrangement of substrates when many samples are batch produced in one single trough. We examined the dichroic behavior for two different cases of the batch production. In the case of substrates aligned side by side, the dichroic behavior is similar to that in the single-substrate production and agrees with the flow orientation model. In the face-to-face case, however, the tendency is quite different from both the single-substrate production and the side-by-side case, clearly deviating from the theoretical predictions. This discrepancy is suggested to be due to a dead water area which should be formed around the stagnation point.
Optically induced restructuring of a hydrogenated amorphous silicon thin-film surface
Authors: Dutta Joydeep , Ganguly Gautam
Published: July 2002

Hydrogenated amorphous silicon thin films have been characterized using specular reflectance spectra. An ultraviolet light-induced irreversible increase in reflectance has been attributed to changes in surface microstructure. These changes have been explained as being caused by phonons emitted during photocarrier thermalization. An irreversible increase of photoconductivity substantiates these observations.
Intensity noise reduction in semiconductor lasers by amplitude-phase decorrelation
Authors: Vahala Kerry J. , Newkirk Michael A.
Published: July 2002

Detuned operation of a laser results in coupling of field amplitude and phase fluctuations. In a semiconductor laser, this coupling is known to be very large. We demonstrate that it can be used to significantly reduce intensity noise below its intrinsic limit.
AlGaAs/GaAs p
n
p
n differential optical switch operable with 400 fJ optical input energy
Authors: Hara Kunihiko , Kojima Keisuke , Mitsunaga Kazumasa , Kyuma Kazuo
Published: July 2002

Differential optical switching operation with an optical input of as low as 400 fJ (0.07 fJ/μm2) was realized by using parallel-connected AlGaAs/GaAs pnpn optical switches. An improvement in the sensitivity of more than two orders of magnitude has been attained by introduction of a new operating concept. The electrical transient time was 10 ns, almost independent of optical input levels.
Quantitative analysis of on bevel electrical junction shifts due to carrier spilling effects
Authors: Clarysse T. , Vandervorst W. , Casel A.
Published: July 2002

A quantitative comparison is made of the junction depths determined by spreading resistance (SR) and secondary-ion mass spectrometry (SIMS) for submicron abrupt pn junctions (grown by molecular beam epitaxy) and Gaussian implants. The discrepancies between SR and SIMS are explained in terms of carrier spilling. From the comparison with a theoretical model, general trends can be adequately explained. In order to overcome the uncertainties imposed by the boundary conditions in this model, experimental diagrams are derived which can be used in routine analysis to assess the importance of carrier spilling effects in SR.
Dissimilarity between thermal oxide and buried oxide fabricated by implantation of oxygen on Si revealed by etch rates in HF
Authors: Vanheusden K. , Stesmans A.
Published: July 2002

A comparative study of diluted HF etch rates was performed on thermally grown oxide (1120 °C; O2 pressure ≊1.1 atm) and buried oxide layers [formed by implanting n-and p-type (100)Si maintained at ≊600 °C with 150–200 keV O+ ions to a dose of ≊1.8×1018 cm−2, and subsequent annealing at 1250–1325 °C]. From accurate mechanical thickness measurements, a difference in etch rate between thermally grown and buried oxide is observed. This is direct evidence for a structural and/or stoichiometrical difference between both oxides. Additionally, plots of the etch rate as a function of oxide thickness reveal detailed information on the local structure of the oxide layers.
Metastable states of a low-frequency mesodynamic pendulum
Authors: Peters Randall D.
Published: July 2002

A preliminary study has been made of the free decay of a physical pendulum whose mass is dominated by two metal bobs, and whose period can be adjusted to exceed 30 s. The decay mechanism is predominantly anelasticity from internal friction of creep. The relaxation spectrum of this creep suggests a mechanical Barkhausen effect. In surprising contrast to exponential decay at large energy, the motion at low energy and long period is characterized by repeatable metastable states. Phase is preserved in the transition between most states even though the transitions may be chaotic. There is a lowest harmonic state which is different for Pb and Cu bobs, and below which the system transitions from free decay to stochastic fluctuation-dissipation. Noise of this stochastic state is larger than electronic noise, and power spectral density plots show that it contains mixtures of subharmonics at integral multiples of 1/4 the pendulum frequency.
Buried-heterostructure lasers fabricated by in situ processing techniques
Authors: Wang Y. L. , Temkin H. , Harriott L. R. , Logan R. A. , Tanbun-Ek T.
Published: July 2002

