bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimized random/ordered grating for an n-type quantum well infrared photodetector
Authors: Borenstain Shmuel I. , Arad U. , Lyubina I. , Segal A. , Warschawer Y.
Published: July 2002

Coupling efficiency of infrared radiation to electron intersubband transition in quantum well infrared photodetector by a two-dimensional (2D) grooved grating is examined. A resonant enhancement of the coupling efficiency at a certain optimal groove depth is predicted and confirmed experimentally. It is argued that a detector with a properly designed ordered cross grating performs better than a detector with optimized 2D random grating. In a detector with ordered grating a quantum efficiency of 75% is obtained with a doping level of only 3.5×1017 cm−3 in each quantum well and dark current density of 0.34 mA/cm2 at 78 K.
Single-event keV proton detection using a delta-doped charge-coupled device
Authors: Nikzad Shouleh , Croley Donald , Elliott S. Tom , Cunningham Thomas J. , Proniewicz W. K. , Murphy G. B. , Jones Todd J.
Published: July 2002

Using a delta-doped charge-coupled device (CCD), we have demonstrated an order-of-magnitude improvement in the low-energy cutoff for particle detection compared to conventional solid-state detectors. Individual protons with energies in the 1.2–12 keV range were successfully detected using a delta-doped, back-illuminated CCD. Moreover, it is shown that, by measuring the charge generated by the proton, it is potentially possible to use delta-doped CCDs to determine the energy of the incoming particle.
Improvement of far-field pattern in nitride laser diodes
Authors: Takeuchi T. , Detchprohm T. , Iwaya M. , Hayashi N. , Isomura K. , Kimura K. , Yamaguchi M. , Amano H. , Akasaki I. , Kaneko Yw. , Shioda R. , Watanabe S. , Hidaka T. , Yamaoka Y. , Kaneko Ys. , Yamada N.
Published: July 2002

We have clearly demonstrated a single spot in a far-field pattern of nitride-based laser diodes with a thick n-AlGaN layer/low-temperature-deposited buffer layer/sapphire. This AlGaN-based structure has realized a crack-free 1-μm-thick n-type Al0.06Ga0.94N cladding layer, leading to suppression of optical leakage from the waveguide region to the underlying layer and improvement of optical confinement. The threshold current of the laser diode is about 230 mA, which is comparable to or better than that of our laser diodes with the conventional GaN-based structure.
Role of excess As in low-temperature grown GaAs subjected to BCl3 reactive ion etching
Authors: Chang M. N. , Chuo C. C. , Lu C. M. , Hsieh K. C. , Yeh N. T. , Chyi J.-I.
Published: July 2002

The role of excess As in low-temperature (LT) grown Be doped, undoped and Si-doped GaAs subjected to BCl3/Ar reactive ion etching has been investigated using transmission electron microscopy and atomic force microscopy. Etching rate and the extent of ion damage are found to depend on the doping type and thermal treatment. For as-grown LT-GaAs, significant decrease in etching rate is observed as the dopant is changed from Be to Si. Thermal treatment by rapid thermal annealing slightly increases the etching rate of GaAs grown at low temperature while it increases the etching rate significantly for the samples grown at normal temperature. In addition, as-grown LT-GaAs also exhibits superior resistance to the ion damage of reactive ion etching.
The extension of gain spectra and accurate determination of the quasi-Fermi-level separation from measured amplified spontaneous emission spectra
Authors: Fu Liwei , Wu Linzhang , Schweizer Heinz
Published: July 2002

A method for obtaining the gain spectra of semiconductor lasers in an extended energy range from amplified spontaneous emission (ASE) spectra is presented. Hakki–Paoli gain measurement is first used to determine the quasi-Fermi-level separation. By using the fitting process proposed, a self-consistent correction in determining quasi-Fermi separation leads to a reduced error (<1 meV) and a recalibration of the intrinsic absorption coefficient is also self-consistently possible. Subsequently, with measured gain in a restricted energy range, we can obtain gain spectra in a much wider energy range by our proposed algorithm in conjunction with ASE data. The application of this method in obtaining the extended gain spectra of a double-quantum-well GaInP ridge waveguide laser is demonstrated.
Improved structural properties of SiO2 sol-gel films
Authors: González-Hernández J. , Pérez-Robles F. , Manzano-Ramı́rez A. , Ramı́rez-Bon R. , Prokhorov E. , Vorobiev Y. V. , Garcı́a-Rodrı́guez F. J.
Published: July 2002

Silicon oxide films with a small amount of alpha alumina particles embedded in the glass matrix were prepared using the sol-gel method. It is found that the structural properties of these samples are superior to those observed in similarly prepared films, but without the alumina particles. This conclusion was deduced from analysis of the oxygen diffusion measurements through the SiO2 layer, using a novel method, and from the measured dielectric breakdown field. It is found that the oxygen diffusion coefficient is much lower and the dielectric breakdown field is larger in samples with the alumina particles.
Direct observation of electron emission site on boron-doped polycrystalline diamond thin films using an ultra-high-vacuum scanning tunneling microscope
Authors: Kim Y. D. , Choi W. , Wakimoto H. , Usami S. , Tomokage H. , Ando T.
Published: July 2002

Surface morphology characteristics and electron emission properties of boron-doped polycrystalline diamond thin films grown by microwave plasma-assisted chemical-vapor deposition were investigated using an ultra-high-vacuum scanning tunneling microscope. Small secondary grains with average size less than 10 nm were observed to be on top of the isolated crystal surfaces. The current imaging tunneling spectroscopy (CITS) study revealed that high electron emission occurred at some crystalline facets while others showed relatively no measurable electron emission. The CITS study at high magnification also indicated that the electron emission was initiated at the grain boundaries rather than at the top of the grains. This observation suggests that the electrons transport through the grain-boundary conductive channels and preferentially emit at the low electron affinity facets.
Photoresponse studies of ZnSSe visible–blind ultraviolet detectors: A comparison to ZnSTe detectors
Authors: Sou I. K. , Ma Z. H. , Wong G. K. L.
Published: July 2002

