bluuebunny/crossref_metadata_2025 huggingface dataset:
New method for comprehensive phase-amplitude contrast imaging of the internal structure of matter using high-energy radiation
Authors: Nikulin A. Yu.
Published: July 2002

A nondestructive method for structural imaging is proposed. The method is based on direct measurements of phase and amplitude changes in a two-dimensional x-ray image. A standing wave is formed between two separated crystals allowing high-resolution imaging of the complex refractive index. A comprehensive analysis of the amplitude-phase contrast is possible because of the precisely controlled variation of the phases between the reference and reflected beams from a crystalline mirror.
Transfer of temporal fluctuations in photorefractive two-beam coupling
Authors: Juul Jensen S. , Saffman M.
Published: July 2002

Transfer of temporal fluctuations between the signal and pump beams in diffusion dominated photorefractive two-beam coupling is studied experimentally. The dependence on the gain, beam intensity ratio, and frequency of the fluctuations is found to agree well with a linearized analysis. The transfer of perturbations is frequency dependent at low frequencies, and becomes constant at frequencies large compared to the inverse material time constant. We discuss the possibility of pump noise suppression when amplifying weak signals.
ZnSe nitrogen doping using an ion-free electron-cyclotron-resonance plasma beam
Authors: Tsukamoto Hironori , Nagai Masaharu , Katoh Eisaku , Tamamura Kohshi , Ishibashi Akira , Ikeda Masao
Published: July 2002

Nitrogen doping in ZnSe using a new type of electron-cyclotron-resonance (ECR) source has been investigated. Selective nitrogen radical doping is performed using the ECR source with an external electrode, which can remove charged particles in the nitrogen plasma by the electrode applied electric field. Nitrogen ions are trapped by the electrode and the ion current is measured as a function of the electric field. The activation ratio of nitrogen atoms is investigated for various doping conditions by comparing the carrier profile and the atomic nitrogen profile, which are measured by capacitance–voltage techniques and secondary ion mass spectrometry. It was confirmed that nitrogen ions are removed and do not play a role as p-type dopants in ZnSe growth by molecular beam epitaxy. The activation ratio of nitrogen atoms is increased by removing the nitrogen ions.
Anomalous photoluminescence from 3C-SiC grown on Si(111) by rapid thermal chemical vapor deposition
Authors: Shim H. W. , Kim K. C. , Seo Y. H. , Nahm K. S. , Suh E.-K. , Lee H. J. , Hwang Y. G.
Published: July 2002

Single crystal 3C-SiC epitaxial films are grown on Si(111) surfaces using tetramethylsilane by rapid thermal chemical vapor deposition. Strong blue/green photoluminescence (PL) was observed at room temperature from the free films of SiC prepared by etching the Si substrate. The main PL peak energy varies from 2.1 to 2.4 eV with full widths at half-maximum between 450 and 500 meV, depending on the growth condition, excitation wavelength and excitation light intensity. A weak peak at 3.0 eV also appeared. The infrared (IR) spectra of free films of SiC exhibit modes associated with CH and OH groups. We also compared PL characteristics of free films of SiC with those from porous SiC produced by anodization of SiC/Si to determine the origin of the PL. Porous SiC shows a PL peak centered at 1.9 eV, different from those in SiC. From the analysis of the IR spectra and scanning electron microscopic images, we tentatively suggest that the origin of the PL from free films of SiC might be associated with an OH group adsorbed on defects or some localized states as is the case for an amorphous SixC1−x alloy.
Fast mutually pumped phase conjugation using transient photorefractive coupling
Authors: Raita Erik , Kamshilin Alexei A. , Prokofiev Victor V. , Jaaskelainen Timo
Published: July 2002

Unusually fast mutually pumped phase-conjugation (MPPC) is achieved in a Bi12TiO20 crystal by using transient photorefractive beam coupling under a dc electric field. Pulses of phase-conjugate waves with a buildup time of 4.5 ms and a width of 50 ms at an input intensity of 2×0.8 W/cm2 are obtained after applying a rising front of external electric field to the crystal. A phase-conjugation efficiency as high as 25% of the incident light power is measured.
Low temperature shallow junction formation using vacuum ultraviolet photons during rapid thermal processing
Authors: Singh R. , Cherukuri K. C. , Vedula L. , Rohatgi A. , Narayanan S.
Published: July 2002

In this letter, we have demonstrated phosphorus diffusion into silicon at a temperature of 700 °C using dual spectral source rapid thermal processing (RTP). The optical energy of vacuum ultraviolet irradiation in conjunction with tungsten halogen lamps (light source used in conventional RTP) is responsible for diffusion at low temperatures. Shallow junctions with high surface concentration were formed and no significant degradation in the bulk minority carrier lifetimes was observed. A qualitative explanation for the observed results is offered based on the role of photoeffects in RTP.
Planar p-on-n HgCdTe heterostructure infrared photodiodes on Si substrates by molecular beam epitaxy
Authors: Dhar N. K. , Zandian M. , Pasko J. G. , Arias J. M. , Dinan J. H.
Published: July 2002

We have developed a low temperature procedure for molecular beam epitaxy of CdTe buffer layers on {211} Si wafers and have used Si/ZnTe/CdTe composite substrates for molecular beam epitaxy of double layer Hg1−xCdxTe heterostructures. Planar p-on-n double layer heterostructures were formed by an implantation technique and test diodes were fabricated and characterized. At 77 K, devices with 30×30 μm2 junction area had R0A values in the range 1.5×106–1×107Ω cm2 with a uniform cut-off wavelength of 4.65 μm.
Charge-separated state in strain-induced quantum dots
Authors: Gu Y. , Sturge M. D. , Kash K. , Watkins N. , Van der Gaag B. P. , Gozdz A. S. , Florez L. T. , Harbison J. P.
Published: July 2002

