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27 Nov 1995

Volume 67, Issue 22, pp. 3227-3357

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Thermal expansion coefficient of 3C–SiC

D. N. Talwar and Joseph C. Sherbondy

Appl. Phys. Lett. 67, 3301 (1995); http://dx.doi.org/10.1063/1.115227 (3 pages) | Cited 11 times

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Theoretical results for the temperature dependence of the thermal expansion coefficient for 3C–SiC are reported using a phenomenological lattice dynamical theory in the quasiharmonic approximation. The linear thermal expansion coefficient α of 3C–SiC exhibits a variation with temperature much like that of the specific heat and, unlike other tetrahedrally coordinated materials, it does not attain a negative value at lower temperatures. © 1995 American Institute of Physics.
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63.20.-e Phonons in crystal lattices
65.40.De Thermal expansion; thermomechanical effects

Impact ionization in GaAs: Distribution of final electron states determined from hydrostatic pressure measurements

J. Allam, A. R. Adams, M. A. Pate, and J. S. Roberts

Appl. Phys. Lett. 67, 3304 (1995); http://dx.doi.org/10.1063/1.115228 (3 pages) | Cited 9 times

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We have measured the avalanche breakdown voltage (Vb) in GaAs p‐i‐n diodes as a function of hydrostatic pressure up to 14 kbar. The pressure coefficient of Vb was small and opposite in sign compared to that of the band gap. A lucky‐drift calculation of Vb including the effects of pressure on both the phonon scattering and ionization rates showed that the ionization threshold energy does not scale with the band gap. Instead, the effective threshold scales with an average of the energies of the Γ, X, and L conduction‐band minima. This is direct evidence that pair production yields final electron states distributed between conduction‐band valleys. © 1995 American Institute of Physics.
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72.20.Ht High-field and nonlinear effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Modified donor–acceptor pair luminescence in heavily nitrogen‐doped zinc selenide

C. Kothandaraman, G. F. Neumark, and R. M. Park

Appl. Phys. Lett. 67, 3307 (1995); http://dx.doi.org/10.1063/1.115229 (3 pages) | Cited 23 times

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The luminescence from heavily doped ZnSe:N shows a deep broadband whose position was found to depend strongly on the excitation intensity and sample temperature. The peak was found to shift towards higher energies with increasing intensity, but in contrast to the standard donor–acceptor pair (DAP) model, shifted towards lower energies with increasing temperatures. This behavior is explained using a modified DAP model that takes into account the perturbations of the band and impurity states caused by fluctuations in the concentrations of the ionized impurities. This model led to an estimate of 2.52 eV for the PL peak, with a width of 140 meV, for the case of low temperature and low excitation intensity, in rough agreement with our observations. The effect of these fluctuations on film conductivity is also discussed. © 1995 American Institute of Physics.
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71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors

Theoretical analysis of enhanced electroabsorption related to transition from the second valence subband in wide lattice‐matched quantum wells

Takayuki Yamanaka, Koichi Wakita, and Kiyoyuki Yokoyama

Appl. Phys. Lett. 67, 3310 (1995); http://dx.doi.org/10.1063/1.115230 (3 pages) | Cited 1 time

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We formulate on the basis of field‐dependent subband structures a design principle for the TE‐polarized electroabsorption (EA) effect in quantum wells (QWs) that includes all the possible subband‐to‐subband and excitonic absorptions. In contrast with trade‐off between band‐gap‐wavelength shift and exciton oscillator strength in enlarged well widths, the transition from the second valence subband dominantly contributes to the EA enhancement. The reason is clarified in conjunction with the nonparabolicity in the valence‐subband structures. The enhancement of the EA change through the second‐subband transition in lattice‐matched wide QWs can be exploited to build highly efficient EA modulators. © 1995 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
78.20.Jq Electro-optical effects
78.66.Fd III-V semiconductors

Modeling and design of InAs/AlSb‐resonant tunneling diodes

A. Sigurdardottir, V. Krozer, and H. L. Hartnagel

Appl. Phys. Lett. 67, 3313 (1995); http://dx.doi.org/10.1063/1.115231 (3 pages) | Cited 1 time

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In this letter we present a simple but effective single band model for the calculation of the current‐voltage characteristics in InAs/AlSb double barrier resonant tunneling diodes. We have obtained a very good agreement for the overall characteristics and especially for both peak and valley current densities as compared with previously published data. The influence of the doping concentration in the injection layer on the current density is studied, as well as the influence of the quantum well width. We discuss a diode design with a view to tunneling diode oscillators suitable for submillmeter wave mixing. © 1995 American Institute of Physics.
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73.40.Gk Tunneling
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Time resolved blue and ultraviolet photoluminescence in porous GaP

