bluuebunny/crossref_metadata_2025 huggingface dataset:
Boron profile changes during low-temperature annealing of BF+2-implanted silicon
Authors: Kim Yudong , Massoud Hisham Z. , Fair Richard B.
Published: July 2002

BF+2 ions were implanted in (100) silicon at room temperature with an energy of 40 keV through a 140-Å-thick SiO2 layer. Boron profiling by secondary-ion mass spectrometry indicates that subsequent annealing in a conventional furnace in the 650–850 °C range for 30–240 min results in a pronounced secondary peak in the B and F profiles, in addition to the near-surface primary peak located in the vicinity of the projected range of the implanted species. This phenomenon was also observed in BF+2 -implanted samples which were rapid thermal annealed at 900 °C for 15–60 s. The depths of the secondary peaks in the B and F profiles correspond to the depths of a damaged layer observed by cross-sectional transmission electron microscopy. Isochronal furnace annealing revealed that there is no chemical interaction between B and F atoms during annealing. This is also supported by the observation of F atoms not affecting the B segregation coefficient during oxidation of the BF+2 -implanted samples. The end-of-range extended dislocations appear to be responsible for the gettering of B and F atoms during annealing.
Waveguide magneto-optic isolator fabricated by laser annealing
Authors: Ando Koji , Okoshi Tokio , Koshizuka Naoki
Published: July 2002

A compact waveguide optical isolator whose input and output light are TE or TM mode has been realized by making adjacent nonreciprocal and reciprocal TE-TM mode converters in a (BiGdLu)3(FeGa)5O12 film. Designed configurations of the magnetization directions were produced by making use of local laser annealing of the film grown on a Gd3Ga5O12 substrate of which the face normal is tilted from the [111] axis. The laser-annealed and nonannealed regions worked as the nonreciprocal and reciprocal mode converters, respectively. The observed isolation agreed with theoretical calculation. An isolation ratio of 12.5 dB was achieved at a wavelength λ=1.15 μm.
Reliable single-target sputtering process for high-temperature superconducting films and devices
Authors: Sandstrom R. L. , Gallagher W. J. , Dinger T. R. , Koch R. H. , Laibowitz R. B. , Kleinsasser A. W. , Gambino R. J. , Bumble B. , Chisholm M. F.
Published: July 2002

We report a simple, single-target magnetron sputtering process for films of high-temperature superconductors involving an off-axis sputtering geometry. The process lends itself both to film growth with high-temperature post-anneals and to low-temperature in situ film growth. The post-anneal process routinely yields YBa2Cu3O7−x films on SrTiO3 substrates that are fully superconducting at 86–89 K. Current densities at 77 K range from 104 to 8×105 A/cm2. A single-level superconducting quantum interference device (dc SQUID), made by photolithographically patterning a low current density film, has a flux noise level at 77 K of 3×10−4 Φ0/(Hz)1/2 at 20 Hz, dominated by low-frequency noise associated with flux motion in the film.
Effect of SiO2 surface chemistry on the oxidation of silicon
Authors: deLarios J. M. , Kao D. B. , Helms C. R. , Deal B. E.
Published: July 2002

We show that the retardation in the silicon oxidation rate associated with an ammonium hydroxide-hydrogen peroxide preclean is due to trace amounts of aluminum in the region of the SiO2 surface. This aluminum and the retarding effect can be eliminated by removing less than 50 Å of thermal oxide in a HF:H2O etch. Depositing thin films of aluminum with thicknesses between 0.05 and 1 monolayers (ML) on HF cleaned surfaces produced the same retardation as the NH4OH based cleans. These results indicate the importance of the SiO2 surface in silicon oxidation.
Laser deposition of epitaxial titanium nitride films on (100) MgO
Authors: Biunno N. , Narayan J. , Srivatsa A. R. , Holland O. W.
Published: July 2002

We have investigated the formation of epitaxial (100) oriented TiN films grown on (100) MgO substrates using an excimer laser (wavelength 308 nm, pulse duration 45 ns, and energy density (5–6 J cm−2) physical vapor deposition method. The films were deposited by laser ablation of a TiN target pellet in high vacuum (∼3.0×10−7 Torr), with the substrate temperature ranging from 450 to 750 °C. The epitaxial films were obtained at relatively low substrate temperatures (∼450 °C). The deposited films were analyzed using cross-section and plan-view transmission electron microscopy, x-ray diffraction, Rutherford backscattering/channeling, Auger electron spectroscopy, and electron channeling patterns. The results indicate epitaxial film growth (〈100〉 TiN parallel to 〈100〉MgO) near the stoichiometric TiN composition, and low oxygen content. The minimum channeling yield χmin was found to be ≤10%. The room-temperature resistivity was as low as 50 μΩ cm and the lattice parameter was found to be 4.218 Å.
Laser wavelength dependent properties of YBa2Cu3O7−δ thin films deposited by laser ablation
Authors: Koren G. , Gupta A. , Baseman R. J. , Lutwyche M. I. , Laibowitz R. B.
Published: July 2002

YBa2Cu3O7−δ thin films were deposited onto (100) SrTiO3 substrates using 1064, 532, 355, 248, and 193 nm laser ablation. Transport measurements show lower normal-state resistivities and higher critical currents in films deposited by the shorter wavelength lasers. The surface morphology of the films was rough with large particulates when the 1064 nm laser was used whereas much smoother surfaces with fewer and smaller particulates were obtained with the UV lasers. It is suggested that the better film quality obtained when the UV lasers are used is due to a small absorption depth of the UV photons in the ceramic target and to higher absorption by the ablated fragments. This leads to smaller ablated species and further fragmentation in the hotter plume and, therefore, to smoother and denser films.
Effects of post-nitridation anneals on radiation hardness in rapid thermal nitrided gate oxides
Authors: Lo G. Q. , Shih D. K. , Ting W. , Kwong D. L.
Published: July 2002

