bluuebunny/crossref_metadata_2025 huggingface dataset:
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u characterization of diamond nucleation and growth
Authors: Belton David N. , Harris Stephen J. , Schmieg Steven J. , Weiner Anita M. , Perry Thomas A.
Published: July 2002

Filament-assisted chemical vapor deposition (CVD) diamond film growth on Si(100) was studied using x-ray photoelectron spectroscopy (XPS) to examine the sample at selected intervals during the nucleation and growth processes. The sample was transferred under vacuum from the growth chamber to the attached XPS analysis chamber without exposure to air. Before growth XPS showed that the Si sample is covered by a layer of SiO2 and carbonaceous residue; however, after 15 min of growth both of these substances are removed and replaced by a distinct SiC layer [Si(2p)=100.3 eV and C(1s)=282.7 eV].
Vacuum ultraviolet photoelectron spectroscopy of (NH4)2S-treated GaAs (100) surfaces
Authors: Spindt C. J. , Liu D. , Miyano K. , Meissner P. L. , Chiang T. T. , Kendelewicz T. , Lindau I. , Spicer W. E.
Published: July 2002

The surface chemistry and band bending of the ammonium sulfide-treated GaAs (100) surface has been studied using surface-sensitive synchrotron radiation photoemission spectroscopy. We find that the treatment leaves the GaAs surface terminated with roughly a monolayer of sulfur bonded to both As and Ga atoms. An n-type barrier height of 0.8 eV is measured. The thermal stability of the various chemical components is studied and various issues of the passivating mechanism are discussed.
Nucleation and epitaxial growth of InAs on Si (100) by ion-assisted deposition
Authors: Choi C.-H. , Barnett S. A.
Published: July 2002

The nucleation mechanism and crystalline perfection of InAs on Si(100) were found to depend strongly on the substrate bias voltage Vs used to accelerate Ar ions to the growing film during triode ion-assisted deposition. Increasing the Vs value used during the first ∼10 monolayers (ML) of growth from 15 to 30 V decreased the x-ray diffraction rocking curve full width at half maximum (FWHM) by a factor of ∼2. Further increases in Vs yielded an increase in the FWHM. Reflection high-energy electron diffraction studies showed that the use of Vs=30 V promoted layer-by-layer nucleation. While three-dimensional islands formed at a critical coverage θcr of 2 – 3 ML for Vs=15 V, increasing Vs to 30 V increased θcr to ∼10 ML. The fact that Vs=30 V both promoted layer-by-layer growth and decreased the FWHM suggests that defect generation is dependent upon the nucleation mechanism.
Performance limitations of GaAs/AlGaAs infrared superlattices
Authors: Kinch M. A. , Yariv A.
Published: July 2002

The performance of the GaAs/AlGaAs superlattice as an infrared detecting material is modeled as a function of temperature for two cutoff wavelengths, namely, 8.3 and 10.0 μm. The results are compared with HgCdTe, the present industry standard material for infrared systems. The limiting performance of the GaAs/AlGaAs materials system is found to be orders of magnitude below that of HgCdTe for any specific cutoff wavelength and operating temperature.
Ultrahigh doping of GaAs by carbon during metalorganic molecular beam epitaxy
Authors: Abernathy C. R. , Pearton S. J. , Caruso R. , Ren F. , Kovalchik J.
Published: July 2002

Recent advances in heterostructure bipolar transistor technology have created a need for p-type doping at levels ≥1020 cm−3. Furthermore, such levels may eliminate the need for alloying during ohmic contact formation. We have achieved p-type doping levels as high as 5×1020 cm−3 using an unconventional dopant, C, derived from the gaseous source chemical, trimethylgallium (TMG), during metalorganic molecular beam epitaxial (MOMBE) growth of GaAs. We have controllably achieved doping levels between 1019 and 5×1020 cm−3 by diluting the TMG flow with another metalorganic, triethylgallium (TEG). By utilizing the so-called δ-doping or atomic planar doping method we have also been able to grow C-doped spikes with hole concentrations as high as 7×1019 cm−3, with a full width at half maximum of ∼50 Å at 300 K. This doping level is the highest yet reported for planar doping, and the narrow width indicates that the C atoms are restricted to one or two atomic planes. By switching out the TMG, and switching in the TEG to continue the growth of C-free GaAs we have grown sandwich-type structures with C levels of 1020 cm−3, which fall off within 210 Å to C levels of <1017 cm−3. High-temperature annealing of such structures reveals a C diffusion coefficient of ≤10−16 cm2 s−1 at 950 °C, in agreement with other reports. This is at least three orders of magnitude less than for the other conventional p-type dopants, Be and Zn. Finally, we report the presence of strain in the highly C-doped layers, detected by x-ray diffraction. The lattice constant obtained corresponds roughly to that calculated by assuming a Vegard’s law mixture of GaAs and 0.7% GaC. This distortion of the GaAs lattice has not been previously measured.
Eliminating channeling tail by lower dose preimplantation
Authors: Kase Masataka , Kimura Mami , Mori Haruhisa , Ogawa Tsutomu
Published: July 2002

We optimized Ge+ and Si+ preimplantation to eliminate the channeling tail and prevent the rapid diffusion of boron and the formation of serious defects. We examined the dependence of the microchanneling of BF+2 implantation or the lattice disorder of preimplanted silicon using secondary-ion mass spectroscopy and grazing exit Rutherford backscattering spectroscopy. The optimum doses are about 25% those for full amorphization, i.e., preamorphization. The channeling tail is eliminated by disordered layers containing about 60% silicon atoms on irregular sites.
Atomic layer epitaxy of GaP and elucidation for self-limiting mechanism
Authors: Sakuma Y. , Kodama K. , Ozeki M.
Published: July 2002

