bluuebunny/crossref_metadata_2025 huggingface dataset:
Low threshold vertical-cavity surface-emitting lasers based on high contrast distributed Bragg reflectors
Authors: Huffaker D. L. , Deppe D. G.
Published: July 2002

Data are presented on vertical-cavity surface-emitting lasers that use high contrast distributed Bragg reflectors on both sides of the cavity. The upper reflector consists of a six pair ZnSe/MgF quarter-wave stack, while the lower reflector consists of an eleven pair AlxOy/GaAs stack fabricated using selective oxidation. Strain due to the lower reflector is reduced by using AlxOy layers of less than a quarter-wave thickness. Device sizes ranging from 1 to 7 μm diameters are characterized, with a minimum threshold current of 53 μA.
Spontaneous production of 10-nm Si structures by plasma etching using self-formed masks
Authors: Tada Tetsuya , Hamoudi Ali , Kanayama Toshihiko , Koga Kenji
Published: July 2002

When a Si substrate is etched in a SF6 electron cyclotron resonance plasma with the sample maintained at ∼−130 °C, reaction products condense preferentially at nucleation sites on the surface, and automatically form etch masks. Si pillars, ∼10 nm in diameter and ∼0.1 μm high, are then formed. When deposited Au clusters (diameter=1.5±0.7 nm) are used as condensation nuclei, fabricated pillars with an average diameter of 9 nm, standard deviation of 1.5 nm, are formed. This remarkably narrow diameter distribution confirms that the phenomenon is useful in nanostructure formation, and that the process is compatible with electron beam lithography.
Atomic displacement processes in irradiated amorphous and crystalline silicon
Authors: Nordlund K. , Averback R. S.
Published: July 2002

Ion beam mixing was investigated in crystalline and amorphous Si using molecular dynamics simulations. The magnitude of mixing was found to be larger in amorphous Si by a factor of about 2. The difference is attributed to local relaxation mechanisms occurring during the cooling down phase of the cascade. Comparison of mixing between Si and Al shows that short range structural order also has a significant influence on mixing.
Suppression of boron transient enhanced diffusion in SiGe heterojunction bipolar transistors by carbon incorporation
Authors: Lanzerotti L. D. , Sturm J. C. , Stach E. , Hull R. , Buyuklimanli T. , Magee C.
Published: July 2002

In this work, we demonstrate that the incorporation of carbon in the base of a npn Si/SiGe/Si heterojunction bipolar transistor dramatically reduces the outdiffusion of boron from the base under postgrowth implantation and annealing procedures. Without the addition of C, these processes would lead to transistors with vastly degraded transistor characteristics. This reduction in B diffusion, when compared to devices without C, has been observed by both secondary ion mass spectroscopy and improved electrical characteristics.
Midinfrared lasers and light-emitting diodes with InAsSb/InAsP strained-layer superlattice active regions
Authors: Kurtz S. R. , Allerman A. A. , Biefeld R. M.
Published: July 2002

The properties of InAsSb/InAsP strained-layer superlattice (SLS), midwave infrared materials, and devices are reported. SLSs were grown by metal-organic chemical vapor deposition and characterized by magnetophotoluminescence and x-ray diffraction. Excellent performance was observed for an SLS light emitting diode (LED) and an optically pumped SLS laser. The semimetal injected, broadband LED emitted at 4 μm with 80 μW of power at 300 K and 200 mA average current. The laser displayed 3.86 μm emission at 240 K, the maximum operating temperature of the laser, and a characteristic temperature of 33 K.
Scanning laser microscopy of reactive ion etching induced n-type conversion in vacancy-doped p-type HgCdTe
Authors: Siliquini J. F. , Dell J. M. , Musca C. A. , Faraone L.
Published: July 2002

Laser-beam-induced-current measurements have been used to characterize the extent of reactive ion etching (RIE) induced type conversion in vacancy-doped p-type Hg0.69Cd0.31Te. The technique allows the spatial extent of RIE induced type conversion to be determined and the donor level concentration profile within the n-type converted region to be estimated. For the RIE processing conditions used (410 mT, CH4/H2, 0.4 W/cm2) and an etch depth of 0.2 μm, n-type conversion extending ∼1.5 μm into the semiconductor was observed. The simple and powerful approach developed in this work is of general application to the study of semiconductor junctions, and can be applied to a range of processing techniques used in the formation of p-n junctions in HgCdTe (e.g., epitaxially grown heterojunctions, ion implantation, ion milling and Hg in-diffusion).
Structural and optical properties of lattice-matched ZnBeSe layers grown by molecular-beam epitaxy onto GaAs substrates
Authors: Bousquet V. , Tournié E. , Laügt M. , Vennéguès P. , Faurie J. P.
Published: July 2002

We report on the molecular-beam epitaxy of ZnBeSe ternary alloys lattice matched onto GaAs substrates. We demonstrate that these alloys can be grown with a high structural perfection. X-ray linewidths down to 27 arcsec are obtained even though the growth is carried out on bare substrates. Transmission electron microscopy reveals the high quality of the interface. Photoluminescence spectra of undoped layers are dominated by free-exciton recombinations. The excitonic gap is determined to be 2.863 eV at 9 K. Finally, high carrier concentrations are obtained for both n-type and p-type doping. These results are promising in view of fabricating laser diodes with this material system.
Spontaneous lateral alignment of In0.25Ga0.75As self-assembled quantum dots on (311)B GaAs grown by gas source molecular beam epitaxy
Authors: Nishi Kenichi , Anan Takayoshi , Gomyo Akiko , Kohmoto Shigeru , Sugou Shigeo
Published: July 2002