Effects of post-nitridation anneals on radiation hardness of metal-oxide-semiconductor (MOS) capacitors with rapid thermal nitrided (RTN) gate oxides have been studied. Post-nitridation anneals consisted of either rapid thermal reoxidation (RTO) in pure O2 or rapid thermal anneals (RTA) in pure N2 ambient. The radiation was performed by exposing devices to x rays at doses of 0.5–5.0 Mrad (Si). Comparing RTO and RTA anneals at the same temperature and time for given nitrided oxides, it was found that RTO enhanced the radiation hardness while RTA in N2 had detrimental effects, in terms of interface-state generation (ΔDit) and flatband voltage shift (ΔVfb). The strainless interfacial oxide regrowth during RTO of RTN oxides is responsible for the enhanced interface ‘‘hardness’’ of RTN/RTO oxides. A physical mechanism is described to account for the observation.
Nitridation-induced surface donor layer in silicon
Authors: Wu A. T. , Murali V. , Cox N. , Frost M. R. , Triplett B. , Chan T. Y.
Published: July 2002

Thin (11.4 nm) gate quality silicon dioxide films were subjected to high-temperature (850–1150 °C) rapid thermal nitridation cycles in ultrapure ammonia. Secondary-ion mass spectroscopy and neutron depth profiling results indicate a significant level of nitrogen diffusion into the silicon substrate. After stripping the dielectric layers, Schottky diode studies were performed using an electrolyte-based technique. We found, for the first time, the formation of nitridation-induced ultrathin (less than 60 nm) n-type layers at the top surface of nominally p-type silicon substrates used in the study. A nitrogen-oxygen donor complex formation mechanism is invoked to explain the presence of the ultrathin n-type layers.
Photoluminescence and space-charge distribution in a double-barrier diode under operation
Authors: Vodjdani N. , Chevoir F. , Thomas D. , Cote D. , Bois P. , Costard E. , Delaitre S.
Published: July 2002

The low-temperature photoluminescence of a double-barrier diode under operation is studied. Its observation with exciting light above (as well as below) the quantum well absorption edge indicates that the tunneling of holes plays an important role. A new crossed transition identified to occur in the collector spacer layer shows a strong Stark shift with applied bias giving information on the potential distribution in the diode.
Annular dark field electron microscope images with better than 2 Å resolution at 100 kV
Authors: Shin D. H. , Kirkland E. J. , Silcox J.
Published: July 2002

High-resolution scanning transmission electron microscope (STEM) images in the annular dark field (ADF) imaging mode approaching the theoretical point-to-point resolution limit are presented. The ADF images were obtained from a high Tc superconducting YBa2Cu3O7−x thin-film specimen at 100 kV. The 1.9 Å resolution lattice image, which is the smallest lattice spacing in the specimen, corresponds to the minimum resolvable spatial frequency with 5% contrast in the contrast transfer function for annular dark field, and is smaller than the resolution limit given by the Rayleigh criterion. This demonstrates that STEM ADF imaging can have a resolution approximately 40% better than that of the bright field conventional transmission electron microscope (CTEM) imaging at Scherzer condition.
Properties of sputtered superconducting films of Bi2Sr2CaCu2Ox made by low-temperature i
n s
i
t
u growth
Authors: Kampwirth R. T. , Andersen P. H. , McDonald D. B. , Miller D. J. , Gray K. E. , Sungaila Z. F. , Balachandran U. , Wagner A.
Published: July 2002

Superconducting films of Bi2Sr2CaCu2Ox have been fabricated on single-crystal MgO substrates by a low-temperature in situ process. Using a substrate temperature Ts≊645 °C, metallic films with a superconducting onset of 90–100 K and an extrapolated Tc0=56 K have been obtained. X-ray diffraction shows the films to be c-axis oriented. Electron microscopy reveals that the films are not significantly smoother than films which were post-annealed at 865 °C, and that some segregation into nonsuperconducting phases had occurred. The exact mechanism by which crystallization and superconductivity occurs at such low temperatures is not yet known, but it can be speculated that the surface atoms are less constrained and thus have a smaller energy barrier to overcome in forming a crystal structure.
Scanning tunneling microscopy of insulators: CaF2 epitaxy on Si (111)
Authors: Avouris Ph. , Wolkow R.
Published: July 2002

Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) have been used to study the epitaxy of CaF2 on Si (111). Energy-resolved images of the submonolayer structures produced at the initial stages of CaF2 deposition were obtained. We found that in these structures and also at the 1×1 interface, bonding involves the Ca atom in a reduced, Ca+-like state. Using STS we were able to measure the CaSi bonding-antibonding level splitting at the interface. The distribution of charged defects was also imaged by the STM. More important, we found that we can image strongly insulating CaF2 multilayers by tunneling into their conduction band.
Effect of doping on the thermal oxidation of GaAs
Authors: Levinsohn N. , Beserman R. , Cytermann C. , Brener R. , Khait Y. L. , Regel G. K. , Musolf J. , Weyers M. , Brauers A. , Balk P.
Published: July 2002

The influence of n-type Si and p-type Zn dopants on the low-temperature thermal oxidation of GaAs was studied by Raman scattering and Auger electron spectroscopy. It was found that the oxidation process is significantly affected by the dopants, resulting in a much thinner oxide layer than that obtained in undoped GaAs. The arsenic liberated by the oxidation reaction was observed to accumulate at the oxide/GaAs interface. The process of free As buildup at the interface is accompanied by its crystallization and both processes are strongly enhanced by the presence of dopants.
Strain-induced two-dimensional electron gas in [111] growth-axis strained-layer structures
Authors: Snow E. S. , Shanabrook B. V. , Gammon D.
Published: July 2002