We describe, for the first time, the preparation of InGaAs/InP homojunction confined buried-heterostructure lasers by high vacuum processing techniques. Lithography and waveguide mesa etching were carried out using ultrathin native oxide masking, focused Ga ion beam writing, and free Cl2 etching. Base laser structures and overgrowth were carried out by atmospheric pressure metalorganic vapor phase epitaxy. The resulting lasers have low-threshold currents of ∼62 mA.
Epitaxially grown sputtered LaAlO3 films
Authors: Lee A. E. , Platt C. E. , Burch J. F. , Simon R. W. , Goral J. P. , Al-Jassim M. M.
Published: July 2002

We have grown crystalline thin films of LaAlO3 using off-axis rf sputtering from a single stoichiometric target. The films grow epitaxially on SrTiO3 and LaAlO3  (100) substrates as well as on YBa2Cu3O7 thin films. We report on the growth conditions used to make these films, the properties of the films, and the properties of bilayer and trilayer structures containing both LaAlO3 and YBa2Cu3O7 films. Transmission electron microscopy cross-sectional and x-ray diffraction analyses indicate that all the constituent films in the multilayers grow epitaxially and that the interfaces between the films are sharply defined. Preliminary transport measurements on these multilayers show that LaAlO3 can be used for dielectric layers in a variety of high-temperature superconductor electronic circuits.
Transverse stress effect on the critical current of jelly-roll multifilamentary Nb3Al wires
Authors: Zeritis Dimitris , Ando Toshinari , Takahashi Yoshikazu , Nishi Masataka , Nakajima Hideo , Shimamoto Susumu
Published: July 2002

Experiments were conducted to determine the transverse stress sensitivity of the critical current (Ic) of jelly-roll multifilamentary Nb3Al wires at 8 and 12 T. For comparison, similar experiments were conducted on bronze-process (NbTi)3Sn wires. At 12 T and under a transverse compressive stress of 150 MPa−conditions expected in fusion magnets−the Ic degradation of the Nb3Al specimen was ∼20% vs ∼65% for the (NbTi)3Sn specimen. The intrinsic superiority of Nb3Al over (NbTi)3Sn with regard to transverse compressive stress is thus clear. There is optimism that Nb3Al will eventually become a useful superconductor for large-scale, high-field applications.
Fast nanoscale modification of Ag(111) using a scanning tunneling microscope
Authors: Rabe Jürgen P. , Buchholz Stefan
Published: July 2002

Epitaxial Ag(111) films have been grown on mica. They exhibit flat terraces of a few 100 nm diameter, suitable for nanoscale modification with the scanning tunneling microscope (STM). Under ambient conditions, surface modifications of a few nanometers diameter were produced by raising the bias from below 1 V to a bias between 3 and 7 V for less than 50 ns. The steady-state current could be limited to 2 pA. This means that the modification is initiated while only a few electrons pass the tunneling junction, indicating that it is not a current effect. At positive sample bias, usually holes are formed, while at negative bias hillocks occur. In the case of hole formation, the current does not change significantly on a time scale of 10 μs. When hillocks are formed, the current may rise after the application of the voltage pulse. It was limited to 4 nA by the external circuitry and remains saturated until the tip is withdrawn on a time scale of milliseconds, i.e., the characteristic for the feedback loop control. Also in this case the modification is not caused by a current effect, since the limiting current would still allow nondestructive STM imaging. It is concluded that the modifications are caused by field evaporation of sample and tip material, respectively.
Effect of Ca2PbO4 additions on the formation of the 110 K phase in Bi-Pb-Sr-Ca-Cu-O superconducting ceramics
Authors: Chen F. H. , Koo H. S. , Tseng T. Y.
Published: July 2002

