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24 Apr 1995

Volume 66, Issue 17, pp. 2153-2297

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Resonant modulation of single contact monolithic semiconductor lasers at millimeter wave frequencies

David M. Cutrer, John B. Georges, Ta‐Chung Wu, Bin Wu, and Kam Y. Lau

Appl. Phys. Lett. 66, 2153 (1995); http://dx.doi.org/10.1063/1.113930 (3 pages) | Cited 5 times

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Resonant modulation of a single contact semiconductor laser at the cavity roundtrip frequency of 40 GHz is demonstrated. Efficient mode coupling is obtained with a single contact device by utilizing the high attenuation of the millimeter‐wave modulation signal along the laser stripe. The properties and limitations of this technique are analyzed using a distributed circuit model of the laser. © 1995 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Reversible optical storage utilizing pulsed, photoinduced, electric‐field‐assisted reorientation of azobenzenes

R. A. Hill, S. Dreher, A. Knoesen, and D. R. Yankelevich

Appl. Phys. Lett. 66, 2156 (1995); http://dx.doi.org/10.1063/1.113931 (3 pages) | Cited 19 times

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We demonstrate a method of permanent optical recording of digital data which exploits a fast photoisomerization of nonlinear molecules, followed by a slow permanent alignment within a polymer. Write and erase cycles are initiated by rapidly photoisomerizing azobenzene molecules into an intermediate state with a larger mobility. The molecules align or randomly orient within the polymer depending on the presence or absence of an electric field. During orientation, relaxation to a stable isomer occurs and the alignment becomes permanent. The recorded information can then be nondestructively read by second‐harmonic generation. Nanosecond optical exposures were used, demonstrating that extremely fast recording rates are possible. © 1995 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
42.70.Jk Polymers and organics
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Second‐harmonic generation from GaAs/AlAs vertical cavity

S. Nakagawa, N. Yamada, N. Mikoshiba, and D. E. Mars

Appl. Phys. Lett. 66, 2159 (1995); http://dx.doi.org/10.1063/1.113932 (3 pages) | Cited 27 times

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We have demonstrated second‐harmonic generation in a GaAs/AlAs vertical cavity grown on a (311)B GaAs substrate. Second‐harmonic light of 492 nm was observed and its efficiency was measured to be 1.4×10−4 %/W. The cavity confines high intensity of fundamental field, resulting in efficient second‐harmonic generation. Quasiphase matching was realized with the stacked GaAs/AlAs layers inside the cavity, which was designed taking into account the strong absorption of second‐harmonic power in GaAs layers. We show that conversion efficiency of the GaAs/AlAs vertical cavity could be more than 10%/W if the optimization is completed. © 1995 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Fd III-V semiconductors

One‐step absolute frequency stabilization of a Ti:sapphire laser using frequency modulation Lamb‐dip spectroscopy

Kyungwon An, Ramachandra R. Dasari, and Michael S. Feld

Appl. Phys. Lett. 66, 2162 (1995); http://dx.doi.org/10.1063/1.113933 (3 pages) | Cited 1 time

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The frequency of a commercial Ti:sapphire laser is stabilized directly relative to the Lamb‐dip signal from an atomic vapor cell without the Fabry–Pérot cavity as in intermediate frequency reference. The laser spectrum is measured by means of a supercavity spectrum analyzer with a full width at half‐maximum (FWHM) of 110 kHz, which is independently calibrated using a ring‐down technique. The measured spectrum has a FWHM of 220 kHz, thus indicating the laser linewidth to be about 55 kHz RMS. © 1995 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Optical second harmonic images of 90° domain structure in BaTiO3 and periodically inverted antiparallel domains in LiTaO3

Y. Uesu, S. Kurimura, and Y. Yamamoto

Appl. Phys. Lett. 66, 2165 (1995); http://dx.doi.org/10.1063/1.113934 (3 pages) | Cited 66 times

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By using the second harmonic generation (SHG) microscope, which we have recently developed, two‐dimensional images of ferroelectric domain structure were successfully obtained by exploiting the inhomogeneous distribution of the quadratic nonlinear optical constant in specimens. 90° domain structure of BaTiO3 was observed with intensity contrast of the second harmonic wave. A periodically inverted antiparallel domain in LiTaO3 was also observed. This fact indicates that the SHG microscope provides a new method of observing antiparallel ferroelectric domain structure in a nondestructive way, which is especially important for characterizing the quasiphase matched devices for compact blue light lasers. © 1995 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Phase response measurement technique for waveguide grating filters

