bluuebunny/crossref_metadata_2025 huggingface dataset:
Compositional modulation and long-range ordering in GaP/InP short-period superlattices grown by gas source molecular beam epitaxy
Authors: Hsieh K. C. , Baillargeon J. N. , Cheng K. Y.
Published: July 2002

Long-range ordering in a (GaP)2/(InP)2 short-period superlattice and a Ga0.525In0.475P buffer layer grown on a (001)GaAs substrate by gas source molecular beam epitaxy were studied. Transmission electron microscopy and low-temperature cathodoluminesence techniques were used to examine the microstructure of the short-period superlattice and to determine its band-gap energy. The superlattice layer was found to have a [001] long-range ordered structure with a band gap narrowing of about 130 meV, while the Ga0.525In0.475P layer had a 37 meV band-gap narrowing induced by spontaneous long-range ordering in the [111] direction. The ordered superlattice layer was found to have a growth-induced lateral periodic modulation of the composition along the [1̄10] direction. Within the modulating bands, which had a 200 Å periodicity, the In composition was found to vary from 42 to 56% while the Ga correspondingly varied between 58 and 44%.
Step-flow growth on strained surfaces: (Al,Ga)Sb tilted superlattices
Authors: Chalmers S. A. , Kroemer H. , Gossard A. C.
Published: July 2002

We have demonstrated the molecular beam epitaxial growth of (Al,Ga)Sb tilted superlattices (TSLs) on 2° vicinal (100) GaSb and GaAs substrates. The TSLs grown on GaSb substrates exhibit good AlSb/GaSb separation and a uniform short-range superlattice period. The TSLs grown on GaAs substrates are similar, except for the presence of threading dislocations and a decreased uniformity. The existence of TSLs proves that step-flow growth can occur in this material system, and in the presence of strain. Lateral fluctuations in the tilt angle of the superlattice are observed and are found to be caused by a nonuniform adatom distribution which is correlated with the surface step density.
Low-temperature organometallic vapor phase epitaxy of InSb using the novel Sb precursor triisopropylantimony
Authors: Stauf G. T. , Gaskill D. K. , Bottka N. , Gedridge R. W.
Published: July 2002

InSb has been grown by organometallic vapor phase epitaxy using triisopropylantimony (TIPSb) and trimethylindium (TMIn) at temperatures as low as 300 °C, the lowest yet reported for a stable Sb source. Unintentionally doped films were n type, and the best electronic transport result was obtained for a growth at 350 °C yielding a 77 K carrier concentration of 3.7×1016 cm−3 and mobility of 6.3×104 cm2/V s; these impurities are thought to be from the reagent grade chemicals used to synthesize the TIPSb. The morphology, growth rate, and transport properties of these films are reported as a function of growth temperature, molar ratios, and substrate (GaAs or InSb). By comparing these transport properties with Hall measurements of ∼1 μm InSb epilayers on GaAs grown from trimethylantimony and TMIn, it was found that these properties were greatly improved because of the low-temperature epitaxy enabled by this source.
Temperature-dependent critical layer thickness for In0.36Ga0.64As/GaAs single quantum wells
Authors: Ekenstedt M. J. , Wang S. M. , Andersson T. G.
Published: July 2002

A series of In0.36Ga0.64As/GaAs single quantum wells were grown by molecular beam epitaxy to investigate the dependence of the critical layer thickness (CLT) on growth temperature. The layers were grown between 410 and 590 °C. Photoluminescence was then used to determine the CLT as the onset of three-dimensional growth which occurs at 15 Å for 570 °C and at 55 Å when grown at 470 °C. Our results indicate a strong and nearly linear temperature dependence for the CLT.
Growth and characterization of high current density, high-speed InAs/AlSb resonant tunneling diodes
Authors: Söderström J. R. , Brown E. R. , Parker C. D. , Mahoney L. J. , Yao J. Y. , Andersson T. G. , McGill T. C.
Published: July 2002

High quality resonant tunneling diodes have been fabricated from the InAs/AlSb material system (InAs quantum well and cladding layers, AlSb barriers) on (100)GaAs substrates. A diode with a 6.4-nm-thick InAs quantum well and 1.5-nm-thick AlSb barriers yielded a room-temperature peak current density of 3.7×105 A cm−2 and peak-to-valley current ratio of 3.2. This corresponds to an available current density of 2.6×105 A cm−2, which is comparable to that of the best In0.53Ga0.47As/AlAs diodes grown on lattice-matched substrates and is three times higher than that of the best GaAs/AlAs diode reported to date. These results were obtained in spite of a 7.2% lattice mismatch between the InAs epilayers and the GaAs substrates, which leads to a measured threading dislocation density of roughly 109 cm−2. The experimental peak voltage and current density are in good agreement with theoretical calculations based on a stationary-state transport model with a two-band envelope function approximation.
Growth control of GaAs epilayers with specular surface free of pyramids and twins on nonmisoriented (111)B substrates
Authors: Chen P. , Rajkumar K. C. , Madhukar A.
Published: July 2002

Growth control of GaAs epilayers with specular surface, free of superficial pyramid-shape features and bulk twins, is achieved on a nonmisoriented GaAs(111)B substrate via in situ, real time measurement of specular beam intensity of reflection high-energy electron diffraction (RHEED). Regimes of growth conditions are identified in terms of the static surface phase diagram and the temporal RHEED intensity behavior during growth, thus affording the possibility to realize a reproducible control independent of growth systems.
Plastic relaxation of InGaAs grown on GaAs
Authors: Dunstan D. J. , Kidd P. , Howard L. K. , Dixon R. H.
Published: July 2002

