bluuebunny/crossref_metadata_2025 huggingface dataset:
Low power (bistable) opto-electrical threshold switches with high gain based on n-i-p-i doping superlattices
Authors: Höfler A. , Gulden K. H. , Kiesel P. , Kneissl M. , Knüpfer B. , Riel P. , Döhler G. H. , Tränkle G. , Weimann G.
Published: July 2002

We report on the realization of an electro-optical switch on n-i-p-i doping superlattices for both bistable and step-like threshold operation at very low input power levels (≂200 pW) and with high opto-electrical gain (6.8×106). The configuration presented in this letter consists of a (two terminal) photodiode with negative current-voltage characteristic and a novel three-terminal photoconductive detector structure. The minimum optical switching power is determined by the reverse dark currents of the devices that are below pA. The switches are suitable for monolithical integration into arrays.
Enhancement of Si hole mobility in coupled delta-doped wells
Authors: Carns T. K. , Zheng X. , Wang K. L.
Published: July 2002

When two or more highly doped, thin (delta-doped) layers are placed in close proximity to one another it is found that an enhancement of the hole mobility occurs over that of a single delta (δ) layer as well as that of the Si bulk case. Hall mobilities of up to 2400 cm2 V−1 s−1 at 77 K have been obtained with δ layers spaced 200 Å apart compared to a mobility of 280 cm2 V−1 s−1 for the single delta layer. The conductivity of the coupled δ-doped well exceeds that of comparable uniformly doped bulk layers, especially at lower temperatures. These types of structures show great promise in obtaining high mobilities with high carrier densities for semiconductors grown by simple homoepitaxy.
Polarized electroluminescence spectra of GaxIn1−xP/(Al0.6Ga0.4)0.5In0.5P quantum wells
Authors: Bour D. P. , Paoli T. L. , Thornton R. L. , Treat D. W. , Park Y. S. , Zory P. S.
Published: July 2002

Electroluminescence spectra of 80 Å GaxIn1−xP/(Al0.6Ga0.4)0.5In0.5P quantum wells (QWs), with x=0.3, 0.4, 0.5, and 0.6, are examined. The polarization is anisotropic, and the light-hole (lh) and heavy-hole (hh) transitions are resolved at current densities between 1 A/cm2 and threshold. In the compressively strained (x=0.3, 0.4) QWs, the hh is ground state and transverse electric-mode emission dominates. The lh and hh band edges are reversed for the tensile-strained QW, however, and the emission is predominantly transverse magnetic. Near threshold, the bandfilling effect is most pronounced in the compressively strained QWs, suggesting a reduced in-plane hh effective mass. For the most highly compressed QW (x=0.3, λ=707 nm), the threshold current density is 190 A/cm2.
Quasipermanent magnets of high temperature superconductor: Temperature dependence
Authors: Chen In-Gann , Liu Jianxiong , Ren Yanru , Weinstein Roy , Kozlowski Gregory , Oberly Charles E.
Published: July 2002

We report on persistent field in quasipermanent magnets of high temperature superconductors. Magnets composed of irradiated Y1+Ba2Cu3O7 trapped field Bt=1.52 T at 77 K and 1.9 T at lower temperature. However, the activation magnet limited Bt at lower temperature. We present data on Jc(H,T) for unirradiated materials, and calculate Bt at various T. Based upon data at 65 K we calculate Bt in unirradiated single grains at 20 K, and find that 5.2 T will be trapped for grain diameter d∼1.2 cm, and 7.9 T for d=2.3 cm. Irradiated grains will trap four times these values.
Surfactant coverage and epitaxy of Ge on Ga-terminated Si(111)
Authors: Falta J. , Copel M. , LeGoues F. K. , Tromp R. M.
Published: July 2002

We have investigated the role of surfactant coverage and bonding for growth of Ge on Si(111). At 470 °C Ge grows on Si(111)-(7×7) in a Stranski–Krastanov fashion. Preadsorption of 1-ML Ga at 500 °C forms a Ga:Si(111)-(6.3×6.3) structure and alters the Ge growth mode from three-dimensional (3D) islanding to continuous film formation. However, the epitaxial layer contains defects, caused by the presence of domain boundaries of both A- and B-type material. Growth properties depend strongly on the initial Ga coverage: if a (√3×√3) surface with 1/3-mL Ga is used, a modified Stranski–Krastanov growth mode is observed, with 3D islands of a uniform predominant thickness.
Si3N4/Si/n-GaAs capacitor with minimum interface density in the 1010 eV−1 cm−2 range
Authors: Wang Z. , Lin M. E. , Biswas D. , Mazhari B. , Teraguchi N. , Fan Z. , Gui X. , Morkoç H.
Published: July 2002

We report significant improvements in the electrical characteristics of Si3N4/Si/GaAs capacitors with the assistance of atomic hydrogen during the in situ growth of Si on GaAs. Si3N4/Si/GaAs capacitors have shown a minimum interface state density as low as 3×1010 eV−1 cm−2 as determined by the low-frequency capacitance method. The hysteresis and frequency dispersion in the GaAs metal-insulator-semiconductor capacitor are very small (200 and 100 meV, respectively). These results represent significant advances over previous reports.
Calculated room-temperature threshold current densities for the visible II-VI ZnCdSe/ZnSe quantum-well diode lasers
Authors: Aggarwal R. L. , Zayhowski J. J. , Lax B.
Published: July 2002

