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19 Jun 1995

Volume 66, Issue 25, pp. 3399-3527

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Theory for the apertureless near‐field optical microscope: Image resolution

N. García and M. Nieto‐Vesperinas

Appl. Phys. Lett. 66, 3399 (1995); http://dx.doi.org/10.1063/1.113366 (2 pages) | Cited 11 times

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We present a theory that should explain the operation of the apertureless near‐field optical microscope in the limit of smooth variations of both the refractive index and the corrugation of the object. Special emphasis is made on ultimate resolution and the recent experiments by F. Zenhausern, M. P. O’Boyle, and K.H. Wickramasinghe [Appl. Phys. Lett. 65, 1623 (1994)]. We show that, in order to obtain resolution better than 7 nm, the variation of the object refractive index has to satisfy severe conditions. © 1995 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
68.37.-d Microscopy of surfaces, interfaces, and thin films

Optical switching in a metal–semiconductor–metal waveguide structure

Amy E. Bieber, David F. Prelewitz, Thomas G. Brown, and Richard C. Tiberio

Appl. Phys. Lett. 66, 3401 (1995); http://dx.doi.org/10.1063/1.113367 (3 pages) | Cited 6 times

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We report the observation of all‐optical switching in a metal–semiconductor–metal waveguide structure. A silicon‐on‐insulator waveguide with aluminum interdigitated fingers deposited on the surface and overcoated with amorphous silicon provided high‐efficiency coupling and switching of Nd:YAG laser pulses. This structure is fully compatible with very large scale integrated manufacturing processes and represents a substantial leap forward in the quest for full‐scale integration of silicon‐based optoelectronic systems. © 1995 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
85.60.-q Optoelectronic devices

Novel high efficiency copolymer laser dye in the blue wavelength region

Hendrik‐Jan Brouwer, Victor V. Krasnikov, Alain Hilberer, Jurjen Wildeman, and George Hadziioannou

Appl. Phys. Lett. 66, 3404 (1995); http://dx.doi.org/10.1063/1.113368 (3 pages) | Cited 43 times

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The lasing performance and wavelength tunability of a novel high efficiency copolymer poly[(2, 5, 2″, 5″‐tetraoctyl)‐p‐terphenyl‐4,4″‐ylene vinylene‐p‐phenylene vinylene], TOP‐PPV, pumped with third harmonic radiation of a Nd:YAG laser, was studied in various organic solvents. The results were compared with Coumarin 120 and Coumarin 47 in ethanol under identical experimental conditions. The efficiency of the TOP‐PPV copolymer in hexane exceeds that of both coumarin dyes with more than 50%. The laser emission of the polymer dye in hexane is tunable in the wavelength region between 414 and 456 nm (Δλ=38 nm). © 1995 American Institute of Physics.
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42.55.Mv Dye lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Hj Laser materials

Scanning plasmon optical microscope

Y‐K. Kim, P. M. Lundquist, J. A. Helfrich, J. M. Mikrut, G. K. Wong, P. R. Auvil, and J. B. Ketterson

Appl. Phys. Lett. 66, 3407 (1995); http://dx.doi.org/10.1063/1.113369 (3 pages) | Cited 20 times

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A new scanning near‐field optical microscopy based on the surface plasmon resonance is presented. Enhanced fields are localized at individual surface irregularities by the scattering of plasmons and the scattered plasmons produce a conical radiation. Variations in the conical radiation intensity caused by interactions between a raster‐scanned probe tip and the enhanced fields are recorded and related to the surface topography, providing an optical image with lateral resolution exceeding the diffraction limit. This technique is compared to complementary atomic force microscopy and scanning tunneling microscopy measurements and potential advantages are discussed. © 1995 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes

Quasi‐phase‐matched second‐harmonic generation in AlGaAs waveguides with periodic domain inversion achieved by wafer‐bonding

S. J. B. Yoo, R. Bhat, C. Caneau, and M. A. Koza

Appl. Phys. Lett. 66, 3410 (1995); http://dx.doi.org/10.1063/1.113370 (3 pages) | Cited 59 times