We report measurements of the plastic relaxation of InGaAs layers grown above critical thickness on GaAs substrates. The relaxation is accurately hyperbolic, proportional to the reciprocal of the layer thickness, in agreement with a recent geometrical theory of critical thickness [D. J. Dunstan, S. Young, and R. H. Dixon, J. Appl. Phys. 70, 3038 (1991)]. At large thicknesses, work hardening is observed which leads to a residual strain dependent on the original misfit.
Nature of the mechanism of interface state creation on electrically stressed metal-oxide-semiconductors structures
Authors: Vuillaume Dominique
Published: July 2002

The defects generated at the Si-SiO2 interface by electron injection across the oxide under high electric-field stress conditions are studied as a function of the stressing temperature in the range 100–450 K. After stress at temperatures below 300 K, the interface state creation during isochronal annealing at room temperature is analyzed. The defect formation is readily explained by the diffusion of neutral hydrogen-related species and a simple model allows the determination of its diffusion coefficients to be in the range of 1.0×10−14–4.2×10−14 cm2 s−1 at 200 K to 1.6–6.6×10−12 cm2 s−1 at 275 K. These values are in good agreement with the extrapolated values from the known data for the hydrogen diffusion in SiO2 determined at higher temperatures.
Thermal decomposition of triethylgallium on variously reconstructed GaAs (111)B surfaces
Authors: Ohki Y. , Hiratani Y. , Sasaki M.
Published: July 2002

Mass spectrometry was applied to study the thermal decomposition of triethylgallium (TEG) on a GaAs (111)B surface. Gallium-containing species desorbed or reflected from three kinds of differently reconstructed surfaces were measured at 420 °C. The signal intensities of the Ga containing species changed largely with the surface reconstruction in the following order: 2×2 As stabilized ≳√19 ×√19 Ga stabilized ≳1×1 Ga saturated. This result indicates that larger As coverage suppresses the thermal decomposition of TEG on a GaAs (111)B surface.
Molecular beam epitaxial growth of AlxGa1−xAs (x=0.2–0.7) on (111)B-GaAs using As4 and As2
Authors: Hayakawa T. , Nagai M. , Morishima M. , Horie H. , Matsumoto K.
Published: July 2002

Basic properties of AlxGa1−xAs (x=0.2–0.7), grown by molecular beam epitaxy on 0.5°-tilted (111)B-GaAs, are studied. We have employed the wide substrate temperature, Ts, range of 540–740 °C and different As species; As4 and As2. The surface morphology has been found to depend strongly upon the As species; a specular surface morphology cannot be obtained when using As2 whereas a specular smooth surface can be obtained at high temperatures when using As4. Photoluminescence intensity of n-Al0.3Ga0.7As (Si=1×1018 cm−3) grown at low Ts (<620–630 °C) does not depend upon the As species and is considered to be determined by defects, such as microtwins and stacking faults, which have been observed by transmission electron microscopy. At high Ts (≳650 °C) photoluminescence intensity is lower for the case of As2 than As4 and this could be due to point defects, such as As interstitials and/or antisite As (AsGa). Deep level transient spectroscopy has been measured on n-Al0.7Ga0.3As grown on (100)- and (111)B-substrates with As4.
Vertical-cavity surface-emitting laser diodes fabricated by phase-locked epitaxy
Authors: Walker J. D. , Kuchta D. M. , Smith J. S.
Published: July 2002

We report 10 mW cw room-temperature operation of an electrically pumped vertical-cavity surface-emitting laser diode without a heat sink. This same laser produces 19 mW cw when cooled slightly below room temperature. In addition, we present a 9 mW cw laser with a threshold voltage of 1.6 V, and series resistance of 18 Ω. These are the first surface-emitting lasers fabricated by phase-locked epitaxy. They are also believed to be the highest power and lowest threshold voltage electrically pumped vertical-cavity structures reported to date. These results establish that phase-locked epitaxy has important applications in the fabrication of surface-emitting lasers and many other structures with similar materials requirements.
Dependence on doping type (p/n) of the water vapor oxidation of high-gap AlxGa1−xAs
Authors: Kish F. A. , Maranowski S. A. , Höfler G. E. , Holonyak N. , Caracci S. J. , Dallesasse J. M. , Hsieh K. C.
Published: July 2002

The oxidation (H2O vapor+N2 carrier gas, 425–525 °C) of high-gap AlxGa1−xAs of different doping types (p and n) is characterized by oxide depth measurements utilizing scanning electron microscopy. The conductivity type is found to affect significantly the oxidation rate, with p-type samples oxidizing more rapidly than n-type samples. Classical oxidation theory is employed to explain these phenomena which are related to the position of the Fermi level in the samples.
Coalescence of nanosized copper colloid particles formed in Cu-implanted SiO2 glass by implantation of fluorine ions: Formation of violet copper colloids
Authors: Hosono Hideo , Abe Yoshihiro , Matsunami Noriaki
Published: July 2002

Fluorine ions were implanted at an energy of 40 keV at room temperature into Cu-implanted (160 keV, 6×1016 ions/cm2) SiO2 glass substrates in which implanted coppers occur in the form of nanosized metallic colloid particles with spherical shape. After the F implantation, the peak position of a band due to plasma oscillation shifted from 2.21 eV (562 nm) to 2.10 eV (591 nm) and the color changed from bulk copperlike to deep violet, visually. The bimodal distribution of depth Cu concentrations became distinct after the implantation. Cross-sectional transmission electron microscopy observation revealed that the distribution of copper colloid particles remains bimodal in shape and the particles coalesce with each other to form larger colloid particles with nonspherical shape. Fourier transform IR attenuated total reflection spectra showed that implanted F ions are incorporated in the form of O3Si-F units breaking continuity of the Si-O-Si network, suggesting that reduction of local viscosity in collision cascade regions during the implantation plays an important role in the observed coalescence.
Critical thicknesses of highly strained InGaAs layers grown on InP by molecular beam epitaxy
Authors: Gendry M. , Drouot V. , Santinelli C. , Hollinger G.
Published: July 2002