We have measured the time-resolved photoluminescence of strain-induced quantum dots. We show that a long-lived intermediate state is involved in the excitation transfer from the interstitial quantum well to the dot. This intermediate state has the properties expected of the charge separated state predicted by theory.
Correlation of electrical and optical characteristics of selectively oxidized vertical-cavity surface-emitting lasers
Authors: Li J. , Seurin J.-F. , Chuang S. L. , Choquette K. D. , Geib K. M. , Hou H. Q.
Published: July 2002

We investigate the correlation between the electrical and optical characteristics of selectively oxidized vertical-cavity surface-emitting lasers (VCSELs). Electrical derivative analysis is used on VCSELs to study the electrical performance and its correlation with the polarization-resolved optical powers and spectra. Characteristic features are shown in the IdV/dI curves near major transition points of VCSEL operation. From the IdV/dI curve we are able to precisely identify important operating currents such as the lasing threshold, the higher-order mode lasing current, and the cut-off current. Five operation regions are defined in the polarization-resolved L−I curves based on these currents and their temperature dependences are also studied.
A wavelength and polarization selector made of holographic polarization beamsplitting cubes for optical communications
Authors: Chang Jen-Tsorng , Su Der-Chin , Huang Yang-Tung
Published: July 2002

We present a combined wavelength-polarization selector made of holographic polarization beamsplitting cubes in series. Each unit cube comprises a pair of prisms and a transmission-type phase volume hologram. The assembled selector, when examined with an intensity modulated beam of known polarization state, demonstrated our designated target.
Observation of core-level binding energy shifts between (100) surface and bulk atoms of epitaxial CuInSe2
Authors: Nelson A. J. , Berry G. , Rockett Angus , Shuh D. K. , Carlisle J. A. , Sutherland D. G. J. , Terminello L. J.
Published: July 2002

Synchrotron radiation soft x-ray photoemission spectroscopy was used to directly observe Se 3d core-level binding energy shifts from surface atoms of the (100) face of epitaxial CuInSe2/ GaAs(100). High-resolution spectra show two sets of Se 3d5/2,3/2 spin-orbit components separated by 0.6 eV, with the low-binding-energy peaks being associated with the surface atoms. However, surface state emission from Se p states in the valence band was not observed due to the low photoionization cross sections. Cation bonding-antibonding states were observed in the valence band and are centered at about 1.0 and 3.1 eV below the valence band edge.
Flux pinning by Ba-site magnetic rare-earth ions in (rare-earth)1+uBa2−uCu3Ox compounds
Authors: Blackstead Howard A. , Dow John D.
Published: July 2002

The same physics that correctly predicted superconductivity of PrBa2Cu3O7 also explains flux pinning by Ba-site magnetic rare-earth ions in (rare-earth)1+uBa2−uCu3Ox compounds with x≈7. The customary cuprate-plane picture of superconductivity must be revised in the same way to consistently explain the observations either of flux pinning or of PrBa2Cu3O7 superconductivity with Tc≈90 K.
Self-sharpening tip integrated on micro cantilevers with self-exciting piezoelectric sensor for parallel atomic force microscopy
Authors: Indermühle P.-F. , Schürmann G. , Racine G.-A. , de Rooij N. F.
Published: July 2002

Arrays of cantilevers with integrated self-sharpening tips and self-exciting piezoelectric sensors have been fabricated using monocrystalline silicon micromachining. During the fabrication process, tips are first formed with a wet etching technique allowing a good homogeneity of tip shape over a whole wafer and then protected with a local thick silicon dioxide layer. Single cantilevers have been used to achieve atomic force microscopy images of grids with periods of 0.25, 1, and 5 μm and with height differences of 100, 15, and 180 nm, respectively.
Transmission of pulsed CO2 laser beams through “opaque” liquids by a cavitation effect
Authors: German A. , Bunimovich D. , Katzir A.
Published: July 2002

The formation of a stationary cavity by a sequence of CO2 laser pulses was investigated in liquids of different viscosity and surface tension. Decreasing the surface tension of the liquid and increasing its viscosity increases the depth of the cavity and decreases the threshold energy needed for its formation. A theoretical model based on the Bernoulli–Stokes equation was developed. Good agreement between experimental and theoretical results was obtained. A method of reducing thermal damage, involving liquid layer effects during laser cutting of different materials, is proposed.
Single-mode and single-beam surface emission from visible red GaInP/AlGaInP laser diodes
Authors: Kellermann P. O. , Golshani A. , Köck A. , Gornik E. , Gauggel H.-P. , Winterhoff R. , Pilkuhn M. H.
Published: July 2002

Single-mode and single-beam surface emission (675–680 nm) has been achieved from visible red GaInP/AlGaInP laser diodes by applying the surface mode emission technique. The laser diodes emit a single beam via the surface with a beam divergence of 0.16° and show single-mode emission both in ac as well as in dc operation with a minimum spectral linewidth of 0.07 nm. The highest sidemode suppression achieved at present in ac operation is 19 dB.
Optical absorption and light-induced charge transport of Fe2+ in BaTiO3
Authors: Mazur A. , Schirmer O. F. , Mendricks S.
Published: July 2002

Iron doped barium titanate was grown and reduced at various temperatures. Using optical absorption and electron paramagnetic resonance (photo-EPR) simultaneously, a wide absorption band at ∼2.1 eV due to Fe2+ is established. The light-induced charge transport between Fe2+/3+ and shallow Ti4+/3+−VO is identified, showing a two-center type response at low and one-center type response at room temperature.
Grating coupling for intersubband emission
Authors: Xu Bin , Hu Qing
Published: July 2002