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Quasi‐phase‐matched second‐harmonic generation is observed in an AlGaAs waveguide. The AlGaAs waveguide is epitaxially grown on a template substrate where a periodic crystal domain inversion is achieved using wafer bonding and organometallic chemical vapor deposition. A scanning electron micrograph of the waveguide cross section reveals a distinct propagation of the crystal domain boundaries in the epitaxial growth direction. Second‐harmonic generation measurements on a fabricated rib‐loaded waveguide show a clear quadratic dependence of the second‐harmonic power to the input fundamental power. The peak conversion efficiency is 4.9%/W whereas the theoretical value is 124%/W for an ideal waveguide with no loss and with equal domain dimensions. A significant increase in the conversion efficiency is expected with reduced scattering losses realized by improved epitaxial growth and fabrication processes. © 1995 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.79.Gn Optical waveguides and couplers

Cavity characteristics of selectively oxidized vertical‐cavity lasers

Kent D. Choquette, K. L. Lear, R. P. Schneider, and K. M. Geib

Appl. Phys. Lett. 66, 3413 (1995); http://dx.doi.org/10.1063/1.113371 (3 pages) | Cited 44 times

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We show that a buried oxide layer forming a current aperture in an all epitaxial vertical‐cavity surface emitting laser has a profound influence on the optical and electrical characteristics of the device. The lateral index variation formed around the oxide current aperture leads to a shift in the cavity resonance wavelength. The resonance wavelength under the oxide layer can thus be manipulated, independent of the as‐grown cavity resonance, by adjusting the oxide layer thickness and its placement relative to the active region. In addition, the electrical confinement afforded by the oxide layer enables record low threshold current densities and threshold voltages in these lasers. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.60.Jb Light-emitting devices

Experimental observation of efficient generation of femtosecond second harmonic pulses

Gary Y. Wang, Y. Yang, and Elsa Garmire

Appl. Phys. Lett. 66, 3416 (1995); http://dx.doi.org/10.1063/1.113372 (3 pages) | Cited 1 time

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Blues pulses 300 fs long have been generated from 150 fs infrared pulses by compressing second harmonic radiated in the Cerenkov geometry. Mode‐locked Ti:sapphire pulses were prism coupled into a 1‐cm long proton‐exchanged MgO:LiNbO3 planar waveguide. The 2 ps Cerenkov output, chirped due to group velocity mismatch, was then compressed by a diffraction grating down to 300 fs. The use of mode‐locked pulses results in a conversion efficiency of 1000%/W/cm, three orders of magnitude higher than by cw doubling in the same geometry. The Cerenkov geometry ensures that all wavelengths can be phase matched over long crystal length, so that even low power lasers can be efficiently doubled. The dispersion element ensures that the chirped output can be compressed into the femtosecond regime. This concept can be extended to femtosecond pulses in any two‐photon process in any waveguide material and any mode‐locked source. © 1995 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Nv Optical frequency converters

Intensity noise and facet correlation in Fabry–Pérot laser diodes with low facet reflectivities

E. F. Goobar, R. J. Ram, R. Nagarajan, L. A. Coldren, and J. E. Bowers

Appl. Phys. Lett. 66, 3419 (1995); http://dx.doi.org/10.1063/1.113373 (3 pages) | Cited 1 time

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The intensity noise in Fabry–Pérot lasers with low facet reflectivities is studied. A direct comparison between laser intensity fluctuations under noise suppressed and shot‐noise limited current injection is made. Noise levels in excess of the shot‐noise level are observed, even when the pump noise is suppressed. Also, an injection current dependent negative correlation between the intensity noise at the output facets of a laser is demonstrated. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.50.Lc Quantum fluctuations, quantum noise, and quantum jumps
85.60.Jb Light-emitting devices

Single frequency erbium fiber external cavity semiconductor laser

W. H. Loh, R. I. Laming, M. N. Zervas, M. C. Farries, and U. Koren

Appl. Phys. Lett. 66, 3422 (1995); http://dx.doi.org/10.1063/1.113374 (3 pages) | Cited 9 times