Atomic layer epitaxy (ALE) of GaP was performed for the first time in a low-pressure metalorganic vapor phase epitaxial (MOVPE) reactor using trimethylgallium (TMG) and phosphine (PH3) as sources. Growth was self-limiting for the exposure time of each reactant. X-ray photoelectron spectroscopy (XPS) analyses were carried out to identify the adsorbates on the growth surface. There were no methyl groups on the surface Ga and the self-limiting mechanism is due to the selective adsorption of TMG by the surface P atoms. When the substrate was exposed to a sufficient TMG flow after a submonolayer Ga was deposited by triethylgallium (TEG), growth was still self-limiting. This supports the selective adsorption model.
Effects of hydrogen on Al/p-Si Schottky barrier diodes
Authors: Jia Y. Q. , Qin G. G.
Published: July 2002

Hydrogen was incorporated into B-doped p-type crystalline silicon in three different ways: boiling the sample in water, exposing the sample to hydrogen plasma, growing silicon in a hydrogen atmosphere. Al-contact Schottky barrier diodes were made on both the hydrogenated and unhydrogenated samples. It was found that the Schottky barrier height (SBH) is increased due to the hydrogenation. The current-voltage measurement showed an increase of 0.06–0.10 eV in the effective SBH and the activation energy measurement revealed an increase of 0.07–0.09 eV in the SBH under a forward bias of 0.15 V. If the silicon grown in a hydrogen atmosphere was thermal annealed at 650 °C to drive out hydrogen before Schottky metallization, then the SBH approached that of the unhydrogenated sample. It is demonstrated that the SBH in Al/p-Si can be increased with hydrogen incorporated in silicon.
Low-resistivity Cu thin-film deposition by self-ion bombardment
Authors: Bai P. , Yang G.-R. , Lu T.-M.
Published: July 2002

An anomalous reduction of the thin-film resistivity has been observed in the Cu deposition at room temperature using a partially ionized beam in which the self-ions are used to bombard the substrate surface during growth. A minimum thin-film resistivity of 1.83 μΩ cm has been obtained at 2 kV substrate bias voltage with an ion percentage of about 1% in the beam for films of 2500 Å thickness. This is compared to the resistivity of close to 4 μΩ cm obtained by the conventional evaporation technique without the use of self-ions. We discuss the results within the framework of the theory of grain-boundary resistivity proposed by Mayadas and Shatzkets [Phys. Rev. B 1, 1382 (1970)].
Auger recombination in bulk and quantum well InGaAs
Authors: Hausser S. , Fuchs G. , Hangleiter A. , Streubel K. , Tsang W. T.
Published: July 2002

We report the determination of Auger recombination coefficients in bulk and quantum well InGaAs by time-resolved luminescence measurements. In bulk InGaAs the coefficient is C=3.2×10−28 cm6/s and has the temperature dependence of the valence-band Auger effect involving the split-off valence band. In 11 nm quantum well InGaAs we find C=0.9×10−28 cm6/s, independent of temperature. The Auger coefficient decreases slightly with decreasing well width.
Resistivity and morphology of TiSi2 formed on Xe+-implanted polycrystalline silicon
Authors: Kuwano Hiroki , Phillips J. R. , Mayer J. W.
Published: July 2002

Xe ion irradiation of polycrystalline silicon before Ti deposition is found to affect subsequent silicide formation. Silicide films were prepared by implanting 60, 100, or 240 keV Xe+ ions into 500-nm-thick undoped polycrystalline silicon before depositing Ti and annealing in vacuum. Preimplantation altered the subsequent silicide resistivity, x-ray diffraction patterns, and morphology as compared to films prepared on unimplanted polycrystalline Si substrates. We found that minimal TiSi2 resistivities were achieved at lower temperatures with preimplantation, indicating that the Xe-implanted substrate promotes a lower temperature transition from the metastable C49 phase to the low-resistivity equilibrium C54 phase of TiSi2. X-ray diffraction results confirmed the lower temperature formation of the C54 phase with preimplantation. Low-temperature annealing (650 °C, 30 min) of 6×1016 cm−2, 240 keV Xe+-implanted samples yielded low-resistivity (∼22 μΩ cm) silicide films, while simultaneously annealed samples without preimplantation had resistivity five times higher. Lower doses were effective at lower implant energies, with low resistivity achieved after 725 °C, 30 min annealing for 2×1015 cm−2, 60 keV Xe+ preimplantation.
New phase interference technique applied for sensitive photothermal microscopy
Authors: Walther H. G. , Friedrich K. , Haupt K. , Muratikov K. , Glazov A.
Published: July 2002

An interferometric version of mirage technique is reported, whereby one part of the probe beam passes through the center of the thermal lens in air, while the other one avoids it. By mixing the two parts with the help of a diffraction grating, a strong photothermal signal is obtained at predetermined spots of the interference pattern. This photothermal arrangement is integrated into a reflected light microscope.
Bistable conditions for low-temperature silicon epitaxy
Authors: Meyerson Bernard S. , Himpsel Franz J. , Uram Kevin J.
Published: July 2002

We report on the role of hydrogen surface passivation in achieving low-temperature silicon epitaxy by chemical vapor deposition processes. Upon insertion of an HF-etched silicon wafer into an epitaxial silicon deposition apparatus, residual contamination of the Si surface is negligible. Si 2p core level photoemission spectra demonstrate that the silicon surface is stable in air and free of SiO2 for a time period of minutes. The predominant passivating species is found to be silicon hydride. We demonstrate that hydrogen passivation by HF pretreatment leads to two divergent temperature ranges where epitaxy is successful, those being a low-temperature range, 425≲T≲650 °C, and a high-temperature regime, T≳750 °C. Additionally, we employ temperature-programmed desorption techniques to elucidate the role of hydrogen in the transition to a steady-state growth process, employing ultrahigh vacuum/chemical vapor deposition as the model system.
Tunneling of photoexcited holes through a double-barrier resonant tunneling structure observed by time-resolved photoluminescence
Authors: Charbonneau S. , Young Jeff F. , SpringThorpe A. J.
Published: July 2002

