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5 Jan 1998

Volume 72, Issue 1, pp. 1-133

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Advantages of ultraviolet Raman scattering for high temperature investigations

E. Zouboulis, D. Renusch, and M. Grimsditch

Appl. Phys. Lett. 72, 1 (1998); http://dx.doi.org/10.1063/1.121437 (3 pages) | Cited 23 times

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We show that UV Raman spectroscopy is eminently well suited for the in situ investigation of samples at high temperatures. Using sapphire as a test material, we have recorded Raman spectra from ambient temperature to 1700 K using different excitation wavelengths, both in the visible and near UV region of the spectrum. These spectra show that, because of the very rapid decrease of blackbody radiation in the short wavelength region, Raman spectra recorded in the near UV region of the spectrum are free from the blackbody radiation background, which typically hampers experiments in the visible. With 266 nm exciting radiation, we observe no thermal background even at 1700 K. We foresee that the method will become a powerful tool for in situ investigations of high-temperature materials. © 1998 American Institute of Physics.
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78.40.Ha Other nonmetallic inorganics
78.30.Am Elemental semiconductors and insulators

6.1 W continuous wave front-facet power from Al-free active-region (λ=805 nm) diode lasers

J. K. Wade, L. J. Mawst, D. Botez, R. F. Nabiev, M. Jansen, and J. A. Morris

Appl. Phys. Lett. 72, 4 (1998); http://dx.doi.org/10.1063/1.120628 (3 pages) | Cited 19 times

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Al-free active-region diode lasers grown by low-pressure, metal-organic chemical vapor deposition and emitting at λ=805 nm have been optimized for high continuous wave output power. The 1-mm-long devices consisting of an InGaAsP/In0.5Ga0.5P/In0.5(Ga0.5Al0.5)0.5P laser structure have a threshold-current density, Jth, of 310 A/cm2 and relatively high values for the characteristic temperatures of the threshold current, T0 (135 K), and differential quantum efficiency, T1 (900 K). Lasers with 10%/90% coatings and a 100-μm-wide stripe provide a maximum cw output power of 6.1 W at a heatsink temperature of 10 °C. The devices fail due to catastrophic optical mirror damage (COMD), where the internal power density, mathCOMD, is 17.4 MW/cm2; that is, twice that for conventionally facet-coated, 810 nm emitting, AlGaAs active-region diode lasers. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Two-color corrugated quantum-well infrared photodetector for remote temperature sensing

C. J. Chen, K. K. Choi, W. H. Chang, and D. C. Tsui

Appl. Phys. Lett. 72, 7 (1998); http://dx.doi.org/10.1063/1.120629 (3 pages) | Cited 26 times

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A quantum-well infrared photodetector (QWIP) based on the corrugated light-coupling scheme has been fabricated and tested for remote temperature sensing. The QWIP consists of two stacks of multiple quantum wells (MQWs), each sensitive in one of the atmospheric infrared transmission windows and each with a separate readout circuit. High optical coupling efficiency is obtained in both wavelength ranges, demonstrating the use of the corrugated structure for two-color detection. By monitoring the ratio of the photocurrent generated simultaneously in each MQW stack, the temperature of the object emitting the radiation can be determined, regardless of its emissivity and the geometrical factors. This temperature sensing ability is tested by using a blackbody radiator with precision temperature control as the target. The agreement between the measured and the preset temperatures indicates that the corrugated QWIP is capable of precision thermometric measurements. © 1998 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.Qx Range finders, remote sensing devices; laser Doppler velocimeters, SAR, and LIDAR
95.75.Rs Remote observing techniques
93.85.-q Instruments and techniques for geophysical research: Exploration geophysics

Simultaneous optimization of membrane reflectance and tuning voltage for tunable vertical cavity lasers

F. Sugihwo, M. C. Larson, and J. S. Harris

Appl. Phys. Lett. 72, 10 (1998); http://dx.doi.org/10.1063/1.120630 (3 pages) | Cited 15 times