Room-temperature threshold current densities for the visible II-VI ZnCdSe/ZnSe semiconductor quantum-well diode lasers have been calculated using a simple model for the quantum-well gain and spontaneous radiative recombination rate. These results are compared with those for the infrared III-V GaAs/GaAlAs quantum-well lasers, calculated using the same model. By tailoring the epitaxial structure for optimum optical confinement, cw room-temperature operation of the ZnCdSe/ZnSe quantum-well lasers should be possible with threshold current densities as low as 400 A/cm2 for a 1-mm cavity length and uncoated laser facets, assuming the problem of ohmic contacts to the epitaxial structure is resolved.
Stresses and morphological instabilities in silicide/polycrystalline Si layered structures
Authors: Hong Q. Z. , d’Heurle F. M. , Harper J. M. E. , Hong Stella Q.
Published: July 2002

The evolution of stress in silicide/polycrystalline Si (poly-Si) layered structures has been monitored in situ in the temperature range of 25–700 °C. At elevated temperatures, the silicide/poly-Si structure becomes morphologically unstable. The grain growth of poly-Si leads to an inversion of the positions of the two layers. The in situ stress measurement shows that this structural degradation is accompanied by a substantial increase in tensile stress of around 0.4 GPa, for NiSi, Pd2Si, and PtSi. A simple calculation indicates that the magnitude of the stress increase can be accounted for, at least to a large extend, by the volume contraction caused by the grain growth of poly-Si.
Crystallization on supercooled liquid in metallic Zr-Cu-Al glasses
Authors: Kawase Daisuke , Tsai An Pang , Inoue Akihisa , Masumoto Tsuyoshi
Published: July 2002

Crystallization behaviors are isothermally examined on supercooled-liquid and amorphous states in metallic Zr-Al-Cu glasses using differential scanning calorimetry. On the basis of a kinetic analysis, it is examined that the crystallization occurs with a zero nucleation rate below the glass transition temperature Tg and a nearly steady-state nucleation rate above Tg. Arrhenius relation between effective time lag τ of nucleation and isothermal temperature appears as a curvature for alloys revealing a wide supercooled liquid region and a straight line for alloys without wider supercooled-liquid region. The differences are attributed to the effects of viscosity on nucleation at supercooled liquid. The difference in morphology during crystallization between amorphous and supercooled-liquid states was also confirmed.
Blocking of Γ→X transfer in GaAs/AlAs short period superlattices due to X-state band filling
Authors: Blom P. W. M. , Smit C. , Haverkort J. E. M. , Wolter J. H.
Published: July 2002

We report an experimental study of the optical properties of a GaAs/AlAs short period superlattice (SPSL) by photoluminescence and time-resolved two-pulse correlation experiments. Our SPSL is designed in such a way that the lowest confined Γ state in the GaAs is only slight (30–50 meV) above the X states in the AlAs. Therefore the Γ→X transfer due to LO-phonon emission or interface scattering is prohibited by X-band filling at high excitation densities and small excess energies, which allows us to measure a Γ→X transfer time induced by LO-phonon absorption of 20 ps. By adjusting the laser energy, excitation density, and temperature we are able to transform the emission spectrum of the SPSL completely from a type-I into a type-II transition.
Strain effects in the intersubband transitions of narrow InGaAs quantum wells
Authors: Peng L. H. , Smet J. H. , Broekaert T. P. E. , Fonstad C. G.
Published: July 2002

Internal uniaxial stress effects on the degenerate P-like C2 subband Bloch states of Si-doped (001) InGaAs single quantum wells (SQWs) have been studied using polarization-resolved infrared spectroscopy. It is found that a tetragonal strain perturbation of the crystal potential produces a splitting between the TM and TE active intersubband transitions. The magnitude of the linear strain intersubband deformation potential of InGaAs quantum wells is 3 eV.
Second-harmonic generation using heavy-hole/light-hole intersubband transitions in asymmetric quantum wells
Authors: Qu Xiaohua H. , Ruda Harry
Published: July 2002

Second-harmonic generation (SHG) from semiconductor quantum-well (QW) structures has recently attracted a great deal of research interest. In this letter we present a study of SHG in AlGaAs/GaAs QWs based on heavy-hole/light-hole intervalence subband transitions. The enhancement of the SHG efficiency over bulk material is discussed. Both the sign and the magnitude of the second-order susceptibility of the well may be controlled; in this fashion, we demonstrate how long-range quasiphase matching of the SHG is then possible.
Geometrical interpretation of x-ray diffraction patterns of strained-layer superlattice structures
Authors: van der Sluis P.
Published: July 2002

We have derived a new relation that can be used to index the superlattice satellite peaks in an x-ray diffraction scan. At the same time accurate data on the strain in the superlattice and the periodicity of the superlattice are obtained. The new method has been applied to an InGaAs/InP superlattice and is compared with an existing method for the indexing of the superlattice peaks. For both methods, it is best to use only lattice planes that are parallel to the surface, because these rocking curves can be measured more easily, faster, more accurately and by fully automated means. In addition, only these rocking curves can be used for analysis of period variation or interface roughness.
Fabrication of Josephson junctions using heteroepitaxial Bi2(Sr,Ca)3Cu2Ox/Bi2Sr2CuOy/Bi2(Sr,Ca)3Cu2Ox trilayer films
Authors: Satoh T. , Fujita J. , Yoshitake T. , Tsuge H.
Published: July 2002

We have fabricated Josephson junctions from c-axis oriented heteroepitaxial Bi2(Sr,Ca)3Cu2Ox/Bi2Sr2CuOy/Bi2(Sr,Ca)3Cu2Ox trilayer films. The junctions showed resistively shunted junctionlike characteristics up to 30 K. Several junctions showed hysteresis at low temperatures. The highest value of the product of the critical current and the normal state resistance of the junctions was about 0.2 mV. Clear Shapiro steps at the expected voltages were observed in the presence of external microwave irradiation. The height of these steps oscillated to full suppression as a function of the microwave source power. Moreover the periodic magnetic field dependence of the critical current was clearly observed. These results indicated a good uniformity in the Josephson current distribution in these junctions.
In situ reflection electron energy loss spectroscopy measurements of low temperature surface cleaning for Si molecular beam epitaxy
Authors: Nikzad Shouleh , Wong Selmer S. , Ahn Channing C. , Smith Aimee L. , Atwater Harry A.
Published: July 2002