Grating coupling for surface-emitting intersubband light-emitting diodes (LEDs) and lasers are analyzed with a numerical method. The grating efficiency is calculated as functions of the grating periodicity and filling factor, and the vertical confinement thickness. The coupling loss is related linearly with the grating efficiency, which should be maximized for LEDs to couple out the spontaneous emission, but kept low for lasers to reduce the lasing threshold.
Determining the band discontinuities of ZnSe/GaAs and ZnMgSSe/GaAs heterojunctions using free electron laser
Authors: Nishi Kazuhisa , Ohyama Hideaki , Suzuki Toshiji , Mitsuyu Tsuneo , Tomimasu Takio
Published: July 2002

The conduction band discontinuities of ZnSe/GaAs and ZnMgSSe/GaAs heterojunctions were investigated using the free electron laser (FEL) internal photoemission technique. This technique is based on the photocurrent spectroscopy utilizing the tunability and intense peak power of the FEL operative in the infrared range. We found the conduction band discontinuities of 113 (ZnSe/GaAs) and 180 meV (ZnMgSSe/GaAs). It is suggested that the band gap discontinuity between ZnSe and ZnMgSSe is δEc (conduction band): δEv (valence band)=0.45:0.55 at 77 K.
Noncollinear four-wave mixing in a broad area semiconductor optical amplifier
Authors: Zhu Daniel X. , Dubovitsky Serge , Steier William H. , Uppal Kushant , Tishinin Denis , Burger Johan , Dapkus P. Daniel
Published: July 2002

A high-efficiency noncollinear four-wave mixing in a broad area traveling-wave semiconductor optical amplifier is demonstrated. A key feature of the demonstrated configuration is the ability to isolate generated sidebands from the inputs. A wave-mixing efficiency of +8.2 dB with 22.6 dB of sideband isolation at 6° separation between the two pump beams was obtained. The dependence of the efficiency on pump detuning, separation angle, and probe wavelength was also investigated. Use of a high quality traveling-wave amplifier enabled us to achieve ripple-free broadband operation over 37 nm. The demonstrated configuration is a key to practical implementations of four-wave mixing based devices.
Negative differential conductance at room temperature in three-terminal silicon surface junction tunneling device
Authors: Koga Junji , Toriumi Akira
Published: July 2002

Negative differential conductance based on forward biased band-to-band tunneling is demonstrated at room temperature in a three-terminal silicon surface junction tunneling device. The device is fabricated on silicon dioxide to achieve an extremely small bulk leakage current together with a sharp drain impurity profile. A new device structure, in which the active tunneling junction is away from the field isolation, is also employed to totally eliminate excess tunneling current at the field oxide corner. It is observed that the tunneling current is largely controlled by the gate bias which modulates the tunneling distance. This functional device can be easily implemented into the fabrication process for silicon ultralarge scale integrated circuits, and is expected to be a useful post complementary metal–oxide–semiconductor device in future silicon technology.
Effect of carrier diffusion in oxidized vertical-cavity surface-emitting lasers determined from lateral spontaneous emission
Authors: Shin J. H. , Shin H. E. , Lee Y. H.
Published: July 2002

The effect of carrier diffusion on threshold current is studied quantitatively for the oxide-aperturbed 780 nm vertical-cavity surface-emitting lasers (VCSEL) from the measured spontaneous emission. The oxide aperture size of 2–10 μm is prepared and characterized. The diffusion coefficient of 4.6 cm2/s and the nonradiative recombination coefficient of 6.8×107/s are obtained using the independence of the nonradiative recombination coefficient on the laser aperture size. The contribution of carrier diffusion loss is 42% of the threshold current for the 2 μm VCSEL. The relative contribution of the diffusion becomes smaller for the larger devices as is expected.
Laser-induced generation of pure tensile stresses
Authors: Niemz M. H. , Lin C. P. , Pitsillides C. , Cui J. , Doukas A. G. , Deutsch T. F.
Published: July 2002

While short compressive stresses can readily be produced by laser ablation, the generation of pure tensile stresses is more difficult. We demonstrate that a 90° prism made of polyethylene can serve to produce short and pure tensile stresses. A compressive wave is generated by ablating a thin layer of strongly absorbing ink on one surface of the prism with a Q-switched frequency-doubled Nd:YAG laser. The compressive wave driven into the prism is reflected as a tensile wave by the polyethylene-air interface at its long surface. The low acoustic impedance of polyethylene makes it ideal for coupling tensile stresses into liquids. In water, tensile stresses up to −200 bars with a rise time of the order of 20 ns and a duration of 100 ns are achieved. The tensile strength of water is determined for pure tensile stresses lasting for 100 ns only. The technique has potential application in studying the initiation of cavitation in liquids and in comparing the effect of compressive and tensile stress transients on biological media.
Depth analysis of phase formation in Si after high-dose Fe ion implantation by depth-selective conversion-electron Mössbauer spectroscopy
Authors: Kruijer S. , Keune W. , Dobler M. , Reuther H.
Published: July 2002

Fe + ions of 200 keV in energy were implanted into Si(111) at 350 °C with a dose of 7×1017 cm−2. The depth distribution of the two formed phases (ε-FeSi and β-FeSi2) was investigated nondestructively up to a depth of about 800 Å by depth-selective conversion-electron Mössbauer spectroscopy (DCEMS) in combination with depth-profiling (destructive) Auger electron spectroscopy (AES). Near the surface only β-FeSi2 is formed, while a mixture of β-FeSi2 and ε-FeSi is formed at larger depths. The Fe-concentration depth profile calculated from the DCEMS results is in good agreement with that measured by AES.
Correlation between dielectric breakdown and charge generation in silicon oxide films
Authors: Hayakawa Tetsuo , Watanabe Yukihiko , Funabashi Hirofumi , Mitsushima Yasuichi , Taga Yasunori
Published: July 2002