This work focuses on the investigation of the difference between the photoresponse of ZnS, ZnSSe, and that of ZnSTe Schottky-barrier photodiodes, with a particular aim to reveal the underlying causes of the gradual turn-on characteristic of low-Te-containing ZnSTe Schottky barrier photodiodes. To form the bottom electrode layer for the newly developed ZnSSe diode, n-type doping of ZnSSe by incorporating Al flux during molecular beam epitaxial growth was studied. Excellent-to-good dopant activation is achieved for Se composition up to 50%. The measured photoresponse of the diodes clearly indicates that the Te isoelectronic trapping effect is responsible for the gradual turn-on characteristic of low-Te-containing ZnSTe Schottky-barrier photodiodes. The results also reveal that the ZnSSe diode, having a much better visible rejection power, is a more suitable choice for high-performance visible–blind ultraviolet detection applications.
Surface reconstruction of TiC(001) and its chemical activity for oxygen
Authors: Kuramochi H. , Takami K. , Saito A. , Kuwahara Y. , Mori Y. , Otani S. , Aono M.
Published: July 2002

The TiC(001) surface has been observed by scanning tunneling microscopy with atomic resolution in ultrahigh vacuum. After the sample was cleaned by repeated heating at ∼1300 °C, we observed the 1×1 structure. On the other hand, the √×√ structure due to the ordered carbon vacancies formed when the sample was annealed at ∼1150 °C. We demonstrated the chemical activity of carbon vacancies of both structures for oxygen. The TiC(001)-1×1 surface with intentionally increased carbon vacancies and the TiC(001)-√×√ surface changed to a defect-free 1×1 structure with a small amount of oxygen, owing to the preferential adsorption of oxygen on the carbon vacancies.
Alternative method for the activation and measurement of lateral forces using magnetically controlled atomic force microscopy
Authors: Jarvis S. P. , Tokumoto H. , Yamada H. , Kobayashi K. , Toda A.
Published: July 2002

We demonstrate the use of a different design of atomic force microscope cantilever for the study of lateral forces during a tensile transition to contact. The design of the cantilever is based on a seesaw structure which maintains sufficiently high stiffness in the normal direction and lateral scanning direction to enable stability during tip–sample approach and subsequent lateral scanning. Dynamic measurements are made by a combination of magnetic and piezo lever activation. We utilize the resonance modes of the normal and lateral tip motion in order to minimize coupling between the two signals and to increase sensitivity. High-resolution images of a strontium titanate sample are simultaneously acquired in the normal and lateral dynamic modes, and show distinctly different contrast, indicating that indeed the two interactions can be measured independently.
Ohmic contact to p-type GaAs using Cu3Ge
Authors: Aboelfotoh M. O. , Borek M. A. , Narayan J.
Published: July 2002

We have investigated ε1−Cu3Ge as an ohmic contact to p-type GaAs, and found that the ε1−Cu3Ge contact has a specific contact resistivity of 5×10−6 Ω cm2 on p-type GaAs with doping concentrations of ∼7×1018 cm−3. The ε1−Cu3Ge contact exhibits a planar and structurally abrupt interface with the GaAs, and no reaction between the contact metal and the GaAs is required for contact formation. The contact is electrically stable during annealing at temperatures up to 400 °C. It is suggested that Ge is incorporated into the GaAs as a p-type impurity resulting in a low contact resistivity. Furthermore, the addition of Ge to Cu to form ε1−Cu3Ge is found to impede the diffusion of Cu into the p-type GaAs. Along with the results reported for n-type GaAs, the present results indicate that ε1−Cu3Ge is an attractive candidate for ohmic contact formation on both n- and p-type GaAs.
Low-dielectric-constant cross-linking polymers: Film electrets with excellent charge stability
Authors: Schwödiauer Reinhard , Neugschwandtner Gerhard S. , Bauer-Gogonea Simona , Bauer Siegfried , Wirges Werner
Published: July 2002

The cross-linking low-dielectric-constant polymers benzocyclobutene (BCB) and perfluorocyclobutene (PFCB) are identified as film electrets with excellent charge stability, comparable to the members of the polytetrafluoroethylene family. BCB and PFCB films can be easily prepared on substrates by spin coating. The onset of molecular motion at the high- and low-temperature glass-like transitions is revealed by dielectric dilatometry. BCB and PFCB electret films exhibit remarkable stability regarding both negative and positive charging. They enlarge the family of charge electrets and may thus become interesting for miniaturized electret devices.
Nanometer-scale studies of Al–Ga interdiffusion and As precipitate coarsening in nonstoichiometric AlAs/GaAs superlattices
Authors: Lita B. , Ghaisas Smita , Goldman R. S. , Melloch M. R.
Published: July 2002

We have investigated the effects of post-growth annealing on Al–Ga interdiffusion and As precipitate coarsening in AlAs/GaAs superlattices grown by molecular-beam epitaxy at low temperatures. High-resolution x-ray diffraction spectra show a significant decrease in the number and intensity of satellite peaks for the ex situ annealed compared with the as-grown superlattices, a feature which is often attributed to a reduction in interface abruptness. However, our cross-sectional scanning tunneling microscopy images show significant variation in the apparent superlattice period of the ex situ annealed compared with the as-grown superlattices. For the as-grown superlattices, preferential As precipitation on the GaAs side of AlAs/GaAs interfaces is evident. In the ex situ annealed superlattices, a preference for As precipitates at the GaAs on AlAs interface is apparent, although the As precipitates are no longer restricted to the interface region. Thus, the apparent change in superlattice period is likely due to variations in As precipitate density, which may be influenced by AlAs–GaAs alloying at the AlAs/GaAs interfaces.
Direct spectral probing of energy storage in Si:Er by a free-electron laser
Authors: Gregorkiewicz T. , Thao D. T. X. , Langer J. M.
Published: July 2002