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Micromachined wavelength tunable vertical cavity lasers are attractive for applications ranging from wavelength division multiplexing to spectroscopy. An improved tunable structure that incorporates a partial anti-reflection coating to increase coupling between the air gap and the semiconductor cavity, and a more flexible micromachine process that enables independent optimization of the central reflector region and deformable membrane structure are described. This combination of structural and process modifications enables decoupling the tradeoffs between wavelength tuning rate and threshold current, as well as the tradeoffs between top mirror reflectance and tuning voltage. With these improved approaches, a 2.5 pair dielectric distributed Bragg reflector hybrid membrane top mirror produced singlemode devices with a 23 nm wavelength tuning range and multi-transverse-mode devices with a 30 nm wavelength tuning range. Threshold current, differential quantum efficiency, and lasing mode are characterized as a function of membrane bias. © 1998 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.86.+b Optical workshop techniques
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.79.Wc Optical coatings

Red–green–blue light emission from hydrogenated amorphous silicon carbide films prepared by using organic compound xylene as carbon source

Tianfu Ma, Jun Xu, Kunji Chen, Jiafang Du, Wei Li, and Xinfan Huang

Appl. Phys. Lett. 72, 13 (1998); http://dx.doi.org/10.1063/1.120631 (3 pages) | Cited 14 times

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We fabricated hydrogenated amorphous silicon carbide (a-Si1-XCX:H) films by the plasma-enhanced chemical vapor deposition technique using organic compound xylene (C8H10) as the carbon source, which was initially attempted by W. A. Nevin H. Yamagishi, M. Yamaguchi, and Y. Tawada, Nature 368, 529 (1994). Here we used different preparation conditions from those authors to produce xylene-based a-Si1-XCX:H films, and a different light emission behavior of the films has been observed at room temperature. The light emission wavelength can be shifted from 630 nm to 450 nm by changing the optical band gap (Eopt) of the films from 2.3 eV to 3.5 eV, nearly covering the whole visible light range, which was never reported previously. Fourier transform infrared spectra showed that the configuration of the material was a combination of organic aromatic rings and inorganic SiC networks. © 1998 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.05.Gc Amorphous semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
63.50.-x Vibrational states in disordered systems
78.35.+c Brillouin and Rayleigh scattering; other light scattering
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
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Effect of gravitational acceleration on temperature wave propagation in a critical fluid

Koji Ishii, Toru Maekawa, Hisao Azuma, Shoichi Yoshihara, and Mitsuru Onishi

Appl. Phys. Lett. 72, 16 (1998); http://dx.doi.org/10.1063/1.120632 (3 pages) | Cited 9 times

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Temperature propagation near the critical point of a classical fluid is investigated theoretically. The governing equations of thermal energy transfer near the critical point are introduced and a linear analysis is carried out. The dispersion relation between the angular frequency and the wave number is obtained and the wave characteristics are discussed. The effect of gravitational acceleration on the temperature wave propagation is made clear. Through this analysis, the following results were obtained; (1) The propagation speed of temperature waves is math,where γ, ρ0, and κT are, respectively, the ratio of specific heats, the density, and the isothermal compressibility, with or without gravity if the wavelength is larger than 10−3.(2) The amplitude of wave increases with time in the antigravitational direction and decreases in the gravitational direction but the decay time is long if the wave number is small. (3) Waves decay quickly if the wave number is larger than 104. © 1998 American Institute of Physics.
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65.20.-w Thermal properties of liquids
51.30.+i Thermodynamic properties, equations of state
05.70.Ce Thermodynamic functions and equations of state
62.10.+s Mechanical properties of liquids

Generation of ultrashort, discrete spectrum microwave pulses using the dc to ac radiation converter

P. Muggli, R. Liou, J. Hoffman, T. Katsouleas, and C. Joshi

Appl. Phys. Lett. 72, 19 (1998); http://dx.doi.org/10.1063/1.120633 (3 pages) | Cited 9 times

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The output radiation of a dc to ac radiation converter is characterized. A relativistic ionization front passing through a capacitor array of period d = 1 cm produces short pulses of tunable radiation between 39 and 84 GHz with a gas pressure between 0 and 30 mT. The frequency spectra of the produced pulses are discrete and exhibit full widths at half maximum between 12% and 28%, consistent with the expected width for six cycles’ pulses. An upper bound of 750 ps (detection bandwidth limited) is placed on the pulse widths. These are the shortest pulses produced by a source of coherent radiation in this frequency range. © 1998 American Institute of Physics.
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52.59.Ye Plasma devices for generation of coherent radiation
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides

Emission of excimer radiation from direct current, high-pressure hollow cathode discharges