Cameron J. Brooks, Gerald L. Vossler, and Kim A. Winick

Appl. Phys. Lett. 66, 2168 (1995); http://dx.doi.org/10.1063/1.113935 (3 pages) | Cited 8 times

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A simple interferometric technique is described which can be used to accurately measure the phase response of waveguide grating filters. A narrowband, tunable Ti:sapphire laser is used in a Michelson interferometer configuration, where light reflected from a waveguide grating filter is combined with a reference beam. The intensity of the combined beams is measured as the wavelength of the Ti:sapphire laser is tuned. The measured intensity exhibits a quasisinusoidal wavelength dependence, from which the phase response of the filter can be deduced. This method is successfully demonstrated using both an integrated optic waveguide grating filter and a bulk grating pair. © 1995 American Institute of Physics.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Dj Gratings
42.82.Et Waveguides, couplers, and arrays

Detuning of the gain and reflectivity spectra and its effect on the output characteristics of vertical cavity surface emitting lasers

C. H. McMahon, J. W. Bae, C. S. Menoni, D. Patel, H. Temkin, P. Brusenbach, and R. Leibenguth

Appl. Phys. Lett. 66, 2171 (1995); http://dx.doi.org/10.1063/1.113936 (3 pages) | Cited 9 times

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We have investigated the effect of mismatch between the reflectivity resonance and the gain spectra of vertical cavity surface emitting lasers. Detuning was caused by hydrostatic pressure and self‐heating. Hydrostatic pressure shifts the gain peak towards shorter wavelengths with respect to the Fabry‐Pérot (FP) resonance without modifying the gain spectrum. The threshold current remained unchanged for a positive mismatch of up to 18 nm. It increased four‐fold for a negative mismatch of −13 nm at 0.5 GPa, where lasing disappeared. Increased threshold current and quenching of the emission are a consequence of the decrease of the gain at the FP resonance. A similar effect was observed when the gain peak was red‐shifted with respect to the FP resonance by increasing the injected power. Increased mismatch is accompanied by a decrease of the gain at the emission wavelength which is responsible for the laser output quenching at high injected powers. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

Photoinduced changes in the refractive index of azo‐dye/polymer systems

M. Ivanov, T. Todorov, L. Nikolova, N. Tomova, and V. Dragostinova

Appl. Phys. Lett. 66, 2174 (1995); http://dx.doi.org/10.1063/1.113937 (3 pages) | Cited 12 times

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The photoinduced isotropic and anisotropic changes in the refractive index of dye/polymer guest‐host systems are investigated. The values obtained are compared to the diffraction efficiencies of scalar and polarization holographic gratings, recorded in the same polymer systems. It is concluded that the induced anisotropy is related to the dye molecules involved in the photoprocesses, whereas the isotropic changes, which are much stronger, are related to the polymer matrix as well. © 1995 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Jk Polymers and organics
42.65.-k Nonlinear optics

In situ thin film thickness measurement with acoustic Lamb waves

Jun Pei, F. Levent Degertekin, Butrus T. Khuri‐Yakub, and Krishna C. Saraswat

Appl. Phys. Lett. 66, 2177 (1995); http://dx.doi.org/10.1063/1.113938 (3 pages) | Cited 13 times

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In situ thin film thickness measurement is an important problem in semiconductor processing, which is currently limited by the lack of adequate sensors. Most of today’s available techniques are restricted to certain type of films and many have difficulties in performing the measurement in situ. The fact that the velocity of an ultrasonic Lamb wave traveling in a silicon wafer is changed by the thin film coating on the wafer surface can be used as a monitoring method for basically any type of film—opaque, transparent, metal, or insulator. The acoustic sensors are easily implemented into plasma or CVD environments. We have demonstrated the technique in an aluminum sputtering system in which we measure Al film thickness with a resolution of ±100 Å. Even better resolution can be achieved for SiO2, copper, and tungsten films. This system has a variety of potential applications, not only in film thickness measurement, but also in characterization of film properties and multilayer deposition process control. © 1995 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.60.-p Physical properties of thin films, nonelectronic