The tunneling dynamics of photogenerated holes in a biased GaAs/AlGaAs double-barrier resonant tunneling structure is studied using time-resolved photoluminescence. For voltages biasing the structure in the resonant tunneling regime, a single exponential time decay was observed. However, for voltages which bias the structure in the nonresonant tunneling regime, beyond the region of negative differential resistance, the exciton decays with two time constants: one similar to that observed at low voltages and one that is approximately one order of magnitude slower. We attribute the fast time constant to the decay of exciton population originating from holes photoexcited directly in the well. The slower time constant is associated with excitons that are created from holes which are photoexcited in the GaAs contact region, and which subsequently tunnel into the well.
Laser-assisted deposition of nanometer structures using a scanning tunneling microscope
Authors: Yau S.-T. , Saltz D. , Nayfeh M. H.
Published: July 2002

Nanometer-scale deposits as small as 1 nm have been made on graphite surfaces using laser-induced multiphoton fragmentation and ionization of trimethylaluminum (TMA) molecules in the tunneling junction of a scanning tunneling microscope. Laser radiation generates ions, which are guided to the surface by the electric field between the tip and the surface. The resolution of this technique is limited by the extent of the field in the tunneling junction.
Observation of charge storage and intersubband relaxation in resonant tunneling via a high sensitivity capacitive technique
Authors: Schubert E. F. , Capasso Federico , Hutchinson A. L. , Sen S. , Gossard A. C.
Published: July 2002

In suitably designed resonant tunneling double barriers the capacitance-voltage curve exhibits well-defined features corresponding to the charging and discharging of the quantum well. From the bias dependence of the electron density in the well we find that in our thick parabolic wells, electrons tunneling into the excited states relax to the lowest subband and sequentially tunnel out. Our experiments allow us to obtain the charge density accumulated in the well and the tunneling escape rate of electrons out of the well.
Room-temperature exciton absorption in (Zn,Cd)Se/ZnSe quantum wells at blue-green wavelengths
Authors: Ding J. , Pelekanos N. , Nurmikko A. V. , Luo H. , Samarth N. , Furdyna J. K.
Published: July 2002

Excitonic absorption has been investigated in multiple quantum wells of (Zn,Cd)Se/ZnSe in an effort to increase the electron-hole Coulomb interaction. Well-defined absorption peaks for the n=1 heavy hole exciton are observed at room temperature showing evidence for a reduced exciton-optical phonon scattering rate.
Ultraviolet and blue holographic lithography of ZnSe epilayers and heterostructures with feature size to 100 nm and below
Authors: Walecki W. , Patterson W. R. , Nurmikko A. V. , Luo H. , Samarth N. , Furdyna J. K. , Kobayashi M. , Durbin S. , Gunshor R. L.
Published: July 2002

We have employed short-wavelength holographic laser lithography and reactive ion etching to define wire and dot-like patterns in ZnSe thin epitaxial films and heterostructures with spatial feature size to better than 100 nm. Photoluminescence measurements suggest that surface damage from etching may be much less severe than in III-V semiconductors.
Contactless optical evaluation of processing effects on carrier lifetime in silicon
Authors: Baude P. F. , Tamagawa T. , Polla D. L.
Published: July 2002

Contactless, optical modulation of free-carrier absorption has been used to identify minority-carrier lifetime degradation associated with both novel and common very large scale integrated circuit processing steps in p-type silicon wafers. Carrier lifetime degradation and a corresponding increase in surface recombination velocity was found to be associated with the silicon etchants ethylenediamine-pyrocatechol-water (EDP) and potassium hydroxide (KOH), prolonged exposure to hydrofluoric acid (HF and BHF), and ion bombardment associated with a variety of plasma etching steps. Knowledge of process-induced lifetime degradation obtained by this technique may offer significant input into the development of high-yield very large scale integrated circuit processes.
Thermal donor formation in Fe-doped semi-insulating InP
Authors: von Bardeleben H. J. , Bourgoin J. C. , Kainosho K. , Oda O.
Published: July 2002

Single wafers of Fe-doped semi-insulating InP have been annealed under Si3N4 capping in the 663–760 °C temperature range. Electron paramagnetic resonance (EPR) measurements performed on single crystals from different parts of the wafers show that the thermal annealing introduces various deep donor centers in concentration up to 1016 cm−3. The donor formation rate increases strongly for annealing temperatures higher than 700 °C. From EPR transient spectroscopy the thermal ionization energy of the dominant donor has been determined to Ec−0.34 eV. The results are correlated with previous electrical resistivity and photoluminescence measurements.
Strain modification in coherent Ge and SixGe1−x epitaxial films by ion-assisted molecular beam epitaxy
Authors: Tsai C. J. , Atwater H. A. , Vreeland T.
Published: July 2002

We have observed large changes in Ge and SixGe1−x layer strain during concurrent molecular beam epitaxial growth and low-energy bombardment. Layers are uniformly strained, coherent with the substrate, and contain no dislocations, suggesting that misfit strain is accommodated by free volume changes associated with injection of ion bombardment induced point defects. The dependence of layer strain on ion energy, ion-atom flux ratio, and temperature is consistent with the presence of a uniform dispersion of point defects at high concentration. Implications for distinguishing ion-surface interactions from ion-bulk interactions are discussed.
Crystallization of amorphous Si on a glass substrate through nucleation by Si+ ion implantation
Authors: Yamaoka Tomonori , Oyoshi Keiji , Tagami Takashi , Arima Yasunori , Yamashita Ken , Tanaka Shuhei
Published: July 2002