Ahmed El-Habachi and Karl H. Schoenbach

Appl. Phys. Lett. 72, 22 (1998); http://dx.doi.org/10.1063/1.120634 (3 pages) | Cited 79 times

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A novel, nonequilibrium, high-pressure, direct current discharge, the microhollow cathode discharge, has been found to be an intense source of xenon and argon excimer radiation peaking at wavelengths of 170 and 130 nm, respectively. In argon discharges with a 100 μm diam hollow cathode, the intensity of the excimer radiation increased by a factor of 5 over the pressure range from 100 to 800 mbar. In xenon discharges, the intensity at 170 nm increased by two orders of magnitude when the pressure was raised from 250 mbar to 1 bar. Sustaining voltages were 200 V for argon and 400 V for xenon discharges, at current levels on the order of mA. The resistive current–voltage characteristics of the microdischarges indicate the possibility to form arrays for direct current, flat panel excimer lamps. © 1998 American Institute of Physics.
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52.80.Hc Glow; corona
42.72.Bj Visible and ultraviolet sources
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Fuzzy controlled feedback applied to a combined scanning tunneling and force microscope

F. M. Battiston, M. Bammerlin, C. Loppacher, R. Lüthi, E. Meyer, H.-J. Güntherodt, and F. Eggimann

Appl. Phys. Lett. 72, 25 (1998); http://dx.doi.org/10.1063/1.120635 (3 pages) | Cited 5 times

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A feedback mechanism based on fuzzy logic has been applied to operate a combined atomic force microscope (AFM)/scanning tunneling microscope (STM), which is able to measure the resonance frequency shift Δf of the cantilever-type spring and the mean tunneling current Īt simultaneously. Using a decision making logic, the microscope can be scanned over a heterogeneous surface without tip crash. On the conductive parts of the sample, the STM mode is preferred, whereas the noncontact (nc)-AFM mode is used on the poorly conductive parts of the surface. The transition from the STM mode to nc-AFM mode is performed smoothly with the fuzzy logic feedback. © 1998 American Institute of Physics.
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07.79.Cz Scanning tunneling microscopes
07.79.Lh Atomic force microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
07.05.Mh Neural networks, fuzzy logic, artificial intelligence

Thermally activated electron capture by mobile protons in SiO2 thin films

K. Vanheusden, S. P. Karna, R. D. Pugh, W. L. Warren, D. M. Fleetwood, R. A. B. Devine, and A. H. Edwards

Appl. Phys. Lett. 72, 28 (1998); http://dx.doi.org/10.1063/1.121447 (3 pages) | Cited 11 times

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The annihilation of mobile protons in thin SiO2 films by capture of ultraviolet-excited electrons has been analyzed for temperatures between 77 and 500 K. We observe a strong increase in proton annihilation with increasing temperature, and derive an activation energy for electron capture of about 0.2 eV. Based on quantum chemical [(OH)3Si]2�O�H+ cluster calculations, we suggest photoexcitation of electrons from excited vibrational states of the ground electronic (valence band) state to a nearby excited electronic (SiO2 gap) state. It is argued that the latter excitation can result in H0 formation at elevated temperatures. © 1998 American Institute of Physics.
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73.61.Ng Insulators
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Ht Other nonmetals

X-ray photoelectron spectroscopy study of excimer laser treated alumina films

D. G. Georgiev, K. Kolev, L. D. Laude, B. Mednikarov, and N. Starbov

Appl. Phys. Lett. 72, 31 (1998); http://dx.doi.org/10.1063/1.120636 (3 pages) | Cited 2 times

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Amorphous alumina layers are deposited on a single crystal Si substrate by a e-gun evaporation technique. These films are then thermally annealed in oxygen to be crystallized and, further, irradiated with an excimer laser beam. At each stage of the film preparation, an x-ray photoelectron spectroscopy analysis is performed at the film surface and in depth, upon ion beam grinding. Results give evidence for the formation of an aluminosilicate upon thermal annealing of the film in oxygen. At the surface itself, this compound is observed to decompose upon excimer laser irradiation at energy densities exceeding 1.75 J/cm2, giving rise to free Si atoms and SiO2, however with complete disappearance of Al atoms. Model photochemical reactions are proposed to explain such transformations. © 1998 American Institute of Physics.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.Cc Kinetics of defect formation and annealing
82.50.-m Photochemistry