To clarify the correlation between breakdown characteristics and charge generation under high field electrical stress, we have separated the contributions of the charges generated in the oxide bulk and near the Si/SiO2 interface to oxide breakdown. It is found that the density of positive charges generated near the cathode interface increases monotonically with stress time, and that it was independent of stress conditions immediately before breakdown. No correlation between charge generation in the oxide bulk and oxide breakdown has been observed. These results are new experimental evidences which support the model showing that positive charges generated near the cathode interface are responsible for oxide breakdown.
Fabrication of high mobility in situ back-gated (311)A hole gas heterojunctions
Authors: Simmons M. Y. , Hamilton A. R. , Stevens S. J. , Ritchie D. A. , Pepper M. , Kurobe A.
Published: July 2002

Using an n-type (311)A GaAs substrate we have fabricated in situ back-gated GaAs/(Al,Ga)As hole gases with mobilities of μ=1.1×106 cm2 V−1 s−1 at 30 mK. We have investigated both experimentally and theoretically the scattering mechanisms that limit the mobility in both the [2̄33] and [011̄] directions. Using a combination of front and back gates to keep the carrier density constant, we can distinguish between scattering mechanisms which are primarily dependent on the carrier density and those that are sensitive to the shape of the hole wave function. This approach also eliminates complications arising from the variations of the Fermi surface anisotropy with carrier density. Our data confirms that anisotropic interface roughness scattering, arising from the nature of the (311)A GaAs surface, is the dominant scattering mechanism at carrier densities down to ps=5.0×1010 cm−2.
Noise-free avalanche multiplication in Si solid state photomultipliers
Authors: Kim Jungsang , Yamamoto Yoshihisa , Hogue Henry H.
Published: July 2002

Si solid state photomultipliers utilize impact ionization of shallow impurity donor levels to create an avalanche multiplication when triggered by a photoexcited hole. The distribution of pulse height from a single photon detection event shows narrow dispersion, which implies that the avalanche multiplication process in these devices is inherently noise-free. We have measured the excess noise factor using two different techniques, digital pulse height analysis and analog noise power measurement. The results demonstrate nearly noise-free avalanche multiplication accomplished in these devices.
High peak-current-density strained-layer In0.3Ga0.7As/Al0.8Ga0.2As resonant tunneling diodes grown by metal-organic chemical vapor deposition
Authors: Mirabedini Ali R. , Mawst Luke J. , Botez Dan , Marsland Robert A.
Published: July 2002

Peak current densities two times higher than the best values reported for GaAs-based resonant tunneling diode (RTD) structures have been obtained from metal-organic chemical-vapor deposition (MOCVD)-grown deep-quantum-well strained-layer In0.3Ga0.7As/Al0.8Ga0.2As RTDs. By growing on nominally exact (100) +/−0.1° GaAs substrates, we have been able to obtain smooth interfaces between the strained-layer In0.3Ga0.7As quantum well and Al0.8Ga0.2As barriers, which, in turn, enabled us to benefit from resonant tunneling through the second resonant energy level of In0.3Ga0.7As/Al0.8Ga0.2As structures. Peak current densities in excess of 300 kA/cm2, and peak-to-valley current ratios as high as 3:1, at 300 K, have been obtained from structures with 14-Å-thick barriers and a 57-Å-thick well.
Spatial and temperature dependence of magnetic moment perturbations near the (1-10) Fe/Co interface
Authors: Swinnen B. , Dekoster J. , Meersschaut J. , Cottenier S. , Demuynck S. , Langouche G. , Rots M.
Published: July 2002

The spatial dependence of the magnetic moment perturbation near the (1-10)-Fe/Co interface was derived from hyperfine fields determined by perturbed angular correlation. The amplitude of the moment perturbation decays exponentially with the distance to the interface. The moment perturbation itself is modulated by a sine function of the distance d to the interface Δμ=A*exp(−p*|d|)*sin(−k*d). Between 90 K and 570 K, we observe that the amplitude and the penetration depth of the perturbation as well as the wave vector of the modulation are essentially constant within the accuracy of the values. In this temperature region the average values for the parameters determining the exact moment perturbation are A=1.03μB, p=2.25×109 m and k=1.45×1010 m−1 when d is defined positive at the Co side of the interface.
Franz–Keldysh effect in lateral GaAs/AlGaAs based npn structures
Authors: Baumgartner P. , Engel C. , Böhm G. , Abstreiter G.
Published: July 2002

Lateral npn structures, fabricated by focused laser beam-induced doping, combine large potential modulations with a small width of the p-doped regions. This results in strong lateral electric fields, which can be tuned by applying a bias voltage. Photon absorption for energies below the band gap is allowed due to the Franz–Keldysh effect. We estimate the value of the electric fields by analyzing wavelength-dependent photocurrent measurements. The fields are comparable to attainable fields in existing vertical modulator structures. The spatially resolved photocurrent measurements reveal the location of the highest lateral electric field, which is at the edges of the p-doped region.
Dynamic polariscopic imaging of laser-induced strain in a tissue phantom
Authors: Delacrétaz G. , Walsh J. T. , Asshauer T.
Published: July 2002