Crystallization of amorphous Si films on a glass substrate by Si+ implantation (acceleration energy: 180 keV, beam current density: 10 μA/cm, ion dose: 1×1017 ions/cm2) was performed without external heating of the substrate. Transmission electron microscopy images of the crystallized specimens lead to the following conclusions: (1) crystallization was achieved through bulk nucleation by Si+ implantation, which is a low temperature and rapid process compared with the ordinary thermal process, (2) the crystallization is strongly related to the ion-solid interaction, not due to ‘‘pure’’ thermal annealing by ion beam heating.
Vapor deposition of diamond thin films on various substrates
Authors: Lee Y. H. , Bachmann K. J. , Glass J. T. , LeGrice Y. M. , Nemanich R. J.
Published: July 2002

The growth of diamond films on various polycrystalline metal and (001) Si substrates by biased hot-filament chemical vapor deposition is discussed. The deposited films have been characterized by scanning electron microscopy, x-ray diffraction, Auger electron spectroscopy, and Raman spectroscopy. Films grown on Si, Ni, and W exhibited the best quality according to Raman sp3/sp2 peak intensity ratios and the full width at half maximum of the 1332 cm−1 Raman peak. The relationship between this quality and substrate properties such as surface energy and lattice parameter is discussed. Also, the residual stress in the film as measured by the Raman peak shift is correlated with the thermal expansion coefficient of the substrate.
Nb/AlOx/Nb trilayer process for the fabrication of submicron Josephson junctions and low-noise dc SQUIDs
Authors: Bhushan M. , Macedo E. M.
Published: July 2002

A trilayer deposition process for making high quality all-refractory Nb/AlOx/Nb Josephson junctions is described. The sputtering parameters were optimized to deposit very uniform Al films, less than 5 nm in thickness. We found that it was essential to keep the substrate temperature below 40 °C during Al deposition but not during Nb depositions. Rapid anodization of the Nb counterelectrode allowed us to use positive photoresist as an anodization mask even for submicron geometries. The dc superconducting quantum interference devices made with this process have the lowest intrinsic energy sensitivity reported to date for an all-refractory technology.
Simple approximation for Fermi energy in nonparabolic semiconductors
Authors: Altschul V. , Finkman E.
Published: July 2002

We propose a simple approximation relating the Fermi energy to carrier concentration in both parabolic and nonparabolic semiconductors. The solution is in the form of a polynomial correction to Boltzmann’s approximation of semiconductor statistics. The method is similar to the Joyce–Dixon series approximation, but uses polynomial regression to obtain series coefficients which extends the range of the model’s validity. For nonparabolic semiconductors, polynomial coefficients are calculated using Kane’s k■p model for the density of states. The new approximation demonstrates an acceptable accuracy for band gaps larger than 2 kT and for the Fermi energy up to 10 kT. The expression is simple and should be useful in the modeling of advanced semiconductor devices.
Fluence-dependent transmission of polyimide at 248 nm under laser ablation conditions
Authors: Pettit G. H. , Sauerbrey R.
Published: July 2002

Transmission experiments on thin polyimide films under laser ablation conditions using 248 nm KrF laser radiation have been performed. The transmitted temporal pulse shapes and the transmittted intensity show fluence-dependent absorption as predicted by a recent theoretical description of the pulsed ultraviolet laser ablation process.
Optical waveguides in crystalline organic semiconductor thin films
Authors: Zang D. Y. , Shi Y. Q. , So F. F. , Forrest S. R. , Steier W. H.
Published: July 2002

Optical waveguiding in a crystalline organic semiconductor, namely, 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA), has been demonstrated in slab and rib waveguides using both end-fire and grating coupling at λ 1.064 μm. The effective indices of the transverse electric (TE) modes measured by means of grating coupling are in good agreement with theoretical prediction. A very low propagation loss of 2.5 dB/cm in a PTCDA rib waveguide has been determined from measurements of the scattered light intensity from the top surface of the guide.
Preparation of Bi4Ti3O12 films on a single-crystal sapphire substrate with electron cyclotron resonance plasma sputtering
Authors: Masumoto H. , Goto T. , Masuda Y. , Baba A. , Hirai T.
Published: July 2002

Bi-Ti-O oxide thin films were prepared on a sapphire single-crystal substrate by electron cyclotron resonance (ECR) plasma sputtering. The target used was a sintered Bi4Ti3O12(BIT) and the substrate was controlled in the temperature range 400–640 °C(Tsub). The film sputtered at Tsub=400 °C was a pyrochlore type oxide(Bi2Ti2O7), which changed to a Bi4Ti3O12 oxide in the polycrystalline state at 500 °C and in the single crystalline state at 640 °C. In the film sputtered at 640 °C, the (001) plane of the Bi4Ti3O12 grew parallel to the (112̄0) and (11̄02) planes of the sapphire substrate, and the (104) plane of Bi4Ti3O12 grew parallel to the (0001) plane of the sapphire substrate. The deposition rate was about 200 Å/min independent of the sputtering conditions.
High deposition rate laser direct writing of Al on Si
Authors: Lee H. W. , Allen S. D.
Published: July 2002