It is demonstrated that strain-induced electric fields in [111] growth-axis strained-layer structures can be used to induce a two-dimensional electron gas without the necessity of modulation doping. A simple analytic expression is derived for the density of the two-dimensional electron gas. The density has a simple linear relationship to the strain-induced electric fields. The calculation predicts that two-dimensional densities in the range 1011–1012 cm−2 should be easily realized in strained-layer structures. Results are calculated for a variety of material systems.
Integrated waveguide/photodiodes using vertical impedance matching
Authors: Deri R. J. , Yasuoka N. , Makiuchi M. , Wada O. , Kuramata A. , Hamaguchi H. , Hawkins R. J.
Published: July 2002

A novel ‘‘vertical impedance matching’’ approach is demonstrated to improve absorption in evanescently coupled, integrated waveguide/photodiodes by 500% over conventional structures. Our devices exhibit both high absorption at short length (90% at 190 μm) and efficient fiber butt coupling (42%) at 1.3–1.55 μm wavelengths. Unusual transient phenomena are observed in such impedance-matched devices and discussed theoretically.
Theoretical explanation of the control of the Schottky barrier height using an ultrathin interface metal layer
Authors: Tuy T. Q. , Mojzes I.
Published: July 2002

Recently experimental results for a thin interface metal layer to control the Schottky barrier height of Ti/Pt/n-GaAs and Pt/Ti/n-GaAs contacts were presented [X. Wu, M. T. Schmidt, and E. S. Yang, Appl. Phys. Lett. 54, 268 (1989)]. In the present letter a possible explanation of the variation of the Schottky barrier height of the bi-metal-semiconductor contact is presented on the basis of the modification of the theory of the single-layer metal-semiconductor contact for the multilayer metal-semiconductor contact. This model leads to an acceptable agreement between our theoretical results and the experimental results presented in the above-mentioned paper and in an earlier publication [M. Hagio, H. Tagaki, A. Nagashima, and G. Kano, Solid-State Electron. 22, 347 (1979)].
Free-space radiation from electro-optic crystals
Authors: Hu B. B. , Zhang X.-C. , Auston D. H. , Smith P. R.
Published: July 2002

We describe a technique to extract electro-optic Cherenkov radiation from a LiTaO3 crystal into free space. This permits the generation of collimated beams of terahertz radiation into free space and overcomes previous limitations imposed by total internal reflection.
Submilliamp threshold vertical-cavity laser diodes
Authors: Geels Randall S. , Coldren Larry A.
Published: July 2002

We report for the first time room-temperature, continuous-wave operation of individual vertical-cavity laser diodes with submilliampere threshold currents. A single quantum well active region emitting at 979 nm surrounded by GaAs/AlAs Bragg reflector mirrors was used. Threshold currents were as low as 0.7 mA. A record low linewidth-power product of 5 MHz mW and a linewidth as narrow as 85 MHz was measured. High yield and good uniformity were demonstrated.
Complete planarization of via holes with aluminum by selective and nonselective chemical vapor deposition
Authors: Tsubouchi Kazuo , Masu Kazuya , Shigeeda Nobuyuki , Matano Tatsuya , Hiura Yohei , Mikoshiba Nobuo
Published: July 2002

We have developed a new controllable method of selective and nonselective deposition of high quality aluminum by low-pressure chemical vapor deposition using dimethylaluminum hydride with hydrogen. At first, silicon dioxide via holes on silicon substrate were selectively filled with aluminum by thermal decomposition. Then, adding the plasma excitation for 1 min, the aluminum film began to deposit nonselectively on the silicon dioxide as well as the selectively deposited aluminum. Silicon dioxide via holes were completely planarized by the selective and nonselective deposition. The single-crystal structure of aluminum deposited selectively on silicon was observed with a new scanning microreflection high-energy electron diffraction microscope.
Large peak current densities in novel resonant interband tunneling heterostructures
Authors: Ting D. Z.-Y. , Collins D. A. , Yu E. T. , Chow D. H. , McGill T. C.
Published: July 2002

We have observed negative differential resistance (NDR) and large peak current densities in a novel resonant interband tunneling structure grown by molecular beam epitaxy in the InAs/GaSb/AlSb material system. The structure consists of a thin AlSb barrier layer displaced from an InAs(n)/GaSp(p) interface. NDR is readily observable at room temperature with peak current densities greater than 105 A/cm2. The enhancement in peak current density relative to a structure with no AlSb barrier is consistent with the existence of a quasi-bound state in the region between the barrier and the InAs/GaAs interface. Furthermore, we demonstrate that by growing the AlSb layer on either the InAs or GaSb side of the interface, the quasi-bound state can be localized in either material.
Real-time detection of higher hydrides on the growing surface of hydrogenated amorphous silicon by infrared reflection absorption spectroscopy
Authors: Toyoshima Yasutake , Arai Kazuo , Matsuda Akihisa , Tanaka Kazunobu
Published: July 2002

Real-time in situ observations of the growth of a-Si:H films have been carried out in a rf glow discharge plasma reactor by use of infrared reflection absorption spectroscopy. Deuterium substitution of an interface layer is employed so as to differentiate the higher hydride species on the growing surface from those located at the film interface on the substrate. A three-layer model is presented to give a quantitative discussion on the absorption signal intensity in the reflection spectroscopy with respect to the normal incident transmission spectroscopy.
Planar InP/InGaAs avalanche photodetectors with partial charge sheet in device periphery
Authors: Tarof L. E. , Knight D. G. , Fox K. E. , Miner C. J. , Puetz N. , Kim H. B.
Published: July 2002