The growth and relaxation of highly strained In82Ga18As and InAs epilayers grown by molecular beam epitaxy, at 525 and 450 °C, on InGaAs lattice matched (LM) to InP, have been investigated using reflection high energy electron diffraction (RHEED) techniques. RHEED oscillations, three-dimensional growth mode onsets, and relaxation onsets have been measured. Strong strain and temperature effects have been observed on both growth mode and plastic relaxation mechanism. It is suggested that plastic relaxation could occur through two competing mechanisms, misfit dislocations or ‘‘3D island dislocations’’ and that the actual mechanism can be predicted using specific temperature dependent laws for the critical thicknesses.
Very thin oxide film on a silicon surface by ultraclean oxidation
Authors: Ohmi T. , Morita M. , Teramoto A. , Makihara K. , Tseng K. S.
Published: July 2002

Very thin oxide films with a high electrical insulating performance have been grown by controlling preoxide growth using the ultraclean oxidation method. The current level through the ultraclean oxide is lower than that through the conventional dry oxide including thicker preoxide. The barrier height at the silicon-oxide interface for electrons emission from silicon to oxide for the ultraclean oxide is little decreased as the thickness is thinner, while the barrier height for conventional dry oxide is drastically decreased. The growth rate of ultraclean oxide at 900 °C is governed by a simple parabolic law even in the range of 5–20 nm.
Size quantization by faceting in (110)-oriented GaAs/AlAs heterostructures
Authors: Nötzel R. , Däweritz L. , Ledentsov N. N. , Ploog K.
Published: July 2002

On GaAs (110) substrates a distinct step structure exists on the surface during molecular beam epitaxy of GaAs/AlAs multilayer structures which is monitored in situ by reflection high-energy electron diffraction. This peculiar surface structure results in thicker GaAs (AlAs) channels associated with the step planes giving rise to pronounced redshifts of the luminescence. The observation of hot exciton luminescence indicates increased exciton stability and exciton phonon interaction due to strong lateral localization of the excitons in the GaAs channels. The measured optical anisotropy is in agreement with the lateral potential introduced by the faceting of the GaAs/AlAs interface.
Investigation of Pb1−xEuxTe molecular beam epitaxy by reflection high-energy electron diffraction intensity oscillations
Authors: Springholz G. , Bauer G.
Published: July 2002

Reflection high-energy electron diffraction (RHEED) intensity oscillations were observed for the molecular-beam epitaxial growth of Pb1−xEuxTe. For the first time, the influence of vapor composition and surface condition on the damping of the intensity oscillations was studied in ternary IV-VI compounds. The shape of the RHEED intensity oscillations is found to depend critically not only on the Eu-to-Te2 beam-flux ratio, but also on the initial state and the stoichiometry of the surface. For growth on a Te-stabilized surface with Te-rich beam-flux composition, optimum growth conditions were found with up to N=380 oscillation periods.
Transport asymmetry and photovoltaic response in (AlGa)As/AlAs/GaAs/(AlGa)As single-barrier quantum-well infrared detectors
Authors: Schneider H. , Kheng K. , Ramsteiner M. , Ralston J. D. , Fuchs F. , Koidl P.
Published: July 2002

We have studied the wavelength and electric-field characteristics of intersubband photodetectors where a thin AlAs tunnel barrier was introduced between one side of the GaAs quantum well and thicker layers of (AlGa)As. The photoresponse of these structures has an extremely broad (3–11 μm) spectral range and there is a preferential escape direction of the photoexcited carriers towards one direction of the quantum wells giving rise to photovoltaic detector behavior. We found evidence that this transport asymmetry is not only caused by the asymmetric potential distribution, but that interface scattering processes are involved. These scattering processes act differently on the photocurrent and the dark current, which is useful for further optimization of quantum-well infrared detectors.
Optical properties of InGaAs films embedded in plasma etched InP wells
Authors: Georgakilas A. , Christou A. , Lefebvre P. , Allegre J. , Zekentes K. , Halkias G.
Published: July 2002

The optical properties of InGaAs films grown in plasma etched InP wells by molecular beam epitaxy have been investigated and compared to the properties of similar films grown on nonpatterned InP substrates. The excitonic features of the photoluminescence spectra were maintained for the selectively grown well films.
Temperature-dependent transition from two-dimensional to three-dimensional growth in highly strained InxGa1−xAs/GaAs (0.36≤x≤1) single quantum wells
Authors: Wang S. M. , Andersson T. G. , Ekenstedt M. J.
Published: July 2002

Transition from two-dimensional to three-dimensional growth mode has been investigated by photoluminescence in highly strained InxGa1−xAs/GaAs (0.36≤x≤1) single quantum wells. The structures were grown by molecular beam epitaxy from 410 to 590 °C. The critical layer thickness based on this transition decreased as the growth temperature increased. This behavior was well described by the single-kink Matthews model [J. Vac. Sci. Technol. 12, 126 (1975)] including the simplest expression of the Peierls–Nabarro friction stress [J. Appl. Phys. 41, 3800 (1970)].
Compensation processes in nitrogen doped ZnSe
Authors: Hauksson I. S. , Simpson J. , Wang S. Y. , Prior K. A. , Cavenett B. C.
Published: July 2002