The growth of the Bi2Sr2Ca2Cu3Ox phase in the high Tc superconducting Bi-Pb-Sr-Ca-Cu-O system through reacting Bi2Sr2CaCu2Ox with Ca- or Cu-rich intermediate phases, Ca2CuO3, CuO, and Ca2PbO4, has been studied. X-ray diffraction and electrical and diamagnetic analyses revealed that the interaction and interdiffusion of these intermediate phase led to the formation of a high percentage of the 2223 phase and a sharp single-step superconducting transition at Tc(R = 0) = 108 K. Also, Ca2PbO4 proved essential for accelerating the growth rate of the 110 K phase from the 85 K phase.
Single-mode molecular beam epitaxy grown PbEuSeTe/PbTe buried-heterostructure diode lasers for CO2 high-resolution spectroscopy
Authors: Feit Z. , Kostyk D. , Woods R. J. , Mak P.
Published: July 2002

Buried-heterostructure tunable PbEuSeTe/PbTe lasers were fabricated using a two-stage molecular beam epitaxy growth procedure. Improvements in the processing technique yielded lasers that show performance characteristics significantly better than those reported previously. A continuous wave (cw) operating temperature of 203 K was realized, which is the highest cw operating temperature ever reported for lead-chalcogenides diode lasers. This laser exhibited exceptionally low-threshold currents of 1.4 mA at 90 K and 43 mA at 160 K with single-mode operation for injection currents up to 30Ith and 0.18 mW power at 100 K. The usefulness of the laser, when operating cw at 200 K, was demonstrated by the ability to perform high-resolution spectroscopy of a low-pressure CO2 gas sample.
Hole-dependent diffusion of implanted Mg in GaAs
Authors: Robinson Heyward G. , Deal Michael D. , Stevenson David A.
Published: July 2002

Magnesium implants in GaAs exhibit two types of diffusion during annealing: uphill diffusion in the peak of the implant and concentration-dependent diffusion into the bulk. The uphill diffusion predominates at short times and low temperatures, while the concentration-dependent diffusion is dominant at long times and high temperatures. By studying implants that were annealed at temperatures where no uphill diffusion occurs, diffused profiles could be modeled and an expression for the Mg diffusivity obtained. The activation energy for this process is 1.77 eV. Results from Fermi level experiments show that the diffusivity is hole dependent rather than concentration dependent. The hole-dependent exponent is unity for Mg implanted into semi-insulating substrates, but may change to two at high hole concentrations.
Fabrication of patterned Gex/Si1−x/Si layers by pulsed laser induced epitaxy
Authors: Chang Y. , Chou S. Y. , Kramer J. , Sigmon T. W. , Marshall A. F. , Weiner K. H.
Published: July 2002

Selective growth of GexSi1−x on Si is demonstrated for the first time using a pulsed laser induced epitaxy technique, combined with either standard oxide or liftoff patterning processes. Two different dimensions of Ge0.12Si0.88/Si lateral wells are formed, 3.5 μm wide by 1700 Å deep, and 6 μm wide by 1300 Å deep. High-resolution transmission electron microscopy, combined with energy-dispersive x-ray imaging, reveals a well-defined two-dimensional (2D) Ge redistribution profile with no significant line or surface defects observed. The 2D Ge well distribution profiles, governed by heat and mass transport during the laser processing, are discussed.
Magnetic band structure at the Fe/GaAs(100) interface
Authors: Himpsel F. J.
Published: July 2002

Using inverse photoemission, the uppermost minority spin d band of Fe on GaAs(110) is found to move down by 0.9 eV for the first layer. This indicates a nearly complete collapse of the ferromagnetic exchange splitting at the interface. The decrease happens over a range of about 100 Å, which parallels the reported decrease of the magnetization for epitaxial Fe films on GaAs
Unhydrogenated diamond-like carbon films prepared by dc plasma chemical vapor deposition at room temperature
Authors: Kumar Sunil
Published: July 2002