Two new planar coil designs for a high pressure radio frequency plasma source

T. Munsat, W. M. Hooke, S. P. Bozeman, and S. Washburn

Appl. Phys. Lett. 66, 2180 (1995); http://dx.doi.org/10.1063/1.113939 (3 pages) | Cited 6 times

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Two planar coil designs for a high pressure rf plasma source are investigated using spectroscopic techniques and circuit analysis. In an Ar plasma a truncated version of the commonly used ‘‘spiral’’ coil is found to produce improvements in peak electron density of 20% over the full version. A coil with figure‐8 geometry is found to move plasma inhomogeneities off of center and produce electron densities comparable to the spiral coils. Both of these characteristics are advantageous in industrial applications. Coil design characteristics for favorable power coupling are also determined, including the necessity of closed hydrodynamic plasma loops and the drawback of closely situated antiparallel coil currents. © 1995 American Institute of Physics.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.80.Pi High-frequency and RF discharges
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Low voltage electron emission from Pb(ZrxTi1−x)O3‐based thin film cathodes

O. Auciello, M. A. Ray, D. Palmer, J. Duarte, G. E. McGuire, and D. Temple

Appl. Phys. Lett. 66, 2183 (1995); http://dx.doi.org/10.1063/1.113940 (3 pages) | Cited 39 times

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Electron emission from ferroelectric thin films (≤1 μm thick) is demonstrated. In addition, electron energy distributions have been measured using an Auger electron spectrometer. The electron emission measurements were performed using ferroelectric cathodes based on this Pb(Zr0.53Ti0.47)O3 (PZT) films and 80–110 μm Pb0.93La0.07(Z0.53Ti0.47)O3 (PLZT) layered capacitors with Pt top and bottom electrodes. Current densities in the range of 0.5–1.5 mA/cm2 were measured from the PLZT cathodes excited with 100–400 V pulses, which produced electrons of about 265 eV with a narrow energy distribution (full width at half‐maximum of about 30 eV). On the other hand, current densities in the range 0.07–0.15 μA/cm2 were measured for thin film PZT‐based cathodes excited with pulses in the range 10–40 V. The initial results suggest that the electron emission current may depend, among other factors, on the thickness of the ferroelectric layer, the applied excitation voltage, and the interval between the polarizing and switching pulses. © 1995 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption

Radio frequency voltage division between two plasma sheaths in the Gaseous Electronics Conference reference cell

Yicheng Wang

Appl. Phys. Lett. 66, 2186 (1995); http://dx.doi.org/10.1063/1.113941 (2 pages) | Cited 3 times

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A new method is described for calculating the rf voltage division between two plasma sheaths in the capacitively coupled asymmetric Gaseous Electronics Conference reference cell, where the effective area ratio of the electrodes is unknown. The rf voltage across the ground sheath is found to decrease with increasing total electrode rf voltage, indicating that the effective area of the ground electrode increases significantly. © 1995 American Institute of Physics.
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52.80.Pi High-frequency and RF discharges
52.40.Hf Plasma-material interactions; boundary layer effects

Open air photoresist ashing by a cold plasma torch: Catalytic effect of cathode material

Kiyoto Inomata, Hideomi Koinuma, Yoshiyuki Oikawa, and Tadashi Shiraishi

Appl. Phys. Lett. 66, 2188 (1995); http://dx.doi.org/10.1063/1.113942 (3 pages) | Cited 15 times

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A beam plasma was generated and exhausted into air by applying rf voltage to the atmospheric pressure argon flowing through a cylindrical gap between a needle cathode and a grounded cylindrical anode whose surface was covered with an insulator. This torch‐type plasma with gas and electron temperatures of 240 °C (44.2 meV) and 1.0 eV, respectively, has been verified to be useful for ashing a photoresist without using a pumping system. High rate (≥1.2 μm/min) photoresist ashing was achieved by using Ar plasma containing a small amount of oxygen. Also reported are optical emission analysis of plasma and analyses of ashed Si surface by scanning electron microscopy. Fourier transform infrared spectroscopy, electron microprobe analysis, and x‐ray photoelectron spectroscopy. The use of the Pt cathode was found to provide not only a better ashed surface but also a higher ashing rate than the use of the stainless‐steel cathode. © 1995 American Institute of Physics.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Simple Nb metal bonding structure