We have examined the compensation processes in nitrogen doped ZnSe grown by molecular beam epitaxy. Two independent donor–acceptor pair emission processes have been observed in photoassisted grown layers and detailed temperature dependence measurements have allowed us to conclude that a deep compensation donor with a binding energy of 44 meV exists in more heavily doped material. We propose that the compensating donor is a complex involving a native defect such as the (VSe-Zn-NSe) single donor and this suggestion is supported by the observation of changes in the carrier concentration profile with time.
Electrical and optical properties of InP grown by metalorganic vapor phase epitaxy with extremely low V/III ratios using tertiarybutylphosphine
Authors: Horita M. , Suzuki M. , Matsushima Y.
Published: July 2002

Metalorganic vapor phase epitaxy of InP with extremely low V/III ratios less than 10 was successfully carried out by using tertiarybutylphosphine, and detailed electrical and optical properties were investigated for the first time. Featureless surface morphology was obtained even with a V/III ratio of as low as 3. Good electrical properties, such as carrier concentrations of about 6×1014 cm−3 and electron Hall mobilities more than 30 000 cm2/V s measured at 77 K were confirmed, although both Van der Pauw and low-temperature photoluminescence results proved the increased acceptor concentrations in the low V/III ratio range.
Modeling the current to light characteristics of index-guided vertical-cavity surface-emitting lasers
Authors: Scott J. W. , Corzine S. W. , Young D. B. , Coldren L. A.
Published: July 2002

While there have been many advances in the field, vertical-cavity surface-emitting laser performance has been limited by undefined thermal effects. A temperature dependent, physically based model has been developed which simulates the steady state output characteristics of index-guided vertical-cavity surface-emitting lasers. The model has lead to the development of lasers with improved temperature stability and output power. Experimental devices have been fabricated which exhibit a minimum threshold current of 1.6 mA at 70 °C with a variation of less than 0.5 mA over a 80 °C range.
Carrier transport limited bandwidth of 1.55 μm quantum-well lasers
Authors: Grabmaier A. , Schöfthaler M. , Hangleiter A. , Kazmierski C. , Blez M. , Ougazzaden A.
Published: July 2002

We present the first measurements of the dynamic response of InGaAs/InGaAsP multiquantum-well lasers which clearly show the effect of the carrier transport phenomena on the modulation response. Using our parasitic-free optical modulation method, we separate an intrinsic RC-like component in the frequency response from normal resonance behavior. The bandwidth is strongly limited by this low-pass rolloff that can be described by a structure-dependent transport time. It is shown that, therefore, the K factor may not be a reasonable quantity for evaluating the ultimate bandwidth.
AlGaInP multiple-quantum-wire lasers grown by gas source molecular beam epitaxy
Authors: Stellini E. M. , Cheng K. Y. , Pearah P. J. , Chen A. C. , Moy A. M. , Hsieh K. C.
Published: July 2002

GaxIn1−xP/Al0.15Ga0.35In0.5P graded-index separate-confinement heterostructure visible laser structures with multiple quantum wire active regions have been formed in situ during gas source molecular beam epitaxy. No regrowths or ex situ fabrication procedures were employed in the formation of the quantum wires. Quantum wires with cross-sectional dimensions of approximately 50×120 Å were routinely achieved with a linear density of 100/μm. Broad area stripe geometry lasers with contact stripe oriented in the [110] and [1̄10] directions exhibited anisotropic threshold current densities varying in ratio by a factor of more than 3.75. Threshold current densities as low as 400 A/cm2 were obtained for lasers with stripes in the [110] direction, perpendicular to the quantum wires. Strong dependence of electroluminescence polarization on stripe direction was also observed.
Light-emitting porous silicon diode with an increased electroluminescence quantum efficiency
Authors: Steiner P. , Kozlowski F. , Lang W.
Published: July 2002

The fabrication technology and the properties of a light-emitting device including a porous pn junction are presented. We employ the selective formation of different kinds of porous silicon substructures caused by the doping level and the illumination during anodization. The device has a nanoporous light-emitting n layer between a mesoporous p+-doped capping layer and the macroporous n substrate. The pn junction formed in this way has strong rectifying characteristics. It shows bright red-orange light emission under forward bias. Compared to simple metal-porous silicon devices, the structure has an increased quantum efficiency (factor 10–100).
High contrast electro-optic n-i-p-i doping superlattice modulator
Authors: Linder N. , Gabler T. , Gulden K. H. , Kiesel P. , Kneissl M. , Riel P. , Döhler G. H. , Wu X. , Walker J. , Smith J. S.
Published: July 2002

Transmission changes in a n-i-p-i doping superlattice have been measured. The structures were grown by a newly developed epitaxial shadow mask technique allowing to apply selective contacts to the n and p layers. For a voltage swing between only Upn=−4 and 0.8 V relative transmission changes of 65% below the band gap have been measured in a 2.66-μm-thick structure. The changes are larger than 50% in a wavelength range of more than 13 nm. The pure absorption changes are enhanced by a carrier- and field-induced-Bragg effect within the n-i-p-i crystal. The experimental results are in very good quantitative agreement with calculations.
Periodic faceting on vicinal GaAs(110) surfaces during epitaxial growth
Authors: Krishnamurthy M. , Wassermeier M. , Williams D. R. M. , Petroff P. M.
Published: July 2002