Laser ablation and associated bubble formation are known to damage biologic tissue. Imaging of tissue straining during ablation would further the understanding and control of laser-induced damage. We have investigated the use of polariscopic imaging to monitor the strain induced by holmium laser radiation. The laser energy was delivered via an optical fiber either within or 1.7 mm from the surface of a photoelastic tissue phantom, poly(acrylamide) gel, whose viscoelastic properties could be controlled to mimic various tissues. Our results demonstrate that dynamic polaroscopy is a sensitive method to probe the strain experienced by the tissue during pulsed laser irradiations. Only compressive strain is observed when the bubble is formed within the phantom, whereas significant tensile strain is induced when the bubble is formed at or next to the surface.
Threshold behavior in synchrotron-radiation-stimulated recrystallization during Si homoepitaxy on Si(100)
Authors: Akazawa Housei
Published: July 2002

A brilliant synchrotron-radiation beam with a large irradiation area has made it possible to use spectroscopic phase-modulated ellipsometry to monitor vacuum-ultraviolet-excited Si homoepitaxy. We find the crystallinity of Si films grown at 250 °C from Si2H6 depends strongly on the photon intensity. When the photon intensity is higher than a critical value, electronically excited crystallization yields epitaxial Si. At lower intensities, however, the initial epitaxy is terminated halfway by island-shaped regions of polycrystalline Si, which are eventually covered by a uniform nanocrystalline Si overlayer.
Photoluminescence study of implantation dose and dose-rate dependence of Si doping of GaAs
Authors: Kotani M. , Iqbal M. Zafar , Makita Y. , Morton R. , Lau S. S.
Published: July 2002

Photoluminescence spectroscopy is used to investigate some of the recently reported effects of implantation dose and dose rate on the electrical activation of Si dopant in GaAs. Two new luminescence bands are observed to emerge in our spectra with the increasing Si dose at doses (∼2×1013 cm−2) where the carrier concentration is known to saturate. The higher energy band at the ∼840–880 nm wavelength shows a more pronounced rise in strength with increase in dose rate from 3 nA/cm2 beam current density to 60 nA/cm2. The deep-level luminescence band extending from ∼1000 to ∼1600 nm wavelength dominates the spectra for both the low-dose-rate and high-dose-rate samples above a dose of ∼2×1013 cm−2. The observed rapid generation of type-I dislocations above this dose suggests this band is related to some impurity Cottrell atmospheres around the dislocations in GaAs.
High-power (>0.9 W cw) diffraction-limited semiconductor laser based on a fiber Bragg grating external cavity
Authors: Cornwell Donald M. , Thomas Heather J.
Published: July 2002

We have developed a high-power (>0.9 W cw) diffraction-limited semiconductor laser based on a tapered semiconductor optical amplifier using a fiber Bragg grating in an external cavity configuration. Frequency-selective feedback from the fiber grating is injected into the amplifier via direct butt coupling through a single mode fiber, resulting in a spectrally stable and narrow (<0.3 nm) high-power laser for solid-state laser pumping, laser remote sensing, and optical communications.
The suppression of misfit dislocation introduction in heavily carbon doped GaAs
Authors: Westwater S. P. , Bullough T. J. , Joyce T. B. , Davidson B. R. , Hart L.
Published: July 2002

The relaxation of heavily carbon doped GaAs, grown on (001) GaAs substrates was investigated using transmission electron microscopy and x-ray diffraction. Misfit dislocation introduction occurred only significantly above Matthews and Blakeslee’s critical thickness, with the onset of relaxation being delayed as the C concentration was increased. The resultant strain relaxation was highly anisotropic with the introduction of As-cored misfit dislocations being totally suppressed at the highest C levels, resulting in cracking of the epilayer. Locking of As-cored partial dislocations and a reduction in misfit dislocation velocity is proposed as the cause of the anisotropy and lack of relaxation.
A 40-nm-pitch double-slit experiment of hot electrons in a semiconductor under a magnetic field
Authors: Hongo Hiroo , Miyamoto Yasuyuki , Furuya Kazuhito , Suhara Michihiko
Published: July 2002

We report a double-slit experiment of hot electrons in a semiconductor under a magnetic field. The pitch of the double slit buried in the semiconductor is 40 nm and the electron energy is of the order of 100 meV. By applying a magnetic field, the change in current that passes through the slits is observed at the segmented collector. The measured current shows a clear minimum around B=0 T, with this behavior agreeing with a theoretical calculation based on double-slit interference. Quantitative estimation is consistent with this order of current variation. We think that these results show evidence of the observation of hot electron interference by a double slit in a semiconductor.
Phase contrast hard x-ray microscopy with submicron resolution
Authors: Lagomarsino S. , Cedola A. , Cloetens P. , Di Fonzo S. , Jark W. , Soullié G. , Riekel C.
Published: July 2002

In this letter we present a hard x-ray phase contrast microscope based on the divergent and coherent beam exiting an x-ray waveguide. It uses lensless geometrical projection to magnify spatial variations in optical path length more than 700 times. Images of a nylon fiber and a gold test pattern were obtained with a resolution of 0.14 μm in one direction. Exposure times as short as 0.1 s gave already visible contrast, opening the way to high resolution, real time studies.
Measurements of the triplet state nonlinearity of C60 in toluene using a Z-scan technique with a nanosecond laser
Authors: Li Feng , Song Yinglin , Yang Kun , Liu Shutian , Li Chunfei
Published: July 2002

Triplet state nonlinearity of C60 in toluene is studied using the Z-scan technique with 8 ns, 532 nm pulses from a Q-switched Nd:YAG laser. Compared with the Z-scan results of C60 in toluene and iodine in toluene with proper concentration, the solvent instantaneous nonlinearity and the thermal nonlinearity resulting from the C60 intersystem crossing and excited state absorption are estimated. The real part of the C60 triplet state molecular polarizability is obtained.
The determination of activation energy in quantum wells
Authors: Ding Jinli , Tsu Raphael
Published: July 2002