Spontaneous lateral alignment was observed in InGaAs quantum dots formed by self-assembly on (311)B GaAs by gas source molecular beam epitaxy. The alignment occurred in a direction inclined about 60° from the [011] direction on a (3-11) [(311)B] surface. A typical base diameter of the dots was about 120±10 nm. The heights varied from 3 to 13 nm as the nominal thickness of the InGaAs layer increased from 4 to 8 nm. The formation mechanism for the alignment is studied based on the growth thickness dependence of the dot structures. A photoluminescence linewidth of 24 meV was obtained from 9 nm high dots at 77 K, indicating the formation of a uniform dot structure.
Activation energy of nonradiative processes in degraded II–VI laser diodes
Authors: Chao L.-L. , Cargill G. S. , Kothandaraman C. , Marshall T. , Snoeks E. , Buijs M. , Haberern K. , Petruzzello J. , Haugen G. M. , Law K. K.
Published: July 2002

A spatially resolved cathodoluminescence study of 〈100〉 dark line defects (DLDs) of degraded II–VI laser diodes based on a ZnCdSe/ZnMgSSe separate confinement heterostructure has been carried out at temperatures between room temperature and 8 K. Cathodoluminescence line scans were used to measure the change of contrasts between the DLDs and the adjacent material. The contrast decreased with decreasing temperature, which suggests that the nonradiative recombination processes associated with DLDs are thermally activated. Activation energies were found to be about 16 and 6 meV for temperatures above and below 200 K, respectively, which may reflect a transition between free carriers and bound excitons at this temperature.
Enhanced absorption by stimulated emission in three excited states of Er3+ in yttrium aluminum garnet
Authors: Maeda Yoshinobu , Migitaka Masatoshi
Published: July 2002

Using a laser diode modulated at 250 and 500 MHz, dependence of enhanced absorption on both sample length and temperature was investigated in an erbium doped yttrium aluminum garnet crystal. The transmitted laser intensity decreased with a decay time of 300 ps for sample lengths greater than 3.0 mm and temperatures higher than 50 K when the incident laser intensity increased. In addition, an emission peak was observed near 835 nm corresponding to the transition from the S3/24 level to the I13/24 in Er3+. It was suggested that the enhanced absorption was caused by stimulated emission in three excited states.
Ionized donor bound excitons in GaN
Authors: Šantic B. , Merz C. , Kaufmann U. , Niebuhr R. , Obloh H. , Bachem K.
Published: July 2002

The temperature and excitation power dependence of a bound exciton photoluminescence line S with a localization energy Q=11.5 meV has been studied in undoped and moderately Mg-doped wurtzite GaN of high resistivity. The data provide strong evidence that line S is due to recombination of excitons bound to ionized shallow donors. The consistency of this assignment with theoretical predictions is demonstrated.
Self-consistent eigenmode analysis of the dielectrically apertured Fabry–Perot microcavity
Authors: Deppe D. G. , Deng Q.
Published: July 2002

Analysis is presented to calculate the eigenmode of a Fabry–Perot microcavity containing an optically thin dielectric aperture. The treatment yields the eigenmode field distribution, frequency, and threshold susceptibility. It is also suggested that self-focusing phenomena in large area vertical-cavity surface-emitting lasers can arise due to aperture formation by the complex susceptibility of a quantum well active region.
Si/Ge heterostructure on sulphur passivated GaAs(110)
Authors: Huang L. J. , Rajesh K. , Lau W. M. , Wu X. Z. , Landheer D. , Baribeau J.-M. , Ingrey S.
Published: July 2002

The structure and interface state density of thin Si and Si/Ge heterolayers on sulphur passivated GaAs (110) were studied by capacitance–voltage measurements, x-ray scattering, and x-ray absorption with synchrotron radiation. The results show that the reduction of interfacial state density by utilizing Si or Si/Ge thin heterolayers on sulphur passivated GaAs (110) correlates better with the short-range electronic structure at the interface than the commonly believed long-range atomic abruptness.
Gas source molecular beam epitaxy of wurtzite GaN on sapphire substrates using GaN buffer layers
Authors: Grandjean N. , Leroux M. , Laügt M. , Massies J.
Published: July 2002

Wurtzite GaN was grown by gas source molecular beam epitaxy on (0001) sapphire substrates. Taking advantage of the catalytic decomposition of ammonia on the growing surface, high growth rates (>1 μm/h) were achieved for substrate temperatures ranging between 800 and 850 °C. Surface morphology, structural, and optical properties of thick (2–4 μm) GaN films were investigated versus the growth temperature of the GaN buffer layer. It is shown that this parameter has a drastic influence on the GaN properties.
Switching behavior of surface stabilized ferroelectric liquid crystals induced by pulse voltages
Authors: Sako Teiyu , Itoh Nobuyuki , Sakaigawa Akira , Koden Mitsuhiro
Published: July 2002

The switching behavior of surface stabilized ferroelectric liquid crystals has been studied using a simple uniform switching model in an applied electric field. We measured the response time as a function of pulse voltage for a ferroelectric liquid crystal material with a negative dielectric anisotropy, which shows a minimum in the response time-voltage curve, and found good agreement between the theory and the experimental results. Accordingly, the parameters appearing in the switching model, the initial azimuthal angle, rotational viscosity, and surface anchoring energy can be determined.
The effective masses in strained InGaAs/InP quantum wells deduced from magnetoexcitation spectroscopy
Authors: Dalfors J. , Lundström T. , Holtz P. O. , Radamson H. H. , Monemar B. , Wallin J. , Landgren G.
Published: July 2002