The formation and evolution of quasiperiodic microfacets on vicinal GaAs(110) surfaces grown by molecular beam epitaxy was investigated with transmission electron microscopy and modeled using Monte Carlo simulations. Layers of GaAs and (Al,Ga)As were grown on surfaces misoriented 0°–2° toward (010) (steps in the [001] direction). Under the growth conditions studied, the vicinal surfaces form quasiperiodic microfacets oriented along the step direction. The time evolution of the facet density and facet height as a function of vicinal angle indicate that the formation of microfacets is a result of kinetically limited step bunching during step-flow growth.
Growth and characterization of serpentine superlattices in the GaSb-AlSb system
Authors: Wong K. C. , Krishnamurthy Mohan , Brar Berinder , Yi Jong Chang , Kroemer Herbert , English John H.
Published: July 2002

We report the growth of GaSb/AlSb serpentine superlattices (SSLs) on vicinal GaAs and GaSb substrates. Cross-sectional transmission electron microscopy confirms the SSL structure and shows excellent lateral uniformity, better than previous arsenide-SSLs. Photoluminescence (PL) measurements indicate a good-quality lateral superlattice with a spectral linewidth between 13 and 15 meV. Polarization-dependent PL measurements give a normalized linear polarization around 60%, the strongest that has been seen for SSL structures. Preliminary estimates suggest much better segregation between the Ga-rich and Al-rich regions than arsenide-SSLs, with the change in aluminum concentration Δx≊0.35.
Room temperature ZnSe/ZnCdSe bistable self-electro-optic effect device operating at 488 nm
Authors: Wang S. Y. , Horsburgh G. , Thompson P. , Hauksson I. , Mullins J. T. , Prior K. A. , Cavenett B. C.
Published: July 2002

Optical bistability at room temperature has been observed for the first time in a II-VI semiconductor self-electro-optic effect device fabricated by molecular beam epitaxy. The optical switch is based on a ZnSe/ZnCdSe multiple quantum well structure situated within a p-n junction and the devices operate at 488 nm in the blue-green spectral region.
Normal incidence infrared modulator using direct–indirect transitions in GaSb quantum wells
Authors: Xie H. , Wang W. I.
Published: July 2002

We propose a novel normal incidence infrared modulator using the direct–indirect transitions induced by an applied electric field in GaSb quantum wells (QWs). The device is based on the principles that the quantum-confined Stark shift is proportional to the effective mass, and that the interconduction subband absorption at normal incidence is forbidden in direct-gap QWs but allowed in indirect-gap QWs. Since the effective mass of the L valleys is larger than that of the Γ valley, the corresponding Stark shift is also larger. As a result, the ground state of a QW associated with the Γ point at zero voltage becomes L state under bias (direct–indirect transition). Consequently the device switches from being transparent to normal incidence light to strongly absorbing it. Based on our calculations for a GaSb/Ga0.5Al0.5Sb QW with a well width of 85 Å, changes in absorption coefficients up to 104 cm−1 in the modulation wavelength range of 14–18 μm could be achieved under an electric field in the range of 200 kV/cm. This is the most effective mechanism ever reported for normal incidence infrared modulators.
Abrupt compositional transition in luminescent Si1−xGex/Si quantum well structures fabricated by segregant assisted growth using Sb adlayer
Authors: Usami N. , Fukatsu S. , Shiraki Y.
Published: July 2002

Luminescent Si0.8Ge0.2/Si single quantum well structures with abrupt interfaces were successfully grown by segregant assisted growth (SAG) using Sb adlayer. The emission energy shifted to the lower side compared to the sample grown without Sb adlayer due to the suppression of the surface segregation of Ge atoms. Improved abruptness of interfaces was confirmed by sputter depth profile measurement, where no segregation edge was seen in the sample grown by SAG technique. Light emitting p-i-n diode structure can be fabricated by utilizing the incorporation of Sb during SAG.
Effect of surface treatment on visible luminescence of porous silicon: Correlation with hydrogen and oxygen terminators
Authors: Kumar Rajesh , Kitoh Yasuo , Hara Kunihiko
Published: July 2002

The effect of hydrogen and oxygen surface termination atoms on the visible luminescence of porous Si was investigated for underlying physical mechanism. Atmospheric thermal treatment up to 1000 °C was carried out to study the functional relationship between the surface coverage and photoluminescence (PL). The results show that oxygen incorporation induces surface modification that enhance the PL efficiency after the removal of all SiHx (x=1–3) species. The presence of oxygen atoms can also account for the observed PL redshift along with the usual blueshift. The molecular orbital calculations on the cluster modeling showed the significance of oxygen atoms in modifying the electronic structure of porous Si.
Determination of the lateral periodicity of nanometer quantum dot arrays by triple crystal diffractometry
Authors: Jenichen B. , Ploog K. , Brandt O.
Published: July 2002

The lateral periodicity of InAs quantum dot arrays in a GaAs matrix consisting of submonolayer InAs films grown by molecular beam epitaxy on a terraced (001) GaAs substrate was measured in the differential rocking curve by triple crystal diffractometry. The x-ray diffraction of the array is described in the frame of the kinematical theory. Both the changes in the scattering factor and the tetragonal deformations due to the InAs quantum dots are taken into account. The limits of the description assuming an ideal array are estimated using the Laue interference function. The lateral periodicity of the array along [100] is 11 nm compared with 10 nm obtained from the miscut of the sample. This ideal lateral periodicity extends along [100] over about 10 cells of the array corresponding to 0.1 μm.
Molecular beam epitaxial growth and optical characterization of GaAs/AlxGa1−xAs quantum wells on nominally oriented (111)B GaAs substrates
Authors: García B. J. , Fontaine C. , Muñoz-Yagüe A.
Published: July 2002