In situ analysis of hydrocarbon desorption from hydrogen terminated Si(100) surfaces was performed in a silicon molecular beam epitaxy system, using reflection electron energy loss spectroscopy, in conjunction with conventional reflection high energy electron diffraction analysis. Measurements of C K edge core loss intensities demonstrate that this method is sufficiently sensitive to enable in situ analysis of hydrocarbon desorption at fractional monolayer coverages during low-temperature isothermal anneals. Hydrocarbon desorption was found to begin at 115 °C, and at 200 °C complete desorption occurred within 10 min. Hydrocarbon coverage was not measurably affected by operation of ionization gauge filaments during low temperature anneals, but was increased by transient outgassing of the sample holder, and its environs.
Influence of crystal structure on the magnetoresistance of Co/Cu multilayers
Authors: Le Dang K. , Veillet P. , Vélu E. , Parkin S. S. P. , Chappert C.
Published: July 2002

The saturation magnetoresistance (MR) and Co nuclear magnetic resonance (NMR) spin echo have been measured in a series of sputtered Co/Cu multilayers, with Co thicknesses ranging from 10 to 30 Å. The multilayers were grown on 50 Å Cu or Fe buffer layers. A clear correlation has been established between the MR and the Co NMR line profile. The sample with the highest MR exhibits a single fcc Co line with weak-intensity wings. Increasing the number of (111) layer stacking faults and grain boundaries leads to decreasing MR.
Low temperature (313 °C) silicon epitaxial growth by plasma-enhanced chemical vapor deposition with stainless steel mesh
Authors: Shieh Ming-Deng , Lee Chiapyng , Chen Cheng-Hsien , Yew Tri-Rung , Kung Chung-Yuan
Published: July 2002

This letter presents the low temperature silicon epitaxial growth on p-type, 〈100〉 Si wafers by plasma-enhanced chemical vapor deposition with a stainless steel mesh. Following a modified ex situ spin-etch cleaning and an in situ H2 baking step, the epitaxial layer was grown at 313 °C using SiH4 (30 sccm)/H2 (22 sccm) with a pressure of 61 mTorr and a rf power of 10 W. Epitaxial layers were also grown at 323 °C with different silane flow rates. The epitaxial film contains higher defect density when the silane flow rate is low.
Method of determining metal contamination by combining p-type Si and n-type Si recombination lifetime measurements
Authors: Itsumi Manabu
Published: July 2002

A method is proposed for determining heavy-metal impurities by combining p-type Si and n-type Si recombination lifetime measurements. The experimental results show three trends in the relationships between p-type Si lifetime and n-type Si lifetime depending on the heavy-metal impurities. One trend is related to iron (I line), another is to copper (C line), and the other is to stainless-steel components (S line: iron and nickel). These three trends are used to estimate the unknown metallic impurities. Several examples are shown to demonstrate the advantages of this method. It is also shown that lifetime data associated with plasma processes are distributed near the S line. This method is convenient for monitoring and reducing metallic contamination levels.
Superconducting transport properties of Bi2Sr2CaCu2O8+x bicrystal grain boundary junctions
Authors: Mayer B. , Alff L. , Träuble T. , Gross R. , Wagner P. , Adrian H.
Published: July 2002

We have performed a detailed study of the superconducting transport properties of Bi2Sr2CaCu2O8+x bicrystal grain boundary junctions (GBJs). The GBJs were fabricated by the deposition of c-axis oriented epitaxial Bi2Sr2CaCu2O8+x films on SrTiO3 bicrystal substrates. The measured resistive transition R(T), the current-voltage characteristics (IVCs), the temperature dependence of the critical current density Jc(T), and the magnetic field dependence of the critical current Ic(B) of the Bi2Sr2CaCu2O8+x GBJs are similar to those observed for YBa2Cu3O7−δ GBJs. However, for the same misorientation angle the magnitude of Jc is almost an order of magnitude smaller for the BSCCO-GBJs. The R(T) dependencies and the IVCs of the BSCCO-GBJs are close to the prediction of the resistively shunted junction (RSJ) model. The Ic(B) dependencies are close to those of large Josephson junctions with overlap geometry. Our results show that BSCCO-GBJs may be useful for cryoelectronic applications.
Tunneling through AlxGa1−xAs single barriers under hydrostatic pressure
Authors: Rossmanith M. , Syassen K. , Böckenhoff E. , Ploog K. , von Klitzing K.
Published: July 2002

Transport properties of AlxGa1−xAs single barrier tunneling diodes with barrier compositions ranging from x=0.38 to x=1.00 are investigated. The pressure dependence of the tunneling current is used to monitor two distinct transport channels in these devices. The first channel is governed by the conduction-band offset between Γ-like states in the GaAs contacts and the AlxGa1−xAs barrier, which is independent of pressure. The barrier height for the second channel is determined by the X minima and not by the Γ minimum in the AlxGa1−xAs layer. Only this second conduction-band profile is pressure dependent. The crossover from the first to the second transport regime is observed directly in the sample with x=0.50.
High-conductance, low-leakage diamond Schottky diodes
Authors: Geis M. W. , Efremow N. N. , von Windheim J. A.
Published: July 2002

Schottky diodes formed of Al, Au, and Hg on diamond have been characterized as a function of plasma treatment and thermal annealing. Plasmas formed from N2O, H2, or O2 result in high surface leakage, while plasmas formed from N2 or from CF4 with 8.5% O2 result in total leakage <1000 e/s. Annealing the diamond at 660 °C before the Schottky diode is fabricated causes an increase in the forward conductance with n-factors approaching one. This annealing removes a compensated subsurface layer that often occurs in diamond during normal processing.
The irreversibility line of HgBa2CuO4+δ
Authors: Welp U. , Crabtree G. W. , Wagner J. L. , Hinks D. G. , Radaelli P. G. , Jorgensen J. D. , Mitchell J. F. , Dabrowski B.
Published: July 2002