The reduced effective masses in InxGa1−xAs/InP quantum wells have been determined as a function of strain (x value) and well width by means of magneto-optical methods. Magnetoexcitons have been observed in photoluminescence excitation spectra in the presence of a magnetic field. At higher magnetic fields, the observed magnetoexcitons will asymptotically approach the free Landau levels. From a least square fit, the dependence of the reduced effective masses on strain and well width has been deduced. Also, the reduced effective mass including the light hole state has been determined for the tensile strained quantum well structure.
Second-harmonic generation in germanosilicate glass poled with ArF laser irradiation
Authors: Fujiwara Takumi , Takahashi Masahide , Ikushima Akira J.
Published: July 2002

We report on a remarkably large second-harmonic generation (SHG) in a germanosilicate glass (15.7 GeO2–84.3 SiO2 in mol %), which was induced by poling while the sample was irradiated with the ArF laser at the wavelength of 193 nm. The SHG coefficient, d, thus induced was measured at various poling electric-field strengths using the Maker-fringe technique. The value of d increases with increasing poling field and then saturates around 1.5×105 V/cm. The largest d coefficient value obtained in this work, which is 3.4±0.3 pm/V, seems to exceed d22 of LiNbO3. Furthermore, polarization dependence of the induced SHG shows an anisotropy of the refractive index.
Persistent photoconductivity in n-type GaN
Authors: Hirsch Michèle T. , Wolk J. A. , Walukiewicz W. , Haller E. E.
Published: July 2002

We report on the spectral and temperature dependence of persistent photoconductivity (PPC) in metal-organic chemical vapor deposition grown unintentionally doped n-type GaN. The PPC effect is detectable up to temperatures of at least 352 K, the highest temperature used in this study. At 77 K, the conduction persists at a level 80% higher than the equilibrium dark conduction for over 104 s after removing the excitation. We have determined the spectral dependence for the optical cross section for PPC and obtain an optical ionization energy of ∼2.7 eV. The temperature dependence of the photoconductivity decay and its nonexponential shape are explained by a distribution of capture barriers with a mean capture barrier of 0.2 eV and a width of ∼26 meV.
Stimulated emission from optically pumped GaN quantum dots
Authors: Tanaka Satoru , Hirayama Hideki , Aoyagi Yoshinobu , Narukawa Yukio , Kawakami Yoichi , Fujita Shizuo , Fujita Shigeo
Published: July 2002

Stimulated emission was observed from optically pumped GaN quantum dots in an AlxGa1−xN separate confinement heterostructure fabricated on 6H-SiC(0001) substrate by metal organic chemical vapor deposition. Nanostructural GaN quantum dots, with an average size of ∼10 nm width, ∼1–2 nm height, and density of ∼1011 cm−2, were self-assembled on the AlxGa1−xN cladding layer surface. The stimulated emission peak was observed at ∼3.48 eV, which is ∼50 meV lower than that of spontaneous emission. The excitation power dependence on the emission intensity clearly indicates threshold pump power density of 0.75 MW/cm2 for the onset of stimulated emission.
Simultaneous electronic and magnetic transitions in La1−xKxMnO3 thin films
Authors: Chen Chun-Che , de Lozanne Alex
Published: July 2002

We have fabricated perovskite La1−xKxMnO3 (x=0.14 and 0.2) thin films on SrTiO3 (100) by e-beam/thermal coevaporation. From the electrical and magnetic studies, we found a simultaneous occurrence of the paramagnetic to ferromagnetic state and insulating to metallic state, as predicted by the double exchange theory. The magnetoresistance is relatively small compared to that of the divalent cation doped La1−xAxMnO3 in fields up to 5 T.
Soft x-ray circular polarizer using magnetic circular dichroism at the Fe L3 line
Authors: Kortright J. B. , Kim S.-K. , Warwick T. , Smith N. V.
Published: July 2002

Linearly polarized soft x-rays are converted to elliptical polarization at the Fe L3 line (707 eV) using magnetic circular dichroism (MCD) on transmission through thin Fe films. A linear polarizer measured the transmitted polarization at different incidence angles to vary as expected from a model for in-plane magnetization, and also to exhibit a weak MCD effect at normal incidence interpreted to originate from perpendicular interface anisotropy. An MCD signal from a downstream Fe film was produced by switching the helicity of x-rays transmitted through an upstream circular polarizer. Practical considerations for optimizing the production of circular polarization are discussed, and synchrotron radiation applications using these circular polarizing filters are suggested.
YBa
2
Cu
3
O
7−δ
trilayer junction with nm thick PrGaO3 barrier
Authors: Tsuchiya R. , Kawasaki M. , Kubota H. , Nishino J. , Sato H. , Akoh H. , Koinuma H.
Published: July 2002

We have established a deposition process of high quality a axis oriented YBa2Cu3O7−δ (a-YBCO) and insulating epitaxial PrGaO3 (PGO) films to fabricate a-YBCO/PGO(2.0–3.2 nm)/a-YBCO trilayer junction. The precipitate formation on the bottom a-YBCO was greatly suppressed by the atomic layer modification of the substrate surface with a wet etching and successive atomic layer epitaxy of SrO and BaO atomic layers prior to the YBCO deposition. Crack formation and residual stress in the film due to the thermal expansion mismatch along c axis of YBCO could be eliminated by inserting a buffer layer of a-YBCO deposited with changing the substrate temperature from 580 to 735 °C. The junctions showed a clear hysteresis with its current jump as large as 30%, together with the Fraunhofer diffraction.
Polarization-independent large field-induced refractive index change in a strained five-step GaAs–InAlGaAs asymmetric coupled quantum well
Authors: Feng H. , Tada K. , Nakano Y.
Published: July 2002