We report, for the first time, the direct write laser patterning of highly conductive Al from a liquid precursor, triisobutylaluminum (TIBA). Al wires were written on Si with a scanned Ar+ laser from liquid TIBA at speeds of up to several mm/s. Wires 3 μm wide by 1 μm high with a resistivity of 5.6 μΩ cm were routinely achievable.
Bonding by atomic rearrangement of InP/InGaAsP 1.5 μm wavelength lasers on GaAs substrates
Authors: Lo Y. H. , Bhat R. , Hwang D. M. , Koza M. A. , Lee T. P.
Published: July 2002

A technique, namely bonding by atomic rearrangement has been invented to realize high quality heteroepitaxy for lasers and optoelectronics. High performance lasers of 1.5 μm wavelength have been fabricated on GaAs substrates using this method. The laser has the same threshold current and quantum efficiency as lasers on InP substrates. No performance degradation has been observed. The transmission electron microscopic results show that the heteroepitaxy is excellent, without a single threading dislocation or stacking fault.
Metastable behavior of deep levels in hydrogenated GaAs
Authors: Cho Hoon Young , Kim Eun Kyu , Min Suk-Ki , Chang K. J. , Lee Choochon
Published: July 2002

New metastable behavior of deep levels is found in hydrogenated GaAs doped with Si. A deep level at 0.60 eV below the conduction-band minimum (Ec) is generated during hydrogenation and shows metastable for the Ec − 0.42 eV trap. From the defect transformations observed in biased anneals, these defects are found to be metastable defects associated with hydrogen atoms. Especially, the 400 K biased-anneal experiments indicate that an Ec−0.33 eV trap could be an electric field induced defect, transformed from other intrinsic defects. The Ec − 0.60 eV trap in hydrogenated GaAs could be a hydrogen complex associated with Ec − 0.42 eV trap and the hydrogen atom plays an important role in a metastability of deep level defects in GaAs.
Stress in metal lines under passivation; comparison of experiment with finite element calculations
Authors: Greenebaum Barbara , Sauter Anne I. , Flinn Paul A. , Nix William D.
Published: July 2002

The elastic strain in Al-0.5% Cu metal lines under silicon nitride passivation has been determined by x-ray diffraction. The experimental stress tensor calculated from these strain values is in excellent agreement with the results of a finite element model calculation. The intrinsic stress in the dielectric plays no role in influencing the stress in the metal; only thermal stress effects are important.
Quantitative evaluation of elastic properties of LiTaO3 crystals by line-focus-beam acoustic microscopy
Authors: Kushibiki J. , Takahashi H. , Kobayashi T. , Chubachi N.
Published: July 2002

The line-focus-beam acoustic microscope system is applied to investigate the elastic properties of LiTaO3. Elastic inhomogeneities are detected quantitatively as a significant variation of leaky surface acoustic wave (LSAW) velocities in X-112.2°Y LiTaO3 wafers. Large changes, about 2.5%, in LSAW velocities are observed in some wafers, which correspond to a difference between the velocities for single and multidomains. One of the causes is found to be in the poling process during wafer fabrication.
Near-unity quantum efficiency of AlGaAs/GaAs quantum well infrared detectors using a waveguide with a doubly periodic grating coupler
Authors: Andersson J. Y. , Lundqvist L.
Published: July 2002

Quantum well infrared detectors based on a waveguide with a doubly periodic grating coupler are shown to provide quantum efficiencies of nearly unity with respect to unpolarized polarization. This is a factor of six larger than for a conventional 45° polished edge detector with the same quantum well characteristics. As a further advantage the detector response becomes nearly insensitive to the polarization direction of the incident radiation. Detectors have been fabricated and tested. Measurements lead to a maximum quantum efficiency of 92% with respect to unpolarized radiation, with a response linewidth =0.8 μm, thus confirming theory.
Quantum effect in the accumulation layer on field-induced photoluminescence of double-barrier resonant tunneling structures
Authors: Wu J. S. , Chang K. H. , Lee C. P. , Chang C. Y. , Liu D. G. , Liou D. C.
Published: July 2002

The photoluminescence (PL) of double-barrier resonant tunneling structures (DBRTSs) with undoped electrodes under bias has been studied. The strong band bending across the cathode causes the quantum size effect in the accumulation layer. The resonant tunneling of electrons from the first excited quantum level in the accumulation layer produces a kink in the current-voltage characteristic. It is found that the PL intensity from the quantum well (QW) as a function of bias sharply peaks at the voltage corresponding to the kink. This provides evidence of the interaction between the first excited quantum state in the accumulation layer and the resonant state in the QW.
Native-oxide stripe-geometry In0.5(AlxGa1−x)0.5P-In0.5Ga0.5P heterostructure laser diodes
Authors: Kish F. A. , Caracci S. J. , Holonyak N. , Dallesasse J. M. , Sugg A. R. , Fletcher R. M. , Kuo C. P. , Osentowski T. D. , Craford M. G.
Published: July 2002

Data are presented demonstrating the formation of stable, device-quality native oxides from high Al composition In0.5(AlxGa1−x)0.5P (x ∼0.9) via reaction with H2O vapor (in N2 carrier gas) at elevated temperatures (≥500 °C). The oxide exhibits excellent current-blocking characteristics and is employed to fabricate continuous room-temperature stripe-geometry In0.5(AlxGa1−x)0.5P-In0.5Ga0.5P double-heterostructure laser diodes.
Electrical characteristics of Si3N4/Si/GaAs metal-insulator-semiconductor capacitor
Authors: Mui D. S. L. , Liaw H. , Demirel A. L. , Strite S. , Morkoç H.
Published: July 2002

