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15 Dec 1997

Volume 82, Issue 12, pp. 5891-6372

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Optical spectra of the layered Cd2P2S6 and Cd2P2Se6 compounds in the region from 1.6 to 5.5 eV

C. Calareso, V. Grasso, and L. Silipigni

J. Appl. Phys. 82, 6228 (1997); http://dx.doi.org/10.1063/1.366508 (7 pages) | Cited 6 times

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Room temperature absorption and reflectivity data are presented for Cd2P2S6 and Cd2P2Se6 crystals in the range of photon energies between 1.6 and 5.5 eV. For both compounds the characteristic feature of the optical absorption is that their absorption edge appears to correspond to an indirect allowed transition with an optical energy gap of 3.06 eV for Cd2P2S6 and 2.29 eV for Cd2P2Se6. An associated phonon energy of 74 meV for Cd2P2S6 and 50 meV for Cd2P2Se6 is also deduced. The Cd2P2X6 (with X = S or Se) reflectivity spectra are compared with the early reflectivity spectrum of Zn2P2S6. As observed in previous reflectivity spectra of the Hg2P2X6 compounds, near the fundamental absorption edges the Cd2P2X6 reflectivity spectra show a pronounced rise in reflectivity, a feature common to most layered compounds. For photon energies greater than their absorption edges, the reflectivity spectra of both materials look similar to one another and to that of Zn2P2S6. On the basis of these similarities we have adopted the so-called transition metal weakly interacting model and interpreted the spectral structures as direct allowed interband transitions. For both compounds, these electronic transitions are described by a simplified energy-band scheme. © 1997 American Institute of Physics.
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78.40.Ha Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.-e Optical properties of bulk materials and thin films
71.20.Ps Other inorganic compounds

Strain effects on InSb phonons in bulk and superlattice layers

M. Siakavellas, Y. S. Raptis, E. Anastassakis, and D. J. Lockwood

J. Appl. Phys. 82, 6235 (1997); http://dx.doi.org/10.1063/1.366509 (5 pages)

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We have studied the effect of uniaxial stress on the long-wavelength optical phonons of InSb at room temperature using Raman spectroscopy. From the observed frequency shifts and degeneracy splittings we obtain values for the phonon deformation potentials. The results are used to analyze previously reported Raman measurements of phonons in strained InSb/In1−xAlxSb superlattices. © 1997 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.66.Fd III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.60.Bs Mechanical and acoustical properties
78.30.Fs III-V and II-VI semiconductors
68.35.Ja Surface and interface dynamics and vibrations

Observation of suppressed radiative recombination in single quantum well p-i-n photodiodes

Jenny Nelson, Jenny Barnes, Nicholas Ekins-Daukes, Benjamin Kluftinger, Ernest Tsui, Keith Barnham, C. Tom Foxon, Tin Cheng, and John S. Roberts

J. Appl. Phys. 82, 6240 (1997); http://dx.doi.org/10.1063/1.366510 (7 pages) | Cited 14 times

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We have measured electroluminescence (EL) spectra of GaAs/InGaAs and AlGaAs/GaAs single quantum well (QW) p-i-n photodiodes at temperatures between 200 and 300 K and forward biases close to the open circuit voltage. Integrated EL spectra vary like eqV/nkT with an ideality factor n = 1.05±0.05 over five decades, indicating purely radiative processes. The spectra are calibrated into absolute units enabling comparison to be made with the predictions of a theoretical model. For each temperature and bias we calculate the EL spectrum and radiative current expected in the detailed balance limit, integrating the theoretical emission spectrum over the surface of the device, in order to establish the quasi-Fermi potential separation, Δϕf, in the QW and, where possible, in the host material. For the GaAs/InGaAs cell we are able to model emission from the QW and the host material simultaneously. We find that, in all cases, the QW emission is overestimated by theory if it is assumed that Δϕf = V. QW emission corresponds instead to a value of Δϕf which a few tens of mV less than V. In contrast, emission from the host material, where visible, is well fitted by the model with Δϕf = V at all biases and temperatures. We attribute the variation in Δϕf to irreversible thermally assisted escape from the QWs. © 1997 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Dw Photodiodes; phototransistors; photoresistors
78.60.Fi Electroluminescence
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
73.25.+i Surface conductivity and carrier phenomena
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Characterization of GaAs wire crystals grown on porous silicon by Raman scattering

