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12 Aug 1991

Volume 59, Issue 7, pp. 753-878

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Reflectance modulator based on tandem Fabry‐Perot resonators

I. J. Fritz, J. F. Klem, and J. R. Wendt

Appl. Phys. Lett. 59, 753 (1991); http://dx.doi.org/10.1063/1.105332 (3 pages) | Cited 5 times

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We present calculations and data on a novel, electrically tunable reflector structure consisting of tandem Fabry–Perot resonators grown as a single epitaxial device. The device consists of three mirrors (quarter‐wave stacks of AlGaAs and AlAs) separated by two cavities (one an AlGaAs alloy and the other a GaAs/AlGaAs superlattice) on a GaAs substrate. The tandem cavities produce a characteristic double‐dipped reflectance spectrum which can be modulated by tunable electro‐optic effects in the superlattice cavity. Our demonstration device has a modulation depth of ≳10% over a 20 nm bandwidth with <4 V of bias swing.
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85.60.-q Optoelectronic devices
42.79.Hp Optical processors, correlators, and modulators
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Étalon enhancement of nonlinear optical response in Bi1−xSbx

E. R. Youngdale, J. R. Meyer, C. A. Hoffman, F. J. Bartoli, D. L. Partin, C. M. Thrush, and J. P. Heremans

Appl. Phys. Lett. 59, 756 (1991); http://dx.doi.org/10.1063/1.105333 (3 pages) | Cited 5 times

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Measurements of the nondegenerate four‐wave mixing of CO2 laser beams in a Bi1−xSbx film have yielded the largest high‐power third‐order nonlinear susceptibilities ever reported at that wavelength (χ(3)≳6×10−4 esu at P0≳2×105 W/cm2). Furthermore, an étalon effect resulting from the high reflectivity of the Bi1−xSbx films at both the air and substrate interfaces leads to an additional enhancement of the four‐wave signal by as much as a factor of 30. A theoretical model based on optical modulation of the free‐carrier susceptibility gives results which are in excellent agreement with the data.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Bz Metals and metallic alloys
78.20.-e Optical properties of bulk materials and thin films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Operation of five individual diode lasers as a coherent ensemble by fiber coupling into an external cavity

C. J. Corcoran and R. H. Rediker

Appl. Phys. Lett. 59, 759 (1991); http://dx.doi.org/10.1063/1.105334 (3 pages) | Cited 10 times

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Five diode lasers that each have one facet antireflection coated were fiber coupled into an external cavity and operated as a coherent ensemble by the use of a spatial filter placed at the Fourier plane of the cavity. The resulting output was shown to be in a single spectral line with a linewidth less than the instrumental resolution (7.5 MHz) of the Fabry–Perot spectrum analyzer used. The effect of rotating the polarization of the radiation inside one of the fibers is described.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.81.Dp Propagation, scattering, and losses; solitons

Ultraviolet absorption studies on photosensitive germanosilicate preforms and fibers

D. L. Williams, S. T. Davey, R. Kashyap, J. R. Armitage, and B. J. Ainslie

Appl. Phys. Lett. 59, 762 (1991); http://dx.doi.org/10.1063/1.105335 (3 pages) | Cited 7 times

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Detailed measurements of the ultraviolet absorption spectra of germanosilicate preforms, multimode and single‐mode fibers are presented. Significant differences between the spectra of preforms and fibers are revealed and these differences are thought to be caused by the stresses induced during fiber pulling. Measurements are also presented of the changes in the absorption spectra in single‐mode fibers into which reflection gratings have been written using an ultraviolet laser. These results suggest that changes in the absorption between 200 and 600 nm are not responsible for the inferred changes in the refractive index.
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78.40.Ha Other nonmetallic inorganics
42.81.Dp Propagation, scattering, and losses; solitons

Theory of asymmetric dual quantum well lasers

Akira Shimizu and Sotomitsu Ikeda

Appl. Phys. Lett. 59, 765 (1991); http://dx.doi.org/10.1063/1.105336 (3 pages) | Cited 5 times