A. Anedda, A. Serpi, V. A. Karavanskii, I. M. Tiginyanu, and V. M. Ichizli

Appl. Phys. Lett. 67, 3316 (1995); http://dx.doi.org/10.1063/1.115232 (3 pages) | Cited 47 times

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Porous GaP layers prepared by electrochemical anodization of (100)‐oriented bulk material was found to exhibit blue and ultraviolet photoluminescence when excited by a KrF excimer laser. The energy position of the UV luminescence band (3.3 eV at 300 K) is explained on the basis of charge carrier confinement in crystalline quantum wires of about 25 Å in diameter. Additional evidence for quantum size effect in porous GaP was obtained by Raman scattering measurements. © 1995 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.55.Cr III-V semiconductors

Determination of the band offsets of the 4H–SiC/6H–SiC heterojunction using the vanadium donor (0/+) level as a reference

A. O. Evwaraye, S. R. Smith, and W. C. Mitchel

Appl. Phys. Lett. 67, 3319 (1995); http://dx.doi.org/10.1063/1.115233 (3 pages) | Cited 13 times

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Optical admittance spectroscopy has been used to study defects in 4H–SiC; the vanadium donor level at EC‐1.73 eV has been identified. The optical admittance spectrum of 4H–SiC is similar to that of 6H–SiC, where the vanadium donor level is at EC‐1.59 eV. The band gaps of 6H–SiC and 4H–SiC were measured. The values of 3.10±0.03 eV for 6H–SiC and 3.41±0.03 eV for 4H–SiC are in reasonable agreement with reported values. Using the vanadium donor level in both 4H–SiC and 6H–SiC as a common reference, the band offsets for 6H–SiC/4H–SiC heterojunction are estimated to be ΔEC=0.14 eV and ΔEV=0.17 eV. © 1995 American Institute of Physics.
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71.55.Ht Other nonmetals
73.20.At Surface states, band structure, electron density of states

Properties of a Si doped GaN/AlGaN single quantum well

A. Salvador, G. Liu, W. Kim, Ö. Aktas, A. Botchkarev, and H. Morkoç

Appl. Phys. Lett. 67, 3322 (1995); http://dx.doi.org/10.1063/1.115234 (3 pages) | Cited 29 times

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Quantization of band‐to‐band transition in a Si doped GaN/AlGaN quantum well was investigated. A good fit to the room‐temperature photoluminescence (PL) spectrum of the GaN quantum well studied was obtained using values 0.3me and 0.19me for the heavy hole and conduction electron effective masses, respectively, and a 67:33 conduction to valence band offset. © 1995 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

High‐resolution x‐ray analysis of compressively strained 1.55 μm GaInAs/AlGaInAs multiquantum well structures near the critical thickness

A. Krost, J. Böhrer, A. Dadgar, R. F. Schnabel, D. Bimberg, S. Hansmann, and H. Burkhard

Appl. Phys. Lett. 67, 3325 (1995); http://dx.doi.org/10.1063/1.115235 (3 pages) | Cited 6 times

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Compressively strained InP/GaInAs/AlGaInAs multiquantum well (MQW) laser structures with up to 15 QWs designed for 1.55 μm emission wavelength were grown by metalorganic chemical vapor deposition (MOCVD) on p‐type InP(001) substrates. Crystallographic and optical properties are studied using double crystal x‐ray diffraction and photoluminescence measurements. The rocking curves of the complicated MQW structure can be perfectly modeled using dynamical diffraction theory. The critical thickness observed for strain relaxation upon growth and laser processing is found to be in good agreement with that predicted by Matthews and Blakeslee [J. Cryst. Growth 27, 118 (1974)] taking into account the MQW structure and the cap layer. © 1995 American Institute of Physics.
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61.05.cc Theories of x-ray diffraction and scattering
68.55.-a Thin film structure and morphology
78.55.Cr III-V semiconductors

Electroluminescence from spark‐processed silicon

J. Yuan and D. Haneman

Appl. Phys. Lett. 67, 3328 (1995); http://dx.doi.org/10.1063/1.115236 (3 pages) | Cited 9 times

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We have fabricated spark‐processed silicon so as to produce electroluminescence which is readily visible in semidark conditions. There are three emission peaks at around 1.3, 1.6, and 1.9 eV. The photoluminescence spectrum shows only one peak at around 1.9 eV. The electroluminescence is polarity dependent. Although the average efficiency over areas of several mm2 is low, the emission is concentrated at various spots which are bright and have a much higher efficiency. © 1995 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Db Elemental semiconductors and insulators
81.65.-b Surface treatments