S. W. da Silva, D. I. Lubyshev, P. Basmaji, Yu. A. Pusep, P. S. Pizani, J. C. Galzerani, R. S. Katiyar, and G. Morell

J. Appl. Phys. 82, 6247 (1997); http://dx.doi.org/10.1063/1.366511 (4 pages) | Cited 5 times

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We measured the Raman spectra of GaAs wirelike crystals grown on porous silicon (PS) using two different excitation radiations which probe the near surface and the bulk. The transverse optic and longitudinal optic vibrational bands appear redshifted and broadened when compared to bulk GaAs, and with shoulders on their low frequency sides. These features are attributed to a disorder-induced relaxation in the selection rules for Raman activity arising from point defects. In addition, the bands show a strong frequency and bandwidth dependence on excitation energy. Differences in penetration depth together with a gradient in defect density are invoked to account for the observations. This analysis yields a picture in which there is a predominantly amorphous GaAs region buried at the PS–GaAs interface followed by microcrystalline GaAs cylindrical structures that become less defective as they grow farther from the interface. The near surface tends to approach the low defect density of crystalline GaAs. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
61.72.J- Point defects and defect clusters

Refractive index of interdiffused AlGaAs/GaAs quantum well

E. Herbert Li

J. Appl. Phys. 82, 6251 (1997); http://dx.doi.org/10.1063/1.366512 (8 pages) | Cited 9 times

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A model is developed for the polarization dependent refractive index of interdiffused AlGaAs/GaAs quantum well at room temperature for wavelengths ranging from 0.6 to 2 μm. The present model is based on a semianalytic and semiempirical method through the Kramers–Krönig transformation. The multi-quantum-well structures, including the exciton effect and above barrier gap contributions, are fully considered in this model. The distinct structures at energies of the E0,E0+Δ0,E1, and E2 critical points are revealed. Moreover, the birefringence at room temperature is also analyzed in the wavelength range varying from 0.7 to 1.0 μm. The calculated refractive index results are in satisfactory agreement with the experimental measurements over the quantum well band edge, i.e., 0.8–0.9 μm. The effect of interdiffusion on the change of refractive index is discussed. The polarization dependent absorption coefficients are also calculated with all the bound excitons, and results agree well with experiments. These results are important, since refraction index in a particular wavelength region of interest, where experimental data are not available, can be determined and thus are very useful in the design of devices. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Fm Birefringence
68.35.Fx Diffusion; interface formation
71.35.-y Excitons and related phenomena

Optical transitions of Er3+ ions in ZnCl2-based glass

M. Shojiya, M. Takahashi, R. Kanno, Y. Kawamoto, and K. Kadono

J. Appl. Phys. 82, 6259 (1997); http://dx.doi.org/10.1063/1.366545 (8 pages) | Cited 19 times

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Optical absorption and emission properties of Er3+ ions in ZnCl2-based glasses are investigated. The electric dipole line strengths for various transitions were estimated from the measured optical absorption spectra. The spontaneous emission probabilities for various transitions were predicted using the Judd–Ofelt theory. Among Ωt(t = 2,4,6) phenomenological intensity parameters, the Ω2 value is larger than that measured for ZrF4-based glass. On the contrary, the Ω4 and Ω6 values are comparatively small. Multiphonon relaxation rates follow a so-called “energy-gap law” which is given by WMPR = C exp(−αΔE). The C value is quite smaller than that of the ZrF4-based glass by about two orders of magnitude. This result is attributed to the very low-phonon-energy of the chloride glass matrix. On the other hand, the α value is almost the same as those of other glass hosts. Because of the low-phonon-energy and the host-independent α value, the electron–phonon coupling constant ϵ of the ZnCl2-based glass is extremely large compared with those of oxide and fluoride glasses. It was also found that several emissions due to transitions between the excited 4 f-levels are detectable, which are hardly observed in other glass hosts. Radiative quantum efficiency is definitively high even for emitting levels of which the energy-gap to the next-lower level is small. © 1997 American Institute of Physics.
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78.40.Pg Disordered solids
71.38.-k Polarons and electron-phonon interactions
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
61.43.Fs Glasses