Results of a two-color spectroscopy in the visible and the mid-infrared on erbium-doped silicon (Si:Er) are presented. In the experiments, pulsed beam provided by a free-electron laser is directed on a sample under primary above-band-gap excitation with another laser. It is shown that the powerful infrared beam can be ionize carriers localized at shallow traps. Liberation of these carriers makes them available for excitation of erbium and thereby enhances the luminescence intensity. Identification of shallow levels responsible for the effect is discussed.
Comparative study of broadband electrodynamic properties of single-crystal and thin-film strontium titanate
Authors: Findikoglu A. T. , Jia Q. X. , Kwon C. , Reagor D. W. , Kaduchak G. , Rasmussen K. O/. , Bishop A. R.
Published: July 2002

We have used a coplanar waveguide structure to study broadband electrodynamic properties of single-crystal and thin-film strontium titanate. We have incorporated both time- and frequency-domain measurements to determine small-signal effective refractive index and loss tangent as functions of frequency (up to 4 GHz), dc bias (up to 106 V/m), and cryogenic temperature (17 and 60 K). The large-signal impulse response of the devices and the associated phenomenological nonlinear wave equation illustrate how dissipation and nonlinearity combine to produce the overall response in the large-signal regime.
Photoacoustic shock generation in carbon suspensions
Authors: Beveridge Andrew C. , McGrath Thomas E. , Diebold Gerald J. , Karabutov Alexander A.
Published: July 2002

This letter discusses photoacoustic shock wave generation and the origin of nonlinear sound wave generation in carbon suspensions. The Burgers equation for an inviscid fluid is solved for an exponential acoustic wave. The solution shows an increasingly steep wave form that gradually coalesces into a shock front. Large dynamic range measurements of photoacoustic waves generated by a pulsed-laser beam in carbon suspensions show the pressure in the wave to depart significantly from the predictions of linear response theory. Acoustic sound speed and amplitude measurements indicate that weak shocks are produced from the photoacoustic sound generation process rather than from nonlinear propagational effects.
Linear holographic recording at 514 nm in amorhpous As2S3
Authors: Spektor Boris , Lisiansky Michael , Shamir Joseph , Klebanov Matvei , Lyubin Victor
Published: July 2002

It is shown that the linear recording of holographic gratings can be obtained at 514 nm in the amorphous arsenic trisulfide films. While strong nonlinearity was observed during recording at room temperature, these effects were eliminated when the recording was performed at temperatures below 275 K. To verify the linearity of the recording, the first- and second-order diffraction of a recorded grating were monitored during exposure. Since temperature appeared to be an important factor in obtaining the linearity of the recording, the experimental results support our qualitative model in which photoinduced structural changes, the main recording process, are deteriorated by a competitive relaxation process.
Template-synthesized BN:C nanoboxes
Authors: Johansson M. P. , Suenaga K. , Hellgren N. , Colliex C. , Sundgren J-E. , Hultman L.
Published: July 2002

Box-shaped nanostructures of B–C–N compounds were synthesized by reactive sputtering of boron carbide in mixed argon and nitrogen discharges. Transmission electron microscopy showed that these nanoboxes were grown on self-patterned NaCl substrate with projected areas ranging from ∼1×102 to ∼5×104 nm2, sizes 50–100 nm, and number density ∼100 μm−2. Electron energy loss spectroscopy revealed a phase separation of BN and C:N layers.
Transient breakdown behavior in electron-irradiated and proton-irradiated silicon p–n junctions
Authors: Shen Z. Y. , Lee H. S. , Lee J. H. , Park J. , Kim H. J. , Lee S. H. , Jo J. , Nishihara Y.
Published: July 2002

We studied the turn-off transient behavior of electron- and proton-irradiated silicon p–n junction diodes. Electron-irradiated n+–p diodes showed transient current peaks at lower reverse voltages. When the forward current was increased, the height and the number of the peaks increased, and at each peak the diode voltage showed a sharp decrease. We explain that the increased ionization coefficients by the electron irradiation caused the current peak to appear during the turn-off transients. p+–n diodes irradiated under the same condition did not show the large peak. This suggests that only the defects in the p-type silicon are responsible for the current peaks.
Determination of the mesostructure of lead borate glasses using laser photoionization mass spectroscopy
Authors: Stentz D. , Blair S. , Goater C. , Feller S. , Affatigato M.
Published: July 2002

We have investigated the structure of lead borate glasses up to high lead contents using a high-resolution reflectron time-of-flight mass spectrometer. The glasses showed the repeatable presence of intermediate-range units, which varied in relative abundance depending on composition. This direct measurement of the network showed a high abundance of (B3O5) and (PbB3O6) groups, which are likely to arise from metaborate rings, as well as the rise of ortho- and pyroborate units. Smaller quantities of entire diborate units (B4O9, with added lead and boron atoms for charge compensation) were also observed.
Zn(Mg)BeSe-based p-i-n photodiodes operating in the blue-violet and near-ultraviolet spectral range
Authors: Vigué F. , Tournié E. , Faurie J.-P.
Published: July 2002