H. S. Chen, D. D. Bacon, C. H. Chen, G. Kammlott, G. K. Jeng, D. J. Werder, and K. L. Tai

Appl. Phys. Lett. 66, 2191 (1995); http://dx.doi.org/10.1063/1.113943 (3 pages) | Cited 2 times

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A simple metallic bonding structure, has been developed consisting of a pure metal Nb and an alloy containing Sn, which can be employed to bond a semiconducting laser device and/or a silicon integrated circuit die to a submount with Au–Sn solder. Differential scanning calorimetry, transmission electron microscopy, and scanning electron microscopy reveal that the Nb layer acts effectively both as an adhesion layer to SiO2 and diamond submounts and as a perfect diffusion barrier against Au–Sn solder. The metallization structure shows no indication of dewetting of the Au–Sn solder. The excellent bonding characters have been attributed to the unique metallurgical properties of Nb. © 1995 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
68.60.Dv Thermal stability; thermal effects
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Lateral patterning of arsenic precipitates in GaAs by a surface stress structure

R. A. Kiehl, M. Saito, M. Yamaguchi, O. Ueda, and N. Yokoyama

Appl. Phys. Lett. 66, 2194 (1995); http://dx.doi.org/10.1063/1.113944 (3 pages) | Cited 10 times

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Lateral patterning of arsenic precipitates in GaAs is reported. The positions of near‐surface precipitates in a GaAs layer grown by molecular beam epitaxy at low temperature are controlled by InGaAs stressors 45 nm in width covered by a SiO2 film. The stressors form a surface grating which governs the precipitate position by modulating the strain in the GaAs near the surface. Electron microscopy clearly reveals the formation of precipitates about 15 nm in diameter aligned with the stressors at a depth of ∼50 nm. It is suggested that this capability to control the position of nanometer‐size metallic particles within a semiconductor could open up new possibilities for novel devices. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Structural and electrical properties of Ba0.5Sr0.5TiO3 thin films with conductive SrRuO3 bottom electrodes

Q. X. Jia, X. D. Wu, S. R. Foltyn, and P. Tiwari

Appl. Phys. Lett. 66, 2197 (1995); http://dx.doi.org/10.1063/1.113945 (3 pages) | Cited 86 times

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Epitaxial Ba0.5Sr0.5TiO3 (BST) thin films were deposited on LaAlO3 substrates with the conductive metallic oxide SrRuO3 (SRO) as a bottom electrode by pulsed laser deposition. The BST and SRO films were (h00) and (00l) oriented normal to the substrate surface, respectively. The epitaxial nature of both BST and SRO layers was determined by the measurement of in‐plane orientation with respect to the major axes of the substrate. Ion beam channeling with a minimum yield of around 10% from Rutherford backscattering spectrometry demonstrated the films to be of high crystallinity. A dielectric constant around 500 and dielectric loss less than 0.01 at a frequency of 10 kHz were measured on the capacitors with a configuration of Ag/BST/SRO. Electrical measurements on such epitaxial BST films showed a breakdown voltage above 106 V/cm and a leakage current density of less than 5×10−8 A/cm at a field intensity of 2×105 V/cm. These results prove the BST/SRO heterostructure to be a good combination for microelectronic device applications. © 1995 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
73.40.Rw Metal-insulator-metal structures
68.55.-a Thin film structure and morphology

Direct writing of Mo microstructures using high brilliance synchrotron radiation

P. Väterlein, V. Wüstenhagen, and E. Umbach

Appl. Phys. Lett. 66, 2200 (1995); http://dx.doi.org/10.1063/1.113946 (3 pages) | Cited 2 times

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Direct deposition of Mo microstructures on Si is demonstrated by photolytic decomposition of condensed Mo(CO)6 using the aperture‐limited, high‐intensity radiation from an undulator at the BESSY storage ring. A particular advantage of the instrument, a new photon‐induced scanning Auger microscope, is the possibility of quasisimultaneous exposure (writing) and analysis employing photoemission (PES) or x‐ray induced Auger spectroscopy (XAES) with sufficient energy resolution for detection of chemical differences. The present spatial resolution is 20–30 μm (for PES and writing) and 3 μm (for XAES), but this will be improved by adding focusing mirrors. © 1995 American Institute of Physics.
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82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Effect of misorientation angles on the surface morphologies of (001) homoepitaxial diamond thin films