Effects of thermal annealing on emission characteristics and surface properties of field emitter arrays

Fuminori Ito, Kazuo Konuma, Akihiko Okamoto, Akihiro Yano, and Souichiro Miyano

J. Appl. Phys. 82, 6267 (1997); http://dx.doi.org/10.1063/1.366513 (6 pages) | Cited 3 times

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The effects of thermal annealing below 500 °C on Spindt-type Mo field emitter arrays (FEAs) were studied through emission characteristics and Mo surface analysis. The anode current of the FEAs increases with increasing annealing time and then saturates after a certain period that is shorter for higher-temperature annealing. X-ray photoelectron spectroscopy and temperature programmed desorption show that MoO3 formed on the Mo surface desorbs at around 500 °C. The enhancement of the anode current is caused mainly by MoO3 desorption, since the period required for MoO3 desorption corresponds to that required for current saturation.© 1997 American Institute of Physics.
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85.45.Db Field emitters and arrays, cold electron emitters
79.70.+q Field emission, ionization, evaporation, and desorption
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
79.60.Jv Interfaces; heterostructures; nanostructures

Photoresist etching with dielectric barrier discharges in oxygen

Zoran Falkenstein and John J. Coogan

J. Appl. Phys. 82, 6273 (1997); http://dx.doi.org/10.1063/1.366514 (8 pages) | Cited 9 times

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This article presents results on the surface etching of a Novolak-type polymer (Shipley, SPR2) on Si wafers using dielectric barrier discharges in oxygen at high pressures and room temperature. The etching depth is measured by mechanical profilometry as a function of gap spacing and gas pressure. Figures of merit are generated allowing comparison with conventional plasma surface treatment, as etch rate per power density coupled onto the sample surface (nm J−1 cm2), or coupled into the gas volume (nm J−1 cm3). Energy-density specific etch rates were measured as a function of the gap spacing (d) and the total oxygen gas pressure (p), as well as a function of the product of pd in the gas pressure range of 50–1500 mbar and of the gap spacing range of 1–20 mm. At a constant gap spacing and pressure, the removal rate is a linear function of the applied power density. The highest achieved etching rate per surface energy density is 2.2 nm J−1 cm2 at 730 mbar and 1 mm (0.2 nm J−1 cm3) and the highest etching rate per volumetric energy density is 0.85 nm J−1 cm3 at 290 mbar and 7 mm (0.87 nm J−1 cm2). The surface of the etched photoresist is characterized using mechanical profilometry and scanning electron microscopy. The results obtained in this work suggest that dielectric barrier discharges can be an efficient, alternative plasma source for general surface processing, because they can provide nonthermal discharges also near atmospheric pressures and thereby eliminate the need of costly vacuum systems. © 1997 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.20.Pm Rate constants, reaction cross sections, and activation energies
52.50.Dg Plasma sources

Growth and characterization of silicon thin films employing supersonic jets of SiH4 on polysilicon and Si(100)

C. B. Mullins, K. A. Pacheco, and S. Banerjee

J. Appl. Phys. 82, 6281 (1997); http://dx.doi.org/10.1063/1.366515 (8 pages) | Cited 4 times

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Supersonic jets of silane were employed to deposit silicon on both polysilicon and Si(100) at substrate temperatures ranging from 500 to 650 °C. The growth rate and film uniformity were studied as a function of silane kinetic energy. Increasing the SiH4 precursor kinetic energy from 0.4 eV (10% SiH4 in He mixture) to 1 eV (1% SiH4 in H2 mixture) results in as much as an order of magnitude increase in reaction probability. The advantage of using high kinetic energy precursors to enhance deposition is reflected in the centerline growth rates obtained employing supersonic jets of SiH4. At higher substrate temperatures, the high kinetic energy SiH4 jet has a higher growth rate than the low kinetic energy SiH4 jet, although, the flux of the high energy jet at the centerline is a factor of 8 less than the flux of the low energy jet. The silane flux distribution from the supersonic jet is dependent on the gas mixture; a flux distribution of cos55 θ results from the 1% silane in hydrogen jet (1 eV) compared to a cos28 θ distribution from the 10% silane in helium jet (0.4 eV). © 1997 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Enhanced silicon oxide film growth on Si (100) using electron impact