Using magnetization hysteresis loops we have determined the irreversibility line of polycrystalline samples of HgBa2CuO4+δ and Hg0.8Pb0.2Ba2CuO4+δ. The irreversibility line is found at rather high temperatures. It does not show the drastic depression with increasing temperature as is observed in highly anisotropic Bi/Tl-based CuO superconductors. At 77 K the irreversibility field is around 0.3 T, which is substantially higher than in Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10. The advantages of this material for large-scale applications are outlined.
Solid-phase regrowth of amorphous GaAs grown by low-temperature molecular-beam epitaxy
Authors: Twigg M. E. , Fatemi M. , Tadayon B.
Published: July 2002

We have shown that solid-phase recrystallization of an amorphous GaAs film can form a single-crystal film. We observed the phenomenon in GaAs, deposited by molecular-beam epitaxy at a growth temperature (Tg) of 190 °C and annealed at 775 or 850 °C. Observations in the transmission electron microscope indicate that annealing brings about a lower degree of As precipitation in the as-grown amorphous films (Tg<215 °C) than in the as-grown single-crystal films (340 °C≳Tg≳215 °C). The lower degree of As precipitation in the initially amorphous material appears to insure a high concentration of As donors rather than a high concentration of resistivity increasing As precipitates. Electrical measurements show that the low-range (Tg<215 °C) annealed sample has an extremely high n-type carrier concentration (1018 cm−3) and mobility (800 cm2 V−1 s−1).
High efficiency thin film silicon solar cells prepared by zone-melting recrystallization
Authors: Ishihara T. , Arimoto S. , Morikawa H. , Kumabe H. , Murotani T. , Mitsui S.
Published: July 2002

A new type of silicon solar cell is demonstrated using chemical vapor deposited silicon thin films on a silicon dioxide layer. In order to improve the crystal quality of the thin films, zone-melting recrystallization (ZMR) is applied and grain boundaries of polycrystalline Si films are passivated with H+. It is found that H+ passivation is quite effective for thin film Si solar cells and ZMR conditions to provide dominant (100) orientation is essential for achieving higher conversion efficiency. This (100) nature is also favorable for making effective light confinement scheme with pyramidal textured surface using anisotropic chemical etching. The conversion efficiency as high as 14.2% for a practical size of 10×10 cm2 is achieved. This is the highest for large area thin film polycrystalline Si solar cells so far.
Carrier-induced reduction of the index of refraction of GaInP measured with distributed feedback lasers
Authors: Kaden C. , Griesinger U. A. , Schweizer H. , Geng C. , Moser M. , Scholz F. , Benner S. , Blank R. , Haug H.
Published: July 2002

We present new results on the effective refractive index of GaInP/AlGaInP distributed feedback (DFB) lasers with grating periods around 100 nm, operated at 77 K and at room temperature. Double heterostructure (DH) lasers as well as multiple quantum well lasers show DFB-laser emission at 300 K over a range of 15 nm. For the DH lasers a clear difference of absolute value and dispersion of the effective refractive index was observed between 77 and 300 K, which is explained by high carrier density effects. For a carrier density of N=2.5×1018 cm−3 the refractive index of GaInP decreases by 0.05, which is compared with an ab initio calculation.
High single-mode output power from compact external microcavity surface-emitting laser diode
Authors: Wilson G. C. , Hadley M. A. , Smith J. S. , Lau K. Y.
Published: July 2002

Transverse mode control is demonstrated in an electrically pumped surface-emitting laser diode coupled to an external microcavity with room-temperature single-mode powers reaching 2.0 mW continuous wave and 36.7 mW pulsed. The wavelength chirp is less than 0.044 nm for the pulsed results. The external microcavity is formed with a flat dielectric mirror placed less than 700 μm from the wafer surface. Diffraction and spatial filtering in the external cavity provide high-order mode suppression and produce a large fundamental mode of width 36 μm. This external cavity geometry readily lends itself to integration.
Structure of (001) GaAs surfaces during epitaxial growth by organometallic chemical vapor deposition
Authors: Kamiya Itaru , Tanaka H. , Aspnes D. E. , Koza M. , Bhat R.
Published: July 2002

Under typical atmospheric pressure (AP) organometallic chemical vapor deposition (OMCVD) growth conditions with trimethylgallium (TMG) and arsine sources, reflectance-difference (RD) spectra show that the (001) GaAs surface is in the d(4×4)-like state. With sufficiently high TMG and low AsH3 exposures, we observe RD spectra similar to those obtained during atomic layer epitaxy (ALE) at lower temperatures.
Oxygen isotopic exchange between an 18O+ implanted Si layer and a natural SiO2 capping layer during high-temperature annealing
Authors: Li Yupu , Kilner J. A. , Chater R. J. , Nejim A. , Hemment P. L. F. , Marsh C. D. , Booker G. R.
Published: July 2002

To understand the effects of the SiO2 capping layer on the growing buried SiO2 layer a silicon wafer was implanted at 680 °C with 90 keV 18O+ to a dose of 4.3×1017 18O+/cm2. After the deposition of an ∼500 nm natural SiO2 cap by the plasma sputtering, one piece of the implanted wafer was annealed at 1360 °C for 6 h in a quartz silica tube in flowing nitrogen. There is clear evidence of diffusional mixing of the oxygen isotopes from the cap into the 18O+ implanted layer during this annealing step, indeed a surprisingly large amount has taken place, in that approximately 41% of 18O contained within the buried SiO2 layer has been exchanged with the cap.
Time-resolved photocurrent response of metal-semiconductor-metal photodetectors to double-pulse excitation
Authors: Klingenstein M. , Kuhl J. , Rosenzweig J. , Moglestue C. , Hülsmann A. , Schneider Jo.
Published: July 2002