Naesung Lee and Andrzej Badzian

Appl. Phys. Lett. 66, 2203 (1995); http://dx.doi.org/10.1063/1.113947 (3 pages) | Cited 22 times

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Etching and homoepitaxial growth were performed on 0.1°, 3.5°, and 11.0° off (001) diamond substrates using microwave plasma‐assisted chemical vapor deposition. Etched surfaces showed a sequential morphological change from etch pits to stepped surface to flat surface with increasing misorientation angle. In homoepitaxial growth hillock formation on the (001) surface was ascribed to the lack of surface steps on the well‐oriented substrate, while the growth on the misoriented surfaces proceeded via step flow along 〈110〉. Reflection high‐energy electron diffraction showed that the films were single crystals and their surfaces were composed of the 2×1 and 1×2 double‐domain structure. © 1995 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.-b Surface treatments

Polycrystalline silicon oxidation method improving surface roughness at the oxide/polycrystalline silicon interface

Myung‐Chul Jun, Yong‐Sang Kim, Min‐Koo Han, Jin‐Won Kim, and Ki‐Bum Kim

Appl. Phys. Lett. 66, 2206 (1995); http://dx.doi.org/10.1063/1.113948 (3 pages) | Cited 22 times

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A polycrystalline silicon oxidation method, which considerably improves the surface roughness at the oxide/polycrystalline silicon interface, is presented. The surface roughness at the interface is observed by transmission electron microscopy and is also evaluated by atomic force microscopy after the oxide layer is removed using buffered HF acid. The oxide/polycrystalline silicon interface by the new oxidation method with the 50 Å thick intermediate oxide has the rms surface roughness of 30 Å, while that of the interface by the conventional method is 120 Å. © 1995 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.65.-b Surface treatments
68.55.-a Thin film structure and morphology

Extended x‐ray absorption fine structure analysis of the difference in local structure of tantalum oxide capacitor films produced by various annealing methods

Hidekazu Kimura, Jun’ichiro Mizuki, Satoshi Kamiyama, and Hiroshi Suzuki

Appl. Phys. Lett. 66, 2209 (1995); http://dx.doi.org/10.1063/1.113169 (3 pages) | Cited 28 times

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Extended x‐ray absorption fine structure (EXAFS) above the Ta L3 edge on tantalum oxide capacitor films has been measured. Tantalum oxide films were prepared by low‐pressure chemical vapor deposition (CVD) using a Ta(OC2H5)5 and O2 gas mixture. Four kinds of tantalum oxide films were studied: as‐deposited (amorphous), N2 annealed (crystalline), dry O2 annealed (crystalline), and O2‐plasma annealed (amorphous). From EXAFS analysis, differences in the local structures of tantalum oxide capacitor films, in terms of oxygen deficiency around Ta, were observed in the various annealed films. The leakage current characteristics of tantalum oxide capacitors correspond to the differences in the local structures around Ta. © 1995 American Institute of Physics.  
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77.55.-g Dielectric thin films
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.70.Dm X-ray absorption spectra

Crystallization upon thermal annealing of a glass‐forming liquid crystal in the nematic regime

John C. Mastrangelo, Thomas N. Blanton, and Shaw H. Chen

Appl. Phys. Lett. 66, 2212 (1995); http://dx.doi.org/10.1063/1.113170 (3 pages) | Cited 5 times

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As an example of a novel class of glass‐forming liquid crystals, compound (I) was synthesized and characterized to possess a nematic mesophase between Tg and Tc as the pristine crystal was heated beyond its Tm followed by quenching to below room temperature. Differential scanning calorimetry (DSC) and x‐ray diffraction techniques were employed to investigate its morphological stability. It was found that the nematic mesophase persists upon annealing for a period of up to 22 h without the appearance of new phases. However, after annealing in the nematic regime over a longer period of time, thermally activated phase transformations were observed, resulting in a new crystalline phase plus the pristine crystalline phase based on DSC thermal transition data and x‐ray diffraction patterns. © 1995 American Institute of Physics.
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42.70.Df Liquid crystals
64.70.M- Transitions in liquid crystals