Jiazhan Xu, W. J. Choyke, and John T. Yates

J. Appl. Phys. 82, 6289 (1997); http://dx.doi.org/10.1063/1.366516 (4 pages) | Cited 25 times

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The effect of electron beam impact on the oxidation of Si (100) by oxygen has been studied using x-ray photoelectron spectroscopy and Auger electron spectroscopy. It was found that electron beam impact can enhance the oxidation of Si (100) by oxygen at low temperatures, resulting in silicon dioxide formation. Furthermore, electron energy-dependent film growth experiments were carried out on O2(a) and an electron attachment resonance energy of ∼ 10.1 eV was found. A possible electron-induced oxidation mechanism is proposed which involves dissociative electron attachment for adsorbed O2 species and the formation of O and O− species from adsorbed O2−. © 1997 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.65.Mq Oxidation
79.20.Kz Other electron-impact emission phenomena
79.60.Jv Interfaces; heterostructures; nanostructures
79.20.Fv Electron impact: Auger emission
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

A kinetic Monte Carlo method for the atomic-scale simulation of chemical vapor deposition: Application to diamond

C. C. Battaile, D. J. Srolovitz, and J. E. Butler

J. Appl. Phys. 82, 6293 (1997); http://dx.doi.org/10.1063/1.366532 (8 pages) | Cited 61 times

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We present a method for simulating the chemical vapor deposition (CVD) of thin films. The model is based upon a three-dimensional representation of film growth on the atomic scale that incorporates the effects of surface atomic structure and morphology. Film growth is simulated on lattice. The temporal evolution of the film during growth is examined on the atomic scale by a Monte Carlo technique parameterized by the rates of the important surface chemical reactions. The approach is similar to the N-fold way in that one reaction occurs at each simulation step, and the time increment between reaction events is variable. As an example of the application of the simulation technique, the growth of {111}-oriented diamond films was simulated for fifteen substrate temperatures ranging from 800 to 1500 K. Film growth rates and incorporated vacancy and H atom concentrations were computed at each temperature. Under typical CVD conditions, the simulated growth rates vary from about 0.1 to 0.8 μm/hr between 800 and 1500 K and the activation energy for growth on the {111}: H surface between 800 and 1100 K is 11.3 kcal/mol. The simulations predict that the concentrations of incorporated point defects are low at substrate temperatures below 1300 K, but become significant above this temperature. If the ratio between growth rate and point defect concentration is used as a measure of growth efficiency, ideal substrate temperatures for the growth of {111}-oriented diamond films are in the vicinity of 1100 to 1200 K. © 1997 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
81.05.ub Fullerenes and related materials
81.05.Cy Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)

The response of high-Tc SQUID magnetometers to small changes in temperature

F. P. Milliken, R. H. Koch, S. L. Brown, R. A. Altman, W. J. Gallagher, S. G. Haupt, and D. K. Lathrop

J. Appl. Phys. 82, 6301 (1997); http://dx.doi.org/10.1063/1.366519 (5 pages) | Cited 1 time

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We have investigated the response of the flux-locked output of several high-Tc SQUID magnetometers to small changes in temperature and for magnetic fields 0–30 μT. The temperature response DT ≡ dΦS/dT is observed to be linear in the applied magnetic field Ba and can be as large as 500 mΦ0/K where ΦS is the flux through the SQUID loop and Φ0 is the flux quantum. Our measurements can be explained using a simple model that takes into account the geometry of a given device and is based on the idea that DT is due to the temperature dependence of the superconducting penetration depth. Our results can be used to optimize device performance in applications where the noise of a device is dominated by ambient temperature fluctuations. © 1997 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
85.25.Dq Superconducting quantum interference devices (SQUIDs)
85.25.Am Superconducting device characterization, design, and modeling
07.55.Ge Magnetometers for magnetic field measurements
74.25.Ha Magnetic properties including vortex structures and related phenomena

