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20 Jul 1998

Volume 73, Issue 3, pp. 279-419

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Electric field controlled dynamic holograms on polarization gratings in a ferroelectric liquid crystal

B. Saad, L. Dinescu, R. P. Lemieux, and T. V. Galstyan

Appl. Phys. Lett. 73, 279 (1998); http://dx.doi.org/10.1063/1.121794 (3 pages) | Cited 1 time

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The irradiation at 514.5 nm of a ferroelectric liquid crystal (FLC) film doped with a photochromic chiral thioindigo dye causes a change in the birefringence of the FLC film under a constant dc voltage. This birefringence photomodulation is used to create electric field controlled dynamic holograms. The diffraction efficiency of the hologram is found to depend resonantly on the applied dc voltage. The unwinding of the FLC helical structure into a planar alignment as a result of a photoinduced increase of the spontaneous polarization (Ps) and of the corresponding dielectric torque is thought to be at the origin of the observed birefringence photomodulation. © 1998 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
42.79.Hp Optical processors, correlators, and modulators
78.20.Fm Birefringence
77.22.Ej Polarization and depolarization

Multiple-wavelength vertical-cavity laser arrays based on postgrowth lateral-vertical oxidation of AlGaAs

A. Fiore, Y. A. Akulova, J. Ko, E. R. Hegblom, and L. A. Coldren

Appl. Phys. Lett. 73, 282 (1998); http://dx.doi.org/10.1063/1.121795 (3 pages) | Cited 7 times

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We demonstrate that combined lateral-vertical oxidation of AlGaAs can be used to change the resonant wavelength of an optical cavity after the single epitaxial growth. A multiple-wavelength array of vertical-cavity surface-emitting lasers with a 48 nm wavelength span has been realized using this technique. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.65.Mq Oxidation
81.05.Ea III-V semiconductors

Experimental investigation of physical mechanisms underlying lateral current injection laser operation

Edward H. Sargent, J. M. Xu, Catherine Caneau, and ChungEn Zah

Appl. Phys. Lett. 73, 285 (1998); http://dx.doi.org/10.1063/1.121796 (3 pages) | Cited 5 times

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By comparing theoretical prediction with experimental performance, we gain insight into the physical operation of lateral current injection lasers. By studying the temperature dependence of lasing stimulated efficiency, we demonstrate the influence of lateral heterobarriers (achieved in this experiment by quantum well intermixing) on the confinement of carriers to the active region. By comparing the evolution of threshold current with temperature for devices of differing contact separations with a self-consistent model of lateral current injection laser operation, we reveal the importance of the interplay between the lateral material gain profile and the optical mode. Understanding these mechanisms, unique to the lateral injection family of lasers, is key to realizing the tremendous potential of this class of lasers to enable optoelectronic integration and novel functional devices. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
61.72.uj III-V and II-VI semiconductors

Large third-order optical nonlinearity of nanocluster-doped glass formed by ion implantation of copper and nickel in silica

M. Falconieri, G. Salvetti, E. Cattaruzza, F. Gonella, G. Mattei, P. Mazzoldi, M. Piovesan, G. Battaglin, and R. Polloni

Appl. Phys. Lett. 73, 288 (1998); http://dx.doi.org/10.1063/1.121797 (3 pages) | Cited 41 times

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Composite glasses containing different metal nanoclusters were obtained by implanting copper, nickel, or copper+nickel ions in SiO2 glass. The nonlinear refractive index of the composites was determined by the Z-scan method at a wavelength of 770 nm and with a laser pulse duration of 130 fs. Values of n2 up to 0.68 cm2 gW−1 were measured in the case of the Cu+Ni implanted sample. © 1998 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.-k Nonlinear optics
61.43.Fs Glasses
61.82.Ms Insulators
61.72.up Other materials

Backscattering from a tethered bead as a probe of DNA flexibility

G. V. Shivashankar, G. Stolovitzky, and A. Libchaber

Appl. Phys. Lett. 73, 291 (1998); http://dx.doi.org/10.1063/1.121798 (3 pages) | Cited 18 times

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Using an optical tweezer, we trap a DNA polymer tethered bead. Collinear with the tweezer, a red laser light beam probes the bead fluctuations through backscattered radiation measurement. Those fluctuations give information on the flexibility of DNA and can be used to probe the interaction of proteins with DNA. We use this approach to directly monitor the extension of a single DNA polymer beyond its contour length induced by the polymerization of Rec A protein on DNA. © 1998 American Institute of Physics.
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87.15.H- Dynamics of biomolecules