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A basic theory of asymmetric dual quantum well lasers is presented. The lasers consist of two quantum wells of different energy gaps, which are separated by a high and/or thick barrier layer. The barrier layer blocks carrier transport between the wells so that the rate of the transport becomes comparable to the rate of the radiative recombination. It is shown that this leads to novel phenomena of dual‐wavelength lasing and wavelength switching with increasing injection current, in agreement with recent experimental results.
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42.55.Px Semiconductor lasers; laser diodes
85.60.Jb Light-emitting devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Generation of steerable submillimeter waves from semiconductor surfaces by spatial light modulators

X.‐C. Zhang and D. H. Auston

Appl. Phys. Lett. 59, 768 (1991); http://dx.doi.org/10.1063/1.105337 (3 pages) | Cited 16 times

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We propose a novel optoelectronic technique for optical submillimeter‐wave interaction. By illuminating a spatially periodic pattern of a femtosecond laser beam on a semiconductor surface, optically induced THz electromagnetic beams can be steered by controlling the pattern structure with two degrees of freedom. We also demonstrated the temporal encoding of the radiated electromagnetic wave by the optical intensity spatial distribution.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
06.60.Jn High-speed techniques (microsecond to femtosecond)
85.60.-q Optoelectronic devices

Silicon Mach–Zehnder waveguide interferometers based on the plasma dispersion effect

G. V. Treyz, P. G. May, and Jean‐Marc Halbout

Appl. Phys. Lett. 59, 771 (1991); http://dx.doi.org/10.1063/1.105338 (3 pages) | Cited 36 times

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Silicon Mach–Zehnder waveguide modulators have been fabricated and operation characterized at the wavelength of 1.3 μm. Device operation is based on the free‐carrier‐induced change in the refractive index of silicon. Modulation depths of −4.9 dB and response times τresponse<50 ns have been achieved at λ=1.3 μm for an injected carrier density of 6.5×1017 cm−3.
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85.30.Kk Junction diodes
85.60.-q Optoelectronic devices
85.30.-z Semiconductor devices

Microtransport induced by ultrasonic Lamb waves

R. M. Moroney, R. M. White, and R. T. Howe

Appl. Phys. Lett. 59, 774 (1991); http://dx.doi.org/10.1063/1.105339 (3 pages) | Cited 47 times

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We have observed pumping of water induced by 4.7 MHz ultrasonic Lamb waves traveling in a 4‐μm‐thick composite membrane of silicon nitride and piezoelectric zinc oxide. The observed pumping speed is proportional to the square of the wave amplitude; the speed was 100 μm/s for a rf drive voltage of 8 V and a 6.5 nm wave amplitude. A nonlinear model based on acoustic streaming theory predicts velocities in good agreement with experiment.
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62.65.+k Acoustical properties of solids
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.25.Nm Acoustic streaming

High intensity generation of 9–13 Å x‐rays from BaF2 targets

A. Zigler, P. G. Burkhalter, D. J. Nagel, K. Boyer, T. S. Luk, A. McPherson, J. C. Solem, and C. K. Rhodes

Appl. Phys. Lett. 59, 777 (1991); http://dx.doi.org/10.1063/1.106384 (2 pages) | Cited 15 times

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Studies of the interaction of condensed matter with short pulse (∼ 600 fs) high intensity (∼1017 W/cm2) ultraviolet (248 nm) radiation show that intense spatially compact sources for x‐ray emission in the kilovolt range (0.5–1.0×1015 W/cm2) can be generated from solid targets at close to the maximum volume specific rate allowed.
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79.20.Ds Laser-beam impact phenomena
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
07.85.-m X- and γ-ray instruments

Resonance effects in Raman scattering from polycrystalline diamond films

J. Wagner, C. Wild, and P. Koidl

Appl. Phys. Lett. 59, 779 (1991); http://dx.doi.org/10.1063/1.105340 (3 pages) | Cited 93 times

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We report on a Raman spectroscopic study of polycrystalline diamond films using a wide range of incident photon energies (1.16–4.82 eV). The scattering intensity of amorphous sp2‐bonded carbon is found to vary considerably as a function of the incident photon energy as compared to the strength of the 1332 cm−1 Raman line from sp3‐bonded diamond. There is also a frequency downshift of the apparent peak position for scattering from the sp2‐bonded carbon with decreasing photon energy. Excitation in the infrared range is shown to give a high sensitivity to scattering from amorphous sp2‐bonded carbon whereas ultraviolet excitation enhances the 1332 cm−1 signal from crystalline diamond considerably even in nanocrystalline films.
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78.30.Hv Other nonmetallic inorganics
63.20.-e Phonons in crystal lattices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Molecular beam epitaxy growth of epitaxial barium silicide, barium oxide, and barium titanate on silicon

