bluuebunny/crossref_metadata_2025 huggingface dataset:
The paramagnetic charge state of substitutional oxygen in GaAs
Authors: Linde M. , Spaeth J.-M. , Alt H. Ch.
Published: July 2002

In oxygen-rich GaAs the optical absorption of substitutional oxygen (OAs) in the near infrared was investigated by measuring its magnetic circular dichroism (MCDA). An MCDA was discovered which originates from a paramagnetic ground state. By investigating its thermal decay kinetics and its dependence on optically induced recharging processes involving EL2 defects and by comparison with analogous local vibrational mode measurements, it could be shown that the MCDA is due to the metastable B′ charge state of the OAs centers. The B′ state is thus identified as the paramagnetic charge state of the OAs center.
Degradation of oxynitride gate dielectric reliability due to boron diffusion
Authors: Wristers D. , Han L. K. , Chen T. , Wang H. H. , Kwong D. L. , Allen M. , Fulford J.
Published: July 2002

In this letter, we report on the impact of the suppression of boron diffusion via nitridation of SiO2 on gate oxide integrity and device reliability. SiO2 subjected to rapid thermal nitridation in pure nitric oxide (NO) is used to fabricate thin oxynitride gate dielectrics. Both n+ polycrystalline silicon (polysilicon) gated n-MOS (metal–oxide semiconductor) and p+-polysilicon gated p-MOS devices were subjected to anneals of different times to study the effect of dopant diffusion on gate oxide integrity. As expected, an advanced oxynitride gate dielectric will effectively alleviate the boron-penetration-induced flatband voltage instability in p+-polysilicon gated p-MOS capacitors due to the superior diffusion barrier properties. However, such improvements are observed in conjunction with some degradation of the oxide reliability due to the boron-blocking/accumulation inside the gate dielectric. Results show that even though the oxide quality is slightly degraded for NO-nitrided SiO2 with p+-polysilicon gates, p-MOSFETs (metal–oxide semiconductor field effect transistors) with these dielectrics still show improved interface stability as compared to conventional SiO2 due to the reduced boron penetration into the Si/SiO2 interface and underlying channel region.
InGaN multi-quantum-well structure laser diodes grown on MgAl2O4 substrates
Authors: Nakamura Shuji , Senoh Masayuki , Nagahama Shin-ichi , Iwasa Naruhito , Yamada Takao , Matsushita Toshio , Kiyoku Hiroyuki , Sugimoto Yasunobu
Published: July 2002

InGaN multi-quantum-well (MQW) structure laser diodes fabricated from III-V nitride materials were grown by metalorganic chemical vapor deposition on (111) MgAl2O4 substrates. The mirror facet for a laser cavity was formed by polishing III-V nitride films grown on (111) MgAl2O4 substrates. As an active layer, the InGaN MQW structure was used. The laser threshold current density was 8 kA/cm2. At a current above laser threshold, stimulated emission was observed with a sharp peak of light output at 410 nm that had a full width at half-maximum of 2.1 nm under pulsed current injection at room temperature.
Interface states in nitrogen incorporated gate oxides
Authors: Hirabayashi Kanji
Published: July 2002

In this letter, we calculate the interface state energy in nitrogen incorporated gate oxides by using a one-dimensional two-band model and Penn’s model connecting the refractive index with typical band gap. We estimate the number of dangling bonds which we consider to be the origin of the interface states by the minimization of the free energy. The calculated results seem to explain qualitatively the recent experimental data on NO annealed oxides.
A distance regulation scheme for scanning near-field optical microscopy
Authors: Dräbenstedt A. , Wrachtrup J. , von Borczyskowski C.
Published: July 2002

In this letter we present a detection scheme for shear force distance regulation in scanning near-field optical microscopy. Instead of an optical detection of the amplitude of tip vibrations and damping due to shear forces, a piezoelectric pickup has been developed. It is shown that the signal obtained with this pick up is of comparable or even superior sensitivity than the conventional optical scheme and can be easily incorporated into every near-field microscope. Because of its easy implementation and adjust free performance, the method has the potential to considerably simplify the usage of near-field microscopes.
Effects of hydrogen on structural relaxation and defect evolution in amorphous silicon
Authors: Hiroyama Y. , Motooka T. , Suzuki R. , Hirano Y. , Sato F.
Published: July 2002

Hydrogenation effects on the structural relaxation and defect evolution in amorphous silicon (a-Si) prepared by ion implantation and evaporation have been investigated using Raman scattering spectroscopy and positron lifetime measurements. Bond angle deviation Δθ in nonhydrogenated a-Si was significantly reduced due to 300 °C annealing in atomic hydrogen atmosphere. This indicates that the reduction in Δθ of hydrogenated amorphous silicon (a-Si:H) is not only due to relaxation during the deposition process of a-Si:H films as proposed by Jackson et al. [Philos. Mag. B 64, 611 (1991)] but also due to posthydrogenation of nonhydrogenated a-Si. It was also found that agglomeration of vacancy-type defects in evaporated a-Si during 450 °C annealing is enhanced after posthydrogenation, while no remarkable enhancement can be seen in a-Si prepared by ion implantation.
Theory of the spectral line shape and gain in quantum wells with intersubband transitions
Authors: Gelmont Boris , Gorfinkel Vera , Luryi Serge
Published: July 2002