We present the growth and characterization of p-i-n photodiodes based on ZnBeSe and ZnMgBeSe compounds. High-quality diodes exhibiting dark current as low as 12 nA/cm2 at −2 V bias have been fabricated. The spectral response shows a high responsivity of 0.17 A/W at 450 nm, with a rejection of ∼104 at longer wavelengths. Our results thus demonstrate the potential of ZnSe-based heterostructures for efficient detection in the visible-ultraviolet region.
Top-gating of p-Si/SiGe/Si inverted modulation-doped structures
Authors: Sadeghzadeh M. A.
Published: July 2002

Low-temperature electrical properties of two-dimensional hole gases (2-DHGs) in Si/Si0.8Ge0.2/Si inverted modulation-doped structures have been investigated at different hole densities using a metal semiconductor gate sputtered on top of these structures. The 2-DHG which is supplied to the inverted interface of Si/SiGe/Si quantum well by a Si boron-doped layer spatially grown beneath the alloy, was controlled in the range of 1.5–7.8×1011 cm−2 hole density by biasing the top gate. With increasing 2-DHG sheet density, the hole wave function of these structures expands and moves away from inverted interface, consequently the mobility enhances. These results may be understood theoretically by elaborating the role of interface charge, roughness, and alloy scattering mechanisms in limiting the mobility of holes at the inverted interface.
Microtip-assisted metal–insulator transition in a layered chalcogenide
Authors: Yamaguchi W. , Shiino O. , Endo T. , Kitazawa K. , Hasegawa T.
Published: July 2002

The layered compound 1T–TaS1.7Se0.3 forms a nanoscale domain structure, separated by mesh-like domain walls, above its bulk metal–insulator transition temperature TMI of ∼180 K. Scanning tunneling microscopy and spectroscopy of the compound demonstrated that each metallic domain can be converted to insulating one by successive scans of the probe tip just above TMI. This tip-assisted phenomenon is consistently explained by assuming that the domain structure arises from irregular distortion of charge density waves, and that the stacking pattern of charge density waves plays an essential role in the metal–insulator transition.
Isolation of a metallic Si(111)7×7 surface reconstruction via separation by implanted oxygen
Authors: Noh M. , Jellison G. E. , Namavar F. , Weitering H. H.
Published: July 2002

High-quality Si(111)7×7 surface reconstructions have been observed on (111)-oriented Si/SiO2/Si substrates, prepared via separation by implantation of oxygen, or “SIMOX,” with top layer thicknesses as small as 220 Å. Scanning tunneling microscopy and spectroscopy data indicate that the electrically and physically isolated top layer is electrically conducting, in contrast to that of (100) SIMOX material, which accumulates charge under typical imaging conditions. We speculate that the 7×7 reconstruction on (111) SIMOX material is an efficient conduction channel, allowing atomic resolution imaging of the isolated Si top layer.
Ultradeep, low-damage dry etching of SiC
Authors: Cho H. , Leerungnawarat P. , Hays D. C. , Pearton S. J. , Chu S. N. G. , Strong R. M. , Zetterling C.-M. , Östling M. , Ren F.
Published: July 2002

The Schottky barrier height (ΦB) and reverse breakdown voltage (VB) of Au/n-SiC diodes were used to examine the effect of inductively coupled plasma SF6/O2 discharges on the near-surface electrical properties of SiC. For low ion energies (⩽60 eV) in the discharge, there is minimal change in ΦB and VB, but both parameters degrade at higher energies. Highly anisotropic features typical of through-wafer via holes were formed in SiC using an Al mask.
Electrical characteristics of ultrathin gate oxide prepared by postoxidation annealing in ND3
Authors: Kwon Hyungshin , Hwang Hyunsang
Published: July 2002

The electrical and reliability characteristics of ultrathin gate oxide, annealed in ND3 gas, have been investigated. Compared with a control oxide, which had been annealed in NH3, the ND3-nitrided oxide exhibits a significant reduction in charge trapping and interface-state generation. The improvement of electrical and reliability characteristics can be explained by the strong Si–D bond at the Si/SiO2 interface. This nitridation process of a gate dielectric using ND3 has considerable potential for future ultra-large-scale integration device applications.
Spatial beam switching and bistability in a diode ring laser
Authors: Booth M. F. , Schremer A. , Ballantyne J. M.
Published: July 2002

We report bistable switching of the output direction in certain triangular diode ring lasers. These lasers operate unidirectionally at large drive currents, with up to 98% of the output power emerging from either the clockwise or the counterclockwise direction. The preferred direction can switch back and forth, with a large hysteresis loop, as the drive current is varied. Up to 20 mW of optical power changes direction at each switch. We propose an explanation based on the theory of two-mode competition via gain saturation.
Van der Waals xenotaxy: Oriented growth of hexagonal GaSe(001) on rectangular GaAs(110)
Authors: Rudolph R. , Tomm Y. , Pettenkofer C. , Klein A. , Jaegermann W.
Published: July 2002

The growth of the layered chalcogenide GaSe on cleaved GaAs(110) surfaces was investigated with photoemission and low-energy electron diffraction (LEED). GaSe films grow with their c axis perpendicular to the GaAs(110) surface. LEED patterns after initial film growth are a superposition of rectangular GaAs:Se spots and two hexagonal domains rotated by ±5° with respect to the GaAs 〈001〉 axis. At higher film thickness a hexagonal LEED pattern with GaSe 〈120〉 ‖ GaAs 〈001〉 is obtained.
Multilayered gated lateral quantum dot devices
Authors: Liang C.-T. , Simmons M. Y. , Smith C. G. , Kim Gil-Ho , Ritchie D. A. , Pepper M.
Published: July 2002