A novel planar separate absorption, charge sheet, grading and multiplication avalanche photodiode (APD) structure incorporating a partial charge sheet in the device periphery is described, which allows for straightforward fabrication of APD devices without the use of guard rings. Metalorganic chemical vapor deposition grown, Zn-diffused InP/InGaAs APD devices have been fabricated. High dc gains well in excess of 100 and a low primary dark current of 0.1 nA at 0.99 of the breakdown voltage VB have been measured for a 40-μm-diam device. The receiver sensitivity for a bit error rate of 10−9 at a bit rate of 400 Mbit/s was −41 dBm. The −3 dB electrical bandwidth was 2.5 GHz, and the gain-bandwidth product was 30 GHz.
Fe/Fe-N multilayer films with low coercivity zero magnetostriction and high saturation magnetization
Authors: Shih K. K. , Re M. E. , Dove D. B.
Published: July 2002

A method of fabricating of Fe/Fe-N multilayer films in the form of alternating thin films of Fe separated by very thin interlayers of Fe-N sputtered in the presence of nitrogen is described. It was found that the properties of these films depended on the thickness of Fe and Fe-N layers and the bias voltage. There is a region where the composite films have coercivity less than 1 Oe, with zero or near-zero magnetostriction. The normally high saturation magnetization of Fe with value of 20 kG was preserved.
Hydrogen effusion from hydrogenated amorphous silicon caused by the deposition of a silicon nitride overlayer
Authors: Matsumoto T. , Watanabe J. , Tanaka T. , Mishima Y.
Published: July 2002

The effect of silicon nitride (SiN) deposition on hydrogenated amorphous silicon (a-Si:H) has been investigated to find the origin of the difference of a-Si:H/SiN interface properties caused by the order of deposition. Sheet conductance of the on-state in inverted staggered (a-Si:H on SiN) thin-film transistors (TFTs) increases gradually with the substrate temperature (Tsub) of SiN, but decreases rapidly with the Tsub of SiN in staggered TFTs (SiN on a-Si:H). Photoluminescence experiments indicated that the degradation in staggered TFTs was due to the creation of defects in a-Si:H by the deposition of the SiN overlayer. It was shown by Fourier transform infrared attenuated total reflection that the origin of the defects was hydrogen effusion from a-Si:H.
Temperature effects for current transport in resonant tunneling structures
Authors: Shen G. D. , Xu D. X. , Willander M. , Hansson G. V. , Wang Y. M.
Published: July 2002

Temperature effects on current transport and the negative differential resistance for SiGe/Si and GaAlAs/GaAs resonant tunneling structures (RTS) have been studied, and the maximum working temperature Tm has been estimated. The calculations show that decreases in the carrier effective mass, well width and barrier thicknesses, lead to better temperature characteristics, implying higher peak current and larger peak-to-valley ratio (PVR) at higher temperature. These results are consistent with our experiment on SiGe/Si RTSs and other published experiments. The crucial role of nonresonant tunneling current Jnon in temperature effects for current transport is emphasized. Suggestions for optimizing RTS design to increase its Tm and PVR are discussed.
Flashlamp pumped Cr:LiSrAlF6 laser
Authors: Stalder Martin , Chai Bruce H. T. , Bass Michael
Published: July 2002

Tunable, flashlamp-pumped laser properties are discribed for the crystal Cr:LiSrAlF6 (Cr:LiSAF) in both long pulse and Q-switched modes of operation. Slope efficiencies of 5%, overall efficiency of 3%, and a tuning range from 780 to 1010 nm are reported.
Correlation between preirradiation channel mobility and radiation-induced interface-trap charge in metal-oxide-semiconductor transistors
Authors: Scofield John H. , Trawick M. , Klimecky P. , Fleetwood D. M.
Published: July 2002

We find a strong correlation between preirradiation channel resistance and radiation-induced interface-trap charge in n-channel metal-oxide-semiconductor (MOS) transistors. While it has long been known that the postirradiation mobility of MOS transistors degrades with exposure to ionizing radiation, we believe this is the first time that differences in the postirradiation interface-trap charge have been linked to differences in preirradiation device parameters. A simple model is presented that relates the observed variations in preirradiation channel resistance to scattering from defects at the Si/SiO2 interface which may be precursors to the radiation-induced interface-trap charge.
Electrical properties of GaAs/GaN/GaAs semiconductor-insulator-semiconductor structures
Authors: Martin G. , Strite S. , Thornton J. , Morkoç H.
Published: July 2002

We report on the current-voltage (IV) characteristics of GaAs/GaN/GaAs semiconductor-insulator-semiconductor structures as a function of temperature. IV measurements show a strong temperature dependence indicating a thermal distribution of carriers flowing over a barrier. From these data we deduce an effective conduction band barrier of 0.9 eV between GaAs and GaN.
Hot-carrier thermalization induced self-phase modulation in semiconductor traveling wave amplifiers
Authors: Delfyett P. J. , Silberberg Y. , Alphonse G. A.
Published: July 2002

Pulsewidth dependent self-phase modulation due to ultrafast (∼1 ps) hot-carrier thermalization is observed for the first time in semiconductor traveling wave amplifiers. The information obtained from this study may play an important role in applications where simultaneous temporal and spectral characteristics of optical pulses is required.
Low nonlinear gain in InGaAs/InGaAlAs separate confinement multiquantum well lasers
Authors: Grabmaier A. , Hangleiter A. , Fuchs G. , Whiteaway J. E. A. , Glew R. W.
Published: July 2002

We have determined the differential gain, nonlinear gain factor, spontaneous emission factor, and the K factor for InGaAs separate confinement multiquantum well lasers with InGaAsP and InGaAlAs barriers using a new parasitic-free modulation technique. We find that the nonlinear gain factor ε is more than four times, and the K factor more than two times lower for lasers with InGaAlAs barriers than for those with InGaAsP barriers. This strongly suggests that InGaAs/InGaAlAs lasers are more suitable for high bandwidth applications.
Intersubband absorption in the conduction band of Si/Si1−xGex multiple quantum wells
Authors: Hertle H. , Schuberth G. , Gornik E. , Abstreiter G. , Schäffler F.
Published: July 2002