A tensile-strained five-step asymmetric coupled quantum well (FACQW) structure is proposed for large field-induced refractive index change without polarization dependence and redshift of the absorption edge. A strong exciton absorption peak is caused by electron-hole transitions between symmetric wave functions and antisymmetric wave functions with a small applied electric field. The field-induced refractive index change of strained the FACQW is larger by one order of magnitude compared to that of a rectangular quantum well and the difference in the refractive index change of TE and TM modes is under 2% when the operation wavelength is not at the absorption edge.
Atomic origin of deep levels in p-type GaN: Theory
Authors: Chadi D. J.
Published: July 2002

Experimentally identified deep levels in p-type GaN at approximately 0.9–1, 1.4, and 1.8–2 eV above the valence-band maximum have been attributed to Ga vacancies. From the results of first-principles calculations, we find that from both energetic and electronic level structure standpoints it is necessary to consider the structural modification VGa→Nanti+VN, resulting from the transfer of a nearest-neighbor N atom to a Ga-vacancy site (VGa) to explain the levels at 1 and 2 eV. Isolated N-antisite (Nanti) and nitrogen-vacancy (VN) defects are found to give rise to additional deep levels at 1.4 and 0.8 eV, respectively.
Nucleation and growth of chemical beam epitaxy gallium nitride thin films
Authors: Kim Esther , Berishev I. , Bensaoula A. , Lee S. , Perry S. S. , Waters K. , Schultz J. A.
Published: July 2002

Gallium nitride films have been grown on (0001) sapphire substrates by chemical beam epitaxy (CBE) using triethyl gallium (TEG) and ammonia (NH3) precursors. Prior to the CBE epi-GaN layer growth, electron cyclotron resonance plasma-assisted metal-organic molecular beam epitaxy was utilized to deposit a nucleation layer at lower temperatures. The crystallinity of CBE-grown GaN films was found to be strongly growth–temperature dependent. The degree of crystallinity was correlated with the surface carbon composition as measured in situ by mass spectroscopy of recoiled ions. The optimum growth–temperature range for CBE GaN growth was found to be between 800 and 825 °C. Within this narrow window, thin films with streaky two-dimensional reflection high-energy electron diffraction patterns and good photoluminescence properties were obtained. The surface rms roughness, as measured by atomic force microscopy, was as low as 40 Å/1 μm2 for the highest quality thin films; lattice-resolved images supported the deposition of crystalline GaN revealing hexagonal structures with the spacing anticipated for GaN.
Strong Hall voltage modulation in hybrid ferromagnet/semiconductor microstructures
Authors: Monzon F. G. , Johnson Mark , Roukes M. L.
Published: July 2002

We present a new magnetoelectronic device consisting of a μm-scale semiconductor cross junction and a patterned, electrically isolated, ferromagnetic overlayer with in-plane magnetization. The large local magnetic field emanating from the edge of the thin ferromagnetic film has a strong perpendicular magnetic component, B⊥(r), which induces a Hall resistance, RH, in the microjunction. External application of a weak in-plane magnetic field reverses the magnetization of the ferromagnet and with it B⊥(r), thus modulating RH. Our data demonstrate that this strong “local” Hall effect is operative at both cryogenic and room temperatures, and is promising for device applications such as field sensors or integrated nonvolatile memory cells.
The effect of dose rate on interstitial release from the end-of-range implant damage region in silicon
Authors: Robertson Lance S. , Lilak Aaron , Law Mark E. , Jones Kevin S. , Kringhoj Per S. , Rubin Leonard M. , Jackson John , Simons David S. , Chi Peter
Published: July 2002

Low temperature molecular beam epitaxy was used to grow boron doping superlattices DSLs in Si, with peak boron concentrations of 1×1018/cm3, and spike widths of 10 nm. Amorphization of these DSLs was achieved using a series of Si + implants of 30 and 112 keV, each at a dose of 1×1015/cm2, which placed the amorphous to crystalline interface between the first and second doping spikes. The dose rate of the Si + implants was varied from 0.13 to 1.13 mA/cm2. Post-implantation anneals were performed in a rapid thermal annealing furnace at 800 °C, for times varying from 5 s to 3 min. Secondary ion mass spectrometry was used to monitor the dopant diffusion after annealing. Increasing the implant dose rate appears to increase the amount interstitial flux toward the surface but has no observable effect on the flux into the crystal. Transmission electron microscopy was used to study the end of range defect evolution. Increasing dose rate was observed to decrease the end of range defect density. These observations are consistent with previous findings that indicate the amount of backflow toward the surface decreases as the end of range loop density increases.
Observation of strain relaxation phenomena in buried and nonburied III–V surface gratings through high resolution x-ray diffraction
Authors: Leprince L. , Baumbach G. T. , Talneau A. , Gailhanou M. , Schneck J.
Published: July 2002

We present high-resolution x-ray diffraction studies describing the evolution of the strain relaxation phenomena in a strained InGaAsP surface grating resulting from burying in InP. We have compared reciprocal space maps of symmetrical and asymmetrical reflections from free-strain gratings, strained surface gratings, and strained buried gratings. After burying, modifications in the coherently and diffusely scattered intensity have been observed indicating the counteraction of the embedding material to the laterally nonuniform strain relaxation, which occurs in free-surface (nonburied) strained grating.
Selective positioning of InAs self-organized quantum dots on sub-250 nm GaAs facets
Authors: Tsui R. , Zhang R. , Shiralagi K. , Goronkin H.
Published: July 2002