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A novel external cavity configuration for stable single frequency operation of the semiconductor laser is demonstrated. By using an erbium doped fiber as the external cavity, longitudinal mode‐hopping is suppressed, ensuring single frequency operation. Employing a 3 m long fiber cavity, resolution‐limited optical linewidths of a kHz are obtained. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.81.-i Fiber optics
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Intersubband lasing lifetimes of SiGe/Si and GaAs/AlGaAs multiple quantum well structures

G. Sun, L. Friedman, and R. A. Soref

Appl. Phys. Lett. 66, 3425 (1995); http://dx.doi.org/10.1063/1.113375 (3 pages) | Cited 23 times

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The feasibility of population inversion is studied for the SiGe/Si system and compared with that of GaAs/AlGaAs. Because of the absence of strong polar optical phonon scattering in SiGe/Si, the lifetime difference of the upper and lower lasing levels, to which the population inversion and laser gain are proportional, is consistently an order of magnitude larger than that of GaAs/AlGaAs; nor does it show the sudden drop to zero or negative values when the lasing energy exceeds the optical phonon energy. Both systems studied are superlattices, each period of which consists of three coupled quantum wells and barriers. © 1995 American Institute of Physics.  
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42.55.Px Semiconductor lasers; laser diodes
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Defects responsible for gray tracks in flux‐grown KTiOPO4

M. P. Scripsick, D. N. LoIacono, J. Rottenberg, S. H. Goellner, L. E. Halliburton, and F. K. Hopkins

Appl. Phys. Lett. 66, 3428 (1995); http://dx.doi.org/10.1063/1.113376 (3 pages) | Cited 20 times

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Electron paramagnetic resonance (EPR) has been used to identify the primary electron and hole traps responsible for ‘‘gray tracks’’ in flux‐grown KTiOPO4(KTP). Ionizing radiation (x rays) was used to produce the gray‐track effect. During an irradiation at 0 °C, a broad absorption band peaking near 500 nm is introduced, the EPR spectra from a series of Ti3+ centers appear, and the dominant EPR spectrum associated with Fe3+ ions decreases significantly. Following the irradiation, the decay of the optical absorption and the Ti3+ centers, along with the growth of Fe3+ centers, were monitored over a period of 20 h at room temperature. Changes in the EPR spectra of the Ti3+ and Fe3+ centers during the anneal correlated with the decay of the induced optical absorption (i.e., gray track). These results demonstrate that Fe3+ centers are the primary hole trap and Ti4+‐VO complexes are the primary electron trap responsible for gray track formation in flux‐grown KTP crystals. © 1995 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)

Measurement of nonlinear absorption and refraction in titanium dioxide single crystal by using a phase distortion method

Yuichi Watanabe, Masato Ohnishi, and Toshio Tsuchiya

Appl. Phys. Lett. 66, 3431 (1995); http://dx.doi.org/10.1063/1.113377 (2 pages) | Cited 14 times

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A phase distortion method is applied to examine the optical nonlinearity in titanium dioxide single crystal. The two‐photon absorption coefficient obtained agrees with that reported previously, while the nonlinear index of refraction is larger than that predicted theoretically by a factor of 10. One of the reasons for the discrepancy is given as the applicable limit of the simple theory in which a two‐parabolic band model has been assumed in the analysis. © 1995 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Electron drift mobility of oxadiazole derivatives doped in polycarbonate

Hiroaki Tokuhisa, Masanao Era, Tetsuo Tsutsui, and Shogo Saito

Appl. Phys. Lett. 66, 3433 (1995); http://dx.doi.org/10.1063/1.113378 (3 pages) | Cited 54 times

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Charge drift mobilities of five oxadiazole derivatives doped in polycarbonate (PC) were evaluated with the time‐of‐flight technique. It is demonstrated that oxadiazoles incline to having electron‐transport characteristics. In particular, an oxadiazole with naphthyl substituent (BND) was found to possess high potential of electron transport; the electron drift mobility of 50 wt % BND doped PC was 2.2×10−5 cm2 V−1 s−1 at an electric field of 7.5×105 V cm−1 at room temperature. In addition, incorporating strong electron‐releasing substituents into oxadiazoles was demonstrated to add hole transport characteristics to oxadiazoles. © 1995 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Le Polymers; organic compounds (including organic semiconductors)