The intersubband absorption of electrons in modulation doped Si/Si1−xGex multiple quantum wells has been observed. Various samples with different well widths and carrier densities have been studied. Narrow absorption lines are observed in waveguide geometry. The measured transition energies are in good agreement with self consistent subband calculations.
Epitaxial growth of zinc blende and wurtzitic gallium nitride thin films on (001) silicon
Authors: Lei T. , Fanciulli M. , Molnar R. J. , Moustakas T. D. , Graham R. J. , Scanlon J.
Published: July 2002

Zinc blende and wurtzitic GaN films have been epitaxially grown onto (001)Si by electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy, using a two-step growth process. In this process a thin buffer layer is grown at relatively low temperatures followed by a higher temperature growth of the rest of the film. GaN films grown on a single crystalline GaN buffer have the zinc blende structure, while those grown on a polycrystalline or amorphous buffer have the wurtzitic structure.
An AlGaAs double-heterojunction bipolar transistor grown by molecular-beam epitaxy
Authors: Berger Paul R. , Chand Naresh , Dutta Niloy K.
Published: July 2002

To study AlGaAs p-n heterojunctions and optical and transport properties of electrically injected minority carriers (electrons) in p-Al0.25Ga0.75As, we have tested the performance of Al0.6Ga0.4As/Al0.25Ga0.75 As/Al0.6Ga0.4As NpN double-heterojunction bipolar transistors (DHBTs). The transistors exhibited a common emitter current gain (β) as high as 400 at a current density of 2 kA cm−2. From the Gummel plots, the ideality factors (n) of emitter-base and base-collector junctions were as low as 1.37 and 1.01, respectively, indicating high quality of both the junctions. Assuming a unity current injection efficiency, we obtain an electron diffusion length of 1.2 μm for an acceptor density of 6.0×1018 cm−3 in p-Al0.25Ga0.75As. Due to the wide band-gap materials, the device has the potential for useful operation at very high temperatures. The device also works as a bright red light emitter when the emitter-base junction is forward biased and the collector is either floating or forward biased, indicating dominance of radiative recombination in the base. Furthermore, the device also works as a phototransistor for detection of short wavelengths (<710 nm) with no sensitivity to longer wavelengths.
Surface structures of high-quality diamond crystals synthesized by the oxy-acetylene flame method
Authors: Hirabayashi Keiji , Amanuma Shuji , Hirose Yoichi
Published: July 2002

The microstructures of the {111} surfaces of high-quality diamond crystals deposited by the oxy-acetylene flame method have been studied using a high-resolution scanning electron microscope to clear the mechanism of the crystal growth. On the {111} surfaces of the high-quality diamond crystals, the two-dimensional nucleation rate is suppressed and the two-dimensional crystal growth rate is promoted. The suppression of the two-dimensional nucleation rate and the promotion of the two-dimensional crystal growth rate reduce the number of faults, dislocations, and defects and result in the formation of high-quality diamond crystals.
Inhibition of hydrogen plasma erosion and enhancement in wear resistance of tungsten implanted glassy carbon
Authors: Hoffman A. , Evans P. J. , Cohen D. D. , Clissold R.
Published: July 2002

The hydrogen plasma erosion and abrasive wear resistance of glassy carbon implanted with tungsten has been studied as a function of ion dose. It was found that the onset of hydrogen plasma erosion inhibition occurred at a dose of ∼6.5×1015 ion/cm2. In addition, the tungsten implanted material exhibits an increase in wear resistance similar in magnitude to that obtained with nitrogen and other nonmetallic ions. Carbon ion implantation does not significantly inhibit erosion in a hydrogen plasma. Hence, the resistance to such erosion observed with tungsten implanted glassy carbon is believed to be due to a chemical effect specific to certain metallic ions. In contrast, increased wear resistance is a defect driven effect not specific to the ion used.
Diode-clamped symmetric self-electro-optic effect devices with subpicojoule switching energies
Authors: Lentine A. L. , Chirovsky L. M. F. , Focht M. W. , Freund J. M. , Guth G. D. , Leibenguth R. E. , Przybylek G. J. , Smith L. E.
Published: July 2002

We describe symmetric self-electro-optic effect devices (S-SEEDs) with clamping diodes connected to the center node of the devices to ensure both diodes of the S-SEEDs have an electric field across them at all times. These diode-clamped S-SEEDs operate over a greater wavelength range, with greater powers before saturating, and have lower optical switching energies compared to conventional S-SEEDs. An 8×8 array of diode-clamped S-SEEDs has been built and tested. We have demonstrated bistable operation with voltage swings of only 2 V over a wavelength range of 15 nm. Required optical switching energies of 340–580 fJ were measured at input powers from 500 nW to 100 μW for devices with 10×10 μm mesas. This is the lowest reported switching energy for any SEED with acceptable bistable characteristics.
Characteristics of GaAs, AlGaAs, and InGaAs materials grown by metalorganic chemical vapor deposition using an on-demand hydride gas generator
Authors: Hummel S. G. , Zou Y. , Beyler C. A. , Grodzinski P. , Dapkus P. D. , McManus J. V. , Zhang Y. , Skromme B. J. , Lee W. I.
Published: July 2002