We report on the electrical characteristics of an as-grown Si3N4/Si/n-GaAs metal-insulator-semiconductor capacitors. The GaAs layer is grown by molecular beam epitaxy and both the Si3N4 and the 10 Å Si layers are deposited using silane in a vacuum connected ultrahigh vacuum chemical vapor deposition chamber driven by an electron cyclotron resonance plasma source. The current-voltage characteristics of the Si3N4 films at high fields can be best represented by Fowler–Nordheim tunneling indicative of the high quality of the films. Hole inversion of the n-GaAs layer is clearly seen in the quasi-static capacitance-voltage curve. Despite past reports on the presence of a large amount of bulk traps in Si3N4, a hysteresis of less than 100 meV is observed in the high-frequency capacitance-voltage curves with a bias voltage swing of ±4 V. From the high-low capacitance method we estimated the interface trap density to be of the order of 4×1011 eV−1 cm−2 and from the conductance measurements we found a value of 1012 eV−1 cm−2.
Population inversion through resonant interband tunneling
Authors: Yang Rui Q. , Xu J. M.
Published: July 2002

We show in this letter that population inversion between subbands in a quantum well can be achieved through resonant interband tunneling. Two basic device configurations based on polytype heterostructures are proposed and analyzed. The estimated population inversion (n2−n1) could be as high as 3×1011/cm2 with a moderate injected current density 104 A/cm2 under a forward bias.
Photoluminescent properties of Er-doped In1−xGaxP prepared by metalorganic vapor phase epitaxy
Authors: Neuhalfen A. J. , Wessels B. W.
Published: July 2002

Atmospheric pressure metalorganic vapor phase epitaxy has been used to prepare Er-doped In1−xGaxP layers using an Er beta-diketonate precursor as the dopant source. Temperature-dependent photoluminescent properties were studied as a function of alloy composition for x=0–0.98. All the Er-doped In1−xGaxP layers exhibited strong characteristic Er3+ intra-4f-shell photoluminescent emission at 0.801 eV which was independent of the alloy composition. A thermal quenching of the Er3+-related emission was observed and depended on the alloy composition. For In1−xGaxP alloys with x≳0.2, Er3+-related luminescence is observed at 295 K.
Exchange effect in coupled two-dimensional electron gas systems
Authors: Ruden P. Paul , Wu Zhiqiang
Published: July 2002

The distribution of electrons in two parallel two-dimensional electron sheets in close proximity at low temperatures is investigated. We find that due to the exchange interaction a symmetric structure may have a ground state in which all electrons are transferred to one of the sheets. This occurs if the separation between the two systems is sufficiently small and the two-dimensional electron gas density is sufficiently low. The exchange interaction consequently leads to a bistability with respect to electron population in the two-sheet system which may be useful for future electronic devices, such as memory elements.
Conductance in very clean quantum wires and rings
Authors: Ismail K. , Washburn S. , Lee K. Y.
Published: July 2002

We have observed clear Aharonov–Bohm oscillations in single and multiply connected rings with up to 20% modulation in conductance. The oscillations persist over a very wide range of conductance (0.1–2.0 e2/h) controlled with a gate. Conductance steps as a function of gate bias are observed for the first time in relatively long single and multiple parallel wires and rings. In 2–4 μm long wires, the conductance steps are in multiples of 2e2/h. In the case of the rings, steps of 0.8 and 1.2 e2/h are observed in one and two loops, respectively.
Paramagnetic nitrogen in chemical vapor deposition diamond thin films
Authors: Hoinkis M. , Weber E. R. , Landstrass M. I. , Plano M. A. , Han S. , Kania D. R.
Published: July 2002

Electron-paramagnetic-resonance (EPR) studies demonstrate the presence of nitrogen point defects in microwave-assisted chemical vapor deposition (CVD) diamond thin films. Polycrystalline powder pattern EPR spectra are interpreted with g=2.0023, A∥=114.0 MHz, and A⊥=81.3 MHz. These spin parameters are identical to those of nitrogen in single crystal natural diamonds. Quantitative EPR and secondary ion-mass spectrometry (SIMS) results of CVD diamond thin films suggest that nitrogen point defect formation is favored over aggregate nitrogen formation.
Relaxation due to multiple longitudinal-optical-phonon emission and dissociation of exciton in Cd0.3Zn0.7S/ZnS strained-layer superlattices
Authors: Taguchi Tsunemasa , Endoh Yasuyuki , Nozue Yasuo
Published: July 2002

The optical properties of Cd0.3Zn0.7S/ZnS strained-layer superlattices grown on (100) GaAs substrates by low-pressure metalorganic chemical vapor deposition, were investigated by means of photoluminescence excitation spectroscopy and through the effect of an electric field on exciton emission. A multiple longitudinal optical-phonon emission process, related to the relaxation of excitons, has been observed for the first time in the excitation spectra. The localization of excitons has been found to be the dominant cause of the linewidth broadening. The effects on an axial electric field on exciton emission intensity and peak position have revealed that the dissociation of the localized excitons on the low-energy side of the spectrum principally takes place due to impact ionization.
Electron waveguide coupler: A four-terminal device
Authors: Wang Jian , Guo Hong , Harris R.
Published: July 2002

We model the electron waveguide coupler as a four-terminal device, by considering the scattering at the interaction region between the electron waveguides. Transmission and reflection coefficients are evaluated for a variety of system parameters. Periodic switching of the electron wave between the waveguides are observed. Complete electron transfer occurs at a transfer length as short as 400 Å. This value is much smaller than that predicted by coupled-mode theory and the device is thus experimentally realizable.
Extension of the bi-epitaxial Josephson junction process to various substrates
Authors: Char K. , Colclough M. S. , Lee L. P. , Zaharchuk G.
Published: July 2002