Molecular beam epitaxial growth conditions of GaAs/AlxGa1−xAs quantum wells on nominally oriented (111)B GaAs substrates are reported. Photoluminescence measurements of these structures showed linewidths slightly larger than previously reported for quantum wells grown on (100) and misoriented (111)B substrates, but much lower than observed and reported on nominally oriented (111)B substrates. Good surface morphology and optical properties were obtained by monitoring the specular beam intensity of the reflection high-energy electron diffraction diagram during growth. Growth interruption at the interfaces was found to be detrimental for substrate temperatures higher than 610 °C.
Highly polarized photoluminescence from 2-μm-thick strained GaAs grown on CaF2
Authors: Tessler Leandro R. , Hermann Claudine , Lampel Georges , Lassailly Yves , Fontaine Chantal , Daran Emmanuelle , Muñoz-Yagüe Antonio
Published: July 2002

Intense photoluminescence was measured in a strained 2-μm-thick GaAs film grown on a (100)-oriented CaF2 substrate. Circular polarization of 77%±2% was obtained at 77 K under excitation with circularly polarized photons below 1.575 eV. For excitation above 1.610 eV the polarization is limited to 30%±2%. These results are clear indications of strain induced splitting between the Mj=‖±3/2〉 and the Mj=‖± 1/2〉 hole bands. The deduced splitting was 62.5±2.5 meV, corresponding to a stress of the order of −12 kbar. The polarization is maximum for reception energies very close to the excitation. Strained GaAs/CaF2 is thus a good candidate structure for efficient strongly polarized electron sources.
Design criteria for structurally stable, highly strained multiple quantum well devices
Authors: Houghton D. C. , Davies M. , Dion M.
Published: July 2002

Strain compensation allows the synthesis of infinitely thick heterostructures with many highly strained quantum wells. Design criteria are given for optimized strain and thickness parameters in several device geometries. Strain compensation, using alternating layers of opposite strain, is quantitatively treated using an energy balance analysis. The upper bound to stability for strained multiple quantum wells with and without strain compensation is defined for geometries typically used in optoelectronic devices. Highly metastable structures (composed of many layers of high strain and/or thickness) require low epitaxy temperatures to avoid strain relaxation during growth of individual strained layers, prior to their stabilization in a strain compensated structure.
Molecular-beam-epitaxy growth of GaN on GaAs(100) by using reactive nitrogen source
Authors: He Z. Q. , Ding X. M. , Hou X. Y. , Wang Xun
Published: July 2002

By using a cold cathode ion gun to ionize the nitrogen gas, the molecular-beam-epitaxy growth of GaN is carried out. The zinc-blende structure GaN epilayer grown on the GaAs(100) substrate with a narrow x-ray diffraction peak width (FWHM) of 23 min and a low carrier concentration of 1017 cm−3 is achieved. The surface optical phonon energies of cubic and hexagonal GaN are experimentally determined to be 82 and 90 meV, respectively.
Tunability of one-dimensional self-faceting on GaAs (311)A surfaces by metalorganic vapor-phase epitaxy
Authors: Nötzel Richard , Temmyo Jiro , Tamamura Toshiaki
Published: July 2002

The controlled step bunching on GaAs (311)A oriented surfaces during growth by metalorganic vapor-phase epitaxy (MOVPE) leads to one-dimensional faceting with a lateral period tunable upon growth temperature and layer thickness in the mesoscopic size range 25–80 nm. The surface morphology established during MOVPE growth directly images the microscopic surface structure maintained during growth by conventional solid source molecular beam epitaxy (MBE) and allows us to control the lateral period in GaAs/AlGaAs wire-like heterostructures. The red shift of the luminescence at room temperature from these structures is directly correlated with the lateral period of faceting.
Study of the first-stage relaxation in ZnTe/(001)CdTe strained layers
Authors: Eymery J. , Tatarenko S. , Bouchet N. , Saminadayar K.
Published: July 2002

The first stages of the growth of highly strained ZnTe on (001) CdTe are studied in details by reflection high-energy electron diffraction analysis. Below the critical thickness, small lattice oscillations attributed to a nontetragonal elastic distortion are observed on a system in tensile stress. An effect of Zn excess pressure on the critical thickness is demonstrated. Exposure at 280 °C of the CdTe(001) surface under Zn flux leads to the formation of a c(2×2) Zn terminated surface with about 50% Zn coverage. Such a pretreatment reduces the critical thickness by about half a monolayer.
As capture and the growth of ultrathin InAs layers on InP
Authors: Aspnes D. E. , Tamargo M. C. , Brasil M. J. S. P. , Nahory R. E. , Schwarz S. A.
Published: July 2002

Capture of As by (001) InP surfaces exposed to As fluxes under chemical beam epitaxy conditions is investigated by virtual-interface analysis of real-time kinetic ellipsometric data. Intentional growth of ultrathin InAs layers is readily followed. Arsenic accumulated in the absence of growth can be completely removed by exposure to P, showing that As-P exchange occurs only in the outermost layer.
Improvement in radiation hardness of gate oxides in metal–oxide semiconductor devices by repeated rapid thermal oxidations in N2O
Authors: Wu You-Lin , Hwu Jenn-Gwo
Published: July 2002

Instead of using the conventional one-time N2O oxidation of silicon, repeated N2O rapid thermal oxidations (RNRTO) is proposed as a new gate oxide preparation method. The radiation hardness of metal–oxide semiconductor (MOS) capacitors with RNRTO oxide is found to be better than that with the conventional one-time N2O-grown oxide. The nitrogen content at the SiO2/Si interface as determined by secondary ion mass spectroscopy (SIMS) is constant for all the RNRTO samples but the thickness of the nitrogen-rich interfacial layer increases as the number of RNRTO increases. The less strain gradient caused by this increasing nitrogen-rich interfacial layer thickness is the main cause of improving the radiation hardness of the MOS capacitors.
Texture of vapor deposited parylene thin films
Authors: You L. , Yang G.-R. , Knorr D. B. , McDonald J. F. , Lu T.-M.
Published: July 2002