Mesoscopic caverns and nucleation twins formed in the growth of Co on Cu

G. L. Zhou and C. P. Flynn

Appl. Phys. Lett. 72, 34 (1998); http://dx.doi.org/10.1063/1.120637 (3 pages) | Cited 1 time

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Mesoscopic caverns in the form of facetted voids are observed to form when Cu pumps through pinholes to the outer surface during the epitaxial growth of fcc Co(111) on Cu(111) near 500 °C. We prove that the pinholes are located mainly at boundaries between fcc twin domains that occur with ABC and ACB stacking. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.Mm Grain and twin boundaries
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Scanning Joule expansion microscopy at nanometer scales

J. Varesi and A. Majumdar

Appl. Phys. Lett. 72, 37 (1998); http://dx.doi.org/10.1063/1.120638 (3 pages) | Cited 41 times

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We report a new technique called scanning Joule expansion microscopy that can simultaneously image surface topography and material expansion due to Joule heating with vertical resolution in the 1 pm range and lateral resolution similar to that of an atomic force microscope. By coating the sample with a polymer film, we demonstrate that sample temperature distribution can be directly measured without the need of fabricating temperature-sensing scanning probes.© 1998 American Institute of Physics.  
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07.79.-v Scanning probe microscopes and components
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
07.20.Dt Thermometers
68.35.B- Structure of clean surfaces (and surface reconstruction)

Phase separation in InGaN grown by metalorganic chemical vapor deposition

N. A. El-Masry, E. L. Piner, S. X. Liu, and S. M. Bedair

Appl. Phys. Lett. 72, 40 (1998); http://dx.doi.org/10.1063/1.120639 (3 pages) | Cited 131 times

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We report on phase separation in thick InGaN films with up to 50% InN grown by metalorganic chemical vapor deposition from 690 to 780 °C. InGaN films with thicknesses of 0.5 μm were analyzed by θ–2θ x-ray diffraction, transmission electron microscopy (TEM), and selected area diffraction (SAD). Single phase InGaN was obtained for the as-grown films with <28% InN. However, for films with higher than 28% InN, the samples showed a spinodally decomposed microstructure as confirmed by TEM and extra spots in SAD patterns that corresponded to multiphase InGaN. © 1998 American Institute of Physics.
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68.55.Nq Composition and phase identification
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation

Nanocrystalline-silicon superlattice produced by controlled recrystallization

L. Tsybeskov, K. D. Hirschman, S. P. Duttagupta, M. Zacharias, P. M. Fauchet, J. P. McCaffrey, and D. J. Lockwood

Appl. Phys. Lett. 72, 43 (1998); http://dx.doi.org/10.1063/1.120640 (3 pages) | Cited 125 times

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Nanocrystalline-silicon superlattices are produced by controlled recrystallization of amorphous-Si/SiO2 multilayers. The recrystallization is performed by a two-step procedure: rapid thermal annealing at 600–1000 °C, and furnace annealing at 1050 °C. Transmission electron microscopy, Raman scattering, x-ray and electron diffraction, and photoluminescence spectroscopy show an ordered structure with Si nanocrystals confined between SiO2 layers. The size of the Si nanocrystals is limited by the thickness of the a-Si layer, the shape is nearly spherical, and the orientation is random. The luminescence from the nc-Si superlattices is demonstrated and studied. © 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors

The role of second-neighbor effects in photoemission: Are silicon surfaces and interfaces special?

K. Z. Zhang, K. E. Litz, M. M. Banaszak Holl, and F. R. McFeely

Appl. Phys. Lett. 72, 46 (1998); http://dx.doi.org/10.1063/1.120641 (3 pages) | Cited 8 times

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A widely used assignment scheme for Si 2p core-level photoemission studies of silicon oxidation relies solely on the formal oxidation state of the silicon. The tacit assumption of this assignment methodology is that second-neighbor effects have no measurable effect on observed Si 2p binding energies. In this letter, new experiments are combined with literature precedents to make the case that the second-neighbor effects play an important role in determining binding energy shifts. © 1998 American Institute of Physics.
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79.60.Jv Interfaces; heterostructures; nanostructures
81.65.Mq Oxidation
73.20.At Surface states, band structure, electron density of states
79.60.Dp Adsorbed layers and thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.05.Cy Elemental semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
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A “smarter-cut” approach to low temperature silicon layer transfer