Interferometric quantum wire switch

Curt A. Flory

J. Appl. Phys. 82, 6306 (1997); http://dx.doi.org/10.1063/1.366520 (6 pages) | Cited 3 times

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A device topology is proposed and analyzed which is based upon quantum wire components. The device controls the conductance between an input line and a pair of output lines by varying the phase shift around a quantum wire ring connecting the external nodes. The phase shift is controlled using a simple electron stub tuner. Switching characteristics with efficiencies greater than 95% for certain geometries have been calculated. © 1997 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.35.Ds Quantum interference devices
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.23.-b Electronic transport in mesoscopic systems

Effect of capture and escape phenomena in Monte Carlo technique on the simulation of the nonlinear characteristics in high electron mobility transistors

Michel Abou-Khalil, D. Schreurs, B. Nauwelaers, M. Van Rossum, R. Maciejko, and Ke Wu

J. Appl. Phys. 82, 6312 (1997); http://dx.doi.org/10.1063/1.366521 (7 pages) | Cited 1 time

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The transport properties of electrons in a heterostructure high electron mobility transistor are analyzed by considering the capture and escape phenomena as scattering events in Monte Carlo simulation. Through the variation of the equivalent charge in time, the drain current of an AlInAs/InGaAs/InP quantum-well device with planar doping is deduced for given drain and gate voltages. We studied the energy distribution of carriers in the device and we compared the results to those obtained by other quantum mechanical treatment and the classical treatment of the confinement. We demonstrated that by using our capture procedure for the quantum mechanical treatment, carriers have higher energy values than in the case of classical treatment and therefore the current values are different by an amount of 30%–40%. © 1997 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
02.50.Ng Distribution theory and Monte Carlo studies
02.70.Rr General statistical methods

Device model for single carrier organic diodes

P. S. Davids, I. H. Campbell, and D. L. Smith

J. Appl. Phys. 82, 6319 (1997); http://dx.doi.org/10.1063/1.366522 (7 pages) | Cited 178 times

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We present a unified device model for single layer organic light emitting diodes (LEDs) which includes charge injection, transport, and space charge effects in the organic material. The model can describe both injection limited and space charge limited current flow and the transition between them. We specifically considered cases in which the energy barrier to injection of electrons is much larger than that for holes so that holes dominate the current flow in the device. Charge injection into the organic material occurs by thermionic emission and by tunneling. For Schottky energy barriers less than about 0.3–0.4 eV, for typical organic LED device parameters, the current flow is space charge limited and the electric field in the structure is highly nonuniform. For larger energy barriers the current flow is injection limited. In the injection limited regime, the net injected charge is relatively small, the electric field is nearly uniform, and space charge effects are not important. At smaller bias in the injection limited regime, thermionic emission is the dominant injection mechanism. For this case the thermionic emission injection current and a backward flowing interface recombination current, which is the time reversed process of thermionic emission, combine to establish a quasi-equilibrium carrier density. The quasi-equilibrium density is bias dependent because of image force lowering of the injection barrier. The net device current is determined by the drift of these carriers in the nearly constant electric field. The net device current is much smaller than either the thermionic emission or interface recombination current which nearly cancel. At higher bias, injection is dominated by tunneling. The bias at which tunneling exceeds thermionic emission depends on the size of the Schottky energy barrier. When tunneling is the dominant injection mechanism, a combination of tunneling injection current and the backflowing interface recombination current combine to establish the carrier density. We compare the model results with experimental measurements on devices fabricated using the electroluminescent conjugated polymer poly[2-methoxy, 5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] which by changing the contacts can show either injection limited behavior or space charge limited behavior. © 1997 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling
73.30.+y Surface double layers, Schottky barriers, and work functions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Le Polymers; organic compounds (including organic semiconductors)
72.20.Ht High-field and nonlinear effects

Space-charge limited conduction with traps in poly(phenylene vinylene) light emitting diodes