We investigate the spectral line shape of radiative intersubband transitions in a quantum well as determined by two factors: the electron scattering rate from states of given energy and the mass difference between the two subbands involved. The interplay between these factors leads to an essentially non-Lorentzian form of the spectral line. We develop an analytic theory of the line shape and calculate the dependence of the intersubband optical gain in a quantum well on both the population inversion and the temperature. Under typical conditions, the effect of electron temperature on the gain is similar to that of the lattice temperature, which points to the importance of hot carrier effects in understanding the behavior of intersubband lasers.
Growth and characterization of epitaxial Mo/NbN superlattices
Authors: Madan A. , Chu X. , Barnett S. A.
Published: July 2002

Epitaxial Mo/NbN superlattices were grown on MgO(001) substrates by reactive dc magnetron sputtering. The epitaxial relationship between the bcc metal and the NaCl (B1)-structure compound is Mo(001) ∥NbN(001), Mo[110]∥NbN[010], and the lattice mismatch is 1.4% given the 45° rotation about the (001). Cross-sectional transmission electron microscope images show well-defined and relatively planar layers. High angle x-ray diffraction results show up to 25 superlattice reflections extending over ≊30° in 2θ. Kinematical model fits to the x-ray diffraction data suggest that the interface widths were only ≊0.3 nm, presumably because of the immiscibility of Mo and NbN. Initial nanoindentation results indicate hardness values of ≊28 GPa, about 3 times the rule-of-mixtures value.
Surface photoabsorption study of the effect of V/III ratio on ordering in GaInP
Authors: Murata H. , Hsu T. C. , Ho I. H. , Su L. C. , Hosokawa Y. , Stringfellow G. B.
Published: July 2002

Cu–Pt ordering is widely observed in Ga0.5In0.5P layers grown by organometallic vapor phase epitaxy. The degree of order is a strong function of the input partial pressure of the phosphorus precursor, i.e., the V/III ratio, during growth. By observing the surface structure using in situ surface photoabsorption (SPA) measurements, the concentration of [1̄10]-oriented P dimers, characteristic of the (2×4) reconstructed surface, has been measured as a function of the growth conditions. For growth at 670 °C, the P-dimer concentration is found to increase systematically as the input tertiarybutylphosphine pressure is increased from 10 to 200 Pa. This corresponds directly to a monotonic increase in the degree of order, measured using transmission electron microscopy and low-temperature photoluminescence. These data strongly suggest that the (2×4) surface reconstruction is necessary for formation of the Cu–Pt structure. The step structure at the surface was also observed for these layers using atomic force microscopy. For high V/III ratios the structure of the layers grown on exactly (001) oriented GaAs substrates consists of islands surrounded mainly by bilayer (5.7 Å) steps. As the V/III ratio is reduced, the step height transforms to 2.8 Å (one monolayer).
Observation of internal field in LiTaO3 single crystals: Its origin and time-temperature dependence
Authors: Gopalan Venkatraman , Gupta Mool C.
Published: July 2002

The measured polarization hysteresis loop for a Z-cut LiTaO3 crystal was found to be asymmetric about the field axis indicating the presence of an in-built internal field in the crystal of 5 kV/mm in the direction of the original polarization in the virgin crystal. Upon polarization reversal under electric field, the internal field tends to realign along the new polarization direction. Systematic time–temperature dependence of this realignment process was carried out. At room temperature, this realignment process was incomplete even after many days, while above 200 °C, the recovery process takes less than 30 s. Conductivity measurements also indicate an exponential increase in the dc conductivity of the sample above 200 °C with an activation energy of 1.55 eV. Further experiments related to the behavior of the internal field with change in sample thickness and surface removal revealed that the internal field is a volume effect. Possible origins of this field based on point defect chemistry of the crystal are discussed.
Low-frequency noise in 4H–silicon carbide junction field effect transistors
Authors: Palmour J. W. , Levinshtein M. E. , Rumyantsev S. L. , Simin G. S.
Published: July 2002

Low frequency noise in 4H-silicon carbide junction field effect transistors (JFETs) has been investigated. JFETs with a buried p+n junction gate were manufactured by CREE Research Inc. Very low noise level has been observed in the JFETs. At 300 K the value of Hooge constant α is as small as α∼10−5 and the α value can be decreased by an appropriate annealing to α∼2×10−6. It has been shown that even these extremely low noise values are determined not by the volume noise sources but by the noise at the SiC–SiO2 interface.
Metalorganic chemical vapor deposition of ferroelectric SrBi2Ta2O9 thin films
Authors: Li Tingkai , Zhu Yongfei , Desu Seshu B. , Peng Chien-Hsiung , Nagata Masaya
Published: July 2002

Ferroelectric layered-oxides SrBi2Ta2O9 thin films were prepared on Pt coated Si wafers and single-crystal sapphire by metalorganic chemical vapor deposition (MOCVD). The films were specular and crack-free and showed complete crystallization at temperatures between 650 and 700 °C. Good ferroelectric properties were obtained for a 200 nm thick film with Pt electrodes: 2Pr and Ec were about 8.3 μC/cm2 and 60 kV/cm, respectively. The leakage currents were as low as 8×10−9 A/cm2 at 150 kV/cm. The films also showed fatigue-free characteristics: no fatigue was observed up to 1.4×1010 switching cycles. These high quality MOCVD films make high-intensity (≳1 Mbit) nonvolatile memory devices possible.
AlGaAs/GaAs wire and box structures prepared by molecular-beam epitaxial regrowth on in situ patterned GaAs substrates
Authors: López M. , Tanaka N. , Matsuyama I. , Ishikawa T.
Published: July 2002