Q.-Y. Tong, R. Scholz, U. Gösele, T.-H. Lee, L.-J. Huang, Y.-L. Chao, and T. Y. Tan

Appl. Phys. Lett. 72, 49 (1998); http://dx.doi.org/10.1063/1.120601 (3 pages) | Cited 51 times

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Silicon wafers were first implanted at room temperature by B+ with 5.0×1012 to 5.0×1015 ions/ cm2 at 180 keV, and subsequently implanted by H2+ with 5.0×1016 ions/cm2 at an energy which locates the H-peak concentration in the silicon wafers at the same position as that of the implanted boron peak. Compared to the H-only implanted samples, the temperature for a B+H coimplanted silicon layer to split from its substrate after wafer bonding during a heat treatment for a given time is reduced significantly. Further reduction of the splitting temperature is accomplished by appropriate prebonding annealing of the B+H coimplanted wafers. Combination of these two effects allows the transfer of a silicon layer from a silicon wafer onto a severely thermally mismatched substrate such as quartz at a temperature as low as 200 °C. © 1998 American Institute of Physics.
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61.72.uf Ge and Si
81.05.Cy Elemental semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.Cc Kinetics of defect formation and annealing

Estimation of doping density in HgCdTe p-n junctions using scanning laser microscopy

J. F. Siliquini, J. M. Dell, C. A. Musca, E. P. G. Smith, L. Faraone, and J. Piotrowski

Appl. Phys. Lett. 72, 52 (1998); http://dx.doi.org/10.1063/1.120642 (3 pages) | Cited 12 times

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Quantitative assessment of p- to n- type conversion due to reactive ion etching (RIE) of p-type Hg0.71Cd0.29Te is presented using laser-beam-induced-current (LBIC) measurements. For the RIE processing conditions used (390 mT, CH4/H2, 0.4 W/cm2), n-type conversion was observed in extrinsic arsenic-doped p-type Hg0.71Cd0.29Te which had previously undergone a Hg anneal to eliminate Hg vacancies. Effective doping density of the n-type converted region is determined by fitting a theoretically determined LBIC signature to the measured LBIC signal over a temperature range 80–300 K. Effective n-type doping density is the only fitting parameter used in the simulation, which was carried out using a commercial semiconductor device modeling package (SEMICAD™ DEVICE). This noncontact experimental technique promises to be a useful tool in the characterization of p-n junction diodes in HgCdTe, and for studying the precise nature of p to n conversion in p-type HgCdTe. © 1998 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ga II-VI semiconductors
72.60.+g Mixed conductivity and conductivity transitions
61.72.uj III-V and II-VI semiconductors
61.72.S- Impurities in crystals
72.40.+w Photoconduction and photovoltaic effects
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning
61.72.J- Point defects and defect clusters
73.20.Hb Impurity and defect levels; energy states of adsorbed species

An optical method for studying carrier diffusion in strained (InP)2/(GaP)2 quantum wires

Y. Tang, D. H. Rich, A. M. Moy, and K. Y. Cheng

Appl. Phys. Lett. 72, 55 (1998); http://dx.doi.org/10.1063/1.120627 (3 pages) | Cited 6 times

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The carrier transport in strain-induced laterally ordered (InP)2/(GaP)2 quantum wire (QWR) samples was examined with a noncontact Haynes–Shockley diffusion measurement which utilized time-resolved scanning cathodoluminescence. An anisotropy in ambipolar diffusion along the [110] and [110] directions (perpendicular and parallel to the QWRs, respectively) was observed. The temperature dependence of this anisotropy was measured, revealing that carrier diffusion along the QWR direction is thermally activated. © 1998 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence
78.47.-p Spectroscopy of solid state dynamics
78.66.Fd III-V semiconductors

Auger carrier capture kinetics in self-assembled quantum dot structures

A. V. Uskov, J. McInerney, F. Adler, H. Schweizer, and M. H. Pilkuhn

Appl. Phys. Lett. 72, 58 (1998); http://dx.doi.org/10.1063/1.120643 (3 pages) | Cited 63 times

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We establish rate equations to describe Auger carrier capture kinetics in quantum dot structures, calculate Auger capture coefficients for self-assembled quantum dots, and analyze Auger capture kinetics using these equations. We show that Auger capture times can be of the order of 1–100 ps depending on barrier carrier and dot densities. Auger capture rates depend strongly on dot diameters and are greatest at dot diameters of about 10–20 nm. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Multiple-junction single-electron transistors for digital applications