We have selectively grown GaAs mesas with (100) top facets that range from several μm to less than 250 nm in width on an oxide-patterned GaAs substrate, and InAs self-organized quantum dots (SOQDs) on top of the facets. For a given amount of InAs deposited, the dot density varies with the facet width, and is higher than the density on a planar, nonpatterned substrate. The SOQDs also tend to form at the facet edges. These observations are indicative of a strong surface diffusion effect of In-containing species adsorbed on the various crystalline facets of the GaAs mesas.
Room-temperature near-ultraviolet electroluminescence from a linear silicon chain
Authors: Yuan Chien-Hua , Hoshino Satoshi , Toyoda Seiji , Suzuki Hiroyuki , Fujiki Michiya , Matsumoto Nobuo
Published: July 2002

Single-layer light emitting diodes (LEDs) were fabricated using poly[bis(p-butylphenyl)silane] as the emissive layer. An efficient and stable electroluminescence with a maximum at 407 nm was observed at room temperature under a forward electric field greater than 6×105 V/cm. The coincidence of electroluminescence with photoluminescence suggests the origin of the electroluminescence in an excited silicon chain segment. The high external quantum efficiency (0.1% photons/electron), narrow emission (full width at half maximum=15 nm), improved operating stability, and good solubility in organic solvents provide the possibility of using polysilanes for ultraviolet LEDs.
Midinfrared vertical-cavity surface-emitting laser
Authors: Felix C. L. , Bewley W. W. , Vurgaftman I. , Meyer J. R. , Goldberg L. , Chow D. H. , Selvig E.
Published: July 2002

We report a type-II antimonide midinfrared vertical-cavity surface-emitting laser. The emission wavelength of 2.9 μm is nearly independent of temperature (dλ/dT≈0.07 nm/K) and the multimode linewidth is quite narrow (3.5 nm). The pulsed threshold power at 86 K is as low as 22 mW for a 30 μm spot. Lasing is observed up to T=280 K, and the peak output power from a 600 μm spot exceeds 2 W up to 260 K. The differential power conversion efficiency is >1% at 220 K.
Experimental demonstration for scanning near-field optical microscopy using a metal micro-slit probe at millimeter wavelengths
Authors: Bae Jongsuck , Okamoto Tatsuya , Fujii Tetsu , Mizuno Koji , Nozokido Tatsuo
Published: July 2002

Scanning near-field optical microscopy using a slit-type probe is discussed. The slit-type probe has a width of much less than a wavelength, λ, and a length on the order of λ, and thus has high transmission efficiency. Two dimensional near-field images of objects have been constructed using an image reconstruction algorithm based on computerized tomographic imaging. Experiments performed at 60 GHz (λ=5 mm) show that this type of near-field microscopy can achieve a spatial resolution of better than λ/45 for two dimensional imaging. A method for fabricating a submicron width slit probe at the end of an optical fiber is presented for extending this microscopy to optical waves.
III-V interband 5.2 μm laser operating at 185 K
Authors: Flatté Michael E. , Hasenberg T. C. , Olesberg J. T. , Anson S. A. , Boggess Thomas F. , Yan Chi , McDaniel D. L.
Published: July 2002

We report the operation of a III-V interband laser at a wavelength beyond 5 μm and temperatures above 90 K. The active region consists of a strain compensated broken gap four layer superlattice of InAs/Ga0.6In0.4Sb/InAs/Al0.3Ga0.42In0.28As0.5Sb0.5 grown by molecular beam epitaxy. The maximum operating temperature under 2.01 μm pulsed optical excitation was 185 K at a wavelength of 5.2 μm. The peak pump intensity at the 80 K threshold was 62 kW/cm2, and the characteristic temperature (T0) of the threshold intensity was 37 K. This T0 is comparable to the best observed values for 3–4.5 μm lasers based on the InAs/GaInSb material system.
Sr
0.8
Bi
2.5
Ta
1.2
Nb
0.9
O
9+x
ferroelectric thin films prepared by two-target off-axis radio frequency magnetron sputtering
Authors: Tsai Huei-Mei , Lin Pang , Tseng Tseung-Yuen
Published: July 2002

Ferroelectric Sr0.8Bi2.5Ta1.2Nb0.9O9+x thin films on a Pt/SiO2/Si substrate were prepared by using two-target off-axis radio frequency magnetron sputtering, and their structural and electrical properties were investigated. The films crystallized with high (115) diffraction intensity at a substrate temperature of 600 °C, and showed columnar microstructure. The 600 °C sputtered films with a thickness of 440 nm exhibited remanent polarization (2Pr) of 52 μC/cm2 and coercive field (2Ec) 28 kV/cm at an applied voltage of 1.5 V. The leakage current density was about 6×10−6 A/cm2 at an electric field of 50 kV/cm. The films demonstrated fatigue free characteristics up to 1.0×1010 switching cycles under a 3 V bipolar 1 MHz square wave.
Mapping of the magnetic leakage fields from nanoparticles by Fresnel projection microscopy
Authors: Binh Vu Thien , Purcell S. T. , Semet V. , Feschet F.
Published: July 2002

The magnetic leakage fields from the poles of magnetic nanoparticles down to 105–106 spins, isolated or situated at the edges of clusters, are observed with Fresnel projection microscopy by the presence of interference fringes generated by the magnetic phase shifts in the imaging electron beam. The particle shapes and localization of fringes are imaged simultaneously with nanometer spatial resolution at ∼200 V.
Observation of {105} facetted Ge pyramids inclined towards vicinal Si(001) surfaces
Authors: Zhu Jian-hong , Brunner K. , Abstreiter G.
Published: July 2002