Fabrication of patterned electroluminescent polymers that emit in geometries with feature sizes into the submicron range

John A. Rogers, Zhenan Bao, and Lisa Dhar

Appl. Phys. Lett. 73, 294 (1998); http://dx.doi.org/10.1063/1.121799 (3 pages) | Cited 29 times

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This letter describes the fabrication of structured polymer light-emitting devices (LEDs) that produce patterns of light with feature sizes as small as ∼0.8 μm. Solvent-assisted micromolding of a film of a precursor to poly(p-phenylene vinylene) (PPV), produces variations in its thickness that replicate the relief on the mold. Thermal conversion of this precursor produces a film of PPV with the same surface relief. LEDs formed with the structured PPV emit preferentially in the thin regions of the film. Devices fabricated in this manner may be important for constructing plastic visual displays, and could eventually lead to new subwavelength sources of light suitable for applications in near field optics. © 1998 American Institute of Physics.  
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78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds

Carrier relaxation in an InP/InGaAs nonlinear Bragg reflector

Kensuke Ogawa, Yasuhiro Matsui, Taro Itatani, and Kiyoshi Ouchi

Appl. Phys. Lett. 73, 297 (1998); http://dx.doi.org/10.1063/1.121814 (3 pages) | Cited 2 times

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Carrier dynamics in absorption saturation in an InP/InGaAs nonlinear Bragg reflector is studied by transient reflectance measurements. An ultrafast process of the relaxation time shorter than 100 fs is observed and identified as carrier-carrier scattering. Such an ultrafast process is not observed in the transient reflectance of bulk InGaAs measured with the same photoexcitation level. The difference between these transient reflectance characteristics indicates an enhancement of carrier-carrier scattering in the nonlinear Bragg reflector. © 1998 American Institute of Physics.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Px Semiconductor lasers; laser diodes

Energy level schemes for far-infrared quantum well lasers

I. Lyubomirsky and Q. Hu

Appl. Phys. Lett. 73, 300 (1998); http://dx.doi.org/10.1063/1.121815 (3 pages) | Cited 10 times

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We analyze the physics of three-level and four-level systems for optically pumped far-infrared quantum well lasers. The higher complexity of the four-level system offers a great advantage because it gives more flexibility to design the dipole matrix elements and phonon scattering rates to enhance both the gain and emission efficiency. We propose a four-level scheme that is superior in gain and emission efficiency by an order of magnitude over previous designs. © 1998 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes

Electro-optic beam deflector using epitaxial Pb(Zr,Ti)O3 waveguides on Nb-doped SrTiO3

K. Nashimoto, S. Nakamura, H. Moriyama, M. Watanabe, and E. Osakabe

Appl. Phys. Lett. 73, 303 (1998); http://dx.doi.org/10.1063/1.121816 (3 pages) | Cited 20 times

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Pb(Zr,Ti)O3 (PZT) thin-film optical waveguides were grown on Nb-doped SrTiO3 substrates by solid-phase epitaxy to fabricate an electrode/waveguide/conductor structure. The propagation loss was relatively large for a PZT waveguide on a lightly Nb-doped SrTiO3 as compared with the propagation loss of 4 dB/cm for the structure using undoped SrTiO3. An electro-optic beam deflection device was fabricated by preparing a prism electrode on the surface of the PZT waveguide on a lightly Nb-doped SrTiO3 substrate. Efficient deflection of the coupled laser beam in the PZT waveguide as large as 11 mrad was observed by applying 35 V between the prism electrode and the substrate. © 1998 American Institute of Physics.
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42.79.Fm Reflectors, beam splitters, and deflectors
81.15.Np Solid phase epitaxy; growth from solid phases
42.82.Et Waveguides, couplers, and arrays
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
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Plasma–wall sheath in a positive biased duct of the vacuum arc magnetic macroparticle filter

M. Keidar and I. I. Beilis

Appl. Phys. Lett. 73, 306 (1998); http://dx.doi.org/10.1063/1.121817 (3 pages) | Cited 11 times