The photocurrent response of a GaAs metal-semiconductor-metal (MSM) photodetector was measured after excitation with two femtosecond pulses having a variable delay Δt of 0 ps≤Δt≤100 ps. At low excitation densities the influence of the first pulse on the pulse shape of the second is negligible for Δt≥20 ps. This corresponds to a resolvable pulse train of 50 GHz repetition rate for the detectors used in our experiments. The influence of space charge effects at higher excitation density and/or lower bias could be shown.
Visible photoluminescence of porous Si1−xGex obtained by stain etching
Authors: Ksendzov A. , Fathauer R. W. , George T. , Pike W. T. , Vasquez R. P. , Taylor A. P.
Published: July 2002

We have investigated visible photoluminescence (PL) from thin porous Si1−xGex alloy layers prepared by stain etching of molecular-beam-epitaxy-grown material. Seven samples with nominal Ge fraction x varying from 0.04 to 0.41 were studied at room temperature and 80 K. Samples of bulk stain etched Si and Ge were also investigated. The composition of the porous material was determined using x-ray photoemission spectroscopy and Rutherford backscattering techniques to be considerably more Ge rich than the starting epitaxial layers. While the luminescence intensity drops significantly with the increasing Ge fraction, we observe no significant variation in the PL wavelength at room temperature. This is clearly in contradiction to the popular model based on quantum confinement in crystalline silicon which predicts that the PL energy should follow the band-gap variation of the starting material. However, our data are consistent with small active units containing only a few Si atoms that are responsible for the light emission. Such units are present in many compounds proposed in the literature as the cause of the visible PL in porous Si.
Luminescence studies on porous silicon
Authors: Weng Y. M. , Fan Zh. N. , Zong X. F.
Published: July 2002

We have observed a redshift process of luminescence wavelength in an as-prepared porous silicon layer. Si—H bonds of a significant concentration are gradually replaced by Si—O bonds when porous silicon is exposed to air at room temperature, which coincides well with desorption of hydrogen from the silicon surface. SiH2 termination plays an important role in the emission process, and the surface passivation of the porous silicon layer is important to get effective and stable luminescence.
Novel charge injection transistors with heterojunction source (launcher) and drain (blocker) configurations
Authors: Tian H. , Kim K. W. , Littlejohn M. A.
Published: July 2002

The results of a theoretical study of novel charge injection transistors (CHINTs) with heterojunction source and drain are presented. The proposed device structures employ a wide band-gap (with respect to the channel) material as the device source and/or drain regions, in contrast to the conventional, homojunction source (drain) CHINT structure. It is demonstrated that the spatial location of real-space transfer (RST) is strongly dependent on the initial energy of injected electrons in these devices. The introduction of source and drain heterojunctions serves for enhancing the RST effect and for the blocking electrons which constitute leakage current. Results from two-dimensional, self-consistent ensemble Monte Carlo simulations reveal that the proposed CHINTs feature increased current drive capability, reduced drain leakage current, and faster switching speed.
Rapid thermal low pressure metalorganic chemical vapor deposition of In0.53Ga0.47As films using tertiarybutylarsine
Authors: Katz A. , Feingold A. , Moriya N. , Pearton S. J. , Geva M. , Baiocchi F. A. , Luther L. C. , Lane E.
Published: July 2002

Rapid thermal low pressure metalorganic chemical vapor deposition (RT-LPMOCVD) of lattice-matched epitaxial In0.53Ga0.47As films onto InP substrates was successfully performed using tertiarybutylarsine (TBA) and growth temperatures in the range of 500–550 °C. The undoped, featureless films were grown with a low V:III ratio of 2, and exhibited an excellent morphology with a minimum backscattering yield (χmin) of 3.6% and narrow x-ray full width at half-maximum peak of 28 arcsec of the InGaAs layer on InP, reflecting a lattice mismatch of 0.02%. These films presented good electrical properties, with hole mobility values of about 75 cm2/V S measured at 300 K for nominally undoped layers with p≤5×1015 cm−3.
Hybrid Si molecular beam epitaxial regrowth for a strained Si1−xGex/Si single-quantum-well electroluminescent device
Authors: Kato Y. , Fukatsu S. , Usami N. , Shiraki Y.
Published: July 2002

An n-type Si contact layer for an electroluminescent (EL) diode was successfully grown on a Si/Si1−xGex/Si single-quantum-well (SQW) structure by ‘‘hybrid’’ Si molecular beam epitaxy (MBE) for the first time. The hybrid MBE was performed by regrowing the Si contact layer in a solid-source MBE chamber after transferring the SQW sample through air from a gas-source (GS) MBE chamber, in which the starting SQW structure was grown. A (2×1) reconstruction was observed on a GSMBE-prepared Si(100) surface even after the SQW sample was exposed to air for up to 15 h. An excellent quality of the EL device was evidenced by the sharpest emission lines ever reported in the EL spectra of SiGe system. The spectral features of the EL and photoluminescence were found to be almost identical, and a well-resolved acoustic phonon replica was observed.
Planar field-induced quantum dot transistor
Authors: Wang Y. , Chou S. Y.
Published: July 2002

We propose and demonstrate a new field-induced quantum dot transistor that has a nanoscale dot-gate inside the gap of a split gate. Because of the novel structure and small dot size, strong oscillations in the drain current as a function of the gate bias were observed at a temperature up to 4.2 K or with a drain bias up to 5 mV. Temperature dependent study showed that the energy gaps in the dot are as large as 4.5 meV. Simulation indicates that, in the device, quantum size effect and Coulomb effect are comparable; both contribute significantly to the energy gaps in the quantum dot.
Pressure-induced phase transition in porous silicon
Authors: Ryan J. M. , Wamsley P. R. , Bray K. L.
Published: July 2002