We describe a detailed device fabrication technique for the formation of a lateral quantum dot using a multilayered gated design. In our versatile system, a quantum dot is electrostatically defined by a split gate and two overlaying finger gates which introduce entrance and exit barriers to the dot. Periodic and continuous conductance oscillations arising from Coulomb charging effects are clearly observed in the transport properties at low temperatures.
Energy loss rates of two-dimensional hole gases in inverted Si/Si0.8Ge0.2 heterostructures
Authors: Ansaripour G. , Braithwaite G. , Myronov M. , Mironov O. A. , Parker E. H. C. , Whall T. E.
Published: July 2002

We have investigated the energy loss rate of hot holes as a function of carrier temperature TC in p-type inverted modulation-doped (MD) Si/SiGe heterostructures over the carrier sheet density range (3.5–13)×1011 cm−2, at lattice temperatures of 0.34 and 1.8 K. It is found that the energy loss rate (ELR) depends significantly upon the carrier sheet density, n2D. Such an n2D dependence of ELR has not been observed previously in p-type SiGe MD structures. The extracted effective mass decreases as n2D increases, which is in agreement with recent measurements on a gated inverted sample. It is shown that the energy relaxation of the two-dimensional hole gases is dominated by unscreened acoustic phonon scattering and a deformation potential of 3.0±0.4 eV is deduced.
Temperature dependence of dislocation photoresponse in relaxed GeSi films
Authors: Gray Matthew H. , Hsu J. W. P.
Published: July 2002

Using a near-field scanning optical microscope to perform local photocurrent measurements, we examine the temperature dependence of contrast associated with individual threading dislocations and crosshatch patterns from 12 to 300 K. The observed weak contrast at room temperature and a negative temperature coefficient indicate that the predominant electrical activity comes from shallow centers. This is consistent with intrinsic defects or at most low levels (∼ppb) of contaminants. In addition, the crosshatch contrast displays a long-range variation below 100 K.
Effect of RuO2 growth temperature on ferroelectric properties of RuO2/Pb(Zr, Ti)O3/RuO2/Pt capacitors
Authors: Norga G. J. , Fè Laura , Wouters D. J. , Maes H. E.
Published: July 2002

We present a promising method for obtaining Pb(Zr, Ti)O3(PZT) layers with excellent endurance and pulse-switching properties on RuO2 electrodes using the sol–gel method. As the substrate temperature during reactive sputtering of the RuO2 bottom electrode layer is reduced, the (111) PZT texture component becomes more pronounced, an effect attributed to the change from columnar to granular RuO2 film morphology. Reducing the residual PZT (100) and (101) texture components was found to be a necessary condition for obtaining optimal pulse switching and endurance properties of the layers. Highly (111)-oriented PZT layers, obtained on RuO2 grown at 150 °C exhibit a net switched charge of >60 μC/cm2 during pulse measurement and <10% degradation after 1011 fatigue cycles.
Impurity reduction in In0.53Ga0.47As layers grown by liquid phase epitaxy using Er-treated melts
Authors: Dhar S. , Paul Shampa , Kulkarni V. N.
Published: July 2002

Hall mobility and carrier concentration measurements are done on In0.53Ga0.47As layers grown by liquid phase epitaxy from melts containing 0.1–0.18 wt % Er. The carrier concentration in the layer decreased to 2×1014 cm−3 upon the addition of 0.16 wt % Er to the growth melt but the corresponding mobility of the layer increased only marginally. A detailed analysis of the temperature-dependent Hall mobility data for the samples using a theoretical curve fitting technique revealed that the donor impurities in the material are reduced to a greater extent compared to the acceptors, making the layers compensated. The experimental mobilities are further compared with the published values of theoretically calculated mobilities for InGaAs with similar compensations. It is shown that the space charge scattering effects are to be considered in order to get a good agreement between the experimental and the theoretical values.
Growth of ferroelectric oxide films on n-GaN/c-sapphire structures
Authors: Fuflyigin V. , Osinsky A. , Wang F. , Vakhutinsky P. , Norris P.
Published: July 2002

High-quality (Pb, La)(Ti, Zr)O3 films were grown on n-GaN. The film thickness ranged from 0.5 to 5 μm. The material was prepared by a chemical solution method with compositions of 8/65/35 and 0/52/48. The films grown on GaN buffered with a thin layer of indium in oxide were highly textured and exhibited excellent ferroelectric properties with Pr=20–26 μC/cm2. A large field-induced birefringence of 0.025 was measured in the film with a composition of 8/65/35 under a field strength of 2×105 V/cm.
Influence of phase fluctuation in external environment on Coulomb blockade in an array system of single tunnel junctions/Ni nanowires
Authors: Haruyama Junji , Hijioka Ken-ichiro , Tako Motohiro , Sato Yuki
Published: July 2002

Correlation of Coulomb blockade (CB) with phase fluctuation caused by mutual Coulomb interaction is reported in an array system of single tunnel junctions directly connected to disordered Ni nanowires. At the voltages lower than CB voltage, temperature dependence of the normalized resistance is classified to the following two regimes by a phase transition temperature (Tc), (1) mutual Coulomb interaction regime (T>Tc) and (2) CB regime (T<Tc). It is found that this Tc is very sensitive to a diffusion coefficient (D) of the mutual Coulomb interaction, resulting in a linear Tc vs D1/2 relation. This relation is interpreted as a result of the competition between the charging energy of the CB and the phase fluctuation energy caused by the multiple Coulomb scattering in the Ni nanowire. It is also reconfirmed by the wire diameter dependence of Tc.
Effects of charged self-assembled quantum dots on two-dimensional quantum transport
Authors: Wang Qin , Carlsson N. , Omling P. , Samuelson L. , Seifert W. , Xu H. Q.
Published: July 2002