Unhydrogenated diamond-like carbon films were prepared at room temperature by a simple dc plasma chemical vapor deposition system with a low overall power consumption. A gaseous mixture of methane and argon (1:9) was used as a material gas with the intent of bombarding the growing film with Ar+ ions. The bombardment of the depositing species with Ar+ ions present in the plasma leads to (i) removal of hydrogen from the carbon atoms and (ii) a preferential resputtering of weakly bonded graphite precursors from the film surface giving rise to diamond-like properties of the films. The progressive thermal annealing of the films induces graphitization, and promotes growth of the crystallites at higher anneal temperatures (≥500 °C)
Clear correlations observed between YBa2Cu3O7−δ thin-film properties and GHz microwave resonator performance
Authors: Young K. H. , Negrete G. V. , Hammond R. B. , Inam A. , Ramesh R. , Hart D. L. , Yonezawa Y.
Published: July 2002

We have fabricated and measured 5 GHz microstrip resonators from a series of YBa2Cu3O7−δ thin films grown on LaAlO3(001) substrates by in situ laser ablation. We have studied the correlations between unloaded quality factor and various film properties, such as transition temperature, width of transition, critical current density, narrowness of x-ray rocking curve, sharpness of electron channeling pattern, and most important substrate temperature during growth. We found that in general, higher transition temperature, higher critical current density, sharper transition, sharper channeling pattern, and narrower x-ray rocking curve correlate positively with good microwave performance. The best quality factor exists for a narrow growth temperature window (around 800 °C). We also report the dependence of quality factor on device power for each film.
Europium-doped alkali halides as a selective ultraviolet dosimeter material in the actinic region
Authors: Aguirre de Carcer I. , Lifante G. , Cussó F. , Jaque F. , Calderón T.
Published: July 2002

The NaCl:Eu2+ thermoluminescence characteristics after ultraviolet irradiation as well as solar exposure have been analyzed. The TL excitation spectra of this material is coincident with the actinic region and its sensibility limit is less than 0.2 μJ/cm2 for 240 nm wavelength irradation. A model for the thermoluminescence emission is provided.
High-field electron transport in compensated GaAs
Authors: Wu Ernest Y. , Yu Bernard H.
Published: July 2002

High-field electron transport in compensated GaAs has been determined by Monte Carlo calculation for various compensation ratios at lattice temperatures of 77, 160, and 300 K. The velocity-field characteristics exhibit two maxima at both low and high temperatures for several doping compensations. It is found that doping compensation has a stronger effect on electron transport at low temperatures than at high temperatures over a range of field values. As compared to InP, In0.53Ga0.47As, and Al0.25In0.75As, the negative differential mobilities and the high-field velocities have been noticeably reduced by doping compensations. The origin of this unique two maxima feature in the velocity-field relation for compensated GaAs has been discussed in comparison with other compensated semiconductors.
Electron spin resonance study of laser-annealed (Zn,Mn)O ceramics
Authors: Kawano Katsuyasu , Nakata Ryouhei , Sumita Minoru
Published: July 2002

Investigations have been made on the effects of pulse laser annealing on the ceramics (Zn,Mn)O by means of electron spin resonance (ESR) measurements. A remarkable change in the ESR spectrum was observed after annealing by a Nd:YAG pulse laser (λ=1.064 μm, 5–7 J/cm2). It suggests that segregated Mn2+ precipitates at grain boundaries in ZnO are diffused into crystal grains by preferential heat conduction through the boundaries. The scanning electron microscope observation verified enough melting features within the ceramics.
Enhanced crystallographic selectivity in molecular beam epitaxial growth of GaAs on mesas and formation of (001)-(111)B facet structures for edge quantum wires
Authors: Nakamura Y. , Koshiba S. , Tsuchiya M. , Kano H. , Sakaki H.
Published: July 2002