High pressure studies of porous silicon reveal that a phase transition occurs at ∼170 kbar. The phase transition is detected by an abrupt change in color of porous silicon from orange-yellow to black. Photoluminescence measurements show an initial blue shift of the luminescence peak. At ∼25 kbar the blue shift ceases and a reversal of shift is observed. The red shift continues up to ∼90 kbar at which point the luminescence is quenched. The shift reversal is interpreted as a pressure-induced direct–indirect transition in porous silicon. The results are best explained in the context of the quantum confinement model.
Electronic and atomic structure of metastable phases of boron nitride using core-level photoabsorption
Authors: Chaiken A. , Terminello L. J. , Wong J. , Doll G. L. , Taylor C. A.
Published: July 2002

Soft x-ray core-level photoabsorption has been measured from three forms of boron nitride, namely the hexagonal (hBN), cubic (cBN), and incoherent (iBN) phases. The B 1s and N 1s photoabsorption spectra of the hBN sample show evidence of both σ*- and π*-empty states, indicative of sp2 bonding, while the cBN absorption spectra exhibits only sp3 bonding in absorption features characteristic of the zincblende structure. The incoherent phase of BN in the form of a thin film on a Si substrate possesses σ* and π* states similar to hBN. The B 1s π* absorption features of the iBN film show an angular dependence which suggests that the microstructure consists of hexagonal-phase layer planes oriented normal to the BN/Si interface.
Interfacial reconstruction and short-period oscillatory coupling in Fe/Cr/Fe multilayers after electron bombardment
Authors: Demokritov S. O. , Wolf J. A. , Grünberg P.
Published: July 2002

We have investigated the effect which bombardment by middle energy electrons has on the Cr/Fe interface in the Fe/Cr/Fe layered system. Reflection high-energy electron diffraction (RHEED) patterns reveal interfacial reconstruction and show that the surface is smoothed out by the bombardment. Modification of magnetic properties of the Fe/Cr/Fe system has been observed even in a zone a few millimeters away from the region subjected to the e bombardment.
Andreev reflection at superconducting contacts to GaAs/AlGaAs heterostructures
Authors: Lenssen K.-M. H. , Matters M. , Harmans C. J. P. M. , Mooij J. E. , Leys M. R. , Vleuten W. van der , Wolter J. H.
Published: July 2002

Highly transmissive ohmic contacts to the two-dimensional electron gas in GaAs/AlGaAs heterostructures have been made. For these contacts, which are of μm scale, a newly developed process of Ti/Sn evaporation and diffusion has been used. Devices consisting of these superconducting contacts combined with gate structures have shown clear evidence for the occurrence of Andreev reflection. Moreover a marked effect of the gate voltage on the dV/dI−V characteristics has been found, which proves that superconductivity has been induced into the semiconductor.
Phosphorus doping of epitaxial Si and Si1−xGex at very low pressure
Authors: Jang Syun-Ming , Liao Kenneth , Reif Rafael
Published: July 2002

We report on the in situ P doping of Si1−xGex(SiH4/GeH4) and Si(SiH4) epitaxial films with 1–100 ppm PH3 at 620 °C in a very low pressure chemical vapor deposition reactor. The epitaxial growth rates were found to decrease with P doping. The growth rate reduction is a function of Ge composition and is less pronounced as the Ge content increases. In addition, P incorporation into the growing film is affected by Ge, which improves the concentration range and profile definition of P. A simple model that attempts to explain the results is discussed.
Preferred concentration enhancement of photobleachable defects responsible for 5 eV optical absorption band in SiO2:GeO2 glass preform by heating in a H2 atmosphere
Authors: Hosono Hideo , Kawazoe Hiroshi , Muta Ken-ichi
Published: July 2002

Heat treatment of a 5GeO2-95SiO2 glass preform in a H2 atmosphere at 500 °C for 70 h increased intensities of an absorption band centered at 5 eV by a factor of ∼3. Intensities of photobleachable component, which is the precursor of UV-induced Ge E′ centers and assigned to a neutral oxygen monovacancy, of the 5-eV band were enhanced by a factor of ∼8 by heating. This increment is ∼3 times as large as that of UV-unbleachable component, which is assigned to Ge2+ centers coordinated by two oxygens (neutral oxygen divacancy).
High temperature ballistic transport observed in AlGaAs/InGaAs/GaAs small four-terminal structures
Authors: Hirayama Y. , Tarucha S.
Published: July 2002

Four-terminal structures are fabricated by focused-ion-beam (FIB) scanning on an AlGaAs/InGaAs/GaAs modulation doped structure. The large carrier density of this system results in small depletion spreading and a 260-nm-square four-terminal structure is successfully formed. The bend resistance of this structure indicates that ballistic coupling between two facing terminals remains up to room temperature. Thermal broadening of electron energy enhances the ballistic nature of the system at high temperature.
Room-temperature operation of a tunneling hot-electron transfer amplifier
Authors: Moise T. S. , Kao Y.-C. , Seabaugh A. C.
Published: July 2002

We demonstrate a tunneling hot-electron transfer amplifier that exhibits both dc and rf current gain at room temperature. The measured peak common-emitter current gain of the transistor approaches 7 while the dc differential gain is close to 10. S-parameter measurements, performed at a current density of 1.8×104 A cm−2, yield a current gain cutoff frequency of 6 GHz and a maximum frequency of oscillation of 12.5 GHz.
Growth of laser-quality single crystals of Nd3+-doped calcium fluorapatite and their efficient lasing performance
Authors: Zhang X. X. , Loutts G. B. , Bass M. , Chai B. H. T.
Published: July 2002