The texture of vapor deposited parylene (poly-p-xylylene) thin films on Si is measured using the x-ray pole figure technique to quantify the crystalline portion. The as-deposited sample is the monoclinic α phase where the (020) fiber texture component comprises 48% and the remaining 52% are randomly oriented crystallites. The sample annealed for 350 °C 12 h is hexagonal β phase with an (040) fiber texture component of 68%. The half-width (ω) of the (040) fiber component of the β crystallites is within 25° of the substrate normal (fiber axis). In a β(040) oriented crystallite, the polymer chain is parallel to the Si substrate. This β fiber texture develops by polymer chain movement and rearrangement of the as-deposited α fiber texture.
Si δ-doping of 〈011〉-oriented GaAs and AlxGa1−xAs grown by molecular-beam epitaxy
Authors: Schubert E. F. , Pfeiffer Loren , West K. W. , Luftman H. S. , Zydzik G. J.
Published: July 2002

Silicon δ-doping is studied on 〈011〉-oriented GaAs and AlxGa1−xAs grown by molecular-beam epitaxy. Hall measurements and secondary ion mass spectrometry on as-grown and on annealed samples reveal (i) that the electrical activity is reduced for the 〈011〉-oriented samples as compared 〈001〉-oriented reference samples, (ii) that the electron mobility is lower for 〈011〉-oriented samples, and (iii) that the thermal redistribution of Si impurities is comparable for both orientations. We find a markedly different dependence of the electron mobility on the spacer thickness in selectively doped 〈011〉-oriented AlxGa1−xAs/GaAs heterostructures, which is explained by the reduced doping efficiency of Si in 〈011〉-oriented AlxGa1−xAs.
Amorphous diamond from C60 fullerene
Authors: Hirai Hisako , Kondo Ken-ichi , Yoshizawa Noriko , Shiraishi Minoru
Published: July 2002

Amorphous diamond was successfully quenched from shock-compressed C60 fullerene by rapid cooling technique. This material is transparent and homogeneous glassy chips, and exists stably at ambient conditions. X-ray diffractometry showed a halo, and electron diffractometry showed a diffuse pattern similar to those of common amorphous carbon materials. Electron energy loss spectroscopy represented evidently σ-electron state in sp3 hybridization completely equivalent to that of a typical diamond. Therefore, this material is defined in long range order to be amorphous and in short range order to be diamond, namely it can be said as amorphous diamond.
Optical spectroscopy of a GaAs/AlGaAs quantum wire structure using near-field scanning optical microscopy
Authors: Grober Robert D. , Harris Timothy D. , Trautman Jay K. , Betzig Eric , Wegscheider Werner , Pfeiffer Loren , West Ken
Published: July 2002

We report the first spectroscopic study using a low temperature near-field scanning optical microscope. We have studied an array of GaAs/AlGaAs cleaved edge overgrowth quantum wires. The three luminescence peaks originate from different structures in the sample: The (001)-oriented multiple quantum wells, the (110)-oriented single quantum well, and the quantum wires. The linewidth of the quantum wire emission is related to roughness in the (110)-oriented single quantum well. Quenching of the multiple quantum wells and single quantum well emission near the quantum wires is attributed to diffusion of photoexcited carriers into the wires.
Influence of effective-medium dielectric constant on electronic transport in an arylamine-containing glassy polymer
Authors: Abkowitz M. , Facci J. S. , Stolka M.
Published: July 2002

The extent to which transport behavior can be simply correlated with the macroscopic dielectric properties of a transport polymer is explored by employing a ‘‘vapor doping’’ procedure as a means of reversibly varying its bulk dielectric properties. Under controlled uptake and subsequent outgassing of polar CH3CN vapor, the hole drift mobility of the transport polymer PTPB is monitored, while its relative dielectric constant is reversibly varied between ε=3.7, its undoped value, and ε=6.0, its saturation value at room temperature. There is neither an associated change in hole drift mobility nor in the dispersion of injected carrier transit times. When the same procedure is carried out on a closely related molecularly doped polymer TPD in polycarbonate, an increase in dispersion is clearly indicated but the transit time of the fastest carriers remains unaffected.
High-power diode-laser-pumped midwave infrared HgCdTe/CdZnTe quantum-well lasers
Authors: Le H. Q. , Arias J. M. , Zandian M. , Zucca R. , Liu Y.-Z.
Published: July 2002

Diode-array-pumped HgCdTe/CdZnTe broad-stripe quantum-well lasers operated at 88 K yielded 1.3 W peak power and 10 mW average power per facet at 3.2 μm. The highest operation temperature was 154 K, and the characteristic temperature of the threshold was 16 K. The external quantum efficiency was ∼7.5% at ∼80 K and decreased by an order of magnitude at 150 K.
Current injection GaAs/AlGaAs quantum wire lasers fabricated by cleaved edge overgrowth
Authors: Wegscheider Werner , Pfeiffer Loren , West Kenneth , Leibenguth Ronald E.
Published: July 2002

We report the operation of quantum wire (QWR) semiconductor diode lasers fabricated by cleaved edge overgrowth. The active region in these index guided lasers consists of 15 QWRs formed at the right angle intersection of 15 [001] oriented quantum wells (QWs) each 7 nm wide, with a single 7-nm-wide QW grown along the [110] direction. Doping with Be and Si in the two orthogonal growth directions leads to the formation of a linear p-n junction in which the QWRs are embedded. Efficient current injection into the wires is demonstrated by the almost complete suppression of optical emission from QW states as well as by threshold currents as low as 0.4 mA for uncoated devices at 4.2 K.
Crystalline phases of II-VI compound semiconductors grown by pulsed laser deposition
Authors: Shen W. P. , Kwok H. S.
Published: July 2002