We report results on the properties of GaAs, AlGaAs, and InGaAs materials grown using a new, on-demand hydride gas generator. Low pressure arsine gas is generated from an arsenic containing precursor (KAsH2) by the controlled addition of water as a chemical activator. Both generated and bottled arsine are used to grow GaAs, AlGaAs, and InGaAs structures using atmospheric pressure metalorganic chemical vapor deposition. Using generated arsine, GaAs layers with background carrier concentrations of less than n=3×1013 cm−3 were produced across a growth temperature range of 625–725 °C using a V/III ratio of 30. InGaAs grown at 640 °C with V/III=30 exhibits a background carrier concentration of n=2.5×1014 cm−3 and mobility values of μ300 K=11 350 cm2/V s and μ77 K=71 200 cm2/V s. Photoluminescence measurements show highly resolved exciton spectra using either generated or bottled arsine with donor-bound exciton linewidths as narrow as 0.16 meV full width at half-maximum. Broad area GaAs/AlGaAs laser devices exhibit threshold current densities as low as 195 A/cm2. The results obtained from bulk layer, quantum well structure, and broad area laser device characterization indicate that the quality of materials produced using generated arsine is equivalent or superior to that of materials produced using a high quality bottled arsine source.
Ga adatom diffusion on an As-stabilized GaAs(001) surface via missing As dimer rows: First-principles calculation
Authors: Shiraishi Kenji
Published: July 2002

We have investigated the microscopic processes of Ga adatom diffusions on an As-stabilized GaAs(001) surface by the first-principles pseudopotential method. The results show that Ga adatoms diffuse on the surface by passing through the missing As dimer rows. Comparison with the results of scanning tunneling microscopy (STM) experiments during molecular beam epitaxy (MBE) growth suggests that low As pressure increases the surface Ga adatom diffusion by a formation of the continuous Ga adatom diffusion path. This is consistent with the fact that low temperature growth is possible by migration enhanced epitaxy (MEE), in which As and Ga sources are supplied alternately.
Photomodulation of photocurrent multiplication in a high gain amorphous silicon carbide film
Authors: Hiramoto Masahiro , Yoshimura Kanji , Yokoyama Masaaki
Published: July 2002

The photocurrent multiplication observed under the irradiation of bulk-absorbed red light in amorphous silicon carbide (a-SiC:H) films with a simple configuration SnO2/a-SiC:H/Au cell was found to be photomodulated depressively by superimposing surface-absorbed ultraviolet(UV)-blue light on the red light irradiation. This phenomenon was reasonably interpreted based on the previously proposed multiplication mechanism involving the tunneling injection of electrons from an SnO2 electrode to the a-SiC:H film through a thin SiOx insulating layer in a high electric field issued from the accumulation of trapped holes near SnO2/a-SiC:H interface, which was effectively suppressed by the UV-blue light irradiation.
Traveling-wave polymeric optical intensity modulator with more than 40 GHz of 3-dB electrical bandwidth
Authors: Teng C. C.
Published: July 2002

A traveling-wave electro-optic intensity modulator with a 3-dB electrical bandwidth of more than 40 GHz, negligible phase distortion, low drive voltages, and an extinction ratio of better than 20 dB is reported in nonlinear optical polymers. The velocity matching between the optical and electrical waves is excellent. The frequency response of the optical modulation is in good agreement with theory.
Trap-assisted tunneling in mercury cadmium telluride photodiodes
Authors: Unikovsky A. , Nemirovsky Y.
Published: July 2002

Trap-assisted tunneling in Hg1−xCdxTe photodiodes (with x≂0.22) is modeled quantitatively. The model takes into consideration two types of deep traps: one type of energy trap is located at Et1≂40 meV (∼Eg/3) and the other type is located at Et2≂75 meV (∼2Eg/3). The density of trapped electrons at Et1∼Eg/3 is relatively high (nt1≂1014 cm−3) and is practically independent of temperature while the density of the trapped electrons at Et2≂2Eg/3 is low (nt2≂1010–1012 cm−3) and increases with temperature. An excellent fit is systematically obtained between the calculated and measured dc dark current characteristics of typical ion implanted n+p photodiodes, in a wide range of reverse bias voltages (0<Vd<−1.5 V) and operating temperatures (30–120 K).
Effect of In segregation on the structural and optical properties of ultrathin InAs films in GaAs
Authors: Brandt O. , Tapfer L. , Ploog K. , Bierwolf R. , Hohenstein M.
Published: July 2002

We study the segregation of In during the overgrowth of an InAs monolayer (ML) with GaAs by molecular beam epitaxy. The presence of segregating In adatoms (In floating layer) at the growth surface is observed in situ by reflection high-energy electron diffraction. We demonstrate (i) that the segregation process causes a spatial spread-out of 0.4 ML of In into the first 4–5 ML of the GaAs overlayer and (ii) that this spread-out can be inhibited by the thermal desorption of the In floating layer in the initial stage of overgrowth (flash-off). The flash-off approach creates in fact a single InAs ML in the GaAs matrix.
Novel hydrogen-gold-related deep acceptor in n-type silicon
Authors: Sveinbjörnsson Einar Ö. , Engström Olof
Published: July 2002

Using deep level transient spectroscopy (DLTS) on gold-doped n-type Czochralski (CZ) and float zone (FZ) silicon we observe a new gold-related acceptor level (G) with an activation energy ΔE=0.19 eV and an electron capture cross section σn=1×10−17 cm2. The center is formed after hydrogenation by etching a few microns off the sample surface using HF:HNO3 based etch. We suggest that there are (at least) two possible Au-H complex centers, one which is electrically inactive and another which gives rise to an acceptor level (ΔE=0.19 eV) in the band gap of n-type silicon. The electrically active center anneals out at 250 °C while the electrically inactive one is more stable and has been observed earlier in remote plasma hydrogenation experiments performed at 150–350 °C.
Hydrogen diffusion in polycrystalline silicon thin films
Authors: Jackson W. B. , Johnson N. M. , Tsai C. C. , Wu I.-W. , Chiang A. , Smith D.
Published: July 2002

Grain boundaries in undoped polycrystalline silicon (poly-Si) thin films are shown to act as efficient hydrogen traps rather than as paths of enhanced diffusion. A comparison of hydrogen diffusion in poly-Si and undoped single-crystal silicon (c-Si) demonstrates that the diffusion in poly-Si is significantly suppressed compared to c-Si. These results have significant implications for hydrogenation of poly-Si thin-film transistors.
Masked growth of InGaAsP-based quantum wells for optoelectronic device applications
Authors: Chen Y. , Chiu T. H. , Zucker J. E. , Chu S. N. G.
Published: July 2002