We have developed a processing technique which is conducted entirely under an ultrahigh vacuum environment, called in situ electron-beam (EB) lithography, to pattern GaAs substrates on which AlGaAs/GaAs wire and box structures are subsequently regrown. In this technique a thin GaAs oxide layer is selectively formed by EB-stimulated oxidation under a controlled oxygen atmosphere, and is then used as a mask material to define mesa stripes and mesa squares by Cl2 gas etching. Subsequently, the initial mesa size is reduced by the regrowth of a GaAs layer. Finally, AlGaAs/GaAs wire and box structures are fabricated on the top of the mesas by the growth of a quantum well. These structures were characterized by cathodoluminescence measurements at 77 K.
High quality CuInSe2 films grown on pseudo-lattice-matched substrates by molecular beam epitaxy
Authors: Niki S. , Fons P. J. , Yamada A. , Kurafuji T. , Chichibu S. , Nakanishi H. , Bi W. G. , Tu C. W.
Published: July 2002

CuInSe2 films have been grown by molecular beam epitaxy on pseudo-lattice-matched substrates that consist of a 1-μm-thick In0.29Ga0.71As layer grown on a linearly composition-graded InxGa1−xAs buffer (0≤x≤0.29) grown in turn on GaAs (001). The properties of these films have been compared with those of the films grown directly on GaAs (001). High resolution x-ray diffraction analysis on CuInSe2 grown on pseudo-lattice-matched substrates indicated substantial reduction on residual strain in the CuInSe2 films. A photoluminescence spectrum dominated by sharp free exciton emissions has been observed for the first time from CuInSe2 films indicative of significant improvement in crystalline quality and substantial reduction in the point defect density.
Interband impact ionization by terahertz illumination of InAs heterostructures
Authors: Markelz A. G. , Asmar N. G. , Brar B. , Gwinn E. G.
Published: July 2002

Experimental studies of InAs heterostructures illuminated by far-infrared (FIR) radiation reveal an abrupt increase in the charge density for FIR intensities above a threshold value that rises with increasing frequency. We attribute this charge density rise to interband impact ionization in a regime in which ωτm∼1, where τm is the momentum relaxation time, and f=ω/2π is the FIR frequency. The dependence of the density rise on the FIR field strength supports this interpretation, and gives threshold fields of 3.7–8.9 kV/cm for the frequency range 0.3–0.66 THz.
Co silicide formation on SiGeC/Si and SiGe/Si layers
Authors: Donaton R. A. , Maex K. , Vantomme A. , Langouche G. , Morciaux Y. , St. Amour A. , Sturm J. C.
Published: July 2002

The reaction of Co with epitaxial SiGeC/Si layers is investigated and compared to the reaction of Co with SiGe/Si layers. The sequence of phase formation is the same as the reaction of Co with monocrystalline Si, however, cobalt disilicide is formed at much higher temperatures. The presence of C further delays the disilicide formation, as a result of C accumulation at the silicide/substrate interface during the reaction, which blocks the Co diffusion paths. The CoSi2 layers thus formed exhibit a preferential (h00) orientation. The slow supply of Co atoms to the silicide/Si interface, due to the blocking of Co diffusion paths by Ge and C, is believed to be the reason for this epitaxial alignment.
Self-formed InGaAs/GaAs quantum dot superlattice and direct observation on strain distribution in the capped superlattice
Authors: Pan Dong , Zeng Y. P. , Wu J. , Wang H. M. , Chang C. H. , Li J. M. , Kong M. Y.
Published: July 2002

We have demonstrated a 20 period dislocation-free InGaAs/GaAs quantum dot superlattice which is self-formed by the strain from the superlattice taken as a whole rather than by the strain from the strained single layer. The island formation does not take place while growing the corresponding strained single layer. From the variation of the average dot height in each layer, the strain distribution and relaxation process in the capped superlattice have been examined. It is found that the strain is not uniformly distributed and the greatest strains occur at two interfaces between the superlattice and the substrate and the cap layer in the capped superlattice.
High-sensitivity ferromagnetic resonance measurements on micrometer-sized samples
Authors: Zhang S. , Oliver S. A. , Israeloff N. E. , Vittoria C.
Published: July 2002

Ferromagnetic resonance measurements were taken on a 4 μm diam disk using a planar microwave transmission line device. The absorption modes of a sample placed on this device can be measured by monitoring the microwave power transmitted across the device while a swept magnetic field varies the sample absorption through resonance. Results for the disk, which was etched from a 105 nm thick amorphous Fe80B15Si5 film, followed the Kittel model over the frequency range from 2 to 20 GHz, in agreement with parameters measured on 5 mm diam disks by a microwave cavity. These results indicate the device has a sensitivity of 3×109⋅ΔH spins, almost two orders of magnitude better than microwave cavity measurements.
Metalorganic vapor-phase epitaxy of cubic AlxGa1−xN alloy on a GaAs (100) substrate
Authors: Nakadaira Atsushi , Tanaka Hidenao
Published: July 2002

Cubic AlxGa1−xN was grown on a GaAs (100) substrate by using low-pressure metalorganic vapor-phase epitaxy with a GaN buffer layer grown at low and high temperatures. The high-growth–temperature GaN layer improved the quality of the cubic AlxGa1−xN. Also, the AlN molar fraction could be controlled by changing the carrier gas flow of trimethylaluminum. The AlxGa1−xN epitaxial layers in the range of 0⩽x⩽0.23 exhibited strong near-band-edge photoluminescence at room temperature. Their photoluminescence peak energies show a linear dependence on the molar fraction.
Ti and Ca substitution in SrRuO3 thin films by sequential deposition process
Authors: Miéville L. , Geballe T. H. , Antognazza L. , Char K.
Published: July 2002