Electron beam induced coalescence in plasma polymer silver composite films

Jens Werner, Andreas Heilmann, and Falk Mueller

Appl. Phys. Lett. 66, 3436 (1995); http://dx.doi.org/10.1063/1.113379 (3 pages) | Cited 5 times

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Plasma polymer thin films with embedded silver particles (5‐50 nm) were irradiated by a small focussed electron beam of 10 kV. Before and after irradiation the films were investigated by transmission electron microscopy (TEM) to characterize the microstructure given by size and shape of the embedded silver particles. The changes of the microstructure after the electron beam irradiation were limited to small lines (<2 μm). Most changes were coalescence of the silver particles. Furthermore, after increased irradiation time and higher energy input areas nearly free of silver particles but without destruction of the plasma polymer matrix were found. © 1995 American Institute of Physics.
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81.05.Qk Reinforced polymers and polymer-based composites
68.55.-a Thin film structure and morphology
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
61.80.Fe Electron and positron radiation effects

Piezoelectric interfacial waves in LiNbO3

E. Danicki

Appl. Phys. Lett. 66, 3439 (1995); http://dx.doi.org/10.1063/1.113380 (2 pages) | Cited 1 time

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It is shown, by numerical analysis, that piezoelectric interfacial waves guided by a conducting plane embedded in a lithium niobate crystal exist in ∼6% of the volume of space of three Euler angles describing the plane orientation and the wave propagation direction with respect to crystallographic axes. Example wave solutions are presented. © 1995 American Institute of Physics.
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43.20.Bi Mathematical theory of wave propagation
43.35.Pt Surface waves in solids and liquids
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

In situ real time studies of the formation of polycrystalline silicon films on glass grown by a layer‐by‐layer technique

T. Akasaka and I. Shimizu

Appl. Phys. Lett. 66, 3441 (1995); http://dx.doi.org/10.1063/1.113381 (3 pages) | Cited 29 times

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The effect of atomic hydrogen on thin deposited layers of amorphous silicon was studied. Amorphous silicon layers less than 10 nm thick were first deposited from fluorinated precursors. These layers were then exposed to an atomic hydrogen flux. The amorphous layers quickly relaxed to a crystalline structure. Thick films of high crystalline content were prepared through sequential repetition of the deposition and hydrogen exposure process (layer‐by‐layer technique). The relaxation process was studied by real time in situ ellipsometry and infrared measurements. The relationship between substrate temperature, amorphous layer thickness, hydrogen exposure time, and structure was determined. A new model in which hydrogen acts to ‘‘liquify’’ the subsurface region by breaking Si–Si bonds is suggested. From the ‘‘liquidlike’’ state the subsurface relaxes to its most thermodynamically stable constituents; during relaxation, crystalline silicon is formed with effluence of SiH4, SiFxH4−x, and SiF4 vapors. © 1995 American Institute of Physics.
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68.55.Nq Composition and phase identification
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Effect of intrinsic growth stress on the Raman spectra of vacuum‐arc‐deposited amorphous carbon films

Joel W. Ager, Simone Anders, Andre Anders, and Ian G. Brown

Appl. Phys. Lett. 66, 3444 (1995); http://dx.doi.org/10.1063/1.113382 (3 pages) | Cited 46 times

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Amorphous carbon (a‐C) films grown by vacuum‐arc deposition techniques contain substantial amounts of compressive, residual, growth stress (over 10 GPa). The magnitude of the stress can be controlled by changing the incoming energy of the ions. It is observed that stress shifts the Raman scattering feature in these films to higher frequency by as much as 20 cm−1. The Raman spectra of adhering and delaminated films are used to measure the magnitude of the stress‐induced shift, which is −1.9 cm−1/GPa for compressive biaxial stress. The observed value is compared to that expected from disordered diamond and graphite structures. © 1995 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Phonon replicas in the photoluminescence emission of AlxGa1−xAs alloys