The influence of a layer of InAs quantum dots on the transport properties of a nearby two-dimensional electron gas (2DEG) in an InGaAs/InP quantum well is investigated. The probability of the scattering between edge states is found to increase as the distance between the layer of the dots and the 2DEG decreases. It is shown that Coulomb scattering by electrons in the charged quantum dots play an important role in the scattering between edge states. An effect of the electrons in the dots is to mediate scattering between spin-split edge states. This is demonstrated by showing that the overshoot effect in the quantum Hall regime is only present when the dots are charged with electrons.
Defect-enhanced solid-state amorphization in Zr100−xAlx/Ni thin-film diffusion couples
Authors: Gimbel M. , Schneider S. , Spiecker E. , Seibt M.
Published: July 2002

The interdiffusion reaction between supersaturated nanocrystalline Zr100−xAlx and crystalline Ni films leads to the formation of a planar amorphous Zr–Al–Ni interlayer. This solid-state amorphization reaction has been investigated by in situ measurement of electrical conductance and by transmission electron microscopy. With increasing defect density in the Zr100−xAlx layers, the diffusivity of Ni in the amorphous interlayer increases and the activation energy decreases. These results are discussed with respect to Stephenson’s analysis of interdiffusion and stress formation in systems with components of differing mobilities.
Dynamic photoluminescence change of porous Si upon exposure to thermoelectrons/D atoms and D2O
Authors: Wadayama T. , Arigane T. , Hayamizu K. , Shibahara T. , Hino D. , Hatta A.
Published: July 2002

In situ photoluminescence (PL) and transmission IR spectral measurements have been carried out for porous Si (PS) after exposure to thermoelectrons and subsequent exposure to D atoms or D2O. Upon exposure to thermoelectrons the PL band (765 nm) of the PS almost diminished accompanied by the intensity reduction of the IR bands due to Si-Hx (x=1–3) species. A subsequent D atom exposure resulted in a recovery of the PL band with the formation of Si-Dx bonds. In contrast, D2O exposure gave rise to a new PL band at 650 nm in addition to a 745 nm band accompanied by the emergence of IR bands due to Si-OD and Si-D bonds: the integrated PL intensity after the D2O exposure is 1.2 times larger than the PL intensity of the as-anodized PS. These results suggest that the PL of the PS contains an important contribution from the surface Si-O bonds.
A catchment model of high electric field conduction in high concentration narrow-gap semiconductors
Authors: Rowe A. C. H. , Gatzke C. , Stradling R. A. , Solin S. A.
Published: July 2002

We present a simple model for μ(E), the field dependence of the mobility, in polar semiconductors. The resulting four-parameter expression is based on a streaming motion idea and a catchment model previously applied to layer rigidity in intercalated solids. A fitting parameter p, introduced in the catchment model, is shown to be related to the plasmon screening length. The model is applied to new data for InAs and InSb, and the fit is superior to empirical models of similar complexity. We find that energy loss via pure plasmon or coupled mode scattering is important even for intrinsic InSb.
Growth of oriented lithium niobate on silicon by alternating gas flow chemical beam epitaxy with metalorganic precursors
Authors: Joshkin V. A. , Moran P. , Saulys D. , Kuech T. F. , McCaughan L. , Oktyabrsky S. R.
Published: July 2002

We present the results of investigations of LiNbO3 film growth on Si by conventional chemical beam epitaxy (CBE) and by alternating gas flow deposition with alkoxide precursors. Both growth methods produced films with an intervening interface amorphous layer, whose thickness depends strongly on growth and annealing temperatures. While films grown by chemical beam epitaxy were always polycrystalline, the LiNbO3 films grown by alternating gas flow deposition were oriented materials. Based on our studies, we hypothesize that the alternating layer deposition technique enhances bulk interdiffusion efficiency of metal ions leading to a more controlled epitaxy of LiNbO3 on Si relative to conventional CBE growth.
Superstable neutral electron traps in nonplanar thermal oxides on monocrystalline silicon
Authors: Ono Tsuyoshi , Miura-Mattausch Mitiko , Baumgärtner Hermann , Mattausch Hans Jürgen
Published: July 2002

The existence of superstable neutral electron traps is reported for thermal oxides on nonplanar monocrystalline silicon. These traps are located at the nonplanar corners of the oxide and have measured thermal detrapping energies up to 3.3 eV, nearly an order of magnitude larger than previously observed for planar oxides on monocrystalline silicon. The most likely physical reason for the extremely high stability is relaxation of the strain stress at the corner caused by the trapping of electrons.
Self-organized formation and photoluminescence of Cd1−xMnxTe quantum dots grown on ZnTe by atomic layer epitaxy
Authors: Terai Yoshikazu , Kuroda Shinji , Takita Kôki
Published: July 2002

Self-organized quantum dots (QDs) of Cd1−xMnxTe were grown on the ZnTe(100) surface by atomic layer epitaxy. Atomic force microscope measurement on the surface of a 3.5-ML-thick Cd1−xMnxTe layer revealed dot formation in a high density of the order of 1010–1011 cm−2 when the Mn composition x was less than 10%. The typical dot size was given approximately by 20 nm in diameter and 2 nm in height. In photoluminescence (PL) measurements on the capped QDs, the excitonic emissions from the QDs were observed at 2.16–2.27 eV in the range of Mn composition x=0%–10%. The PL spectra from Cd1−xMnxTe QDs with x=0.6%–10.2% consisted of two lines separated by about 20 meV. The dependence of the PL energies on the Mn composition and the Zeeman shift were compared with the calculation.
In situ barrier formation using rapid thermal annealing of a tungsten nitride/polycrystalline silicon structure
Authors: Lee Byung Hak , Lee Kee Sun , Sohn Dong Kyun , Byun Jeong Soo , Han Chang Hee , Park Ji-Soo , Han Sang Beom , Park Jin Woon
Published: July 2002