The Czochralski growth of laser-quality Nd3+-doped calcium fluorapatite single crystals and their lasing characterization are reported. Low threshold and high efficiency lasing performances were achieved in both continuous-wave and long pulse laser-pump-laser operation. The effect of concentration quenching on laser performance is discussed.
Epitaxial growth and surface structure of (0001) Be on (111) Si
Authors: Ruffner Judith A. , Slaughter J. M. , Eickmann James , Falco Charles M.
Published: July 2002

We report the growth of epitaxial single-crystal (0001) hcp-Be on (111) Si substrates using molecular beam epitaxy. The Be is oriented with Be[101̄0]∥Si[110] and Be[112̄0]∥Si[211]. Crystalline quality improves with increasing deposition temperature T, where T=100, 200, 300, 400, and 500 °C for the results reported here. The films deposited at T≤300 °C are smooth while those deposited at T≥400 °C are rough. A superstructure was observed on the surface, probably √3×√3, R30°, for films grown at T=300 °C. These epitaxial beryllium films are of much better quality than those we previously reported on α-Al2O3.
Very low saturation densities in strained InGaAs/AlGaAs multiple quantum wells
Authors: Moloney M. H. , Hegarty J. , Buydens L. , Demeester P.
Published: July 2002

The saturation of excitonic absorption in strained InGaAs/AlGaAs quantum wells is systematically measured as a function of strain. By comparison with an unstrained GaAs/AlGaAs quantum well sample a reduction by a factor of up to 9 in the saturation carrier density is observed in strained samples with indium concentrations of 10% and 15%. Very low saturation densities, as low as 0.82×1017 cm−3, are reported for the InGaAs/AlGaAs quantum wells with an indium concentration of 15%. The reduction in the saturation density is attributed to the change in the valence band density of states and the fact that these samples were designed to be fully strained. A novel method of measuring the absorption without antireflection coatings is described.
Phosphorus incorporation in plasma deposited diamond films
Authors: Schauer S. N. , Flemish J. R. , Wittstruck R. , Landstrass M. I. , Plano M. A.
Published: July 2002

Phosphorus-doped polycrystalline and homoepitaxial diamond films were grown using both microwave and dc plasma assisted chemical vapor deposition. P incorporation was quantified using secondary ion mass spectrometry, and was approximately ten times greater for polycrystalline films deposited using dc plasmas compared to microwave plasmas. For microwave-assisted growth, P incorporation was approximately ten times greater in polycrystalline than homoepitaxial films. These effects appear to be due to preferential incorporation at grain boundaries, since higher levels of P are measured in samples with smaller grains. The films were highly electrically resistive, with conductivities of 10−10–10−9/Ω cm at room temperature.
Electric field-dependent nonphotorefractive gratings in a nonlinear photoconducting polymer
Authors: Silence S. M. , Donckers M. C. J. M. , Walsh C. A. , Burland D. M. , Moerner W. E. , Twieg R. J.
Published: July 2002

The molecularly doped polymer system polyvinylcarbazole:Lophine 1:2,4,7-trinitro-9-fluorenone, which is both photoconductive and optically nonlinear, forms a grating whose diffraction efficiency is strongly dependent on the externally applied electric field. Two-beam coupling measurements show no energy transfer between the beams and grating translation measurements and reveal an index of refraction grating that is not phase shifted relative to the light intensity pattern at any value of the externally applied field. These results lead to the conclusion that, even though diffraction is field dependent, the grating is not photorefractive in origin. This illustrates the importance of two-beam coupling measurements for characterization of potentially photorefractive polymers. A possible origin of the nonphotorefractive grating based on quadratic electroabsorption is discussed.
Picosecond coherent Raman study of solid-state chemical reactions during laser polymer ablation
Authors: Hare David E. , Dlott Dana D.
Published: July 2002

Multiplex picosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) is used to study the dynamics of a thin film of a polymer, poly-methyl methacrylate (PMMA), undergoing photothermal laser ablation. Time-dependent CARS spectra of a PMMA Raman transition near 810 cm−1 reveal line broadening, attributed to temperature increase, peak shift, attributed to rapid volume expansion, and the appearance of a new peak attributed to the formation of methyl methacrylate by picosecond time scale polymer thermal decomposition. This is believed to be the first direct observation of a chemical reaction product in the solid itself, during laser ablation.
Nondestructive photoacoustic detection of exciton resonances in GaAs/AlGaAs multiple quantum well structures
Authors: Chu J. H. , Bak Y. H. , Kim J. H. , Park H. L. , Park S. H. , Kim U. , Choi J. G. , Kim I. G.
Published: July 2002

We report nondestructive observations of both heavy-hole and light-hole excitons in the GaAs/AlGaAs multiple quantum wells (MQWs) using photoacoustic spectroscopy. The absorption spectra were measured by the gas-microphone photoacoustic technique with a minimal volume cell and grazing incidence method. Two distinct peaks were clearly observed in the photoacoustic signal and phase spectra of the MQW at room temperature. A photoreflectance measurement for the given MQW structure revealed that two peaks originated from the heavy-hole and light-hole excitonic resonances.
Effect of proton irradiation on the critical current and resistance of high T
c grain boundary Josephson junctions
Authors: Jackson E. M. , Weaver B. D. , Summers G. P.
Published: July 2002

We have investigated the effects of defects on the critical current and resistance of high Tc grain boundary Josephson junctions using irradiation with 2-MeV protons. Radiation-induced defects cause the critical current (Ic) to decrease and the shunt resistance (R) to increase such that IcR∝1/R. The data are consistent with a tunneling barrier height increasing with fluence.
Low threshold and broad tunability of an organic optical parametric oscillator
Authors: Josse D. , Khodja S. , Badan J. , Samuel I. D. W. , Zyss J.
Published: July 2002