A. J. Campbell, D. D. C. Bradley, and D. G. Lidzey

J. Appl. Phys. 82, 6326 (1997); http://dx.doi.org/10.1063/1.366523 (17 pages) | Cited 219 times

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Current–voltage, impedance, and transient conductance measurements have been carried out on indium-tin-oxide/poly(phenylene vinylene)/Al light emitting diodes. In these devices injection and transport is expected to be dominated by positive carriers. Fowler–Nordheim tunneling theory cannot account for the temperature dependence, the thickness dependence, or the current magnitude of the current–voltage characteristics. Space-charge limited current theory with an exponential distribution of traps is however in extremely good agreement with all of the recorded current–voltage results in the higher applied bias regime (approximately 0.7 ⩽ V/d ⩽ 1.6×106 V cm−1). This gives a trap density Ht of 5(±2)×1017 cm−3 and the product of μNHOMO of between 1014 and 5×1012 cm−1 V−1 s−1. Assuming NHOMO is 1020 cm−3 gives an effective positive carrier mobility between 10−6 and 5×10−8 cm2 V−1 s−1. The characteristic energy Et of the exponential trap distribution is 0.15 eV at higher temperatures (190 ⩽ T ⩽ 290 K), but this decreases as the devices are cooled, indicating that the distribution is in fact a much steeper function of energy closer to the highest occupied molecular orbital (HOMO) levels. The current–voltage characteristics in the lower applied bias regime (approximately V/d ⩽ 0.7×106 V cm−1) can be fitted to pure space-charge limited current flow with a temperature and field dependent mobility of Arrhnenius form with a mobility at 290 K close to the above values. If NHOMO lies between 1021 and 1019 cm−3, then the trap filled limit bias gives a mobility independent value of Ht of 3(±1)×1017 cm−3. Capacitance–voltage measurements show that at zero bias the devices are fully depleted, and that the acceptor dopant density NA must be less than about 1016 cm−3. The impedance results show that the devices can be modeled on a single, frequency independent, parallel resistor-capacitor circuit with a small series resistor. The variation of the resistor and capacitor in the parallel circuit with applied bias and temperature are consistent with the space-charge limited current theory with the same exponential trap distribution used to model the current–voltage characteristics. Initial results for transient conductance measurements are reported. The transients have decay times greater than 300 s and exhibit a power-law dependence with time. This is shown to be exactly the behavior expected for the decay of an exponential trap distribution. Measurements at higher temperatures (290 ≥ T ≥ 150 K) give an Et of 0.15 eV, in excellent agreement with that found from the current–voltage measurements. This value of Et is exactly that found by similar analysis of the current–voltage characteristics in negative carrier dominated dialkoxy poly(phenylene vinylene) and Mq3 devices. It is proposed that this bulk transport dominated behavior is purely a consequence of hopping conduction through an approximately Gaussian density of states in which the deep sites act as traps. © 1997 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.50.Fq High-field and nonlinear effects
73.61.Ph Polymers; organic compounds
42.70.Jk Polymers and organics
73.50.Dn Low-field transport and mobility; piezoresistance
71.20.Rv Polymers and organic compounds

Shape and stability of a floating liquid zone between two solids

M. Saitou

J. Appl. Phys. 82, 6343 (1997); http://dx.doi.org/10.1063/1.366524 (3 pages) | Cited 2 times

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The shape and stability of a floating liquid zone between two solids are analytically investigated using the principle of variation. The formulas for its shape and stability are obtained. © 1997 American Institute of Physics.
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81.10.Fq Growth from melts; zone melting and refining

Hydrogen passivation of nitrogen in 6H–SiC

B. Theys, F. Gendron, C. Porte, E. Bringuier, and C. Dolin

J. Appl. Phys. 82, 6346 (1997); http://dx.doi.org/10.1063/1.366525 (2 pages) | Cited 2 times

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N-doped 6H–SiC wafers have been annealed in hot hydrogen for two doping levels, corresponding to n- (n ∼ 1017 cm−3) and n+-type (n ∼ 1019 cm−3) material. Electron spin resonance shows little passivation of N by hydrogen in n-type material, where secondary-ion-mass spectroscopy shows better penetration of deuterium. Both observations are accounted for in terms of Fermi-level control of the hydrogen charge state. © 1997 American Institute of Physics.
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81.65.Rv Passivation
76.30.Lh Other ions and impurities
71.55.Ht Other nonmetals
72.80.Jc Other crystalline inorganic semiconductors
61.72.Cc Kinetics of defect formation and annealing