This letter describes the use of rapid thermal annealing (RTA) to form a barrier layer applicable to the gate electrode in dynamic random access memory devices with a stacked structure [tungsten nitride (WNx)/polycrystalline Si (poly-Si)]. After RTA, the reactively sputtered amorphous WNx film on the poly-Si was transformed to a low-resistive α-phase W and nitrogen-segregated layer. Most of the nitrogen in the WNx film was dissipated and a relatively small amount of the nitrogen was segregated at the interface of the α-phase W and poly-Si. The segregated layer was estimated to be 2 nm thick and revealed a silicon nitride (Si–N) bonding status. More importantly, we found that this thin segregated layer successfully protected the formation of tungsten silicide, even after RTA at 1000 °C for 2 min in a hydrogen environment.
Single-crystal hexagonal and cubic GaN growth directly on vicinal (001) GaAs substrates by molecular-beam epitaxy
Authors: Amimer K. , Georgakilas A. , Tsagaraki K. , Androulidaki M. , Cengher D. , Toth L. , Pecz B. , Calamiotou M.
Published: July 2002

Single-crystal hexagonal and cubic GaN thin films have been grown by radio-frequency nitrogen plasma source molecular beam epitaxy directly on vicinal (001) GaAs substrates, misoriented by 2° toward [100], without using an incident As beam during oxide desorption or the following stages of growth. Both the GaAs nitridation and GaN growth conditions were found to control the structure of the layers. Cubic layers could be grown only without nitridation and under stoichiometric N/Ga flux ratio conditions. N-rich conditions favored the growth of hexagonal layers, which exhibited significantly higher photoluminescence intensities compared to cubic ones. Hexagonal single crystalline GaN films were grown with (101̄2) planes and presented characteristic surface roughness striations along a 〈110〉 substrate direction. On the contrary, a stepped surface morphology was observed for cubic GaN.
Single grain boundary characterization of Nb-doped SrTiO3 bicrystals using ac four-point impedance spectroscopy
Authors: Hwang Jin-Ha , Johnson Kevin D. , Mason Thomas O. , Dravid Vinayak P.
Published: July 2002

AC four-point impedance spectroscopy has been applied to Nb-doped SrTiO3 bicrystals. Due to the simplified geometry and highly conductive bulk of the bicrystal, the reference impedance of the electrode was significantly reduced, validating the applicability of ac four-point impedance spectroscopy for electroceramics. DC current–voltage characteristics without any interference due to electrodes confirmed these ac measurements. Using ac four-point impedance spectroscopy, grain boundary contributions are isolated and the corresponding grain boundary thickness and resistivity are estimated.
Quantization energy mapping of single V-groove GaAs quantum wires by femtosecond near-field optics
Authors: Achermann M. , Nechay B. A. , Siegner U. , Hartmann A. , Oberli D. , Kapon E. , Keller U.
Published: July 2002

We demonstrate that femtosecond pump–probe spectroscopy in the optical near field is well suited to study the intrinsic properties of single V-groove GaAs quantum wires. Temporally and spatially resolved experiments show that the shape of near-field pump–probe traces sensitively depends on the detuning between the laser photon energy and the lowest exciton resonance of a quantum wire. This detuning dependence allows one to map the quantization energy fluctuations along a single quantum wire with 200 nm spatial resolution. We measure fluctuations of about 12 meV over 2 μm wire length, resulting from wire thickness variations of 1 ML.
Two-color generation in a rare-earth-doped quasiphase-matched structure
Authors: Kir’yanov A. V. , Mel’nikov I. V. , Wagner K.
Published: July 2002

A numerical study of two-color operation of quasiphase-matched structure in the lasing regime is presented for the case when a 980 nm pump produces the output both at 1550 and 775 nm. Successful operation of the two-color device relies on the use of a novel gain medium which consists of diode-pumped high-density rare-earth ions and on the utilization of a saturable amplification and absorption in the pumped and unpumped section of the device, correspondingly.
Si(011)
16×2
gas-source molecular beam epitaxy: Growth kinetics
Authors: Taylor N. , Kim H. , Desjardins P. , Foo Y. L. , Greene J. E.
Published: July 2002

The growth rates RSi of Si layers deposited on Si(011)“16×2” by gas-source molecular beam epitaxy from Si2H6 were determined as a function of temperature Ts (400–975 °C) and Si2H6 flux JSi2H6(5.0×1015–9.0×1016 cm−2 s−1). RSi ranges from 0.0015 μm h−1 at Ts=400 °C to 0.415 μm  h−1 at Ts=975 °C with JSi2H6=2.2×1016 cm−2 s−1. In the surface-reaction-limited regime at Ts<725 °C, RSi initially exhibits an exponential decrease with 1/Ts, then decreases at a slower rate at Ts⩽550 °C as an additional deposition pathway becomes operative. In the impingement-flux-limited regime, 725⩽Ts⩽900 °C, RSi is independent of Ts but increases linearly with JSi2H6. At Ts>900 °C, RSi(Ts) increases with Ts due to surface roughening. Overall, RSi(JSi2H6,Ts) is well described at Ts⩽900 °C by a kinetic model incorporating two competing film growth mechanisms: (1) dissociative chemisorption of Si2H6 onto dangling bonds followed by fast surface dissociation steps and second-order H2 desorption from the surface monohydride phase; and (2) Si2H6 insertion into Si–H surface bonds followed by second-order desorption of SiH4.
Direct-current characteristics of pnp AlGaN/GaN heterojunction bipolar transistors
Authors: Zhang A. P. , Dang G. T. , Ren F. , Han J. , Baca A. G. , Shul R. J. , Cho H. , Monier C. , Cao X. A. , Abernathy C. R. , Pearton S. J.
Published: July 2002