R. A. McKee, F. J. Walker, J. R. Conner, E. D. Specht, and D. E. Zelmon

Appl. Phys. Lett. 59, 782 (1991); http://dx.doi.org/10.1063/1.105341 (3 pages) | Cited 82 times

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Thin‐film epitaxial structures of BaSi2, BaO, and BaTiO3, have been grown on the (001) face of silicon using ultrahigh vacuum, molecular beam epitaxy (MBE) methods. Source shuttering for the metal species coordinated with a pulsed, or cyclic, oxygen arrival at the growing oxide surfaces significantly improves film quality. The epitaxial growth of BaO is accomplished without silica formation at the BaO/Si interface by stabilizing BaSi2 as a submonolayer template structure. In situ ellipsometric measurements of the indices of refraction for BaO and for BaTiO3 in a BaTiO3/BaO/Si multilayer gave n=1.96 for BaO and n=2.2 for the BaTiO3, within 10% of their bulk values. These values suggest that this structure can be developed as an optical waveguide. BaO is impermeable to silicon for films as thin as 10 nm at temperatures as high as 800 °C, and good epitaxy can be obtained from room temperature to 800 °C. The epitaxy is such that BaTiO3(001)∥BaO(001)∥Si(001) and BaTiO 3〈110〉∥BaO〈100〉∥Si〈100〉.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
74.70.-b Superconducting materials other than cuprates
81.65.-b Surface treatments
42.79.Gn Optical waveguides and couplers

Heteroepitaxy of carbon on copper by high‐temperature ion implantation

S.‐Tong Lee, Samuel Chen, G. Braunstein, X. Feng, I. Bello, and W. M. Lau

Appl. Phys. Lett. 59, 785 (1991); http://dx.doi.org/10.1063/1.105342 (3 pages) | Cited 30 times

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The recently reported carbon‐ion‐implantation‐outdiffusion method [J. F. Prins and H. L. Gaigher, Mater. Res. Soc. Sym. Proc. (to be published, 1991)] of growing epitaxial diamond layers on copper was carefully examined. X‐ray diffraction, Raman scattering, and transmission electron diffraction characterization of films prepared by implanting 200 keV carbon ions into (100), (110), (111), and (210) copper, held at temperatures of 850–1000 °C, showed that the films were invariably highly oriented crystalline graphite. No evidence has been found to support the claim that diamond was formed by this implantation‐outdiffusion method.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Jj Ion and electron beam-assisted deposition; ion plating
61.72.U- Doping and impurity implantation

Assessment of compositional disorder in AlxGa1−xAs superlattices from the analysis of Raman spectra

L. Miglio, C. Molteni, and M. Bernasconi

Appl. Phys. Lett. 59, 788 (1991); http://dx.doi.org/10.1063/1.105343 (3 pages) | Cited 6 times

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We present the calculation of the Raman spectra in backscattering configuration for AlxGa1−xAs (001) superlattices and modulated alloys, based on the bond‐charge‐model dynamics, the average t‐matrix approximation for compositional disorder and the bond polarizability model for the Raman tensor. The features of Raman spectra are shown to reflect the Al concentration profile along the growth axis, hence providing a valuable tool for compositional characterization of superlattices.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.30.Fs III-V and II-VI semiconductors
63.50.-x Vibrational states in disordered systems
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Direct deposition of polycrystalline diamond films on Si(100) without surface pretreatment

R. A. Rudder, G. C. Hudson, J. B. Posthill, R. E. Thomas, and R. J. Markunas

Appl. Phys. Lett. 59, 791 (1991); http://dx.doi.org/10.1063/1.105344 (3 pages) | Cited 47 times