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A model of the electrical sheath between plasma and a positively biased wall has been developed for the case of the magnetic field perfectly parallel to the wall. The magnetized sheath and relatively large positive wall potential with respect to the plasma are considered, so that only electron current is present in the sheath. We show that the sheath thickness increases linearly with duct current density. There is good quantitative agreement between the calculated and experimental current–voltage duct characteristics. © 1998 American Institute of Physics.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
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Electron trapping process in ferroelectric lead–zirconate–titanate thin-film capacitors

Hong-ming Chen and Joseph Ya-min Lee

Appl. Phys. Lett. 73, 309 (1998); http://dx.doi.org/10.1063/1.121818 (3 pages) | Cited 8 times

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The effects of constant voltage stress on ferroelectric lead–zirconate–titanate (PZT) thin-film capacitors have been studied. Two stress effects are observed in the PZT capacitance–voltage (C–V) characteristics. The first is that the capacitance is reduced, and the second is a voltage shift of the C–V curve. These effects are found to depend on the stress electric field and the injected charge fluence. A correlation between the stress effects and the electron trapping inside the films is established. The injected charge fluence can be calculated from the leakage current. The trapping efficiency, electron capture cross section, and the trap density are obtained from the measured injected charge influence and the C–V voltage shift. The calculated value of the electron capture cross-section σT is 1.89×10−19 cm2 and the neutral electron trap density NT is 1.20×1013 cm−2. © 1998 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Enhanced thermal stability of C49 TiSi2 in the presence of aluminum

S.-L. Zhang, F. M. d’Heurle, C. Lavoie, C. Cabral, and J. M. E. Harper

Appl. Phys. Lett. 73, 312 (1998); http://dx.doi.org/10.1063/1.121853 (3 pages) | Cited 14 times

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The introduction of a thin layer of Al at the interface between Ti films and Si substrates enhances the formation of C49 TiSi2 and retards the transition from C49 to C54. An Al interlayer, 0.64 nm thick, reduces the time required to form C49 TiSi2 isothermally at 500 °C from 14 to 7 min. The C49–C54 transformation temperature is increased from 767 to 853 °C, when heating the samples at a constant ramp rate of 3 K/s. Most of the Al is found toward the interface between a Ti-rich silicide at the surface and TiSi2, rather than at the interface between TiSi2 and the Si substrate. The grain size of the C49 TiSi2 formed in the presence of Al is about five times smaller than that formed on a control sample with pure Ti, indicating that the increased density of grain boundaries in C49 TiSi2 in the presence of Al does not help the C49–C54 transformation. Therefore, the improved thermal stability of C49 TiSi2 is likely to be caused by other factors such as a reduced electron/atom ratio when replacing Si with Al in the disilicide. © 1998 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.60.Dv Thermal stability; thermal effects
61.72.Mm Grain and twin boundaries
66.30.Ny Chemical interdiffusion; diffusion barriers
73.40.Ns Metal-nonmetal contacts
64.70.K- Solid-solid transitions

The complex formation of ripples during depth profiling of Si with low energy, grazing oxygen beams

Z. X. Jiang and P. F. A. Alkemade

Appl. Phys. Lett. 73, 315 (1998); http://dx.doi.org/10.1063/1.121819 (3 pages) | Cited 45 times

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Surface roughening of Si under low-energy (0.5–2.0 keV) O2+ bombardment at incidence angles between 45° and 80° has been studied. Surface roughening occurred already at an erosion depth of only a few tens of nanometers. It was found that there were distinctly two angular ranges for sub-keV beams where roughening was strong, and two ranges where it was insignificant. The transition between the different ranges can be very sharp. These observations cannot be explained by the current models for surface roughening. Instead, it is believed that it is the combined sputtering rate dependence on both the surface topography and the oxygen content that determines the occurrence of roughening. © 1998 American Institute of Physics.
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81.05.Cy Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Vacancy defects in (Pb, La)(Zr, Ti)O3 capacitors observed by positron annihilation

D. J. Keeble, B. Nielsen, A. Krishnan, K. G. Lynn, S. Madhukar, R. Ramesh, and C. F. Young

Appl. Phys. Lett. 73, 318 (1998); http://dx.doi.org/10.1063/1.121820 (3 pages) | Cited 32 times