Water degradation of a- and c-axis oriented HgBa2CaCu2Ox superconducting thin films

S. H. Yun and U. O. Karlsson

J. Appl. Phys. 82, 6348 (1997); http://dx.doi.org/10.1063/1.366526 (3 pages) | Cited 1 time

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Degradation of HgBa2CaCu2Ox superconducting thin films with a- and c-axis oriented normal to the substrates in water has been studied with electrical measurement, x-ray diffractometry, scanning electron microscopy, and energy dispersive x-ray spectrometry. We observed the different degradation behavior of a- and c-axis oriented HgBa2CaCu2Ox thin films normal to substrates in water immersion experiments. The a-axis oriented films are much more stable than the c-axis oriented films in water. After a 60 min immersion, the zero-resistance temperature of the a-axis oriented film is still above 110 K, but the zero resistance is not observed in the c-axis oriented film in water even for 5 min. The intensity of (00l) peaks is suppressed at one order of magnitude faster than that of (l00) peaks as the total immersion time increase. © 1997 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.62.Yb Other effects
81.65.-b Surface treatments

Microstructure and magnetic properties of rapidly quenched Sm2(Fe,Al,Zr)17C1.5 ribbons with Zr additions

Wei Tang, Zhi-Qiang Jin, Jian-Ron Zhang, Li-Ya Lu, Shi-Yuan Zhang, and You-Wei Du

J. Appl. Phys. 82, 6351 (1997); http://dx.doi.org/10.1063/1.366527 (3 pages) | Cited 2 times

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The effect of Zr additions on the microstructure and magnetic properties of melt-spun Sm2Fe(15.5−x)ZrxAl1.5C1.5 alloys has been systematically studied. The additions of Zr to Sm2(Fe,Al,Zr)17C1.5 alloys result in the precipitation of a ZrC compound within intergranular regions. It is found that the Zr addition is helpful in eliminating free iron dendrites, and effective on inhibiting grain growth during annealing. The x-ray diffraction analysis and transmission electron microscopy observation show that annealed ribbons with the Zr addition consist of a multiphase of the 2:17-type carbide, α-Fe and ZrC compound with an average grain size of about 25–35 nm. A remanence of up to 55 emu/g along with a coercivity of up to 11.6 kOe is obtained for Sm2Fe15.3Zr0.2Al1.5C1.5 ribbons annealed at 750 °C for 30 min. It is suggested that the high coercivity and remanence may be attributed to the Zr addition. © 1997 American Institute of Physics.
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75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.30.Mh Solid-phase precipitation
75.50.Bb Fe and its alloys
64.75.-g Phase equilibria
81.40.Gh Other heat and thermomechanical treatments
61.72.-y Defects and impurities in crystals; microstructure

Out-of-plane two-dimensional photonic band structure effects observed in the visible spectrum

A. Rosenberg, R. J. Tonucci, and Eric L. Shirley

J. Appl. Phys. 82, 6354 (1997); http://dx.doi.org/10.1063/1.366534 (3 pages) | Cited 4 times

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We have investigated the visible-region transmission spectra of light propagating in directions which lie outside the array plane of a two-dimensional photonic crystal. These photonic crystals consist of arrays of glass rods inside a glass matrix, with periodicities comparable to the wavelengths of interest. When the propagation direction is within the array plane, attenuations corresponding to the Brillouin-zone boundaries are observed, while for out-of-plane propagation all attenuation features shift to shorter wavelengths. Interesting polarization-dependent effects appear for out-of-plane propagation.
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42.70.Qs Photonic bandgap materials
78.40.Ha Other nonmetallic inorganics