AlGaN/GaN pnp heterojunction bipolar transistors were fabricated using a low-damage dry-etch process, and the dc characteristics measured up to 250 °C. In the common–base mode, the collector current was approximately equal to the emitter current under all conditions. Although not optimized for power operations, the devices were tested up to power densities of ∼50 kW cm−2. The dc current gain was in the range 20–25 at room temperature. The pnp configuration avoids the problem of high base sheet resistance encountered with npn-AlGaN/GaN devices.
Acoustic microscope based on magneto-elastic wave phase conjugator
Authors: Brysev A. , Krutyansky L. , Pernod P. , Preobrazhensky V.
Published: July 2002

Acoustic C-scan imaging (acoustic microscopy) by means of supercritical parametric wave phase conjugation (WPC) is studied experimentally. A phase conjugator based on a magneto-acoustic active material is used for compensating phase distortions introduced by solid and polymer aberration layers covering objects (electronic integrated circuits as examples). Improvement of images is demonstrated on an acoustic microscope, operating at a frequency of 10 MHz.
Mechanical behavior of thin buffer layers in InAs/GaAs(111)A heteroepitaxy
Authors: Pelzel Rodney I. , Zepeda-Ruiz Luis A. , Nosho Brett Z. , Li Youli , Weinberg W. Henry , Maroudas Dimitrios
Published: July 2002

The mechanical behavior of thin buffer layers for InAs/GaAs(111)A heteroepitaxy has been investigated by x-ray diffraction (XRD). XRD θ–2θ spectra are presented for the (220) reflection for two monolayers (MLs) of InAs deposited on GaAs buffer layers of both 20 ML and 150 nm (≅ 460 ML) in thickness. For the thicker buffer layer, the XRD spectrum exhibits a single, symmetric peak at a reflected angle corresponding to the bulk GaAs lattice parameter, while for the thinner one it exhibits asymmetry around the GaAs substrate reflection with the spectrum tailing to lower angle. This indicates that the thin buffer layer possesses a distribution of interlayer distances in the [220] direction that are larger than that of the GaAs substrate. The XRD data agree very well with theoretical calculations in which the thin GaAs buffer layer is modeled as unconstrained at its base. Our results provide direct evidence that thin GaAs buffer layers behave mechanically similarly to compliant substrates.
Metal-oxide-silicon diodes on deuterium-implanted silicon substrate
Authors: Misra D. , Jarwal R. K.
Published: July 2002

Ion implantation was used to incorporate deuterium at the Si–SiO2 interface. Polycrystalline silicon gate metal-oxide-semiconductor diodes with 4 nm oxide grown on deuterium-implanted p-type 〈100〉 silicon substrate were investigated. It was observed that deuterium implantation at a light dose of 1×1014/cm2 at 25 keV reduced oxide leakage current due to reduction in oxide charge and interface traps. Low-energy implant indicates possible deuterium loss during oxidation whereas in case of higher energy implant, the observed degradation was caused by enhanced substrate damage. Interface state density Dit as obtained from the conductance measurements suggests that implanted deuterium passivates the interface traps.
Low-frequency noise in gate overlapped lightly doped drain polycrystalline silicon thin-film transistors
Authors: Giovannini S. , Bove A. , Valletta A. , Mariucci L. , Pecora A. , Fortunato G.
Published: July 2002

Low-frequency noise has been investigated in gate overlapped lightly doped drain (GOLDD) polysilicon thin-film transistors (TFTs). We found that as in self-aligned polycrystalline silicon (polysilicon) TFTs, the low-frequency noise GOLDD polysilicon TFTs originates from carrier number fluctuations. In addition, no excess noise was observed when measuring GOLDD TFTs in the kink regime, in contrast to what was observed in self-aligned polysilicon TFTs. This has been explained by attributing the excess noise to supplemental oxide charge fluctuations induced by hot-carrier injection into the gate oxide and showing, by using two-dimensional numerical simulations, that the hot-electron emission current in GOLDD polysilicon TFTs can be much lower than in conventional drain contact configurations.
Ultraviolet photoluminescence of porous silica
Authors: Chiodini N. , Meinardi F. , Morazzoni F. , Paleari A. , Scotti R. , Di Martino D.
Published: July 2002

Excitation pattern and decay kinetics of ultraviolet photoluminescence of porous silica are investigated between 4.5 and 10 eV by means of synchrotron radiation. Spectra are dominated by a 3.7 eV emission similar to the recently observed ultraviolet emission of oxidized porous Si and Si nanostructures. Emission intensity is found to be controlled by the material specific surface. Other emissions are observed at 2.9, 3.8, and 4.2 eV. All emissions show lifetimes of a few nanoseconds. Spectral and kinetic features are sensibly different than in glassy SiO2, suggesting a revision of previous assignments of ultraviolet emissions in oxidized porous Si and Si nanostructures.
Cathodoluminescence wavelength imaging of μm-scale energy variations in InAs/GaAs self-assembled quantum dots
Authors: Rich D. H. , Zhang C. , Mukhametzhanov I. , Madhukar A.
Published: July 2002

Cathodoluminescence wavelength imaging of InAs/GaAs self-assembled quantum dots (SAQDs) was performed to study the spatial variation in the spectral line shape of the broadened quantum dot (QD) ensemble. The line shape was found to vary on a scale of ∼μm, revealing attendant variations in the size distribution of SAQD clusters on this spatial scale. Energy variations in clusters of SAQDs are found to exhibit a spatial correlation with the efficiency of luminescence and the activation energy for thermal re-emission of carriers. A reduction in the energy variation of the QD clusters occurs when the thickness of the spacer layers in vertically self-organized samples is reduced or the number of stacks is increased.