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Dense nucleation of small‐grain polycrystalline diamond films on Si(100) substrates has been accomplished without the use of any surface pretreatment such as abrasive diamond scratching, surface oil treatments, or diamond‐like carbon predeposition. Diamond depositions occurred in a low‐pressure rf plasma‐assisted chemical vapor deposition system using mixtures of CF4 and H2. Films deposited at 5 Torr and 850 °C on as‐received silicon wafers show dense nucleation, well‐defined facets, and crystallites which ranged in size from 500 to 10 000 Å. X‐ray photoelectron spectroscopy and electron energy loss show the films to be diamond with no major impurity and no detectable graphitic component. Raman spectroscopy shows a pronounced 1332 cm−1 line accompanied with a broad band centered about 1500 cm−1.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Jw Organic compounds, polymers
81.10.Bk Growth from vapor

Formation of a thin SiO2 film using synchrotron radiation excited reaction

Taro Ogawa, Isao Ochiai, Kozo Mochiji, Atsushi Hiraiwa, Yuji Takakuwa, Michio Niwano, and Nobuo Miyamoto

Appl. Phys. Lett. 59, 794 (1991); http://dx.doi.org/10.1063/1.105345 (3 pages) | Cited 6 times

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The possibility of altering an oxygen‐adsorbed Si surface to SiO2 using a synchrotron radiation (SR) excited reaction is evidenced for the first time. Oxygen gas is adsorbed on a clean Si surface, and soft x‐ray is irradiated on it by SR. As a result, H partly terminated on the oxygen‐adsorbed Si surface is eliminated and the surface becomes more SiO2‐like. This is proved by x‐ray photoelectron spectroscopy (XPS) analysis. Photostimulated desorption (PSD) of H+ ions, which are emitted from the surface, is also detected during SR irradiation. The Si—O bond formation model followed by H+ PSD explains this oxidation.
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81.65.-b Surface treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.80.-x Physical radiation effects, radiation damage

Heavily phosphorus‐doped epitaxial Si deposited by low‐temperature plasma‐enhanced chemical vapor deposition

K. Baert, J. Vanhellemont, W. Vandervorst, J. Nijs, and M. Konagai

Appl. Phys. Lett. 59, 797 (1991); http://dx.doi.org/10.1063/1.105346 (3 pages) | Cited 2 times

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Heavily P‐doped Si layers have been grown at very low temperature (<600 °C) by rf plasma chemical vapor deposition. Films grown by vapor phase epitaxy (VPE) or solid phase epitaxy (SPE) are compared. By VPE growth, fully electrically activated films with a P concentration in excess of 1021 cm−3 and steep doping profiles (≤4 nm/dec) were obtained. SPE films are not fully activated and an anomalously fast P diffusion is observed during the crystallization at 600 °C. On the other hand, the Hall mobility of VPE films is significantly lower than that of SPE films.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.50.Dn Low-field transport and mobility; piezoresistance

Photoluminescence lifetime of AlAs/GaAs disordered superlattices

Makoto Kasu, Teiji Yamamoto, Susumu Noda, and Akio Sasaki

Appl. Phys. Lett. 59, 800 (1991); http://dx.doi.org/10.1063/1.105347 (3 pages) | Cited 13 times

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Time‐resolved photoluminescences (PL) of AlxGa1−xAs (0≤x≤0.5) bulk alloys, AlAs/GaAs ordered superlattices, and AlAs/GaAs disordered superlattices are measured at 77 K and compared. The PL lifetimes of the AlAs/GaAs disordered superlattices were always shorter than those of the Al0.5Ga0.5As bulk alloy and the AlAs/GaAs ordered superlattices with indirect band gaps. These shorter PL lifetimes of the disordered superlattices suggest a relaxation of the momentum conservation during radiative recombination by intentional disordering.
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78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
61.43.Fs Glasses
61.43.-j Disordered solids
61.44.Br Quasicrystals
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Tunneling between totally quantized levels in GaAs/AlGaAs asymmetric triple‐barrier heterostructures in high magnetic fields

H. Asahi, M. Tewordt, R. T. Syme, M. J. Kelly, V. J. Law, D. R. Mace, J. E. F. Frost, D. A. Ritchie, G. A. C. Jones, and M. Pepper