D. C. Reynolds, D. C. Look, R. Kaspi, and D. N. Talwar

Appl. Phys. Lett. 66, 3447 (1995); http://dx.doi.org/10.1063/1.113383 (3 pages) | Cited 1 time

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Phonon replicas in the photoluminescence spectra of a direct gap AlxGa1−xAs alloy have been observed. The GaAs‐like transverse optical and longitudinal optical as well as AlAs‐like longitudinal optical modes were observed at the Γ‐point. We also observe what we believe to be the longitudinal acoustical phonons at the L‐point in the Brillouin zone. © 1995 American Institute of Physics.
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78.55.Cr III-V semiconductors
63.20.K- Phonon interactions

Plastic stress relaxation in highly strained In0.30Ga0.70As/GaAs structures

Y. Androussi, A. Lefebvre, C. Delamarre, L. P. Wang, A. Dubon, B. Courboulès, C. Deparis, and J. Massies

Appl. Phys. Lett. 66, 3450 (1995); http://dx.doi.org/10.1063/1.113384 (3 pages) | Cited 8 times

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The evolution of surface roughness and the subsequent plastic relaxation mechanisms have been studied by transmission electron microscopy (TEM) as a function of the thickness of highly strained In0.30Ga0.70As layers on GaAs(001). The following stages have been observed: formation of coherent islands, coalescence of islands, and nucleation of dislocations at the troughs of the surface ripples. Dislocations are thus systematically generated where the highest stress concentrations are expected, according to recent theoretical predictions. It is the first time such a plastic relaxation mechanism has been observed in highly strained semiconductor heterostructures. © 1995 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
62.20.-x Mechanical properties of solids

Reactive deposition epitaxial growth of β‐FeSi2 film on Si(111): In situ observation by reflective high energy electron diffraction

Lianwei Wang, Chenglu Lin, Qinwo Shen, Xian Lin, Rushan Ni, and Shichang Zou

Appl. Phys. Lett. 66, 3453 (1995); http://dx.doi.org/10.1063/1.113385 (3 pages) | Cited 7 times

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Reactive deposition epitaxial growth of β‐FeSi2 film on Si(111) has been studied by in situ observation of reflective high energy electron diffraction combined with ex situ Auger electron spectroscopy depth profile analysis. The direct phase formed at the top surface after iron coverage has been determined to be mixture Fe3Si and Fe5Si3, FeSi, and β‐FeSi2, respectively, according to the results of different deposit temperature. Diffraction patterns as well as the depth profile for the Fe/Si ratio have been discussed. © 1995 American Institute of Physics.  
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68.55.-a Thin film structure and morphology
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Anisotropic relaxation during the first stages of the growth of ZnTe/(001) CdTe strained layers studied by reflection high energy electron diffraction

J. Eymery, B. Daudin, D. Brun‐Le Cunff, N. Boudet, and S. Tatarenko

Appl. Phys. Lett. 66, 3456 (1995); http://dx.doi.org/10.1063/1.113386 (3 pages) | Cited 11 times

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The first stages of the growth of highly strained ZnTe on (001)CdTe are studied by reflection high energy electron diffraction (RHEED) with real‐time monitoring of the surface in‐plane lattice spacing and of the width of the streaks along the [100], [110], and [110] azimuths. A large, oscillating, elastic relaxation is measured below the critical thickness (≊5 ZnTe monolayers) in the [110] azimuth while a small excess of tensile stress with regard to the CdTe substrate is observed in the [110] azimuth. These effects are attributed to an anisotropic nontetragonal elastic distortion at the free edges of elongated 2D ZnTe‐monolayer islands. For large deposition times (i.e., after the critical thickness), the RHEED observation gives very good information about the nature of the dislocations occurring in the multiplication process. © 1995 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Interface between low‐temperature grown GaAs and undoped GaAs as a conduction barrier for back gates

K. D. Maranowski, J. P. Ibbetson, K. L. Campman, and A. C. Gossard

Appl. Phys. Lett. 66, 3459 (1995); http://dx.doi.org/10.1063/1.113387 (3 pages) | Cited 7 times