The crystallographic selectivity of molecular beam epitaxial growth of GaAs on mesas consisting of a (001) surface and (111)B facets is studied systematically. It was found that the growth rate on (111)B facets can be drastically reduced to ∼1/30 of the growth rate on (001) surface by the reduction of As flux on the (111)B facets. This enhanced selectivity results from the enhanced intersurface migration, and strongly indicates a feasibility of forming microheterostructures needed for the fabrication of edge quantum wires on (001)-(111)B mesas.
High-frequency operation of heavily carbon-doped Ga0.51In0.49P/GaAs surface-emitting light-emitting diodes grown by metalorganic molecular beam epitaxy
Authors: de Lyon T. J. , Woodall J. M. , McInturff D. T. , Kirchner P. D. , Kash J. A. , Bates R. J. S. , Hodgson R. T. , Cardone F.
Published: July 2002

Single-heterostructure light-emitting diodes (LEDs) consisting of a wide band-gap N-Ga0.51In0.49P emitter and a heavily carbon-doped p-GaAs active layer have been grown by metalorganic molecular beam epitaxy. Trimethygallium has been utilized to dope the GaAs active layer for a hole concentration of 1.5×1020 cm−3 in order to reduce the radiative lifetime of minority carriers in GaAs. The cw electroluminescent spectra of these LEDs indicate that the injection efficiency of the Ga0.51In0.49P/GaAs heterojunction is not degraded by carbon redistribution, even in the absence of an undoped spacer layer between the GaAs active layer and the Ga0.51In0.49P emitter layer. The transient optical response of the LEDs determines an optical 3 dB bandwidth in the range of 0.6–2.0 GHz. The external brightness of the carbon-doped LEDs is shown to be approximately a factor of 20 lower than that of double-heterostructure LEDs containing active layers more moderately doped with Be at 2×1018 cm−3.
Minority carrier lifetime of HgCdTe from photoconductivity decay method
Authors: Reichman Joseph
Published: July 2002

The results of an analytical study of the photoconductivity decay (PCD) method for measuring carrier lifetimes of n-type HgCdTe show that the measurements give much higher values than the minority carrier lifetimes when trapping is significant. In contrast, for p-type HgCdTe, the PCD method gives results equal to or less than the minority carrier lifetime under the same trapping conditions. The difference in results between n-type and p-type HgCdTe is due to the different recombination properties of excess electrons when they are majority carriers or minority carriers, respectively.
Effect of chlorine doping on photostructural defect states in amorphous selenium films
Authors: Chand Suresh , Sharma G. D. , Bhatheja R. C. , Chandra Subhas
Published: July 2002

The effect of chlorine doping on photostructural defect states in amorphous selenium films (∼100 μm) has been studied using the thermally stimulated discharge current technique. Chlorine doping in amorphous selenium results in the shift of deep photostructural defect states C+3 and C−1 to relatively shallower levels, i.e., from 1.6 and 1.7 eV in pure films to 1.4 and 1.5 eV in chlorine-doped films for electrons and holes, respectively. These effects have been explained in terms of the enhancement in the conductivity of amorphous selenium and increase in the mobility of electrons and holes on chlorine doping.
All-optical sub-Tbits/s serial-to-parallel conversion using excitonic giant nonlinearity
Authors: Ema K. , Kuwata-Gonokami M. , Shimizu F.
Published: July 2002

An all-optical serial-to-parallel conversion technique, which is the inverse process of the real-time pulse shaping, is reported. A conversion of 0.14-Tbits/s signals using excitonic-giant nonlinearity of ZnSe film is reported. The response of this conversion system is faster than 13 ps with a conversion efficiency of 0.1%.
The influence of dislocation density on electron mobility in InP films on Si
Authors: Crumbaker T. E. , Hafich M. J. , Robinson G. Y. , Jones K. M. , Al-Jassim M. M. , Davis A. , Lorenzo J. P.
Published: July 2002

The average electron mobility and dislocation density have been measured as functions of the film thickness in InP films grown on Si substrates by gas-source molecular beam epitaxy. In a region extending about 2 μm from the Si interface, the density of dislocations was found to be very high and clustering of dislocations was observed by transmission electron microscopy. The corresponding mobility was very small. Beyond 2 μm, clustering was not observed, the density of dislocations decreased, and the average mobility increased with increasing film thickness. Thus, the threading dislocations created by the large InP/Si lattice mismatch can significantly degrade the free carrier mobility of the InP film.
Activation and diffusion characteristics of implanted Si and Be in Al0.5In0.5P
Authors: Pearton S. J. , Hobson W. S. , Kuo J. M. , Luftman H. S. , Katz A. , Ren F.
Published: July 2002