We report on the growth and properties of (Sr1−xCax)RuO3 and Sr (Ru1−xTix)O3 thin films obtained by sequential deposition of submonolayers from end members of each compound. Magnetization measurements as well as transport properties exhibit a very different behavior for each type of substitution. A simple model, which assumes a random distribution of the substituted sites, allows us to account quantitatively for the reduction of the magnetization with increased doping and further confirms the homogeneity of our samples. A strong distortion due to the presence of the Ti on the Ru site could explain the different behavior observed between both types of doping.
Oxidation of Si(100) in nitric oxide at low pressures: An x-ray photoelectron spectroscopy study
Authors: Kamath A. , Kwong D. L. , Sun Y. M. , Blass P. M. , Whaley S. , White J. M.
Published: July 2002

Ultrathin (8–23 Å) silicon oxynitrides have been studied in the temperature range of 560–1000 °C in 4 Torr of NO using a sequential growth and analysis approach. X-ray photoelectron spectroscopy indicates that with increasing growth temperature and time, a bonding structure with predominantly Si–O rather than Si–N formation is favored. Simultaneously, the average volume fraction of N (N/N+O) in the dielectric decreases, as a consequence of which the N1s binding energy increases by 0.2–0.8 eV from its initial value of 397.8 eV at a thickness of 8 Å. A correlation of the electrical characteristics of NO grown oxynitrides with nitrogen content and location has been made. A film growth mechanism that takes into account the removal of previously incorporated N by NO is also proposed.
Stimulated emission at 34 K from an optically pumped cubic GaN/AlGaN heterostructure grown by metalorganic vapor-phase epitaxy
Authors: Nakadaira Atsushi , Tanaka Hidenao
Published: July 2002

A cubic GaN/AlGaN heterostructure has been grown on a GaAs (100) substrate by metalorganic vapor-phase epitaxy under low V/III ratio conditions, which resulted in a flat GaN layer. Stimulated emission was observed at 387 nm from the cleaved edge of an optically pumped cubic GaN/AlGaN heterostructure at 34 K. The threshold power density was 2.4 MW/cm2.
Influence of nanoscale surface curvature on prenucleation phenomena in chemical vapor deposition diamond growth
Authors: Louchev O. A. , Sato Y. , Dennig P. A.
Published: July 2002

The problem of adsorption desorption of methyl radicals on a surface with nanoscale curvature is numerically studied for typical chemical vapor deposition diamond growth conditions. Surface profiles with concave nanoscale curvature lead to an increase in the energy of adsorption, which can enhance the nucleation of the new phase on the substrates. Moreover, the nanoscale curvature is even able to provoke a nucleation of the new phase on substrates which do not have an affinity for nucleation.
Epitaxial growth of Y2O3 films on Si(100) without an interfacial oxide layer
Authors: Choi S. C. , Cho M. H. , Whangbo S. W. , Whang C. N. , Kang S. B. , Lee S. I. , Lee M. Y.
Published: July 2002

Heteroepitaxial Y2O3 films were grown on Si(100) substrates by the technique of reactive ionized cluster beam deposition. The crystallinity of the films was investigated with reflection high energy electron diffraction (RHEED), glancing angle x-ray diffraction (GXRD), and the interface was examined by high resolution transmission electron microscopy (HRTEM). Under the condition of 5 kV acceleration voltage at the substrate temperature of 800 °C, the Y2O3 film grows epitaxially on the Si(100) substrate. RHEED and GXRD results revealed that the epitaxial relationship between Y2O3 and Si(100) is Y2O3(110)//Si(100), and HRTEM observation showed a sharp interface without an amorphous layer.
Release of metal impurities from structural defects in polycrystalline silicon
Authors: McHugo Scott A.
Published: July 2002

Metal impurity release from structural defects in polycrystalline silicon was studied following thermal treatments, and, in addition, a correlation between impurity distributions and structural defects was established. Impurities were mapped with synchrotron-based x-ray fluorescence in the as-grown state, after rapid thermal annealing and following aluminum gettering treatments. The goal of this work was to determine if impurity release from structural defects limits gettering of metal impurities. The results reveal that nickel and copper metal impurities are primarily found at dislocations in as-grown crystals, and the release of these impurities from defects occurs rapidly with no apparent barrier to dissolution. Gettering treatments dissolved metal impurity precipitates to <2–5 nm in radii; however, the material performance was not greatly enhanced.
Reconfigurable optical properties in InGaN/GaN quantum wells
Authors: Shmagin I. K. , Muth J. F. , Kolbas R. M. , Mack M. P. , Abare A. C. , Keller S. , Coldren L. A. , Mishra U. K. , DenBaars S. P.
Published: July 2002

Reconfigurable optical properties were studied in InGaN/GaN multiple quantum well (MQW) structures. It was observed that a short time exposure to a high intensity ultraviolet light results in long term, but reversible changes of the optical properties of InGaN/GaN MQW samples. The photoinduced changes can be observed using an optical microscope under low intensity ultraviolet light and are visible as a high contrast pattern. The retention time at room temperature for 12 and 20 MQW samples was longer than five days and four weeks, respectively. The effect was studied at room and cryogenic temperatures.
High spatial resolution spectroscopy of a single V-shaped quantum wire
Authors: Bellessa J. , Voliotis V. , Grousson R. , Wang X. L. , Ogura M. , Matsuhata H.
Published: July 2002