II-VI compound semiconductors, ZnS, ZnSe, CdS, CdSe, and CdTe, were grown epitaxially on (111) and (100) InP and GaAs substrates by excimer laser ablation. All of these films have good crystalline quality (fully in-plane aligned) and mirror-like surface morphology. It was found that, on (111)-oriented substrates, CdS and CdSe films were in the hexagonal phase with the c axis perpendicular to the surface, while ZnS and ZnSe films were in the cubic phase. The films grown on (100)-oriented substrates were all cubic. These high quality films should be useful in optoelectronics applications.
Growth by molecular beam epitaxy and electrical characterization of Si-doped zinc blende GaN films deposited on β-SiC coated (001) Si substrates
Authors: Kim J. G. , Frenkel A. C. , Liu H. , Park R. M.
Published: July 2002

We report the electrical characteristics of heavily Si-doped zinc blende GaN epilayers deposited on β-SiC coated (001) Si substrates. The β-GaN films were grown by molecular beam epitaxy using a rf plasma discharge, nitrogen free-radical source, and the doping concentration in the films was controlled over the range 1.5×1018–3.0×1020 cm−3 by suitably adjusting the temperature of a Si effusion cell. We have found that Si incorporation in β-GaN results in a relatively deep donor level (∼62 meV below the conduction band edge at a carrier concentration at room temperature of 1018 cm−3). Also, we present evidence of simultaneous high mobility conduction band conduction (dominant at high temperatures) and low mobility impurity band conduction (dominant at temperatures <70 K) in heavily doped (nRT≳1019 cm−3) material.
Gettering of copper to hydrogen-induced cavities in silicon
Authors: Wong-Leung J. , Ascheron C. E. , Petravic M. , Elliman R. G. , Williams J. S.
Published: July 2002

Hydrogen implantation and subsequent thermal annealing is found to result in a well-defined band of cavities in Si. This band is an extremely efficient gettering layer for Cu which is also introduced into the near surface of Si by ion implantation. Profiling of implanted Cu indicates that ∼95% of an initial 3×1015 cm−2 Cu implant is redistributed following annealing at a temperature of 780 °C from a near-surface damaged layer to a narrow band of cavities of width ∼1000 Å at a depth of ∼1 μm. Furthermore, the Si between the surface and the cavity band is essentially defect-free and that some cavities contain the bulk Cu3Si phase.
Si nanostructures fabricated by anodic oxidation with an atomic force microscope and etching with an electron cyclotron resonance source
Authors: Snow E. S. , Juan W. H. , Pang S. W. , Campbell P. M.
Published: July 2002

Nanometer-scale Si structures have been fabricated by anodic oxidation with an atomic force microscope (AFM) and dry etching using an electron cyclotron resonance (ECR) source. The AFM is used to anodically oxidize a thin surface layer on a H-passivated (100) Si surface. This oxide is used as a mask for etching in a Cl2 plasma generated by the ECR source. An etch selectivity ≳20 was obtained by adding 20% O2 to the Cl2 plasma. The AFM-defined mask withstands a 70 nm deep etch, and linewidths∼10 nm have been obtained with a 30 nm etch depth.
Flow rate modulation epitaxy of AlGaAs/GaAs quantum wires on nonplanar substrate
Authors: Wang Xue-Lun , Ogura Mutsuo , Matsuhata Hirofumi
Published: July 2002

Flow rate modulation epitaxy (FME) is applied to the low-temperature growth of AlGaAs/GaAs quantum wires (QWRs) on nonplanar substrates. The growth selectivity is found to be enhanced greatly by the use of FME, as compared with the conventional metalorganic chemical vapor deposition due to the enhanced migration of Ga species. An AlGaAs/GaAs QWR with a central thickness of about 9 nm and a lateral width of about 28 nm is grown at 600 °C on a V-grooved substrate. Good photoluminescence properties are observed from the grown QWR, with the peak energy being in good agreement with the calculated energy level of a parabolic shape lateral confinement potential.
Electron cyclotron emission diagnostics for mirror devices (invited)
Authors: Ellis R. F. , James R. A. , Lasnier C. J. , Casper T.
Published: July 2002

Electron cyclotron emission (ECE) has proven to be a useful diagnostic in tokamaks for measuring Te and its radial variation. The application of ECE to mirror devices is discussed here, with emphasis on measurements of the properties of energetic electrons in tandem mirror end cells, which can be viewed both parallel and perpendicular to B. The parallel or whistler view is generally optically thick and can yield a measurement of perpendicular temperature. High harmonic perpendicular emission is optically thin and can yield important information about the hot electron buildup and the energy and spatial distribution. Experimental results from TMX-U and appropriate modeling are presented.
Use of photosensitive polyimide for deep x-ray lithography
Authors: White V. , Ghodssi R. , Herdey C. , Denton D. D. , McCaughan L.
Published: July 2002

In this letter, a method is outlined and results presented for an x-ray lithography micromachining process that offers a greatly improved sensitivity over the LIGA process. This process is based on photosensitive polyimide (PPI), which is a commercial photoresist typically used as a passivation layer or dielectric material in the semiconductor industry. The main benefit of this process is its high sensitivity, which is approximately two orders of magnitude greater than that of the PMMA used in the LIGA process. Using a synchrotron radiation x-ray source, we have achieved resist patterns over 1000 μm thick. The capability has also been demonstrated for aspect ratios over 10, as well as the ability to print linewidths down to 0.5 μm.