Optical parametric oscillation in the molecular organic crystal NPP [N-(4-nitrophenyl)-L-prolinol] is reported at a pumping wavelength of 670 nm with pulse duration of 60 ns, and improved performance over the earlier demonstration at 592.7 nm pump wavelength (pulse duration 1 ns). The pumping scheme is simplified, the oscillation threshold substantially decreased by more than an order of magnitude to 0.5 MW/cm2, with the benefit of an increasingly wavelength noncritical configuration as the pump wavelength is shifted towards the infrared.
Energy band lineup at the porous-silicon/silicon heterointerface measured by electron spectroscopy
Authors: Hao P. H. , Hou X. Y. , Zhang F. L. , Wang Xun
Published: July 2002

The energy band gap of light-emitting porous silicon is determined by high-resolution electron energy loss spectroscopy, and the valence band edge of porous silicon with respect to its Fermi level is measured by ultraviolet photoelectron spectroscopy. By combining the results with that measured from clean Si, a picture of band lineup at the porous-silicon/p-Si heterointerface is proposed, in which 70% of the total band gap discontinuity occurs at the valence band edge.
Room-temperature stimulated emission of optically pumped GaAs/AlAs quantum wires grown on (311)A-oriented substrates
Authors: Orth A. , Reithmaier J. P. , Forchel A. , Nötzel R. , Ploog K.
Published: July 2002

Stimulated emission of optically pumped GaAs/AlAs quantum wires directly grown on (311)A-oriented GaAs substrates has been observed at 77 K and room temperature. A significant reduction of the threshold excitation energy density for stimulated emission at room temperature could be measured in comparison to a two-dimensional reference sample as well as a reduction of the temperature sensitivity of the threshold.
Electrical band gap of porous silicon
Authors: Chen Zhiliang , Lee Tzung-Yin , Bosman Gijs
Published: July 2002

The electrical band gap of porous silicon is determined from measurements of the reverse bias current of homojunction pn porous silicon diodes versus temperature, resulting in a value of 2.2 eV. This value is in good agreement with the value of 1.97 eV obtained from photo- and electroluminescence experiments.
Improvement of multiquantum-barrier effect by layer-thickness modulation
Authors: Fujii Hiroaki , Endo Kenji , Hotta Hitoshi
Published: July 2002

We propose a novel modulated-layer-thickness multiquantum-barrier (MQB) structure, or chirped MQB. The chirped MQB has a larger potential increase (240 meV) against overflowing electrons than the uniform MQB by almost 100 meV. It also has a broader optimum well thickness width of 1.9 nm while the uniform MQB has only 0.5 nm optimum width. This indicates that the chirped MQB would work more effectively even under the layer thickness fluctuation caused by step bunching, etc.
Radio frequency performance of superconducting thin films in high magnetic fields
Authors: Hübner H. , Valenzuela A. A.
Published: July 2002

We describe measurements of the specific resistivity of epitaxially grown YBa2Cu3O7−x thin films in the presence of a magnetic field of up to 1 T at 270 MHz. At 77 K and 300 mT a 70-fold reduction of the specific resistance, as compared to liquid nitrogen cooled copper, is achieved. These results suggest a possible application of these films as small receiving coils with improved sensitivity in low field nuclear magnetic resonance imaging systems.
Formation of lanthanum strontium cobalt thin films by metalorganic decomposition
Authors: Mantese Joseph V. , Micheli Adolph L. , Catalan Antonio B. , Schubring Norman W.
Published: July 2002

Electrically conductive films of La0.5Sr0.5CoO3, 1 μm thick, were formed on a variety of substrates by metalorganic decomposition. The lowest resistivity films (1.2×10−3 Ω cm) were obtained on c-axis sapphire by annealing in oxygen at 800 °C. The film conductivity was limited by the diffusion of strontium into the substrate.
Suppression of Cu diffusion from a bulk ZnSe substrate to a homoepitaxial layer by Se-beam irradiation as a pregrowth treatment
Authors: Hishida Yuji , Toda Tadao , Yoshie Tomoyuki , Yagi Katsumi , Yamaguchi Takao , Niina Tatsuhiko
Published: July 2002

Cu diffusion of homoepitaxial ZnSe was investigated through low-temperature photoluminescence (PL) spectra and secondary ion mass spectroscopy. Though Cu in ZnSe normally diffuses easily, we found that Cu in a ZnSe substrate did not diffuse into the homoepitaxial layer when the substrate was heated under Se-beam irradiation prior to growth. Cu-related emissions, such as Ideep1 and Cu-green, disappeared from the PL spectrum of the homoepitaxial layer grown on the Se-beam irradiated substrate. This suppressed Cu diffusion can be explained by site transformation of interstitial Cu atoms in the ZnSe substrate into Cu atoms occupying the Zn lattice site. This treatment is very useful for improving the purity of homoepitaxial ZnSe layers.
Microstructure of epitaxial oxide thin film heterostructures on silicon by pulsed laser deposition
Authors: Ghonge Subodh G. , Goo Edward , Ramesh R. , Haakenaasen R. , Fork D. K.
Published: July 2002

The microstructure of epitaxial La0.5Sr0.5CoO3(LSCO)/ferroelectric lanthanum modified lead zirconate titanate (PLZT)/ La0.5Sr0.5CoO3(LSCO)/bismuth titanate(BT)/yttria-stabilized zirconia (YSZ) heterostructures on [001] silicon has been investigated. X-ray diffraction and pole figure analysis reveal epitaxial growth of the PLZT, LSCO, BT, and YSZ layers. High resolution transmission electron microscopy was done to study the crystal defects and interfacial structure.