We report on microscopic photoluminescence of a single V-shaped AlGaAs/GaAs quantum wire. The experiments are performed at low temperature by selectively exciting 1 μm2 of the sample. The main photoluminescence line is split into sharp peaks of width less than 0.5 meV and separated by a few meV. The energy position and the intensity of the peaks are characteristic of the scanned quantum wire. First microphotoluminescence results suggest that localization phenomena are predominant in the quantum wire. They are due to the formation of extended monolayer-step islands, larger than the exciton radius, as in the case of high-quality quantum wells.
Effects of buffer layer on formation of domain boundaries in epilayer during film growth of GaN by low-pressure metal–organic vapor phase epitaxy on sapphire substrates
Authors: Cheng Lisen , Zhang Ze , Zhang Guoyi , Yu Dapeng
Published: July 2002

Twinning was observed in a GaN buffer layer. The twin boundaries in the buffer layer can extend into the epitaxial layer to form domain boundaries during growth of the epilayer. The domain boundaries, which initiated from the twin boundaries in the buffer layer, are determined to be inversion domain boundaries.
Synthesis of high-temperature superconductive and colossal magnetoresistive surfaces on insulating particles
Authors: Kumar D. , Fitz-Gerald James , Singh Rajiv K.
Published: July 2002

The surfaces of insulating alumina particles have been coated with high-temperature superconducting YBa2Cu3O7−x and colossal magnetoresistive Pr0.65Ba0.05Ca0.3MnO3−x films. These coatings on particulate surfaces have been realized using a technique which is based on laser-assisted generation of a homogeneous flux of ablated materials in front of a fluidized bed of host particles. The coated particulates have been characterized using scanning electron microscopy, energy dispersive x-ray analysis, Auger electron spectroscopy, and superconducting quantum interference device magnetometer.
Low frequency noise in β-FeSi2/n-Si heterojunctions
Authors: Tassis D. H. , Dimitriadis C. A. , Brini J. , Kamarinos G. , Angelakeris M. , Flevaris N.
Published: July 2002

Low frequency noise of β-FeSi2/n-Si heterojunctions has been systematically studied with the silicide layer formed by conventional furnace and rapid thermal annealing processes. The noise was found to exhibit 1/f behavior attributed to fluctuations of the generation-recombination current at the interface states. It is shown that noise measurements provide a means of calculating the density and energy distribution of the interface states. The results show that the interface state density is significantly reduced when the silicide is formed by rapid thermal annealing process.
Low-threshold InAlGaAs vertical-cavity surface-emitting laser arrays using transparent contacts
Authors: Chua C. L. , Thornton R. L. , Treat D. W. , Kneissl M. , Dunnrowicz C.
Published: July 2002

We present top-emitting all-epitaxial planar laterally oxidized vertical-cavity surface-emitting lasers employing transparent indium–tin–oxide electrodes. The transparent contacts facilitate device fabrication and offer significantly denser device packing than similar planar laterally oxidized structures using metal contacts. The InAlGaAs-based devices operate at a wavelength of 817 nm with a minimum threshold current of 175 μA.
Band alignment in Si1−yCy/Si(001) heterostructures
Authors: Williams R. L. , Aers G. C. , Rowell N. L. , Brunner K. , Winter W. , Eberl K.
Published: July 2002

Photoluminescence peak energy shifts under applied [110] and [100] uniaxial stress are interpreted within the framework of a multi-band Kohn–Luttinger model which takes into account the mixing of heavy, light, and spin-orbit split-off holes within the valence band. Experimental data are presented for 0.5%, 1%, and 1.7% Si1−yCy/Si samples which are best fitted with a conduction band offset of approximately 70%. At this value of the conduction band offset, we show that small amounts of space charge induced band bending are required to explain the experimentally observed results.
GaSb vertical-cavity surface-emitting lasers for the 1.5 μm range
Authors: Koeth J. , Dietrich R. , Forchel A.
Published: July 2002

We have developed GaSb/AlGaSb vertical-cavity surface-emitting lasers (VCSELs) by using solid source molecular beam epitaxy. The reflectivity spectra of the VCSELs show a very narrow (0.9 meV) cavity resonance at 1.5 μm. cw optical pumping results in lasing at the wavelength of the cavity resonance with a laser threshold density of 530 W/cm2 at 77 K.
First-principles calculations of SiC(001) surface core level shifts
Authors: Catellani Alessandra , Galli Giulia , Gygi François
Published: July 2002

We have computed chemical shifts of core levels at clean and defected Si-terminated SiC(001) surfaces, by carrying out total energy calculations within the local density approximation of density functional theory. Our results allow one to interpret measured Si 2p core level spectra and in particular to identify the nature of the different peaks observed experimentally. Furthermore, our findings point at ad-dimers as common defects on the Si-terminated SiC(001) surface.
Ordering effect on band-gap lowering in lattice-matched InAlAs epilayers grown on InP by metal–organic chemical-vapor deposition
Authors: Han W. S. , Lee B. , Baek J. H. , Lee J.-H. , Jung B. S. , Lee E.-H. , O Byungsung
Published: July 2002

Band-gap lowering due only to the cation ordering effect is investigated in InAlAs layers grown on InP by using photoluminescence measurement. Double-crystal x-ray diffraction and Rutherford backscattering measurements confirm that both of the InAlAs epilayers studied, grown at 700 and 750 °C, are lattice matched with InP substrates. Through transmission electron diffraction measurements, it is observed that a CuPt-type ordering structure is formed in the InAlAs layers grown at 700 °C but not in the layers at 750 °C. Photoluminescence measurements at 1.7 K reveal that the band-gap energy of the ordered InAlAs is smaller by 60 meV than that of the unordered InAlAs.
Measurements of negative ion densities by absorption spectroscopy
Authors: Quandt E. , Döbele H. F. , Graham W. G.
Published: July 2002