The electrical activation characteristics of implanted Si and Be in Al0.5In0.5P grown lattice matched to GaAs by either organometallic vapor phase epitaxy or gas-source molecular beam epitaxy were investigated as a function of ion dose (1013–1015 cm−2), annealing time (3–60 s) and annealing temperature (600–950 °C). Limiting sheet electron densities of 9×1012 cm−2 for 100 keV Si implants and sheet hole densities of 7×1012 cm−2 for 40 keV Be implants were obtained for optimum 10 s anneals at 850 or 800 °C, respectively. Co-implantation of P with Be failed to substantially improve the Be activation. Apparent activation energies for electrical activation of Si of 0.74±0.05 eV and 0.68±0.05 eV for Be were obtained from the temperature dependence of the saturated carrier density. The implanted Be displayed extensive redistribution upon annealing at 800 °C for 10 s, whereas implanted Si showed no measurable motion under any of our conditions.
Conduction-band discontinuity in InGaP/GaAs measured using both current-voltage and photoemission methods
Authors: Lee T. W. , Houston P. A. , Kumar R. , Yang X. F. , Hill G. , Hopkinson M. , Claxton P. A.
Published: July 2002

Both current-voltage and photoemission measurements of the conduction-band discontinuity of the same InGaP/GaAs p-n heterojunction have been carried out. Interpretation of the current-voltage results using thermionic emission theory applied to a heterojunction bipolar transistor have resulted in a conduction-band offset value of 0.21 eV in the case of a compositionally abrupt junction. This figure has been confirmed by performing independent photoemission measurements on the same junction.
Laser-induced etching of silicon in hydrofluoric acid
Authors: Lim P. , Brock J. R. , Trachtenberg I.
Published: July 2002

Laser-assisted wet etching (LAWE) of n-silicon using a 514.5-nm line from a cw argon-ion laser in the presence of hydrofluoric acid is reported. The effects of laser fluence, doping level, and acid concentration on the etch rate are investigated. By LAWE, vias and lines can be rapidly etched with smooth profiles under conditions described.
Observation of laser emission in an InP-AlInAs type II superlattice
Authors: Lugagne-Delpon E. , Voisin P. , Voos M. , André J. P.
Published: July 2002

We report the observation of laser emission at low temperature from an optically pumped InP-AlInAs superlattice grown by metalorganic chemical vapor deposition. Independent measurements of low level photoluminescence excitation and optical absorption show that laser emission occurs between spatially separated conduction and valence levels localized, respectively, in InP and AlInAs, with a calculated wave function overlap as low as 0.04. High radiative efficiency observed in this system is believed to be a genuine consequence of the type II band lineup.
Highly sensitive Moire technique for direct and real-time observation of electron microscopic phase objects
Authors: Ru Q. , Endo J. , Tonomura A.
Published: July 2002

A Moire modulation which is a sine function of the phase variation of a phase object to be investigated in an interference electron microscope is proposed. When the phase variation is larger than 2π, the conventional cosine-functioned Moire-fringe pattern is observed, and when the phase variation is very less than 2π, phase-contrast Moire modulation which can never be achieved by the conventional Moire method is observed. The analogue and digital formations of this sine-functioned Moire modulation in a photographic film and video camera, respectively, are presented. Real-time observation is realized by the digital method.
Thermal stability of Si1−xCx/Si strained layer superlattices
Authors: Goorsky M. S. , Iyer S. S. , Eberl K. , Legoues F. , Angilello J. , Cardone F.
Published: July 2002