Appl. Phys. Lett. 59, 803 (1991); http://dx.doi.org/10.1063/1.105348 (3 pages) | Cited 10 times

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Electron transport is studied in GaAs/AlGaAs asymmetric triple‐barrier resonant tunneling structures in a high magnetic field perpendicular to the interfaces. Besides the resonance peaks arising from tunneling between two quantum wells, a series of fine structure is observed in the valley region of the current‐voltage characteristics, which is attributed to electron transitions between well defined totally quantized levels (Landau levels) in the two wells, together with the emission of a longitudinal optical phonon. In the voltage region of the main current peak, any structures which shift with magnetic field are not observed, suggesting that the tunneling in this bias region is mainly determined by Δn=0 elastic transitions.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Gk Tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.Fz Weak or Anderson localization

Direct type II–indirect type I conversion of InP/GaAs/InP strained quantum wells induced by hydrostatic pressure

M. Gerling, M.‐E. Pistol, L. Samuelson, W. Seifert, J.‐O. Fornell, and L. Ledebo

Appl. Phys. Lett. 59, 806 (1991); http://dx.doi.org/10.1063/1.105349 (3 pages) | Cited 10 times

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Photoluminescence from thin strained layers of GaAs grown on InP has been studied under hydrostatic pressure. The structures are type II at atmospheric pressure. At higher pressures the structures change to type I with the lowest conduction band edge in the strained GaAs layer being the X minimum. This transformation is characterized by a drastic change in the pressure derivative of the emission energy and a rapid disappearance of the photoluminescence intensity at slightly higher pressures. A hydrostatic pressure derivative of less than one meV/kbar is measured for the valence band offset.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Gettering thresholds for transition metals by oxygen‐related defects in silicon

R. J. Falster, G. R. Fisher, and G. Ferrero

Appl. Phys. Lett. 59, 809 (1991); http://dx.doi.org/10.1063/1.105350 (2 pages) | Cited 24 times

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This letter reports a qualitative study of the gettering of technologically important transition metal contaminants by a wide variety of distributions of oxygen precipitates and related defects in silicon. Various metals were diffused into specially prepared silicon wafers containing densities of oxygen precipitates ranging between 105 and 2×1010 cm−3. The precipitates were of a variety of sizes both with and without punched‐out dislocation networks and associated stacking faults. Following previous work and using the Haze Test to monitor gettering activity, a threshold in precipitate density has been determined for the complete gettering of Cu and Ni (about 1×105 and 3×106 cm−3, respectively). No influence of precipitate size (above an as yet to be determined minimum) or of the presence of punched‐out dislocations or stacking faults could be determined for these two metals, the fastest diffusing of the 3d group. Comments on the gettering of Fe are made.
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61.72.jd Vacancies
61.72.jj Interstitials
81.65.-b Surface treatments

Totally relaxed GexSi1−x layers with low threading dislocation densities grown on Si substrates

E. A. Fitzgerald, Y.‐H. Xie, M. L. Green, D. Brasen, A. R. Kortan, J. Michel, Y.‐J Mii, and B. E. Weir

Appl. Phys. Lett. 59, 811 (1991); http://dx.doi.org/10.1063/1.105351 (3 pages) | Cited 184 times

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We have grown compositionally graded GexSi1−x layers on Si at 900 °C with both molecular beam epitaxy and rapid thermal chemical vapor deposition techniques. Triple‐crystal x‐ray diffraction reveals that for 0.10<x<0.53, the layers are totally relaxed. GexSi1−x cap layers grown on these graded layers are threading‐dislocation‐free when examined with conventional plan‐view and cross‐sectional transmission electron microscopy. Electron beam induced current images were used to count the low threading dislocation densities, which were 4×105±5×104 cm−2 and 3×106±2×106 cm−2 Eq. 2×106 cm−2 for x=0.23 and x=0.50, respectively. Photoluminescence spectra from the cap layers are identical to photoluminescence from bulk GexSi1−x.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination

Characterization of Si/SiGe strained‐layer superlattices grown by ultrahigh vacuum/chemical vapor deposition technique

P. J. Wang, M. S. Goorsky, B. S. Meyerson, F. K. LeGoues, and M. J. Tejwani

Appl. Phys. Lett. 59, 814 (1991); http://dx.doi.org/10.1063/1.105352 (3 pages) | Cited 20 times