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A study of vacancy-related defects in ferroelectric capacitors was performed using a variable energy positron beam (VEPB). Heterostructures of (Pb0.9La0.1)(Zr0.2Ti0.8)O3 (PLZT) ferroelectric with La0.5Sr0.5CoO3 (LSCO) electrodes were deposited by pulsed laser deposition and the effects of oxygen deficiency studied using structures grown with 760 and 1×10−5 Torr oxygen. The VEPB depth profile showed an increase in vacancy-related defects with increased oxygen nonstoichiometry. A study of LSCO and PLZT thin films was also performed. The formation of vacancy clusters in the LSCO top electrode, and VPb−VO defects in the PLZT layer, with increased oxygen deficiency is inferred. © 1998 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
84.32.Tt Capacitors
81.15.Fg Pulsed laser ablation deposition
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
61.66.Bi Elemental solids
61.66.Dk Alloys
61.72.J- Point defects and defect clusters
78.70.Bj Positron annihilation

Conduction of heat in inhomogeneous solids

M. D. Dramićanin, Z. D. Ristovski, V. Djoković, and S. Galović

Appl. Phys. Lett. 73, 321 (1998); http://dx.doi.org/10.1063/1.121821 (3 pages) | Cited 11 times

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In this letter we present a method for calculation of linear heat flow in inhomogeneous solids. The method is based on the evaluation of transfer matrices for each layer in a multilayered structure from the Laplace transformation of the partial differential equation of heat conduction. The multilayered structure is then described by a matrix obtained as a chain of products of individual layer transfer matrices and corresponding boundary thermal resistivity matrices. The analytic expression for the nth power of the multilayered transfer matrix is found, describing a periodic multilayered structure composed of n equal multilayered structures. The application of the presented method for calculation of photothermal signals is also shown. Dispersion relation for the thermal waves in inhomogeneous solids is obtained from the matrix elements of the transfer matrix. Finally, from the dispersion relation explicit expressions for the effective values of thermal diffusivity and conductivity of both the discontinuously and continuously inhomogeneous solids are evaluated. © 1998 American Institute of Physics.
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44.30.+v Heat flow in porous media
05.70.Ce Thermodynamic functions and equations of state

Oxidation resistance of tantalum–ruthenium dioxide diffusion barrier for memory capacitor bottom electrodes

Dong-Soo Yoon, Hong Koo Baik, Sung-Man Lee, Chang-Soo Park, and Sang-In Lee

Appl. Phys. Lett. 73, 324 (1998); http://dx.doi.org/10.1063/1.121822 (3 pages) | Cited 17 times

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The effect of the RuO2 addition into a Ta film on the oxidation resistance of a diffusion barrier for the Ta+RuO2/Si system was investigated. The Ta+RuO2/Si system was sustained up to 800 °C without an increase in resistivity, while the Ta/Si structure completely degraded after annealing at 450 °C. The Ta+RuO2 diffusion barrier showed an amorphous microstructure for an as-deposited state and formed a conductive RuO2 phase after annealing. Ta was sufficiently bound to oxygen of RuO2 for an as-deposited state, but RuO2 was divided into Ru and Ru–O binding states. Ta–O bonds showed a little change compared to the as-deposited state with increasing annealing temperature, whereas Ru–O bonds significantly increased. Therefore, the Ta layer deposited by the RuO2 addition effectively prevented the indiffusion of oxygen up to 800 °C and its oxidation resistance was superior to those of polycrystalline nitride (TiN, TaN) and ternary amorphous (TaSiN) barriers reported by others. © 1998 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
81.65.Mq Oxidation
81.65.Kn Corrosion protection
84.32.Tt Capacitors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Cg Contact resistance, contact potential
81.40.Gh Other heat and thermomechanical treatments

Charge transport, optical transparency, microstructure, and processing relationships in transparent conductive indium–zinc oxide films grown by low-pressure metal-organic chemical vapor deposition

Anchuan Wang, Jiyan Dai, Jizhi Cheng, Michael P. Chudzik, Tobin J. Marks, Robert P. H. Chang, and Carl R. Kannewurf

Appl. Phys. Lett. 73, 327 (1998); http://dx.doi.org/10.1063/1.121823 (3 pages) | Cited 44 times