The use of an Arrhenius plot of the temperature dependent current-voltage at some appropriate voltage leads to a temperature and voltage dependent activation energy, which is shown to be identical to the average energy carried by the electrons in flowing between the contacts separated by a quantum well structure. An optimal temperature range is limited by the highest temperature the system can tolerate without deleterious effects. The effective barrier height determined in a limited voltage range V⩽2(E1−Ef)/e is equal to the ground state energy E1, of the quantum well structure.
Photoluminescence from C+-implanted SiNxOy films grown on crystalline silicon
Authors: Liao L. S. , Xiong Z. H. , Zhou X. , Liu X. B. , Hou X. Y.
Published: July 2002

Carbon ions at an energy of 35 keV with a dose of 5×1016 cm−2 were implanted into SiNxOy films grown on crystalline silicon by plasma enhanced chemical vapor deposition. Intense photoluminescence (PL) peaked at about 550 nm is observed in the implanted films under an excitation of 441.6 nm laser line. The PL intensity varies with annealing temperature, and reaches a maximum at the annealing temperature of 600 °C. The luminescence may originate from the complex of Si, N, O, and C in the films.
Halide-modified Ga–La sulfide glasses with improved fiber-drawing and optical properties for Pr3+-doped fiber amplifiers at 1.3 μm
Authors: Wang Ji , Hector Jason R. , Brady Dominic , Hewak Dan , Brocklesby Bill , Kluth Miles , Moore Roger , Payne David N.
Published: July 2002

We report Cs halide-modified Ga–La sulfide glasses, a new class of chalcohalide glasses with improved fiber-drawing and optical properties suitable for Pr3+-doped fiber amplifiers at 1.3 μm. Cs halide-modified Ga–La sulfide glasses retain the essential characteristics of low phonon-energy and good rare-earth solubility of pure Ga–La sulfide glasses. However, they transmit further into the UV/visible region of the spectrum, and can meet the need of high thermal stability for fiber fabrication.
Interferometric roughness measurement of Ohmic contact/III–V semiconductor interfaces
Authors: Montgomery P. C. , Benhaddou D. , Montaner D.
Published: July 2002

The nondestructive measurement of the internal roughness of Ohmic contacts on GaAs and InP using near-infrared interferometry through the rear of the wafer is investigated. The main difficulties were found to be associated with the thick high refractive index viewing window leading to conflicting requirements in the position of the interface along the optical axis for forming the image and the fringes. Two solutions are proposed: the first using a low numerical aperture objective, and the second using a rear surface reflecting GaAs reference mirror, giving an axial resolution of approximately 8 nm.
Energy conversion with Zr-rich lead zirconate/titanate ceramics
Authors: Duan Ning , Cereceda Noé , Noheda Beatriz , Raúl Fernandez-del-Castillo José , Gonzalo Julio A.
Published: July 2002

The conversion efficiency and power output to convert thermal energy to electrical energy by means of a ferroelectric–ferroelectric phase transition has been investigated. The material used was the ceramic mixed system lead zirconate/titanate (PZT) with a very Zr-enriched composition (Zr/Ti=97/3%). We have studied the performance dependence on sample thickness and working frequency, the main relevant parameters for a given PZT composition. The observed optimum values of efficiency and power output are analyzed in terms of the two main characteristic relaxation times of the process, the thermal time (sample thickness dependent) and the electric time (thickness independent). Possible ways of improving the overall performance are discussed.
X-ray reciprocal space mapping of a (112) oriented HgTe/Hg0.1Cd0.9Te superlattice
Authors: Li M. , Becker C. R. , Gall R. , Faschinger W. , Landwehr G.
Published: July 2002

Strain in a HgTe/Hg0.1Cd0.9Te superlattice grown on (112)B Cd0.96Zn0.04Te substrate has been investigated by x-ray reciprocal space mapping. It is shown that the shear strain in the superlattice results in monoclinic unit cells, whereas the cubic symmetry of the substrate is retained. The reciprocal lattice points of the superlattice are shifted by the shear strain such that the conventional analysis fails to interpret them correctly. Instead, reciprocal space maps should be constructed for two azimuths in opposite directions and analyzed simultaneously in a coordinate system with nonorthogonal axes. The shear strain is obtained from the angle between the [1¯1¯1] directions of the superlattice and the substrate. After a position correction taking the measured shear strain into account, longitudinal strains are calculated with conventional methods.
A study on Au/Ni/Au/Ge/Pd ohmic contact and its application to AlGaAs/GaAs heterojunction bipolar transistors
Authors: Kim Il-Ho , Park Sung Ho , Lee Tae-Woo , Park Moon-Pyung
Published: July 2002

An Au/Ni/Au/Ge/Pd ohmic contact system on n-type InGaAs was studied and applied to AlGaAs/GaAs heterojunction bipolar transistors (HBTs). Good ohmic behavior was achieved by rapid thermal annealing (RTA) at temperatures up to 400 °C, and the specific contact resistance was reduced to low-10−6 Ω cm2. However, by annealing at temperatures above 400 °C the characteristics were deteriorated by intermixing and phase reaction of the ohmic metals and InGaAs substrate. The HBTs using the Au/Ni/Au/Ge/Pd ohmic contact scheme showed reliable dc and rf performances with strong dependence on the ohmic contact, especially emitter ohmic contact with RTA temperature.
Changes in electrical conductance of hydrogenated amorphous silicon deposited on optical waveguides in glass
Authors: Danesh P. , Pantchev B.
Published: July 2002