We investigate selective area growth of lattice-matched InGaAsP/InP, and strained InGaAs/InP and InAsP/InP multiple quantum wells on SiO2-masked InP substrate by chemical beam epitaxy. This method can be used to produce quantum well p-i-n waveguide modulators with a single growth step. Photoluminescence measurements performed on waveguide stripes ranging from 1–50 μm in width reveal a red shift of the band edge with decreasing stripe width in InGaAsP/InP and InGaAs/InP quantum well systems, but no shift in InAsP/InP quantum wells for stripe widths larger than 1 μm. In addition, we find that this band-gap tunability is stripe orientation dependent.
Normal incidence intervalence subband absorption in GaSb quantum well enhanced by coupling to InAs conduction band
Authors: Katz J. , Zhang Y. , Wang W. I.
Published: July 2002

We demonstrate a novel infrared (IR) detector structure based on the type II p-doped InAs/GaSb multiquantum well system. Due to the coupling of the first conduction subband in InAs to the valence band states in GaSb, the normal incidence absorption coefficient for intervalence subband transitions between heavy and light hole subbands in GaSb quantum wells is significantly enhanced. An absorption coefficient as large as 6500 cm−1 has been achieved in the wavelength range of 8–17 μm. This is the strongest absorption ever observed among all the IR materials in this wavelength range.
New oxide phase with wide band gap and high electroconductivity CdGa2O4 spinel
Authors: Omata Takahisa , Ueda Naoyuki , Hikuma Naoko , Ueda Kazushige , Mizoguchi Hiroshi , Hashimoto Takuya , Kawazoe Hiroshi
Published: July 2002

CdGa2O4 spinel was found to be a promising material as a transparent electronic conductor. By measurements of diffuse reflectance spectra, CdGa2O4 was found to have a wider band gap (∼3.5 eV) than indium tin oxide. The electrical conductivity of the sintered sample of CdGa2O4 was over 102 S cm−1 with no intentional doping.
Band-gap narrowing determination by photoluminescence on strained B-doped Si0.82Ge0.18 layers grown on Si
Authors: Souifi A. , Brémond G. , Benyattou T. , Guillot G. , Dutartre D. , Warren P.
Published: July 2002

This work reports on photoluminescence (PL) characterization of heavy boron-doped SiGe(p+)/Si(p) heterostructures and Si(p+)/Si(p) pseudoheterostructures grown by rapid thermal chemical vapor deposition. For the pseudoheterostructures, the band-gap narrowing is measured in the 4×1018–1.5×1019 cm−3 doping level range in very good agreement with bulk silicon results. The band-gap narrowing of SiGe strained layers has been determined for the first time, by means of PL measurements on boron-doped Si0.82Ge0.18 strained alloy up to 4×1019 cm−3. The reduced band gap of the Si0.82Ge0.18 alloy is deduced, taking into account both strain and heavy doping effects and compared to band-gap narrowing found in Si.
Variable growth modes of CaF2 on Si(111) determined by x-ray photoelectron diffraction
Authors: Denlinger J. D. , Rotenberg Eli , Hessinger Uwe , Leskovar M. , Olmstead Marjorie A.
Published: July 2002

Chemical discrimination of bulk and interface Ca 2p x-ray photoelectron diffraction modulations is used to identify three growth regimes during the initial stages of CaF2 epitaxy on Si(111). Low flux, high temperature conditions produce island growth atop a nonwetting, chemically reacted Ca-F interface layer. Changing the growth kinetics by increasing the flux produces more laminar growth. Lowering the substrate temperature produces a more stoichiometric CaF2 interface layer that results in immediate wetting and laminar growth.
ZnSe-ZnCdSe quantum confined Stark effect modulators
Authors: Wang S. Y. , Kawakami Y. , Simpson J. , Stewart H. , Prior K. A. , Cavenett B. C.
Published: July 2002

We report room temperature operation of a II-VI p-i-n quantum confined Stark effect modulator using a ZnSe-Zn0.8Cd0.2Se multiple quantum well structure within a ZdSe p-n junction. A n-type ZnSe layer was used as a novel contact to the p-type ZnSe. Results are given for photovoltage spectroscopy, absorption, and differential absorption as a function of the applied electric field.
Spatial analysis of electronic noise in submicron semiconductor structures
Authors: González Tomás , Pardo Daniel , Varani Luca , Reggiani Lino
Published: July 2002

We present an original method to investigate electronic noise in semiconductor structures by providing a spatial analysis of the spectral density of voltage fluctuations under constant-current conditions. Monte Carlo simulations performed for submicron n+nn+ structures of Si and GaAs show that at equilibrium most of the low-frequency noise originates from the n-region while at increasing voltages relevant contributions come from the hot electrons which penetrate the drain region.
Atomic-scale view of AlGaAs/GaAs heterostructures with cross-sectional scanning tunneling microscopy
Authors: Johnson M. B. , Maier U. , Meier H.-P. , Salemink H. W. M.
Published: July 2002

Atomically resolved cross-sectional scanning tunneling microscope topographic images of heterostructures that include a sequence of 1, 2, 5, and 10 nm AlGaAs and GaAs layers are presented. These layers clearly show alloy fluctuations and interface roughness on an atomic scale. In the thick AlGaAs layers a mottled structure with regions of higher Al content about 2 nm wide and elongated in [1̄12] or [11̄2] directions are observed. Similarly, the interfaces are rough on a 2 nm length scale. These results suggest that, for the conditions used for the epitaxial growth of the ternary layers, Al-rich regions nucleate and grow anisotropically.
Optical intensity modulation in a vertically stacked coupler incorporating electro-optic polymer
Authors: Hikita Makoto , Shuto Yoshito , Amano Michiyuki , Yoshimura Ryoko , Tomaru Satoru , Kozawaguchi Haruki
Published: July 2002