Self-assembled Ge and SiGe islands, which are compact pyramids with four equivalent {105} facets, have been grown by molecular beam epitaxy on vicinal Si(001) surfaces with biatomic surface steps along the [110] direction. Revealed by atomic force microscopy, they appear as regularly facetted pyramids which are inclined by the miscut angles of 2.8° or 4° toward the sample surfaces and consequently have a distorted rhomb base. Characteristic patterns are observed by reflection high-energy electron diffraction from these facetted islands. They agree well with simulated patterns scattered by {105} facets. Avoiding elongated Ge hut clusters by using vicinal surfaces is promising for an improved homogeneity in island shape and size.
Stacked GaAs multi-quantum wires grown on vicinal GaAs(110) surfaces by molecular beam epitaxy
Authors: Kato Takehiko , Takeuchi Toshikazu , Inoue Yoshiji , Hasegawa Shigehiko , Inoue Koichi , Nakashima Hisao
Published: July 2002

Stacked GaAs quantum wires (QWRs) are grown on the surfaces with giant steps which are naturally formed on vicinal GaAs(110) substrates by molecular beam epitaxy. Transmission electron microscopy observation clearly shows stacked structures of coherently aligned quantum wires which are induced by GaAs layer thickness modulation at the step edges. Photoluminescence peak shifts with the thickness of the AlGaAs barrier layers are explained as due to the coupling between the QWRs.
Realization and optical characterization of etched mirror facets in GaN cavities
Authors: Binet F. , Duboz J. Y. , Laurent N. , Bonnat C. , Collot P. , Hanauer F. , Briot O. , Aulombard R. L.
Published: July 2002

We report on the realization of etched mirror facets in GaN cavities by chemically assisted ion-beam etching. The etching conditions are adjusted to obtain a high degree of verticality and smoothness. Optical pumping experiments and gain measurements are performed in etched GaN cavities of various geometries. Stimulated emission and lasing are observed. The study of the value of the gain at threshold as a function of the cavity length allows a determination of the reflection coefficient of the etched mirror. The measured value of 15% is in good agreement with the one expected for a perfect air–GaN interface. This demonstrates the high quality of the etched mirror facets.
Optical absorption of composites of nanocrystalline silver prepared by electrodeposition
Authors: Banerjee S. , Chakravorty D.
Published: July 2002

Silver particles of average diameters in the range 10.3–25.7 nm have been grown within a gel medium by an electrodeposition technique. Detailed optical absorption characteristics in the wavelength range 250–600 nm have been investigated for nanocomposites comprising these particles dispersed in a polystyrene matrix. Absorption maximum occurs at a wavelength around 350 nm, which increases as the metal particle size is increased. Mie theory with the incorporation of a distribution of particle size gives remarkable agreement with the experimental data. The electrical conductivity as extracted from the theoretical analysis for particles with diameters ∼3 nm is found to be less than Mott’s minimum metallic conductivity. This indicates the possibility of a metal insulator transition in this system, which appears to be consistent with earlier electrical conductivity measurements.
Fabrication and evaluation of a localized plasmon resonance probe for near-field optical microscopy/spectroscopy
Authors: Ashino M. , Ohtsu M.
Published: July 2002

A technique that excites a localized plasmon on the apex of probe for near-field optical microscope and spectroscope is presented. Vapor deposition and heating of several tens nm thick gold films on 1 nm thick germanium-covered tapered optical fiber probe make highly adherent and smooth overlayers. A “tunneling-photon-mode” experimental system combined with a dye laser is used to excite a localized plasmon. The enhancement of near-field intensity was measured varying incident photon energies with its maximum occurring at 2.11 eV. This local field enhancement could be estimated to generate only in the close proximity of the substrate.
X-ray emission by multiple passes of electrons through periodic and crystalline targets mounted inside a synchrotron
Authors: Andreyashkin M. Yu. , Kaplin V. V. , Uglov S. R. , Zabaev V. N. , Piestrup M. A.
Published: July 2002

The number of passes of high-energy electrons through multiple foil and crystal radiators mounted inside of the Tomsk “Sirius” synchrotron, and the resulting increase in x-ray production efficiencies from these radiators, have been measured. The influence of electron transmission on the spectral and spatial distributions of parametric x radiation and on the spatial distribution of transition radiation has also been observed. We find that multiple passes increase the yields of these sources without destroying their angular distributions and spectra. Thus, multiple passes of electrons through these novel radiators may make them useful as x-ray sources for scientific and industrial purposes.
Lattice parameter in Si1−yCy epilayers: Deviation from Vegard’s rule
Authors: Berti M. , De Salvador D. , Drigo A. V. , Romanato F. , Stangl J. , Zerlauth S. , Schäffler F. , Bauer G.
Published: July 2002

The precise C content of a series of Si1−yCy epilayer samples (0<y<0.012) was determined by resonant backscattering experiments using a He+4 ion beam at 5.72 MeV. This beam energy is more suitable for the determination of the C content than the previously used 4.265 MeV. From the correlation of these investigations with x-ray diffraction experiments, a significant deviation of the lattice parameter variation in Si1−yCy from Vegard’s rule between Si and diamond or β-SiC was observed, which amounts up to 30% or 13%, respectively, for y<0.012. This negative deviation is in agreement with recent theoretical predictions by Kelires.
Intense photoluminescence from self-assembling InGaN quantum dots artificially fabricated on AlGaN surfaces
Authors: Hirayama Hideki , Tanaka Satoru , Ramvall Peter , Aoyagi Yoshinobu
Published: July 2002