Vertical exchange reaction in (Ga, In)As during migration-enhanced epitaxy

S. Harris and D. L. Dorsey

J. Appl. Phys. 82, 6357 (1997); http://dx.doi.org/10.1063/1.366528 (2 pages)

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We formulate a kinetic description of the vertical exchange reaction in which Ga replaces In during migration enhanced epitaxy of GaAs on InAs. Considering the Ga deposition rate R to be finite rather than infinite, as was done previously, leads to a reinterpretation of experimental results. The kinetic coefficient k as found by comparison with the In concentration profile determined by secondary ion mass spectroscopy is found to be 25% greater at 500 °C, cycle time of 5 s and R = ½ s−1 than that found earlier. The probability of an In atom being replaced by a newly deposited Ga atom, which depends on the details of the Ga deposition schedule, is determined and found to be identical, 98%, for these conditions to that found earlier. © 1997 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
66.30.H- Self-diffusion and ionic conduction in nonmetals
68.55.-a Thin film structure and morphology
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Investigation of L-related indirect transitions in GaAs/GaAlAs multiquantum wells under hydrostatic pressure

N. Dai, D. Huang, X. Q. Liu, Y. M. Mu, W. Lu, and S. C. Shen

J. Appl. Phys. 82, 6359 (1997); http://dx.doi.org/10.1063/1.366529 (3 pages) | Cited 1 time

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Intersubband transitions in GaAs/GaAlAs multiquantum wells (QW) under hydrostatic pressure have been investigated with photomodulated transmission spectroscopy and free-standing QW samples. In addition to the direct transitions associated with the Γ critical points, several L-related transitions between the L conduction band and the Γ valence band of the GaAlAs barriers and between the L conduction subbands and the Γ valence subbands inside the GaAs quantum wells are observed. The distinct L-related spectral features are a clear indication that photomodulated transmission is particularly useful for enhancement of the weak phonon-assisted indirect transitions. © 1997 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
62.50.-p High-pressure effects in solids and liquids
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
68.35.Ja Surface and interface dynamics and vibrations

Influence of Al content on formation of InAlGaAs quantum dots grown by molecular beam epitaxy

O. Baklenov, D. L. Huffaker, A. Anselm, D. G. Deppe, and B. G. Streetman

J. Appl. Phys. 82, 6362 (1997); http://dx.doi.org/10.1063/1.366530 (3 pages) | Cited 24 times

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Data are presented on the dependence of Al content on the formation of InAlGaAs quantum dots grown by strained-layer molecular beam epitaxy. Atomic force microscopy and reflection high-energy electron diffraction patterns show that the addition of Al both slows the formation of the quantum dots in the brief time following layer deposition, and results in smaller dots of higher density. The effects might be qualitatively explained by reduced surface migration of the column III atoms due to the stronger Al bond strength. © 1997 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.50.Lt Crystal binding; cohesive energy
68.35.Fx Diffusion; interface formation
61.66.Bi Elemental solids
61.66.Dk Alloys

Improvement of infrared detector performance in carrier depleted strained layer type II superlattices

C. H. Grein and H. Ehrenreich

J. Appl. Phys. 82, 6365 (1997); http://dx.doi.org/10.1063/1.366531 (3 pages) | Cited 3 times

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The combined effects of suppressing Auger recombination in strained layer superlattices (SL), photon recycling, and the suppression of both Auger and radiative recombination with carrier depletion are calculated quantitatively for a 11 μm 35.9 Å InAs/15.7 Å In0.225Ga0.775Sb and a 3.5 μm 16.7 Å InAs/35 Å In0.25Ga0.75Sb SL operating at temperatures between 200 and 300 K. The results are compared to their HgCdTe counterparts. The SL performance is better in all cases. However, the carrier concentrations required for background limited performance (300 K, 2π field of view), ranging between about 1×1013 and 4×1013 cm−3 at 300 K in both SLs, are seen to be impractically low. The carrier concentration in a 11 μm photon detector yielding equivalent performance to a 300 K thermal detector is about 1014 cm−3. Large performance enhancement using carrier depletion therefore appears impractical even in optimized SLs. © 1997 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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