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We employed high‐resolution double‐crystal x‐ray diffraction and transmission electron microscopy to characterize Si/Si1−xGex strained‐layer superlattices grown by ultrahigh vacuum/chemical vapor deposition technique. Rocking curve analyses showed uniform layer thickness and alloy composition across superlattices of 10 periods. Extensive dynamical x‐ray simulation indicated that heterointerfaces were abrupt and the Si layer was found to be 206±5 Å thick and SiGe layer was 8.25% Ge and 185±5 Å thick. The thickness values were confirmed by the cross‐sectional transmission electron microscopy. A tilt angle of 26 arcsec was observed between the (001) planes in the superlattice and the substrate, resulting from steps on the surface of 〈100〉 2° off oriented Si substrates.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Low‐temperature growth of GexSi1−x/Si heterostructures on Si(100) by remote plasma‐enhanced chemical vapor deposition

D. Kinosky, R. Qian, J. Irby, T. Hsu, B. Anthony, S. Banerjee, A. Tasch, C. Magee, and C. L. Grove

Appl. Phys. Lett. 59, 817 (1991); http://dx.doi.org/10.1063/1.105272 (3 pages) | Cited 8 times

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Low‐temperature growth processes are needed in order to fully exploit the potential of GexSi1−x/Si heterostructures. Remote plasma‐enhanced chemical vapor deposition has been successful for silicon homoepitaxy at substrate temperatures as low as 150 °C. We report the growth of GexSi1−x/Si heterostructures with values of x between 0.07 and 0.73, and at substrate temperatures of 305 and 450 °C. The films grown at 450 °C have excellent crystallinity, low defect densities, and very abrupt interfaces, while films grown at 305 °C have degraded crystallinity.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.Dv Composition, segregation; defects and impurities

Modulated beam epitaxial growth of high quality GaAs single quantum wells at low temperature

K. F. Longenbach, S. Xin, C. Schwartz, Y. Jiang, and W. I. Wang

Appl. Phys. Lett. 59, 820 (1991); http://dx.doi.org/10.1063/1.105273 (3 pages) | Cited 3 times

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High quality AlGaAs/GaAs quantum wells and low‐threshold current density lasers (<1 kA/cm2) have been successfully grown at low temperatures (500 °C) by a modulated beam epitaxy process in which the group III flux is held constant while the As flux is periodically shut off to produce a metal‐rich surface. The improved quality of these low‐temperature‐grown quantum structures is attributed to both a smoothing of the growth front and a reduction of excess As during the modulated beam epitaxy process. The high growth rates and less frequent shutter operation of this technique make it more practical than migration‐enhanced epitaxy or atomic layer epitaxy for low‐temperature growth.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Giant anisotropies in the dielectric properties of quasi‐epitaxial crystalline organic semiconductor thin films

D. Y. Zang, F. F. So, and S. R. Forrest

Appl. Phys. Lett. 59, 823 (1991); http://dx.doi.org/10.1063/1.105274 (3 pages) | Cited 38 times

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We have measured the indices of refraction and dielectric constants along different directions in thin films of the crystalline organic semiconductor compound 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA). The films were deposited via organic molecular beam deposition, resulting in single‐crystalline, ‘‘quasi‐epitaxial’’ films. Due to inherent asymmetries in the molecular crystal structure, film ordering results in giant anisotropies in their dielectric properties. For example, the index of refraction measured at a wavelength of λ=1.064 μm in the direction perpendicular to the substrate plane is n⊥ = 1.36 ± 0.01, whereas parallel to the plane, n∥=2.017±0.005, resulting in an index difference of Δn=0.66. Furthermore, the low‐frequency dielectric constant of the films is ϵ⊥ = 1.9 ± 0.1 and ϵ∥ = 4.5 ± 0.2. To our knowledge, these are the largest anisotropies ever measured for thin films. We discuss a guided wave polarization‐selective device which takes advantage of the large dielectric anisotropies characteristic of the thin organic films.
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77.55.-g Dielectric thin films
72.80.Le Polymers; organic compounds (including organic semiconductors)
78.66.Qn Polymers; organic compounds
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