We demonstrate photoluminescence (PL) from self-assembling InGaN quantum dots (QDs), which are artificially fabricated on AlGaN surfaces via metalorganic chemical vapor deposition. InGaN QDs are successfully fabricated by the growth mode transition to three-dimensional nanoscale island formation by using “antisurfactant” silicon on AlGaN surface. The diameter and height of the fabricated InGaN QDs are estimated to be ∼10 nm and ∼5 nm, respectively, by an atomic-force microscope (AFM). Indium mole fraction of InxGa1−xN QDs is controlled from x=∼0.22 to ∼0.52 by varying the growth temperature of QDs. Intense photoluminescence is observed even at room temperature from InGaN QDs embedded with the GaN capping layers. In addition, from the temperature dependence of the PL-peak energy, we convincingly show that the PL emission actually comes from the InGaN QDs.
The four-level stimulated emission in sexithiophene single crystals
Authors: Garnier Francis , Horowitz Gilles , Valat Pierre , Kouki Fayçal , Wintgens Véronique
Published: July 2002

Single crystal of conjugated sexithiophene oligomer shows stimulated emission when excited with a low-energy photonic pulse. This phenomenon is interpreted in terms of the excitonic energy diagram of the crystal, which presents a four-level pathway for the photoexcitation and emission, similar to the one observed in classical inorganic-based laser materials.
All-optical beam deflection and switching in strontium–barium–niobate waveguides
Authors: Kip D. , Wesner M. , Krätzig E. , Shandarov V. , Moretti P.
Published: July 2002

Self-focusing by thermal heating because of absorption of a guided light beam in a planar strontium–barium–niobate waveguide is of interest for all-optical data processing. When a guided probe beam intersects the pump beam under a small angle inside the waveguide, the self-focusing effect in conjunction with self-bending because of the photorefractive effect can be used for large angle deflection of the probe beam and for switching with time constants of fractions of milliseconds. Deflection angles of the outcoupled probe light up to 0.23 rad in air and frequencies up to 3 kHz for optical switching are reached in the experiment.
Persistent high density spectral holeburning in CaS:Eu and CaS:Eu,Sm phosphors
Authors: Hasan Z. , Solonenko M. , Macfarlane P. I. , Biyikli L. , Mathur V. K. , Karwacki F. A.
Published: July 2002

Persistent spectral hole-burning has been reported for singly, Eu-doped, and doubly, Eu- and Sm-doped, CaS phosphors. Efficient photon gated holeburning in the 4f7 (8S7/2)−4f65d1 transition of Eu2+ is a result of photoionization of Eu2+ to Eu3+. These holes have a width of <5 GHz (2 K), survive thermal cycling of the phosphor up to the room temperature, 300 K, and have no detectable deterioration over more than a day of storage time at low temperature (2 K). Although self-gated holeburning is observed with the reading laser at higher powers, the photon budget for reading these holes is so small that in excess of 1000 reading cycles can be performed without destroying the optical signal. The nature of holes burned by photon-gating is found to be very different from the self-gated holes. The characteristics for the holeburning are the same in singly and doubly doped phosphors, suggesting that under the conditions of our experiments, Sm traps do not play any significant role in spectral holeburning. Possibilities of high density optical memory storage using photon-gated holeburning in this THz broad transition are discussed.
Phonon-resolved photoluminescence at λ=1.55 μm from undulating Si0.5Ge0.5 epitaxial layers
Authors: Lafontaine H. , Rowell N. L. , Janz S.
Published: July 2002

Si 0.5 Ge 0.5 /Si multiquantum well structures are grown using a production-compatible ultrahigh vacuum chemical vapor deposition system. The structures are designed in order to obtain dislocation-free undulating strained layers. A photoluminescence emission corresponding to the direct “no phonon” transition is measured at energies systematically smaller than calculated for planar layers, implying that any increase in band gap due to elastic relaxation of the lattice strain at the undulation crests is compensated for by a confinement energy decrease together with a Ge accumulation at the undulation crests. The photoluminescence “no phonon” emission peaks at a wavelength that increases with nominal well thickness up to 1.55 μm. This opens the possibility of using dislocation-free silicon–germanium undulating layers as an absorber for photodetector applications at the telecommunication wavelengths of λ=1.3–1.55 μm.
Diffusion of Pt in molecular beam epitaxy grown ZnSe
Authors: Slotte J. , Salonen R. , Ahlgren T. , Räisänen J. , Rauhala E. , Uusimaa P.
Published: July 2002

Diffusion of platinum in zinc selenide has been studied by the use of the He4 and C12 ion backscattering techniques. The samples were thin films grown by molecular beam epitaxy on GaAs (100) epitaxial layers followed by evaporation of platinum and annealing in the temperature range 500–800 °C. The diffusion coefficients were determined by the fitting of a concentration independent solution of the diffusion equation to the experimental depth profiles. The activation energy and the pre-exponential factor of the diffusion process were found to be 1.7 eV and 6.4×10−6 cm2/s, respectively.
Capacitance measurements of junction formation and structure in polymer light-emitting electrochemical cells
Authors: Campbell I. H. , Smith D. L. , Neef C. J. , Ferraris J. P.
Published: July 2002

We present capacitance–voltage and current–voltage measurements of polymer light-emitting electrochemical cells and compare these results with steady state device model calculations. The capacitance–voltage characteristic is used to assess the formation and structure of the electrochemical junction in the device. The cell capacitance and current both increase sharply above a threshold voltage as the bias is increased. The threshold voltage for the rapid increase in capacitance is lower than that for the increase in current, indicating that the electrochemical junction begins to form prior to significant current flow. The electrochemical junction width, estimated from the capacitance measurements, is about 15 nm at a current density of 0.1 A/cm2. The steady state device model calculations are in reasonable agreement with these observations.
Gratinglike modulation of GaAs/AlGaAs quantum well intermixing fabricated with laser interference
Authors: Shin Jaw-Jung , Gurtler Steffen , Chang Yih , Yang C. C.
Published: July 2002