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We present a back gated 2DEG (two‐dimensional electron gas) structure using low‐temperature grown (LTG) GaAs as a barrier layer between the back gate and the undoped GaAs channel. The sheet concentration of the 2DEG can be linearly varied from full depletion up to 3×1011 cm−2 at 12 K. When this charge modulation is modeled by a simple parallel plate capacitor, we find that the distance between the plates is approximately equal to the channel thickness rather than the actual spacing between the 2DEG and the back gate (which is the channel thickness plus the LTG GaAs thickness). We explain this behavior by observing that the leakage path is limited by the triangular barrier to conduction formed at the interface between the LTG GaAs defect band and the undoped GaAs channel conduction band. © 1995 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Wide band gap MgZnSSe grown on (001) GaAs by molecular beam epitaxy

B. J. Wu, J. M. DePuydt, G. M. Haugen, G. E. Höfler, M. A. Haase, H. Cheng, S. Guha, J. Qiu, L. H. Kuo, and L. Salamanca‐Riba

Appl. Phys. Lett. 66, 3462 (1995); http://dx.doi.org/10.1063/1.113388 (3 pages) | Cited 12 times

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We report molecular beam epitaxial study of wide band gap (≳2.9 eV at room temperature) MgZnSSe on (001) oriented GaAs using ZnS, Mg, Zn, and Se sources. Although the growth is under group II rich condition, the compositions of S and Mg in the MgyZn1−ySxSe1−x are linear functions of flux ratios, PZnS/PSe and PMg/PZnS, up to 35%, respectively. Mirrorlike surface and low defect density (5×104 cm−2) MgZnSSe with band gap close to 3.1 eV can be achieved. Composition modulation, tweedlike contrasts and strain contrasts in the MgZnSSe are observed from transmission electron microscope analysis. For the first time, a miscibility gap at high S and Mg compositions is reported. Nitrogen‐free radicals are used as the p‐type dopant for the doping study. For the MgZnSSe with room‐temperature band gap energy higher than 2.9 eV, the net acceptor concentration decreases as the band gap energy increases. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors

First‐principles calculations for zinc‐blende AlInN alloys

A. F. Wright and J. S. Nelson

Appl. Phys. Lett. 66, 3465 (1995); http://dx.doi.org/10.1063/1.113389 (3 pages) | Cited 31 times

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First‐principles calculations have been performed for ordered and disordered zinc‐blende Al0.5In0.5N alloys including full relaxation of bond lengths and bond angles. The disordered alloy is predicted to have a mixing enthalpy of +39 meV/atom and a bowing parameter of +2.53 eV at the Γ‐point transition. The similarity of the bulk zinc‐blende and wurtzite Γ‐point transitions also allows an estimate to be made of the energy gap versus composition for wurtzite alloys. In particular, the wurtzite AlInN alloy lattice matched to GaN is predicted to have an energy gap of 5.0 eV. © 1995 American Institute of Physics.
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71.10.-w Theories and models of many-electron systems
61.43.Dq Amorphous semiconductors, metals, and alloys

Electronic structure of Si(111)‐7×7 phase boundary studied by scanning tunneling microscopy

Koji Miyake, Hidemi Shigekawa, and Ryuzo Yoshizaki

Appl. Phys. Lett. 66, 3468 (1995); http://dx.doi.org/10.1063/1.113766 (3 pages) | Cited 9 times

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Remarkably low electron density of Si adatoms at the Si(111)‐7×7 phase boundary was found by scanning tunneling microscopy. The observed charge transfer was apparent with sample bias voltages down to ∼−0.8 eV, close to the value of the dangling bond state of the rest atoms in the Si(111) 7×7 surface. In consideration of the DAS (dimer‐adatom‐stacking fault) model, the observed charge transfer could be related to the structural change in the dimer layer caused by phase mismatching at the boundary. In fact, such charge transfer was not observed at the less disordered boundaries formed by introducing 5×5 half unit cells. Similar large charge transfer was found to occur in the quenched disordered 1×1 structure. These results agree with the similar chemical reactivity observed in the two disordered structures. © 1995 American Institute of Physics.
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73.20.-r Electron states at surfaces and interfaces
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.35.Rh Phase transitions and critical phenomena
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