R. H. Chen and K. K. Likharev

Appl. Phys. Lett. 72, 61 (1998); http://dx.doi.org/10.1063/1.120644 (3 pages) | Cited 22 times

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The concept of the capacitively coupled single-electron transistor (CSET) is generalized to a device based on a linear array of N tunnel junctions. The basic characteristics of such multiple-junction CSETs are calculated for several distributions of tunnel junction and coupling capacitances. The results indicate that for optimized parameters, the operating temperature and parameter tolerances increase appreciably with N, with the most striking gains for N≲5. For example, a five-junction transistor may provide a 2.5-fold increase of the maximum operating temperature, for the same minimum feature size. © 1998 American Institute of Physics.
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85.35.Gv Single electron devices
85.35.Ds Quantum interference devices
84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

The influence of the deformation on the two-dimensional electron gas density in GaN–AlGaN heterostructures

R. Gaska, J. W. Yang, A. D. Bykhovski, M. S. Shur, V. V. Kaminski, and S. M. Soloviov

Appl. Phys. Lett. 72, 64 (1998); http://dx.doi.org/10.1063/1.120645 (3 pages) | Cited 44 times

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We report on the effect of external strain on the two-dimensional electron gas density in AlGaN/GaN heterostructures grown on sapphire by low pressure metalorganic chemical vapor deposition. The electron sheet concentration in the studied samples was 4×1012–2×1013 cm−2 and decreased with compressive strain. Lower doped heterostructures had a higher sensitivity to applied strain. The comparison between the experimental data and our model shows that the GaN layers are primarily nitrogen terminated at the heterointerface. © 1998 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Capture of vacancies by extrinsic dislocation loops in silicon

S. B. Herner, H.-J. Gossmann, F. H. Baumann, G. H. Gilmer, D. C. Jacobson, and K. S. Jones

Appl. Phys. Lett. 72, 67 (1998); http://dx.doi.org/10.1063/1.120646 (3 pages) | Cited 4 times

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The capture of a flux of vacancies in Si by a band of extrinsic dislocation loops has been observed in Sb doping superlattices. Annealing Sb doping superlattices containing a band of dislocation loops in NH3 results in an injection of vacancies, which enhances the diffusion of Sb spikes located between the surface and loop band. By extracting the diffusivity in the Sb spikes on either side of the loop band, we conclude that over 90% of the injected vacancies are captured by the loops. © 1998 American Institute of Physics.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.J- Diffusion of impurities

Excitation density dependence of photoluminescence in GaN:Mg

Eunsoon Oh, Hyeongsoo Park, and Yongjo Park

Appl. Phys. Lett. 72, 70 (1998); http://dx.doi.org/10.1063/1.120647 (3 pages) | Cited 41 times

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Continuous redshift of an emission from 3.23 to 2.85 eV with decreasing excitation density is observed in the photoluminescence spectra of highly doped GaN:Mg. It has been explained by the formation of minibands originating from the overlap of deep levels and shallow acceptor levels. For nominally undoped samples the intensity ratio of a donor-bound exciton line and a donor–acceptor pair line changes dramatically with excitation density due to the limited number of acceptors. © 1998 American Institute of Physics.
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78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Phonon confinement effects in the Raman scattering by TiO2 nanocrystals

D. Bersani, P. P. Lottici, and Xing-Zhao Ding

Appl. Phys. Lett. 72, 73 (1998); http://dx.doi.org/10.1063/1.120648 (3 pages) | Cited 162 times

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Nanocrystalline TiO2 has been obtained by a sol-gel process by controlling the crystal size through the water/alkoxide ratio. Raman spectra of anatase nanocrystals with average sizes of 9.5–13.4 nm are reported and the correlation between the Raman band shape (peak position and linewidth) of the main feature at 144 cm−1 and the crystals dimension is discussed. While in this system a minor role is played by nonstoichiometry and pressure effects, a model based on the phonon confinement, which takes into account the size distribution as determined by the transmission electron microscopy images, correctly reproduces the Raman band shape change. © 1998 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
61.46.-w Structure of nanoscale materials
61.66.Bi Elemental solids
61.66.Dk Alloys
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
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