A novel diagnostic technique for the measurement of negative ions is presented. The absorption of a cw-laser beam with a wavelength close to the maximum of the photodetachment cross section is measured. The laser beam undergoes multiple reflections through the discharge volume using a multipass cell (here a Herriott arrangement). Proof-of-principle measurements of negative hydrogen ions in a hybrid volume source are presented. The measured H− density is in agreement with results of conventional, Langmuir probe-based photodetachment measurements.
Determination of negative ion density with optical emission spectroscopy in oxygen afterglow plasmas
Authors: Ishikawa T. , Hayashi D. , Sasaki K. , Kadota K.
Published: July 2002

A diagnostic scheme for the measurement of the O− density in afterglow plasmas is proposed and demonstrated. The present method is based on the fact that excited oxygen atoms (O*) are produced by mutual neutralization between positive and negative ions (O++O−→O*+O). The absolute value of the emission coefficient εn due to O*→O+hν is determined by visible emission spectroscopy with a calibrated detection system. The O+ density nO+ is measured by a Langmuir probe combined with mass spectrometry. With the rate coefficient for the above reaction kn, the O− density can be evaluated as nO−=εn/(knnO+). In the present letter, the rate coefficient kn has been determined experimentally from nO− measured by probe-assisted laser photodetachment.
Solid phase recrystallization of ZnS thin films on sapphire
Authors: Bandić Z. Z. , Piquette E. C. , McCaldin J. O. , McGill T. C.
Published: July 2002

High quality ZnS thin films are important for light emitting diodes based on ZnS, which is a very efficient phosphor. To improve as grown, molecular beam epitaxial, (111)-oriented cubic ZnS films, where defects were introduced due to the large mismatch between ZnS and a sapphire substrate (∼20%), the ZnS was recrystallized by annealing at temperatures in the 825–1000 °C range, and sulfur pressures of 10 atm. The films have been structurally characterized by high-resolution x-ray diffraction, and electron diffraction by electron channeling patterns. Structural properties of the films annealed at temperatures above 900° have improved significantly. Tilting in the recrystallized films has been reduced more than tenfold, with the recrystallized grains being defect-free. Most films were recrystallized in the as-grown, cubic form, as shown by electron channeling patterns. The surfaces of the films have been inspected with scanning electron microscope, and on most samples they have been found to remain smooth, although on some of the films annealed at elevated temperatures we have observed hexagonal pits. The role of sulfur gas overpressure in the recrystallization has been discussed, and possible effects on film evaporation, grain boundary migration and compliancy of sapphire substrate have been analyzed.
Direct correlation of transition metal impurities and minority carrier recombination in multicrystalline silicon
Authors: McHugo Scott A. , Thompson A. C. , Périchaud I. , Martinuzzi S.
Published: July 2002

Impurity and minority carrier lifetime distributions were studied in as-grown multicrystalline silicon used for terrestrial-based solar cells. Synchrotron-based x-ray fluorescence and the light beam induced current technique were used to measure impurity and lifetime distributions, respectively. The purpose of this work was to determine the spatial relation between transition metal impurities and minority carrier recombination in multicrystalline silicon solar cells. Our results reveal a direct correlation between chromium, iron, and nickel impurity precipitates with regions of high minority carrier recombination. The impurity concentration was typically 5×1016 atoms/cm2, indicating the impurity-rich regions possess nanometer-scale precipitates. These results provide the first direct evidence that transition metal agglomerates play a significant role in solar cell performance.
Improvement in performance of electrically tunable devices based on nonlinear dielectric SrTiO3 using a homoepitaxial LaAlO3 interlayer
Authors: Jia Q. X. , Findikoglu A. T. , Reagor D. , Lu P.
Published: July 2002

Improved structural and dielectric properties of nonlinear dielectric SrTiO3 thin films on LaAlO3 substrates were accomplished by incorporating a homoepitaxial LaAlO3 interlayer between the substrate and the dielectric film. Using this interlayer, the quality factor of SrTiO3 films with high-temperature superconducting YBa2Cu3O7−x electrodes on LaAlO3 substrates was improved by more than 50% at 4.2 GHz and 4 K. This improvement, combined with no change in nonlinearity, led to greater than a 50% enhancement of the finesse factor (defined as the product of the quality factor and the fractional shift resonant frequency) for the coplanar waveguide microwave resonators. The reduced planar defect density in the SrTiO3 films was attributed to this improvement.
Observation of the Abrikosov vortex lattice in NbSe2 with magnetic force microscopy
Authors: Volodin A. , Temst K. , Van Haesendonck C. , Bruynseraede Y.
Published: July 2002

We have imaged the Abrikosov vortex lattice on the surface of a conventional superconductor with a low-temperature magnetic force microscope, which is based on commercially available piezoresistive cantilevers. The heat dissipation at low temperature is limited by operating the cantilevers at higher mechanical resonances, allowing one to improve the signal-to-noise ratio by a factor of 3. Using a Co/Au multilayer for the magnetic tip coating, the interaction with the vortices can be kept small, and it is possible to observe a stable vortex lattice on the surface of a cleaved NbSe2 crystal. The stability of the vortex lattice can be understood in terms of collective pinning effects.
Magnetoresistance of mechanically induced grain boundaries in La0.7Ca0.3MnO3 films
Authors: Srinitiwarawong Chatchai , Ziese Michael
Published: July 2002