Magneto‐optical determination of light‐heavy hole splittings in As‐rich, InAsSb alloys and superlattices

S. R. Kurtz, R. M. Biefeld, and A. J. Howard

Appl. Phys. Lett. 67, 3331 (1995); http://dx.doi.org/10.1063/1.115237 (3 pages) | Cited 10 times

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Interband magnetophotoconductive spectroscopy was used to determine the reduced masses of several optical transitions in an InAs1−xSbx/In1−xGaxAs strained‐layer superlattice and a superlattice constituent, InAs1−xSbx alloy (x≊0.1). In both the alloy and the superlattice, light and heavy hole transitions were identified. From the light‐heavy hole splitting in the superlattice, we estimate the valence band offset and find type I behavior. Effective masses and band gap energy are measured for the CuPt ordered alloy. © 1995 American Institute of Physics.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.20.At Surface states, band structure, electron density of states
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Theoretical study of chlorine adsorption on GaAs(111)A surfaces

Jiang Guo‐Ping and Harry E. Ruda

Appl. Phys. Lett. 67, 3334 (1995); http://dx.doi.org/10.1063/1.115238 (3 pages) | Cited 2 times

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The mechanism for Cl atom adsorption on GaAs(111)A surfaces is investigated using ab initio Hartree–Fock molecular orbital calculations on specially designed cluster models. The energy‐minimized geometry and binding energies are obtained for Cl adsorbed on the (111)A surfaces. Cl is shown to bond to surface Ga atoms and result in (a) a lowering of the occupied surface electronic state energy, (b) a strongly enhanced surface dipole moment, and (c) a profound effect on the surface Ga–As bonding. The different bonding characteristics of Cl and H adsorbed on such surfaces are shown to manifest themselves in the local density of states. Model results are used to explain the observed enhanced photoluminescence response of chlorinated GaAs(111)A surfaces. © 1995 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Fabrication of ZnO thin films using charged liquid cluster beam technique

Choon Kun Ryu and Kyekyoon Kim

Appl. Phys. Lett. 67, 3337 (1995); http://dx.doi.org/10.1063/1.115239 (3 pages) | Cited 17 times

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A thin‐film deposition technique utilizing a charged liquid cluster beam was applied in the fabrication of ZnO thin films on silicon substrates with a thin layer of native oxide. The liquid precursor was prepared by dissolving Zn‐trifluoroacetate in methanol. The film was very uniform, densely packed, and predominantly c‐axis oriented. The initially resistive ZnO thin film became conductive after annealing in a hydrogen atmosphere for 5 min. The electrical resistivities of the annealed films ranged from 7.99×10−3 to 1.60×10−2 Ω cm. The electron carrier concentrations were in the range of 3.33–5.35×1019 cm−3 and the mobilities were 7.30–19.07 cm2 V−1 s−1. The refractive index varied from 1.89 to 1.96 as the growth temperature increased from 340 to 440 °C. © 1995 American Institute of Physics.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Influence of a NbN overlayer on Nb/Al–AlOx/Nb high quality Josephson tunnel junctions for x‐ray detection

R. Cristiano, E. Esposito, L. Frunzio, S. Pagano, L. Parlato, G. Peluso, G. Pepe, U. Scotti di Uccio, H. Nakagawa, M. Aoyagi, H. Akoh, and S. Takada

Appl. Phys. Lett. 67, 3340 (1995); http://dx.doi.org/10.1063/1.115240 (3 pages) | Cited 4 times

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Nb/Al–AlOx/Nb–NbN Josephson junctions for use as x‐ray detectors have been fabricated. The NbN overlayer has been used to realize the trapping of quasiparticles in the Nb top layer with an increase of the charge collection efficiency. The temperature dependence of quasiparticle and Josephson critical current have been investigated and compared with that without a NbN overlayer, showing low leakage currents, about 200 pA (V=0.5 mV, T=0.67 K, A=20×20 μm2), and high dynamical resistances in the subgap region. Preliminary measurements under 6 keV x‐ray irradiation have shown an increased value of the maximum collected charge. © 1995 American Institute of Physics.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Observation of intercalation of excess oxygen in Bi2Sr2CaCu2O8+y single crystal

G. S. Shekhawat, Ram P. Gupta, A. Agarwal, P. D. Vyas, P. Srivastava, N. L. Saini, S. Venkatesh, and K. B. Garg

Appl. Phys. Lett. 67, 3343 (1995); http://dx.doi.org/10.1063/1.115241 (3 pages)