The thermal stability of epitaxial silicon-carbon alloys grown by molecular beam epitaxy on (001) silicon was investigated using high resolution x-ray diffraction, transmission electron microscopy, and secondary ion mass spectroscopy measurements. Different superlattices, with alloy compositions of Si0.997C0.003, Si0.992C0.008, and Si0.985C0.015, all nominally 6 nm thick, with 24 nm Si spacer layers were employed. Annealing studies determined that there are different pathways to strain relaxation in this material system. At annealing temperatures of 900 °C and below, the structures relax only by interdiffusion, indicating that these layers are stable during typical device processing steps. At temperatures of 1000 °C and above, SiC precipitation dominates with enhanced precipitation in the Si1−xCx layers with the highest initial carbon content.
dc characterization of the Ga0.51In0.49P/GaAs tunneling emitter bipolar transistor
Authors: Lu S. S. , Wu C. C. , Huang C. C. , Williamson F. , Nathan M. I.
Published: July 2002

Ga0.51In0.49P/GaAs tunneling emitter bipolar transistors (TEBTs) grown by gas source molecular beam epitaxy with different barrier thicknesses (50 and 100 Å) have been fabricated and measured at different temperatures (77 and 300 K) for the first time. A current gain of 141 and an offset voltage of 50 mV at room temperature were achieved in the thick barrier (100 Å) device with heavily doped p+ (1×1019 cm−3) base. The thinner device had a lower gain (∼53) than the thick barrier device at room temperature. The functional dependence of gain on thickness was attributed to carrier tunneling through the barrier inserted between the base and the emitter. The low-temperature (77 K) results showed that the gain of the thick barrier device was almost the same as that at 300 K while that of the thin barrier device increased, which was explained by the nonequilibrium electron transport in the base.
Oxygen content and disorder in a-axis oriented YBa2Cu3O7−δ thin films
Authors: Sodtke Erik , Münder Herbert
Published: July 2002

Using results of Raman spectroscopy, it is shown that the transition temperature Tc (R=0) of a-axis oriented YBa2Cu3O7−δ thin films strongly depends on the disorder in the oxygen sublattice. Regardless of deposition temperature Td, the films have an oxygen deficiency δ<0.1. However, at low Td, films show Tc≊50 K and a significant disorder in the distribution of chain and/or apex oxygen atoms. Using a template growth procedure we show that, at a sufficiently high Td, the oxygen disorder vanishes and Tc≳80 K, although the crystalline disorder, measured by the width of the (200) x-ray rocking curve, is increasing with Td.
Coupled-stripe in-phase operation of planar native-oxide index-guided AlyGa1−yAs-GaAs-InxGa1−xAs quantum-well heterostructure laser arrays
Authors: Kish F. A. , Caracci S. J. , Holonyak N. , Gavrilovic P. , Meehan K. , Williams J. E.
Published: July 2002

High-performance, coupled-stripe, planar, index-guided AlyGa1−yAs-GaAs-InxGa1−xAs quantum-well heterostructure (QWH) laser arrays are fabricated by the formation of a relatively thick, current-blocking, native oxide from the high-gap AlyGa1−yAs upper confining layer between active stripes. Precise control of the thickness of the native oxide layer between emitters provides a means of varying the index step between stripes, and permits tailoring of the optical profile to produce in-phase operation. The 10-stripe coupled QWH laser arrays (∼3-μm-wide stripes on 4 μm centers) exhibit near-diffraction-limited, single-lobed, far-field patterns with low continuous (cw) thresholds (∼45 mA) and cw output powers (total external differential quantum efficiency ≳50%) of over 100 mW per uncoated facet.
Preparation of multilayered thin silicon-on-insulator structure by low-energy oxygen ion implantation
Authors: Ishikawa Yukari , Shibata Noriyoshi
Published: July 2002

Multilayered thin silicon-on-insulator (SOI) structures have been produced by multiple 25 keV oxygen implantation and in situ silicon growth by molecular beam epitaxy. The structures were analyzed by Auger electron spectroscopy and cross-sectional transmission electron microscopy. A double SOI structure after high temperature annealing has the top silicon layer, upper buried oxide layer, buried silicon layer, and lower oxide layer with thicknesses of 32, 40, 85, and 32 nm, respectively. The multilayered structure has abrupt interfaces between silicon and oxide layers and crystal quality comparable to that produced by the conventional separation by the implanted oxygen (SIMOX) process.