The magnetoresistance of mechanically induced grain boundaries in La0.7Ca0.3MnO3 thin films is investigated. The grain boundaries are fabricated by a mechanical deformation of the LaAlO3 substrate prior to film deposition. During film deposition, the deformed substrate region induces some growth disorder in the film leading to a wide grain boundary. The resulting structures show a reproducible, substantial magnetoresistance in magnetic fields below 2 kG. We discuss the temperature and direction dependence of the magnetoresistance and argue that two contributions due to spin-polarized electron tunneling and the suppression of magnetic frustration by a magnetic field can be identified.
Hole trap levels in Mg-doped GaN grown by metalorganic vapor phase epitaxy
Authors: Nagai H. , Zhu Q. S. , Kawaguchi Y. , Hiramatsu K. , Sawaki N.
Published: July 2002

Hole trap levels in a Mg-doped GaN grown by metalorganic vapor phase epitaxy (MOVPE) are studied with deep level transient spectroscopy (DLTS). The Mg concentration of the sample was 4.8×1019 cm−3, but the hole concentration was as low as 1.3×1017 cm−3 at room temperature. The DLTS spectrum has a dominant peak D1 with activation energy of 0.41±0.05 eV, accompanied by two additional peaks with activation energies of 0.49±0.09 eV(D2) and 0.59±0.05 eV(D3). It was found that the dominant peak D1 consists of five peaks, each of which has different activation energy and capture cross section. A relevant model for these levels is presented in relation to the Mg–N–H complexes.
Ultrahigh density data storage from local polymerization by a scanning tunneling microscope
Authors: Ma L. P. , Yang W. J. , Xie S. S. , Pang S. J.
Published: July 2002

Ultrahigh density data storage from local polymerization on an organic thin film is demonstrated by using a scanning tunneling microscope (STM) operating in air. An organic monomer material, which may become electrical conductive by polymerization, is selected as data storage material. Films prepared by the monomer material are used for data recording. By applying a high electric field with the STM tip to realize local polymerization, highly stable recorded patterns with molecule-sized recorded marks have been performed. One recorded mark corresponds to a polymeric molecule in the film. The marks are 0.8 nm in size. The nearest distance between two recorded marks is 1.2 nm. Having been read 2000 times the recorded patterns show no discernible change.
Wavelength tuning of InAs quantum dots grown on (311)B InP
Authors: Fréchengues S. , Bertru N. , Drouot V. , Lambert B. , Robinet S. , Loualiche S. , Lacombe D. , Ponchet A.
Published: July 2002

We report on the synthesis of InAs quantum dots on (311)B InP substrates. It is found that the use of such high index surfaces allows the formation of a high density (5×1010 islands/cm2) of small InAs islands (diameter≈350 Å) on InP. Moreover, a large improvement of the size uniformity is obtained in comparison with deposition on (100) surface. The standard height deviations are ±13% and ±50% for islands grown on (311)B and (100) surfaces, respectively. Then, we show that the modification of the As/P flux sequences, after the island formation, permits the control of the quantum dot emission wavelength. The achievement of quantum dots emitting at 1.55 μm at 300 K indicates that this method is promising for telecom device making.
Effect of ion mass on the evolution of extended defects during annealing of MeV ion-implanted p-type Si
Authors: Fatima S. , Wong-Leung J. , Fitz Gerald J. , Jagadish C.
Published: July 2002

Evolution of extended defects during annealing of MeV ion-implanted p-type Si has been characterized using deep level transient spectroscopy and transmission electron microscopy. The p-type Si was implanted with Si, Ge, and Sn ions with varying energies and doses from 5×1012 to 1×1014 cm−2 then annealed at 800 °C for 15 min. For all implanted species, the critical dose for transformation from point to extended defects has been determined. The type of extended defects formed depends upon the mass of the implanted species even though the dose was adjusted to create a similar damage distribution for all implanted species.
Polymerization in nematic emulsions
Authors: Lanzo J. , Nicoletta F. P. , De Filpo G. , Chidichimo G.
Published: July 2002

This letter deals with a procedure to obtain polymer-dispersed liquid-crystal films by photopolymerization of nematic emulsions. The major advantage of such a procedure is that homogeneously micron-sized liquid-crystal droplets in an organic monomer matrix can be obtained before polymerization takes place. The electro-optical changes induced in nematic emulsions by the polymerization of the fluid matrix are reported. The effects due to the application of an external field during the polymerization process on the resulting films are also discussed.
Investigation of nanolocal fluorescence resonance energy transfer for scanning probe microscopy
Authors: Shubeita G. T. , Sekatskii S. K. , Chergui M. , Dietler G. , Letokhov V. S.
Published: July 2002

Fluorescence resonance energy transfer (FRET) has been observed between donor dye molecules deposited onto the sample surface and acceptor dye molecules deposited onto the scanning near-field optical microscope (SNOM) or atomic force microscope tip. FRET was observed only when the tip acquired a contact with the sample and took place in a region of few tens of square nanometers in size when thousands (hundreds) of molecules are involved. In view of the obtained results, the perspectives for the construction of a one-atom FRET SNOM are described.
Phonon-assisted tunneling and interface quality in nanocrystalline Si/amorphous SiO2 superlattices
Authors: Tsybeskov L. , Grom G. F. , Fauchet P. M. , McCaffrey J. P. , Baribeau J.-M. , Sproule G. I. , Lockwood D. J.
Published: July 2002