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Effects arising from the intercalation of excess oxygen in Bi–O layer has been observed at room temperature using atomic force microscopy. The excess oxygen is incorporated by oxygenating the pure sample. The oxygen is trapped between the alternating Bi–O layers along the b direction. This leads to a change in the local interatomic bond length along the b axis, while the periodicity remained invariant along the a axis. In addition, in‐plane atomically resolved structure of single crystal has been imaged at room temperature using AFM. The lattice spacings indicate that the observed structure corresponds to the in‐plane bismuth and oxygen positions. Furthermore, high‐resolution scanning tunneling spectroscopy measurements show that oxygen doping increases the Bi–O layer density of states near the Fermi level giving rise to metallicity, whereas the pure sample reveals a semiconducting energy gap in the tunneling spectrum. © 1995 American Institute of Physics.
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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
74.62.Dh Effects of crystal defects, doping and substitution
74.72.-h Cuprate superconductors

Longitudinal and transverse magneto‐impedance in amorphous Fe73.5Cu1Nb3Si13.5B9 films

R. L. Sommer and C. L. Chien

Appl. Phys. Lett. 67, 3346 (1995); http://dx.doi.org/10.1063/1.115242 (3 pages) | Cited 75 times

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Magneto‐impedance effects have been observed in thin films of amorphous Fe73.5Cu1Nb3Si13.5B9. Large magneto‐impedance values have been obtained in field‐annealed samples, but not in as‐deposited samples. Transverse magneto‐impedance effects with magnitudes comparable to the longitudinal case have been observed. These results are discussed in terms of appropriate magnetic permeability. © 1995 American Institute of Physics.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Epitaxial ferromagnetic MnAs thin films grown by molecular beam epitaxy on Si (001) substrates

K. Akeura, M. Tanaka, M. Ueki, and T. Nishinaga

Appl. Phys. Lett. 67, 3349 (1995); http://dx.doi.org/10.1063/1.115243 (3 pages) | Cited 56 times

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We have grown ferromagnetic MnAs thin films on Si(001) substrates by molecular beam epitaxy. Epitaxial monocrystalline MnAs films with the growth plane of (1101) were obtained when the Si surface was first exposed to an As4 flux and then Mn and As4 fluxes were codeposited. It was found that the very first monolayer of As on Si(001) plays an essential role to obtain epitaxial MnAs thin films. Magnetization measurements indicate that the easy axis of the MnAs thin films is in‐plane, along the [1120] of MnAs and the [110] of Si, normal to the substrate misorientation. The M‐H curve of a 300‐nm‐thick film shows a hysteresis with a saturation magnetization Ms of 694 emu/cm3 and a coercive field Hc of 94 Oe, when the magnetic field is applied along the easy axis. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Micro‐Raman study of polydioxolane/LiClO4 and NaClO4 electrolytes

R. A. Silva, G. Goulart Silva, and M. A. Pimenta

Appl. Phys. Lett. 67, 3352 (1995); http://dx.doi.org/10.1063/1.115244 (3 pages) | Cited 5 times

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A micro‐Raman study of polydioxolane (PDXL)/NaClO4 and PDXL/LiClO4 polymeric electrolytes has been carried out in a wide range of salt concentration, at room temperature. The ion–ion interactions and the precipitation of salt microcrystals in the host polymer have been evidenced by means of a line shape analysis of the band associated to the totally symmetric stretching mode (ν1) of the ClO4− anion. The Raman spectra results reveal changes of the crystallinity of the PDXL/MCLO4 systems which are directly related to the salt concentration. © 1995 American Institute of Physics.
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66.10.Ed Ionic conduction
78.30.-j Infrared and Raman spectra
82.45.-h Electrochemistry and electrophoresis

Plasma assisted conversion of carbon fibers to diamond

S. Ismat Shah, D. J. Walls, Matthew M. Waite, and D. Guerin

Appl. Phys. Lett. 67, 3355 (1995); http://dx.doi.org/10.1063/1.115245 (3 pages) | Cited 4 times

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Pitch based carbon fibers have been converted to diamond through exposure to a pure hydrogen microwave plasma. The conversion depends strongly on the process pressure. At low pressure only part of the surface of the fiber was converted to diamond, however under optimum conditions a thick continuous diamond layer could be obtained. The carbon conversion efficiency to form diamond at the high pressure was at least an order of magnitude higher than is obtained in a regular CH4+H2 plasma assisted diamond deposition. © 1995 American Institute of Physics.
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81.20.-n Methods of materials synthesis and materials processing
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