Shear piezoelectric properties of vinylidene fluoride trifluoroethylene copolymer, and its application to transverse ultrasonic transducers

Kenji Omote and Hiroji Ohigashi

Appl. Phys. Lett. 66, 2215 (1995); http://dx.doi.org/10.1063/1.113171 (3 pages) | Cited 4 times

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Shear piezoelectric properties of a vinylidene fluoride trifluoroethylene copolymer [P(VDF/TrFE)] have been studied in a temperature range from 10 to 350 K. The shear electromechanical coupling factors k15 and k24 at 290 K are found to be 0.19 and 0.20, respectively, the values being largest among the piezoelectric polymers known at present. The factors k15 and k24 remain constant below 200 K, while k24 increases and k15 decreases above 200 K. The effectiveness of P(VDF/TrFE) as a transverse ultrasonic transducer material was demonstrated by measurements of transverse sound velocities and absorptions in aluminum and poly(methyl methacrylate) with P(VDF/TrFE) shear transducers. © 1995 American Institute of Physics.
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77.84.Jd Polymers; organic compounds
77.65.-j Piezoelectricity and electromechanical effects
43.38.Fx Piezoelectric and ferroelectric transducers

Rubbed polyimide films studied by scanning force microscopy

Y. B. Kim, H. Olin, S. Y. Park, J. W. Choi, L. Komitov, M. Matuszczyk, and S. T. Lagerwall

Appl. Phys. Lett. 66, 2218 (1995); http://dx.doi.org/10.1063/1.113172 (2 pages) | Cited 29 times

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The surfaces of rubbed polyimide films for aligning liquid crystal have been studied by atomic force microscopy. The unrubbed films consisted of randomly distributed polyimide clusters of different sizes. On the rubbed surface, however, the clusters are aligned in long chains along the rubbing direction. The cluster chains were separated by about 100 nm for small rubbing strength. For higher strength the cluster chains coalesced into wider ones. © 1995 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
61.30.-v Liquid crystals

GaxIn1−xAs multiple‐quantum‐wire lasers grown by the strain‐induced lateral‐layer ordering process

S. T. Chou, K. Y. Cheng, L. J. Chou, and K. C. Hsieh

Appl. Phys. Lett. 66, 2220 (1995); http://dx.doi.org/10.1063/1.114148 (3 pages) | Cited 31 times

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Long wavelength (∼1.55 μm) GaxIn1−xAs multiple‐quantum‐wire (MQWR) lasers have been grown by a single‐step molecular beam epitaxy technique. The MQWR heterostructure was fabricated in situ using the strain‐induced lateral‐layer ordering process. The wire formation was confirmed by cross‐sectional transmission electron microscopy and polarized photoluminescence spectroscopy. The 77 K threshold current densities for the MQWR laser diodes with laser cavities along [110] and [110] directions show an anisotropy ratio of ∼10. Lasers with contact stripes aligned perpendicular to the quantum wire direction consistently show a lower threshold current density than those with stripes aligned parallel. The typical threshold current density for the MQWR laser with a stripe perpendicular to the quantum wires is ∼1 kA/cm2 at 300 K. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Sequential tunneling in [100]‐ and [111]‐oriented InGaAs/GaAs multi‐quantum wells by photocapacitance

J. L. Sánchez‐Rojas, A. Sacedón, E. Calleja, and E. Muñoz

Appl. Phys. Lett. 66, 2223 (1995); http://dx.doi.org/10.1063/1.113173 (3 pages) | Cited 1 time

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The features present in the capacitance– and conductance–voltage characteristics of [100]‐ and [111]‐oriented InGaAs/GaAs multi‐quantum well (MQW) p‐i‐n structures under illumination are described. Sequential tunneling of electrons and holes is proposed to explain the different peaks observed, as they occur at voltages corresponding to resonant alignment of energy levels of adjacent wells. Two kinds of piezoelectric [111] devices are analyzed, with positive or negative average electric fields in the MQW region. The voltage corresponding to zero average electric field in the MQW is detected by a feature in the dark device capacitance. For the sample with negative average electric field, the capacitance characteristics clearly reflect the presence and evolution with voltage of a long range screening of the piezoelectric fields by the photogenerated carriers. © 1995 American Institute of Physics.
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73.40.Gk Tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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