A vertically stacked directional coupler incorporating electro-optic poled polymer was fabricated by spin coating, photolithography, and reactive ion etching processes, based on the fabrication technique used for polymeric single-mode channel waveguides. Vertically coupled operation at 1.3 μm have been achieved between two stacked channels which were kept 3.5–5 μm apart by a narrow cladding layer. The intensity modulation has been clearly demonstrated in the coupler with electrodes when a voltage is applied at 10 kHz between them.
Tailoring of internal fields in InGaAs/GaAs multiwell structures grown on (111)B GaAs
Authors: Pabla A. S. , Sanchez-Rojas J. L. , Woodhead J. , Grey R. , David J. P. R. , Rees G. J. , Hill G. , Pate M. A. , Robson P. N. , Hogg R. A. , Fisher T. A. , Willcox A. R. K. , Whittaker D. M. , Skolnick M. S. , Mowbray D. J.
Published: July 2002

We present a study of internal field distributions in strained InGaAs/GaAs multiple quantum wells in p-i-n structures grown on (111)B-oriented GaAs. Room temperature photocurrent spectroscopy shows clear blueshifting of the e1-hh1 transition as the well fields are reduced by external bias. The relative length of total well to total barrier material is shown to be an important factor in determining the well and barrier fields. We demonstrate a photocurrent contrast ratio of 4.5:1 for only 3 V applied bias across a 25 quantum well In0.13Ga0.87As p-i-n diode and discuss the implication of our results to the design of high performance electro-optic modulators and self electro-optic effect devices in this material system.
Electron transport properties of Si/SiGe heterostructures: Measurements and device implications
Authors: Ismail K. , Nelson S. F. , Chu J. O. , Meyerson B. S.
Published: July 2002

We report electron transport properties of modulation-doped Si/SiGe at 300 and 77 K. Record mobilities of 2830 and 18 000 cm2/V s at 300 and 77 K, respectively, have been measured. Depending on the spacer layer thickness, the sheet resistance of the Si channel is in the range of 2000–10 000 Ω/⧠ at 300 K and 450–700 Ω/⧠ at 77 K. The low field electron drift velocity is 2–3 (5–10) times higher than the corresponding velocity measured in Si/SiO2 structures at 300 K (77 K). The saturation velocity is measured to be only 5% higher than in bulk Si, at both 300 and 77 K, but appears at a lower electric field. The effect of the enhanced transport properties in modulation-doped Si/SiGe on device design and performance is investigated.
Organic photo- and electroluminescent devices with double mirrors
Authors: Nakayama Takahiro , Itoh Yuzo , Kakuta Atsushi
Published: July 2002

Luminescent spectra of organic thin films sandwiched with two mirrors were measured in an effort to detect optical microcavity effects. Narrowing and enhancement of photoluminescent spectra were observed from the tri-(8-hydroxyquinolinol)aluminum monolayer with the mirrors at both sides. Furthermore, the narrowing of spectra was also observed from electroluminescent devices fabricated with two mirrors.
Observation of polarization-dependent electroabsorption in (In,Ga)As/GaAs modulator structures oriented in the [110] crystallographic direction
Authors: Sun D. , Towe E. , Hayduk M. J. , Boncek R. K.
Published: July 2002

We report room-temperature observation of polarization-dependent optical electroabsorption in a p-i-n quantum-confined Stark-effect modulator structure prepared from strained (In,Ga)As/GaAs layers. The strained-layer structure is grown on a vicinally oriented (110)-GaAs substrate.
On the transport mechanism in porous silicon
Authors: Mareš J. J. , Krištofik J. , Pangrác J. , Hospodková A.
Published: July 2002

We have measured the temperature dependence of dark conductance of porous silicon (PS) in the range between 200 and 300 K. It is possible to interpret the observed Berthelot type dependence as the surface conductance controlled by the tunneling through a thermally vibrating barrier.
Increased fiber communications bandwidth from a resonant cavity light emitting diode emitting at λ=940 nm
Authors: Hunt N. E. J. , Schubert E. F. , Kopf R. F. , Sivco D. L. , Cho A. Y. , Zydzik G. J.
Published: July 2002

Substrate-emitting InGaAs/AlGaAs resonant cavity light emitting diodes (RCLEDs) emitting at λ=940 nm have been fabricated for use in optical communications. The devices exhibit a high output efficiency, with a far-field intensity of 85 μW/Steradian from a planar surface at a current of 14 mA. The spontaneous spectrum exhibits a very narrow peak of only 5 nm width, as opposed to the 50-nm-wide peak of an 875 nm wavelength reference LED. We show that the narrow spectrum drastically reduces the effects of chromatic dispersion within a 3.37 km length of 62.5 μm core graded index multimode fiber. The resulting −3 dB frequency is 102 MHz for the RCLED and fiber system, as opposed to only 33 MHz for the chromatic dispersion limited reference device.
Tip-induced anodization of titanium surfaces by scanning tunneling microscopy: A humidity effect on nanolithography
Authors: Sugimura Hiroyuki , Uchida Tatsuya , Kitamura Noboru , Masuhara Hiroshi
Published: July 2002

A scanning tunneling microscope was employed for tip-induced anodization of titanium (Ti) surfaces. Spatial resolution of fabricated patterns was remarkably affected by the tip shape and humidity in the atmosphere. The amount of adsorbed water on the Ti surface determined by humidity has a key role in controlling the resolution, and the resolution becomes worse with increasing humidity. Under the optimized conditions, tip-induced anodization of Ti was successfully achieved with a spatial resolution of 30 nm.