A study of electrical conductance of hydrogenated amorphous silicon (a-Si:H) films deposited on optical waveguides in a soda-lime glass (SLG) substrate is carried out, from the viewpoint of electrical instability of a-Si:H caused by the penetration of Na ions from the glass into the film. The optical waveguides were prepared by K+–Na+ or Ag+–Na+ ion exchange using thermal or field-assisted methods. The effective thickness of optical waveguides was of several micrometers. The obtained results show that in the case of a-Si:H film deposited on silver waveguide there is a dependence of electrical conductance on measurement duration, if strongly weakened as compared with film deposited on the original SLG substrate. The a-Si:H films deposited on potassium waveguide and on Na-extracted surface are as stable, as the referent samples with Corning 7059 (Na-free) glass substrate.
The effect of nitrogen ions emitted from a plasma source on molecular beam epitaxial growth of p-ZnSe:N
Authors: Kimura K. , Miwa S. , Kajiyama H. , Yasuda T. , Kuo L. H. , Jin C. G. , Tanaka K. , Yao T.
Published: July 2002

Excited neutral nitrogen species emitted from a rf plasma source were characterized by the laser-induced fluorescence (LIF) spectroscopy, while nitrogen ions were detected by the ion counting method. The LIF intensity for nitrogen molecules increases monotonously up to the rf power of 100 W and saturates over 100 W. On the contrary, ion count of nitrogen ions shows a gradual increase up to 100 W, then rapidly increases above 100 W. The correlation between the number of excited nitrogen species and the net acceptor concentration (NA−ND) of nitrogen doped ZnSe epitaxial layers for various rf powers has been studied. We confirm that the excited neutral nitrogen molecules are effective for acceptor doping, while nitrogen ions enhance carrier compensation presumably due to degradation of crystal quality. We show that the activation ratio {(NA−ND)/[N]} of p-ZnSe:N is greatly improved by removing ions from the nitrogen plasma.
Halogen impurities in silicon: Shallow single donors
Authors: Chadi D. J.
Published: July 2002

From the results of first-principles calculations, we find that substitutional Cl, and Br and I impurities in Si are stable shallow single donor dopants that are mostly immune to deactivation processes preventing superhigh n doping of Si with column V impurities. In the absence of acceptor impurities, such as H and F, room-temperature carrier densities above 1020/cm3 are proposed to be possible, particularly with Cl, which causes the least lattice strain.
Nanoscale caliper for direct measurement of scanning force microscopy probes
Authors: Biscarini Fabio , Levy Pablo
Published: July 2002

We show the possibility to measure the effective tip shape and the lateral resolution of a scanning force microscopy (SFM) probe on the nanometer-scale directly from SFM images of SiC(0001). On this surface there are grooves 10–100-nm-wide related to cleavage planes. The SFM tip penetrates the groove but does not reach the bottom since its side walls touch both rims. The width of the narrowest groove resolved is the lateral resolution. The apparent topography across a groove yields directly the tip radius of curvature in excellent agreement with the values estimated from scanning electron micrographs.
Nonlinear absorption and gain in InGaAs/GaAs quantum wells
Authors: Coli Giuliano , Passaseo Adriana , Greco Donato , Cingolani Roberto , Tagliaferri Marco , di Trapani Paolo , Andreoni Alessandra
Published: July 2002

We present a detailed study of the excitonic nonlinearities in InGaAs/GaAs multiple quantum wells based on both stationary and transient pump-and-probe transmission spectroscopy. Bleaching of the excitonic resonance and free carrier gain have been observed. A quantitative analysis of the observed nonlinearity is provided by means of a rigorous solution of the Bethe–Salpeter equation for the investigated heterostructures.
Single-crystal Si field emitter fabricated by anodization
Authors: Higa Katsuya , Nishii Kiyoaki , Asano Tanemasa
Published: July 2002

A process for fabrication of field emitter arrays using anodization of single-crystal Si is demonstrated, when anodization is carried out in the dark on Si having n/p junctions, porous Si is preferentially formed in the p-type region. A needlelike tip structure can be formed beneath the unanodized n-type Si layer, since the anodization proceeds almost isotropically. The porous region can be easily oxidized and selectively removed by chemical etching. The shape of emitter can be controlled by changing the dimension of the n/p junction and varying the resistivity of p-type region. Fabrication of an emitter array and its field emission characteristic are reported.
Analysis of polarization anisotropy along the c axis in the photoluminescence of wurtzite GaN
Authors: Domen K. , Horino K. , Kuramata A. , Tanahashi T.
Published: July 2002

The polarization of photoluminescence (PL) was investigated on (11̄00) GaN grown by metalorganic vapor phase epitaxy. We found that the PL intensity and wavelength have polarization dependence parallel and perpendicular to the c axis. We quantitatively analyzed the dependence and found that, since the crystal field of wurtzite GaN along the c axis is strong enough to fix the |z〉 axis of p functions at the c axis, the difference in symmetry between three valence bands appears as the polarization anisotropy in radiative emission, even in bulk GaN.
Stimulated luminescence from chromate ions adsorbed on disperse silica surfaces under intense ultraviolet excitation
Authors: Glinka Yuri D.
Published: July 2002

Luminescence measurements of chromate ions (CrO42−) adsorbed onto disperse silica (SiO2) surfaces under intense pulsed ultraviolet excitation (λexc=354.7 or 266 nm, τp=20 ns) were performed at room temperature. The luminescence spectra were collected for different values of the excitation intensity (I). The luminescence yield in the red band corresponding to emission from CrO42− ions varies linearly with I under 354.7 nm excitation. However, the intensity dependence of the luminescence yield under 266 nm excitation is characterized by a threshold (I∼0.6×106 W cm−2), after which the intensity dependence of the luminescence yield is described by a power law with index n=1.7 and then saturated at I∼1.0×106 W cm−2. This feature of the excitation dynamics has been attributed to stimulated emission and considered by means of a four-level scheme. The cross section of stimulated emission was estimated as ∼3.3×10−21 cm2.
Effect of growth phase on intrinsic Stark effect in CdS–ZnSe superlattices
Authors: Bradley I. V. , Creasey J. P. , O’Donnell K. P. , Neubauer B. , Gerthsen D.
Published: July 2002