We report an extension of the bi-epitaxial Josephson junction process that permits the use of a variety of substrate materials and allows junctions to be placed at any level of a multilayer structure. The new materials, SrTiO3, MgO, and CeO2, serve as a base layer, a seed layer, and a buffer layer, respectively, and replace Al2O3, MgO, and SrTiO3 in the original bi-epitaxial process. This new process offers much more flexibility in designing a circuit. Bi-epitaxial junctions made with the new set of materials show much improved electrical properties, especially at 77 K. We attribute the improved electrical characteristics to a better thermal expansion match between the substrate and the thin-film layers. Important junction properties such as critical currents and junction resistances are compared to other types of grain boundary junctions.
Study of Si(001) 2×1 domain conversion during direct current and radiative heatings
Authors: Ichikawa M. , Doi T.
Published: July 2002

Si(001) 2×1 domain conversions induced by sample electric current are observed using microprobe reflection high-energy electron diffraction. Samples are heated by using both direct current and a radiative heater. It is found that diffusion anisotropy of Si adatoms exists on 2×1 surfaces and that the domain conversion velocity is proportional to a voltage applied between the sample edges. This indicates that the conversion process is induced by the diffusion anisotropy and the electric force acting on positively charged adatoms. Minor 2×1 domain terraces always spread when the sample is heated radiatively. This preserves narrow 2×1 and 1×2 domain terraces after the conversion process and during Si growth process.
Split-gate dual-electron waveguide device
Authors: Eugster Cristopher C. , del Alamo Jesús A. , Rooks Michael J. , Melloch Michael R.
Published: July 2002

A split-gate technology on an AlGaAs/GaAs heterostructure is used to implement a novel quantum-effect device which allows two electron waveguides to come into very close proximity to each other over a certain length. The field-effect action of a middle gate controls the height and width of the energy barrier between the waveguides. This allows a gradual transition from two isolated waveguides to two closely spaced waveguides and finally to the merging of both waveguides into a single broad waveguide. Two side gates can control the number of occupied subbands in each waveguide. This is confirmed by the observation of sharp 2e2/h conductance steps in each waveguide at 1.8 K as the side-gate voltage is modulated.
Critical layer thickness on (111)B-oriented InGaAs/GaAs heteroepitaxy
Authors: Anan Takayoshi , Nishi Kenichi , Sugou Sigeo
Published: July 2002

The critical layer thickness of lattice-mismatched InGaAs on (111)B-oriented GaAs was investigated by monitoring surface lattice relaxation using streak spacing on the reflection high-energy electron diffraction pattern. The critical layer thickness (hc) grown on (111)B was about twice that of a (100) under the same growth conditions. A qualitative explanation for the enhancement of hc is given based on the mechanical equilibrium theory developed by J. W. Matthews and A. E. Blakeslee [J. Cryst. Growth 27, 118 (1974)] for a strained single heterostructure.
Screening effects in (111)B AlGaAs-InGaAs single quantum well heterostructures
Authors: Moise T. S. , Guido L. J. , Barker R. C. , White J. O. , Kost A. R.
Published: July 2002

A reduction in luminescence decay time and a shift toward higher optical transition energy is observed in response to an increase in photogenerated carrier density for a p-i-n (111)B Al0.15Ga0.85As-In0.055Ga0.945As strained-layer single quantum well heterostructure. These effects, which are attributed to free-carrier screening of the strain-induced electric field, are expected to be useful for designing novel optoelectronic devices that exploit the unique electro-optic properties of (111) strained quantum wells.
Confined phonons in GaAs/AlAs superlattices with periodically corrugated interfaces
Authors: Shields A. J. , Nötzel R. , Cardona M. , Däweritz L. , Ploog K.
Published: July 2002

Using resonant Raman spectroscopy we have studied novel GaAs/AlAs superlattice (SL) structures, grown on (113) substrates, where the GaAs and AlAs layer widths vary periodically on a nanometer scale along the lateral [11̄0] direction. We observe sharp confined LO phonon lines for both (113) and simultaneously grown (001) SLs, for a range of different layer widths, whose frequencies map the bulk GaAs LO dispersion. The confined phonon lines of the (113) SLs show a side peak, which can be assigned to a mode with finite k vector parallel to the layers, induced by the lateral periodicity.
Nanometer-scale morphology of homoepitaxial diamond films by atomic force microscopy
Authors: Sutcu L. F. , Thompson M. S. , Chu C. J. , Hauge R. H. , Margrave J. L. , D’Evelyn M. P.
Published: July 2002

We present the first atomic force microscopy images of diamond films grown homoepitaxially in a hot filament reactor on (100), (111), and (110) natural diamond substrates. (100)-oriented diamond films grown with 0.3% CH4 at a substrate temperature of 810 °C were rough on the micron scale, exhibiting pyramidal features and penetration twins, while films grown with 1.6% CH4 at 1000 °C were nearly atomically smooth and showed evidence of a (2×1) reconstruction. A (111)-oriented film cracked due to tensile stress and was rough on the 50–500 nm scale, while a (110)-oriented film was rough on the micron scale but nearly atomically smooth on the 0.5–5 nm scale. Implications of the observed morphologies for diamond growth mechanisms are discussed.
Nature of band bending at semiconductor surfaces by contactless electroreflectance
Authors: Yin X. , Guo Xinxin , Pollak Fred H. , Pettit G. D. , Woodall J. M. , Chin T. P. , Tu C. W.
Published: July 2002

The nature of the band bending at semiconductor surfaces (and related carrier type) is an important materials parameter. We demonstrate that an electroreflectance mode which employs a capacitorlike configuration can conveniently be used for this evaluation in a contactless manner. Results will be presented on n- and p-type bulk GaAs, semi-insulating GaAs, nominally undoped In0.15Ga0.85As and n- and p-type GaAs and InP structures with large, almost uniform electric fields.
New doped multiple-quantum-well avalanche photodiode: The doped barrier Al0.35Ga0.65As/GaAs multiple-quantum-well avalanche photodiode
Authors: Aristin P. , Torabi A. , Garrison A. K. , Harris H. M. , Summers C. J.
Published: July 2002