We report on the interface quality and phonon-assisted tunneling in nanocrystalline Si (nc-Si)/amorphous SiO2 (a-SiO2) superlattices (SLs) prepared by magnetron sputtering and thermal crystallization of nanometer-thick a-Si layers. Phonon-assisted tunneling is observed in a bipolar nc-Si based structure, which confirms that the nc-Si/a-SiO2 junction is not only abrupt but also nearly defect free. The conclusion is supported by capacitance–voltage measurements from which the estimated interface defect density is found to be ∼1011 cm−2 for an eight-period SL. Such high quality interfaces hold considerable promise for the development of nc-Si SL quantum devices.
Effective g* factor of two-dimensional electrons in GaN/AlGaN heterojunctions
Authors: Knap W. , Frayssinet E. , Sadowski M. L. , Skierbiszewski C. , Maude D. , Falko V. , Khan M. Asif , Shur M. S.
Published: July 2002

The conduction band parameters of two-dimensional (2D) electrons in high density GaN/AlGaN heterojunctions were studied using the cyclotron resonance and magnetotransport techniques in high magnetic fields (24 T) and low temperatures (300 mK). The Landau level splitting determined from the cyclotron resonance experiment yielded the effective mass of 2D carriers, m*=0.242±0.002 m0. The Lande g factor for the 2D electrons (g=2.06±0.04) was determined from the angular dependence of the amplitude of Shubnikov–de-Haas oscillations experiments in tilted magnetic field.
Electroluminescence from Au/(nanoscale Ge/nanoscale SiO2) superlattices/p-Si
Authors: Qin G. G. , Heng C. L. , Bai G. F. , Wu K. , Li C. Y. , Ma Z. C. , Zong W. H. , You Li-ping
Published: July 2002

Nanoscale Ge/nanoscale SiO2 superlattices (SLs) with four periods have been grown using the two-electron-beam alternation evaporating technique. Visible electroluminescence (EL) from the semitransparent Au film/(nanoscale Ge/nanoscale SiO2) SL/p-Si structures was observed when the forward bias exceeded 5 V, and their EL power efficiencies were significantly higher than that of a semitransparent Au film/nanoscale Ge particles embedded SiO2 film/p-Si structure. The effects of thicknesses of nanoscale Ge layers in the SLs and of annealing temperatures on the EL were studied. It is found that the intensity and position of the major EL peak being located in a range of 640–680 nm vary synchronously, while the EL shoulder around 520 nm remains unchanged in wavelength with increasing Ge layer thickness. The results strongly support the viewpoint that EL originates from the luminescence centers in the SiO2 layers.
Spin-wave quantization and dynamic coupling in micron-size circular magnetic dots
Authors: Jorzick J. , Demokritov S. O. , Hillebrands B. , Bartenlian B. , Chappert C. , Decanini D. , Rousseaux F. , Cambril E.
Published: July 2002

We report on the observation of spin-wave quantization in square arrays of micron-size circular magnetic Ni80Fe20 dots by means of Brillouin light-scattering spectroscopy. For a large wave-vector interval several discrete, dispersionless modes with a frequency splitting of up to 2.5 GHz were observed. The modes are identified as magnetostatic surface spin waves laterally quantized due to in-plane confinement in each single dot. The frequencies of the lowest observed modes decrease with increasing distance between the dots, thus indicating an essential dynamic magnetic dipole interaction between the dots at small interdot distances.
A pump and probe study of photoinduced internal field screening dynamics in an AlGaN/GaN single-quantum-well structure
Authors: Shikanai A. , Deguchi T. , Sota T. , Kuroda T. , Tackeuchi A. , Chichibu S. , Nakamura S.
Published: July 2002

Photogenerated carrier dynamics in an AlGaN/GaN single quantum well has been studied using a conventional degenerate pump and probe technique at room temperature. Photoinduced absorption at the exciton resonance has been observed. It is explained by the absorption coefficient change, through the quantum-confined Stark effect and the quantum-confined Franz–Keldish effect, caused by the photoinduced internal electric-field screening. In comparison with biased GaAs multiple quantum wells, a slower time evolution of differential transmission signals has been also found. Its origin is attributed to the longer carrier sweep-out time due to the potential profile of the sample in conjunction with the longer carrier recombination time.
Brittle-ductile relaxation kinetics of strained AlGaN/GaN heterostructures
Authors: Hearne S. J. , Han J. , Lee S. R. , Floro J. A. , Follstaedt D. M. , Chason E. , Tsong I. S. T.
Published: July 2002

We have directly measured the stress evolution during metal-organic chemical vapor deposition of AlGaN/GaN heterostructures on sapphire. In situ stress measurements were correlated with ex situ microstructural analysis to determine directly a critical thickness for cracking and the subsequent relaxation kinetics of tensile-strained AlxGa1−xN grown on GaN. Cracks appear to initiate the formation of misfit dislocations at the AlGaN/GaN interface, which account for the majority of the strain relaxation.
Ordering and shape of self-assembled InAs quantum dots on GaAs(001)
Authors: Zhang K. , Heyn Ch. , Hansen W. , Schmidt Th. , Falta J.
Published: July 2002

Quantitative grazing-incidence small-angle x-ray scattering experiments have been performed on self-assembled InAs quantum dots (QDs) grown by molecular-beam epitaxy. We find pronounced nonspecular diffuse scattering satellite peaks with high diffraction orders, indicating a lateral ordering in the spatial positions of the InAs QDs. The mean-dot–dot distance and correlation lengths of the dot lateral distribution are found to be anisotropic. We observe the sharpest dot distribution in the [110] direction. Additional broad diffraction peaks are observed and associated with dot facet crystal truncation rods of the {111} and {101} facet families. This suggests an octagonal-based dot shape.