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Indium–zinc oxide films (ZnxInyOx+1.5y), with x/y = 0.08–12.0, are grown by low-pressure metal-organic chemical vapor deposition using the volatile metal–organic precursors In(TMHD)3 and Zn(TMHD)2 (TMHD = 2,2,6,6–tetramethyl–3,5–heptanedionato). Films are smooth (rms roughness = 40–50 Å) with complex microstructures which vary with composition. The highest conductivity is found at x/y = 0.33, with σ = 1000 S/cm (n-type; carrier density=3.7×1020 cm3; mobility=18.6 cm2/V s; dσ/dT<0). The optical transmission window of such films is broader than Sn-doped In2O3, and the absolute transparency rivals or exceeds that of the most transparent conductive oxides. X-ray diffraction, high resolution transmission electron microscopy, microdiffraction, and high resolution energy dispersive X-ray analysis show that such films are composed of a layered ZnkIn2O3+k phase precipitated in a cubic In2O3:Zn matrix. © 1998 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
72.80.Jc Other crystalline inorganic semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Hd Other semiconductors
78.66.Li Other semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
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Annealing cycle dependence of preferential arsenic precipitation in AlGaAs/GaAs layers

C.-Y. Hung, J. S. Harris, A. F. Marshall, and R. A. Kiehl

Appl. Phys. Lett. 73, 330 (1998); http://dx.doi.org/10.1063/1.121824 (3 pages) | Cited 3 times

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The spatial distribution of arsenic precipitates formed in a nonstoichiometric AlGaAs/GaAs quantum well is examined for different annealing temperatures and times. Preferential precipitation in the GaAs layer of samples annealed at 600 °C is found to be much weaker than in samples annealed at 850 °C because of the reduced diffusion of arsenic at lower temperatures. Nevertheless, it is demonstrated that strong preferential precipitation is possible at low annealing temperatures, provided that the annealing time is sufficiently long. Limitations to the preferential precipitation process imposed by interface mixing and the decrease in gallium vacancy concentration during annealing are also examined. © 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Selective-area and lateral epitaxial overgrowth of III–N materials by metal organic chemical vapor deposition

J. Park, P. A. Grudowski, C. J. Eiting, and R. D. Dupuis

Appl. Phys. Lett. 73, 333 (1998); http://dx.doi.org/10.1063/1.121825 (3 pages) | Cited 30 times

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We describe the characteristics of single-crystal GaN regions obtained by selective-area and subsequent lateral epitaxial overgrowth using metal organic chemical vapor deposition. Under certain deposition conditions, the surface kinetics of the metal organic chemical vapor deposition process results in lateral growth of single-crystal GaN over the masked region. The lateral-to-vertical relative growth rate depends upon the orientation of stripe openings, the ratio of the “open” stripe width to the “masked” stripe width, and the growth conditions (e.g., temperature and V/III ratio). The specific orientations of the growth facets on the sidewalls of the laterally growing stripes are also dependent upon the growth conditions. The cathodoluminescence intensity of the GaN films indicate that improved materials are grown over the oxide mask. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors

Study of microstructure of high stability hydrogenated amorphous silicon films by Raman scattering and infrared absorption spectroscopy

Shuran Sheng, Xianbo Liao, Guanglin Kong, and Hexiang Han

Appl. Phys. Lett. 73, 336 (1998); http://dx.doi.org/10.1063/1.121826 (3 pages) | Cited 13 times

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The microstructure, hydrogen bonding configurations and hydrogen content of high quality and stable hydrogenated amorphous silicon (a-Si:H) films prepared by a simple “uninterrupted growth/annealing” plasma enhanced chemical vapor deposition technique have been investigated by Raman scattering and infrared absorption spectroscopy. The high stability a-Si:H films contain small amounts of a microcrystalline phase and not less hydrogen (10–16 at. %), particularly, the clustered phase hydrogen. Besides, the hydrogen distribution is very inhomogeneous. Some of these results are substantially distinct from those of conventional device-quality a-Si:H film or stable a-Si:H films prepared by the other techniques examined to date. The stability of a-Si:H films appears to have no direct correlation with the hydrogen content or the clustered phase hydrogen concentration. The ideal a-Si:H network with high stability and low defect density is perhaps not homogeneous. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Jg Amorphous semiconductors; glasses
78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.05.Cy Elemental semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
81.05.Gc Amorphous semiconductors
78.30.Am Elemental semiconductors and insulators

Effects of piezoelectric field on defect formation, charge transfer, and electron transport at GaN/AlxGa1−xN interfaces

L. Hsu and W. Walukiewicz

Appl. Phys. Lett. 73, 339 (1998); http://dx.doi.org/10.1063/1.121827 (3 pages) | Cited 30 times