The operation of the intrinsic Stark effect at visible wavelengths is reported, for both cubic and wurtzite type-II CdS–ZnSe strained layer superlattices grown on CdS buffer layers on (111)A GaAs. An observed increase of the effective piezoelectric coefficient from the measured cubic bulk value is attributed to a nonlinear effect, as previously reported for CdTe quantum wells [R. André, J. Cibert, Le Si Dang, J. Zeman, and M. Zigone, Phys. Rev. B 53, 6951 (1996)]. Exciton peak shifts of 70 meV per decade change of excitation intensity are similar in magnitude to those found in CdS–CdSe superlattices of similar period. These shifts are attributed to screening of the internal piezoelectric fields by photoexcited carriers. Exciton peak shifts that are smaller by an order of magnitude appear in CdS–ZnSe samples, grown on (100) ZnSe buffers and therefore predicted to exhibit no piezoelectric effects of any order. These small shifts, which we attribute to space charge buildup, are a characteristic feature of type-II superlattices.
Using phthalocyanine precursors to prepare oxide thin films: Decoupling the growth rate from the evaporation rate
Authors: Mächler E. , Arrouy F. , Fritsch E. , Bednorz J. G. , Berke H. , Huber J. R. , Locquet J.-P.
Published: July 2002

Major challenges concerning the use of chemical beam epitaxy deposition techniques are posed by the lack of reliable in situ composition control and well-behaved metal–organic precursors. To circumvent these shortcomings, we propose the use of a different type of metal–organic precursors, namely molecules resistant to high temperatures, for the growth of thin films. As these molecules cannot be decomposed by the substrate temperature, they are subjected to a chemical reaction with a beam of activated species. The major advantages of this novel deposition process are listed and illustrated by the growth of CuO and YBa2Cu3O7 thin films.
Bistable GaAs–InGaP triangular-barrier optoelectronic switch
Authors: Guo Der-Feng
Published: July 2002

A bistable GaAs–InGaP triangular-barrier optoelectronic switch (TBOS), grown by metalorganic chemical vapor deposition, was fabricated. By introducing avalanche multiplication and carrier confinement into the device operation, S-shaped negative-differential-resistance performances are observed in the current–voltage (I–V) characteristics under normal and reverse operation modes. The TBOS shows a flexible optical function related to the potential barrier height controllable by incident light. The dependence of the carrier transport mechanism on the illumination was investigated. The I–V characteristics at different temperatures were also discussed.
Efficient route to TlBa2Ca2Cu3O9+x thin films by metal-organic chemical vapor deposition using TlF as a thallination source
Authors: McNeely R. J. , Belot J. A. , Hinds B. J. , Marks T. J. , Schindler J. L. , Chudzik M. P. , Kannewurf C. R. , Zhang X. F. , Miller D. J.
Published: July 2002

Thin TlBa2Ca2Cu3O9+x films were grown on single crystal (110) LaAlO3 from metal-organic chemical-vapor deposition-derived Ba–Ca–Cu–Ox precursor films employing Ba(hfa)2⋅mep, Ca(hfa)2⋅tet, and Cu(dpm)2 (hfa=hexafluoroacetylacetonate; dpm=dipivaloylmethanate; tet=tetraglyme; mep=methylethylpentaglyme) as the volatile metal sources. Thallination is then accomplished by annealing the precursor films in the presence of a bulk BaO+CaO+CuO+TlF source at 885 °C in flowing O2. The presence of TlF is essential for nucleating the Tl-1223 phase. The resulting Tl-1223 films are nearly phase-pure, highly oriented, epitaxial by x-ray diffraction, and contain negligible fluoride by windowless energy-dispersive x-ray measurements. The films exhibit a transport measured Tc=103 K and Jc=4.4×104 A/cm2 (77 K, 0 T). Magnetic hysteresis measurements yield Jc=1.9×105 A/cm2 (30 K, 0.01 T) and show considerable flux pinning at low temperatures with Jc=1.4×105 A/cm2 (5 K, 4.5 T).
Single-layer organic electroluminescent devices by vapor deposition polymerization
Authors: Wen Weng-Kou , Jou Jwo-Huei , Chiou Jeng-Feng , Chang Win-Pin , Whang Wha-Tzong
Published: July 2002

A novel method is presented herein regarding the preparation of a single-layer organic electroluminescent (EL) polymer thin film device. The device was made by simultaneously co-depositing two polymer thin film forming monomers, a hole-transporting molecule triphenyldiamine derivative (TPD) and an EL active molecule 1,1,4,4-tetraphenyl-1,3-butadiene (TPB) on an indium-tin-oxide (ITO) glass substrate. The device structure was composed of the ITO glass, the TPD, and TPB co-doped polymer thin film, and a thermally evaporated aluminum electrode. Carrier injection from the two electrodes was significantly observed and the blue light in EL spectra, with an emission maximum at 435 nm, was triggered at a driving voltage of 17 V.
Optical phonons of strained GaAs/GaP quantum wells studied by Raman spectroscopy
Authors: Castrillo P. , Armelles G. , Silveira J. P. , Briones F. , Barbolla J.
Published: July 2002

We have studied the optical phonons of GaAs quantum wells strained to GaP. The phonon frequencies have been measured by Raman spectroscopy. The results have been compared with calculations based on the linear chain model and the random isoamplitude model. The comparison suggests a certain degree of atomic intermixing at the interfaces, mainly due to a limited but measurable arsenic carry-over during growth.