We report the observation of a μm range periodical modulation of a band gap caused by gratinglike quantum well intermixing in an intrinsic GaAs/AlGaAs quantum well structure. The intermixing grating was formed with the irradiation of the interference fringe of the second harmonic of a Q-switched Nd:YAG laser followed by a rapid thermal annealing process. The intermixing grating periods were measured with an optical setup for simultaneously monitoring the photoluminescence intensities of two closely spaced wavelengths with a sub-μm spatially scanning resolution. The measured periods included a cluster of features around 2 μm which was consistent with that of the laser interference fringe.
SiC/Si heterostructure negative-differential-resistance diode for high-temperature applications
Authors: Wu Kuen-Hsien , Fang Yean-Kuen , Ho Jyh-Jier , Hsieh Wen-Tse , Chen Tzer-Jing
Published: July 2002

In this letter, we report the observation of N-shaped negative-differential-resistance (NDR) characteristics in a SiC/Si heterostructure diode. The typical NDR in this device has a peak-to-valley current ratio (PVCR) of 44 and a high peak current of 4.8 mA at room temperature. A possible model based on the multi-tunneling process was proposed to explain the origin of the NRD in this device. The most attractive feature of this device is its high-temperature NDR characteristics. An obvious NDR with a PVCR of as high as 9 is obtained at 200 °C, indicating that this SiC/Si heterostructure NDR diode is promising for high-temperature electronic applications.
Electrical characterization of the threshold fluence for extended defect formation in p-type silicon implanted with MeV Si ions
Authors: Fatima S. , Wong-Leung J. , Fitz Gerald J. , Jagadish C.
Published: July 2002

Preamorphous damage in p-type Si implanted with MeV Si ions and annealed at elevated temperature is characterized using deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM). P-type Si was implanted with 4 MeV Si at doses from 1×1013 to 1×1014 cm−2 and annealed at 800 °C for 15 min. For doses below this critical dose, a sharp peak is observed in the DLTS spectrum, corresponding to the signature of point defects. Above the critical dose, a broad DLTS peak is obtained, indicating the presence of extended defects. This behavior is found to be consistent with TEM analyses where extended defects are only observed for doses above the critical dose. This suggests a critical dose at which point defects from implantation act as nucleating sites for extended defect formation.
Focused ion-beam fabrication of fiber probes with well-defined apertures for use in near-field scanning optical microscopy
Authors: Pilevar Saeed , Edinger Klaus , Atia Walid , Smolyaninov Igor , Davis Christopher
Published: July 2002

We present a focused ion-beam (FIB) fabrication method for very clean and well-defined subwavelength fiber probes with metallic apertures of a desired diameter for use in near-field scanning optical microscopy. Such probes exhibit improved features compared to probes coated with metal by the conventional angled evaporation technique. Examples of FIB fabricated fiber probes are shown and images of a test sample are presented using one of the probes in a near-field microscope.
Near-field optical spectroscopy and imaging of single InGaAs/AlGaAs quantum dots
Authors: Chavez-Pirson A. , Temmyo J. , Kamada H. , Gotoh H. , Ando H.
Published: July 2002

We use near-field optical probing at low temperatures (T=5 K) to image and examine the linear and nonlinear luminescence properties of single InGaAs/AlGaAs quantum dots grown on (311)B oriented GaAs substrates. The high spatial resolution of near-field “nanoprobing,” which is typically 200 nm or less, makes the observation of single dots at different locations on the sample possible, even though the spatial density of quantum dots is on the order of 100/μm2. We observe narrow excitonic emission lines at low excitation powers and, with increasing excitation, we observe biexcitonic emission strongly shifted (3 meV) to the low-energy side of the exciton emission.
Low-loss high-efficiency and high-power diode-pumped mid-infrared GaInSb/InAs quantum well lasers
Authors: Le H. Q. , Lin C. H. , Pei S. S.
Published: July 2002

A 4 μm GaInSb/InAs type-II quantum well (QW) laser has shown a substantial improvement in internal loss and quantum efficiency, which has been a problem for this type of laser. It yielded 0.9–1.5 W peak, 90–150 mW average single-ended output for 0.1–1 ms pulses at 71 K, with a net power efficiency of ∼3.5%–4%. The power and efficiency are among the highest long-pulse results reported for any semiconductor laser of comparable wavelength. Comparison with similar QW lasers suggests that the improvement is a result of better material growth.
Efficient 300 K light-emitting diodes at λ∼5 and ∼8 μm from InAs/In(As1−xSbx) single quantum wells
Authors: Tang P. J. P. , Hardaway H. , Heber J. , Phillips C. C. , Pullin M. J. , Stradling R. A. , Yuen W. T. , Hart L.
Published: July 2002

300 K light-emitting diodes which emit at 5 and 8 μm with quasi-cw output powers of up to 50 and 24 μW, respectively, are reported. The devices have a single molecular beam epitaxy grown InAs/In(As, Sb) quantum well in the active region with a strong type-IIa band alignment giving mid-IR emission at energies up to 64% lower than the alloy band gap. The emission energies are shown to be in good agreement with a k⋅p bandstructure model where Qc, the ratio of the strained conduction-band offset to the band-gap difference between the two strained superlattice components, is found to be ∼2.0.