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We have calculated the donor defect profiles in pseudomorphic AlxGa1−xN layers grown on GaN, taking into account the effects of the strain polarization field on the defect formation energy. Under certain conditions, the defect concentration may be enhanced by more than one order of magnitude. These large concentrations combined with the band bending effects of the piezoelectric field makes the charge transfer from the AlxGa1−xN barrier to the GaN well extremely efficient, resulting in a two-dimensional electron gas of very high density and low mobility. These results explain recent experimental observations of large electron densities found in nominally undoped GaN/AlGaN heterostructures. © 1998 American Institute of Physics.
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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
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Bi4Ti3O12 ferroelectric thin film ultraviolet detectors

L. Pintilie, M. Alexe, A. Pignolet, and D. Hesse

Appl. Phys. Lett. 73, 342 (1998); http://dx.doi.org/10.1063/1.121828 (3 pages) | Cited 25 times

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Bi4Ti3O12 (BiT) ferroelectric thin films were used as photoconductive or photovoltaic ultraviolet detectors. The maximum of the spectral distribution lies around 370 or 390 nm, depending on whether the incident light is continuous or modulated. The maximum current responsivity obtained for the films annealed at 700 °C is about 0.01 A/W. The specific detectivity is 5.5×108 cm W−1 Hz1/2 at a modulation frequency of 20 Hz. The frequency characteristics of the photovoltaic signal measured in modulated light suggests a 1/f frequency dependence of this signal. © 1998 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Pw Imaging detectors and sensors
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Optical monitoring of InP monolayer growth rates

P. J. Parbrook, K. B. Ozanyan, M. Hopkinson, C. R. Whitehouse, Z. Sobiesierski, and D. I. Westwood

Appl. Phys. Lett. 73, 345 (1998); http://dx.doi.org/10.1063/1.121829 (3 pages) | Cited 1 time

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Reflection anisotropy (RA) spectroscopy has been used to examine the in vacuo (001) surface of InP before and during growth by molecular beam epitaxy (MBE). The dominant effect on the RA signal occurring the initiation of growth is the change in the surface V/III ratio, caused by the exposure of the surface to the incident indium flux. During MBE growth of InP under commonly used conditions, RA oscillations are clearly observed. These oscillations have been confirmed to correspond to the growth of InP monolayers. The oscillations are tentatively ascribed to the variation in P coverage during the growth of each monolayer of material. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.-e Optical properties of bulk materials and thin films

Heteroepitaxy of ZnO on GaN and its implications for fabrication of hybrid optoelectronic devices

R. D. Vispute, V. Talyansky, S. Choopun, R. P. Sharma, T. Venkatesan, M. He, X. Tang, J. B. Halpern, M. G. Spencer, Y. X. Li, L. G. Salamanca-Riba, A. A. Iliadis, and K. A. Jones

Appl. Phys. Lett. 73, 348 (1998); http://dx.doi.org/10.1063/1.121830 (3 pages) | Cited 166 times

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ZnO thin films have been grown heteroepitaxially on epi-GaN/sapphire (0001) substrates. Rutherford backscattering spectroscopy, ion channeling, and high resolution transmission electron microscopy studies revealed high-quality epitaxial growth of ZnO on GaN with an atomically sharp interface. The x-ray diffraction and ion channeling measurements indicate near perfect alignment of the ZnO epilayers on GaN as compared to those grown directly on sapphire (0001). Low-temperature cathodoluminescence studies also indicate high optical quality of these films presumably due to the close lattice match and stacking order between ZnO and GaN. Lattice-matched epitaxy and good luminescence properties of ZnO/GaN heterostructures are thus promising for ultraviolet lasers. These heterostructures demonstrate the feasibility of integrating hybrid ZnO/GaN optoelectronic devices. © 1998 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
68.55.-a Thin film structure and morphology

Electrical characterization of alternating-current thin-film electroluminescent devices

A. N. Krasnov, R. C. Bajcar, and P. G. Hofstra

Appl. Phys. Lett. 73, 351 (1998); http://dx.doi.org/10.1063/1.121831 (3 pages) | Cited 4 times

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We suggest a formalism built on the analogy between the pressure-volume (P–math) diagram of a gas system and the charge-voltage (Q–V) characteristics of the alternating-current thin-film electroluminescent (ACTFEL) device. The formalism extends the understanding of the processes in ACTFEL devices and the complete characterization of their internal parameters based on the Q–V diagram.© 1998 American Institute of Physics.
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85.60.Jb Light-emitting devices
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