The performance of doped barrier, multiple-quantum-well avalanche photodiodes (MQW APDs) is reported for the first time. Investigations are presented for a 800 Å/200 Å MQW Al0.35Ga0.65As/GaAs undoped structure with a p-n junction in each barrier. The devices exhibit low dark currents, low breakdown voltages (−10 V), and gains up to 20 for electron injection. Noise measurements show an enhancement of the electron to hole ionization rates ratio, α/β, to values between 50 and 12.5 for gains up to 5, and to 5 for gains above 5. α/β is enhanced by a factor of 6 over the bulk GaAs, and a factor of at least 2 over the simple MQW APD. The particular design we report provides medium gain and very-low-noise characteristics at low bias voltage. These experimental noise results are the best reported so far for AlGaAs/GaAs MQW APD structures.
Electrochemical sulfur passivation of GaAs
Authors: Hou X. Y. , Cai W. Z. , He Z. Q. , Hao P. H. , Li Z. S. , Ding X. M. , Wang X.
Published: July 2002

An anodic sulfurized treatment of GaAs has been developed to passivate its surfaces preventing oxidation. The photoemission core level spectra show that the surface Ga and As atoms are bonded to S atoms to form a thick sulfurized layer. No oxygen uptakes on the sulfurized GaAs surface as illustrated by the high resolution electron energy loss spectroscopy. The results of photoluminescence spectra verify that the passivated surface has low surface recombination velocity and can protect the photoassisted oxidation under laser illumination.
Frequency stabilization of an internal-mirror He-Ne laser using axial-mode beat
Authors: Sasaki A. , Okada T. , Kawai J. , Aoyama H.
Published: July 2002

A frequency stabilization of a 633-nm internal-mirror He-Ne laser using the axial-mode beat frequency has been reported. The frequency stability achieved is 2.2 MHz (4.6×10−9) for an averaging time 1 s. The amplitude stability of this stabilized laser is 0.21%.
Highly sensitive photodetector using porous silicon
Authors: Zheng J. P. , Jiao K. L. , Shen W. P. , Anderson W. A. , Kwok H. S.
Published: July 2002

A highly sensitive photodetector was made with a metal-porous silicon junction. The spectral response was measured for the wavelength range from 400 nm to 1.075 μm. It was demonstrated that close to unity quantum efficiency could be obtained in the wavelength range of 630–900 nm without any antireflective coating. The detector response time was about 2 ns with a 9 V reverse bias. The possible mechanisms are discussed.
Technique for lateral temperature profiling in optoelectronic devices using a photoluminescence microprobe
Authors: Hall D. C. , Goldberg L. , Mehuys D.
Published: July 2002

A photoluminescence microprobe technique with ≤0.2 °C and <5 μm resolution is demonstrated for measuring lateral temperature profiles in GaAs-based optoelectronic devices. The technique is used to measure the junction-heating induced temperature gradient in both single-stripe and broad-area diode lasers. The effective focal length of the thermally induced refractive index gradient lens is determined from the temperature gradient in a broad-area device.
X-ray absorption study of the atomic environment in Sb+ and Sb+/B+ implanted silicon
Authors: Allain J. L. , Bourret A. , Regnard J. R. , Armigliato A.
Published: July 2002

The electrical deactivation of Sb atoms highly implanted (2 and 5×1016 ions/cm2) in crystalline silicon is studied by the extended x-ray absorption fine structure (EXAFS) method. By following the evolution of the local atomic environment around the Sb atoms it is shown that the description of the deactivation process must take into account the existence of vacancy complexes, SbV2, in addition to the usual antimony rhombohedric precipitates. These vacancy complexes are already present after laser annealing in the 5×1016 ions/cm2 case. Co-implantation with boron delays the precipitation of Sb particles, by forming new complexes, SbBV or SbB2, with a Sb atom surrounded by two sites (B and/or vacancy).
Suppressing of island formation in surfactant-controlled solid phase epitaxy of germanium on Si(100)
Authors: Osten H. J. , Bugiel E. , Klatt J.
Published: July 2002

Smooth epitaxial 10 and 30 nm germanium layers have been grown on Si(100) by surfactant-controlled solid phase epitaxy. The layers were characterized by reflection high energy electron diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy. By depositing one monolayer antimony on top of the amorphous germanium layer it was possible to crystallize the germanium directly into a smooth epitaxial structure without any island formation. The obtained low-defect layers are relaxed.
Synthesis of diamond/β-SiC composite films by microwave plasma assisted chemical vapor deposition
Authors: Jiang X. , Klages C.-P.
Published: July 2002

A new kind of microcrystalline composite films consisting of diamond and cubic silicon carbide (β-SiC) has been synthesized in a microwave plasma assisted chemical vapor deposition process (MWCVD), using a gas mixture of hydrogen, methane, and tetramethylsilane. Single crystalline (111) silicon wafers and polycrystalline tungsten carbide, which were treated with diamond paste before the deposition, were used as substrates. Scanning electron microscopy, electron probe microanalysis, infrared absorption, Raman scattering, and x-ray diffraction analysis were performed to characterize the film quality and the crystallographic structure. The results show that the film structure and the volume fractions of diamond and β-SiC components depend mainly on the reactive gas concentrations and on the diamond nucleation density. By adjusting the reactive gas concentration, the volume fraction of the components can be varied over the film thickness. In addition, the growth texture of the diamond phases can be influenced by the β-SiC phase orientation.