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16 Dec 2002

Volume 81, Issue 25, pp. 4685-4871

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Photonic crystal enhanced narrow-band infrared emitters

M. U. Pralle, N. Moelders, M. P. McNeal, I. Puscasu, A. C. Greenwald, J. T. Daly, E. A. Johnson, T. George, D. S. Choi, I. El-Kady, and R. Biswas

Appl. Phys. Lett. 81, 4685 (2002); http://dx.doi.org/10.1063/1.1526919 (3 pages) | Cited 78 times

Online Publication Date: 9 December 2002

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We have experimentally and theoretically developed a unique thermally stimulated midinfrared source that emits radiation within a narrow range of wavelengths (δλ/λ⩽0.2). The emission wavelengths are defined by the periodicity of a metal coated silicon–air photonic crystal etched into the emitter surface. The lattice of the holes in the metal mediate the coupling of light into discrete surface plasmon states. This yields surfaces with spectrally nonuniform infrared reflection properties where over much of the IR 90+% of photons are reflected yet, in a narrow spectral region, 90% absorption is observed. Transfer matrix calculations simulate well the position and strength of the absorption features. This technology will afford tunable infrared emitters with high power in a narrow spectral band that are critical for sensing, spectroscopy, and thermophotovoltaic applications. © 2002 American Institute of Physics.
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07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
42.70.Qs Photonic bandgap materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.72.Ai Infrared sources

Plasma etching of AlN/AlGaInN superlattices for device fabrication

K. Zhu, V. Kuryatkov, B. Borisov, G. Kipshidze, S. A. Nikishin, H. Temkin, and M. Holtz

Appl. Phys. Lett. 81, 4688 (2002); http://dx.doi.org/10.1063/1.1527986 (3 pages) | Cited 19 times

Online Publication Date: 9 December 2002

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We report a study of plasma etching of GaN, AlN, and AlN/AlGaN superlattices for the processing of deep ultraviolet light emitting diodes. Etching was carried out using inductively coupled plasma of chlorine diluted with argon under reactive ion etching conditions. Using parameters selected for etch rate, anisotropy, and surface smoothness, we study etching of n- and p-type superlattices. The former etches at a rate of 250 nm/min, which is intermediate to that of AlN and GaN, while the latter exhibits a slower etch rate of 60 nm/min. Based on these studies, we prepare low-leakage p–n junctions and mesa light emitting diodes with peak emission at 280 nm. © 2002 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
85.60.Jb Light-emitting devices
68.65.Cd Superlattices

Light-induced backward scattering in LiNbO3:Fe,Zn

Qiang Wu, Jingjun Xu, Qian Sun, Xinzheng Zhang, Haijun Qiao, Baiquan Tang, Guangyin Zhang, and Min Gu

Appl. Phys. Lett. 81, 4691 (2002); http://dx.doi.org/10.1063/1.1529083 (3 pages) | Cited 1 time

Online Publication Date: 9 December 2002

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We investigated the light-induced backward scattering in doubly doped lithium niobate crystals and observed an intensity threshold effect. It will be shown that scattering microregions are locally recorded in the sample by holographic interaction due to the existence of the threshold effect. Experimental results of multilayer recording point out that this property could be used for high-density multilayer-like bit data optical storage while keeping high signal-to-noise ratio. © 2002 American Institute of Physics.
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42.40.Ht Hologram recording and readout methods
42.79.Vb Optical storage systems, optical disks
42.70.Ln Holographic recording materials; optical storage media
42.25.Fx Diffraction and scattering
42.25.Dd Wave propagation in random media

Nonlinear optical absorption of antimony and lead oxyhalide glasses

Renato E. de Araujo, Cid B. de Araújo, Gäel Poirier, Marcel Poulain, and Younes Messaddeq

Appl. Phys. Lett. 81, 4694 (2002); http://dx.doi.org/10.1063/1.1529310 (3 pages) | Cited 12 times

Online Publication Date: 9 December 2002

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Nonlinear optical properties and optical limiting behavior of antimony and lead oxyhalide glasses were studied using laser pulses of 80 ps at 532 nm. The standard Z-scan technique was used to determine large nonlinear absorption coefficients which range from 11 to 20 cm/GW, using intensities of 100 MW/cm2. Photodarkening was observed when intensities larger than ≈200 MW/cm2 were incident on the samples. © 2002 American Institute of Physics.
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42.70.Ce Glasses, quartz
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.20.-e Optical properties of bulk materials and thin films
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption

Rigid bubble pit formation and huge signal enhancement in super-resolution near-field structure disk with platinum-oxide layer

T. Kikukawa, T. Nakano, T. Shima, and J. Tominaga

Appl. Phys. Lett. 81, 4697 (2002); http://dx.doi.org/10.1063/1.1529078 (3 pages) | Cited 45 times

Online Publication Date: 9 December 2002

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Huge signal enhancement was observed by a super-resolution near-field structure disk with a platinum-oxide layer. The carrier-to-noise ratio of 200-nm-mark trains reached 46.1 dB, and 42.3 dB was obtained even at 150-nm-mark trains. The sizes of the marks were one-fifth to one-seventh of the laser spot diameter of the readout system. The cross section of the mark trains was also observed by transmission electron microscopy. It was confirmed that 200-nm-size bubble pits were rigidly formed in good separation and ∼20-nm-platinum particles precipitated inside the bubble. The computer-simulation based on the model supported the huge signal enhancement. © 2002 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
02.70.Bf Finite-difference methods

Electroluminescence from strain-compensated Si0.2Ge0.8/Si quantum-cascade structures based on a bound-to-continuum transition

L. Diehl, S. Menteşe, E. Müller, D. Grützmacher, H. Sigg, U. Gennser, I. Sagnes, Y. Campidelli, O. Kermarrec, D. Bensahel, and J. Faist

Appl. Phys. Lett. 81, 4700 (2002); http://dx.doi.org/10.1063/1.1528729 (3 pages) | Cited 45 times

Online Publication Date: 9 December 2002

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Intersubband electroluminescence from strain-compensated Si/Si0.2Ge0.8 quantum cascade (QC) structures, consisting of up to 30 periods grown by molecular beam epitaxy on Si0.5Ge0.5 pseudosubstrates is reported. The design of the active region is based on a so-called “bound-to-continuum transition.” The intersubband radiation is emitted at a wavelength of 7 μm and is polarized, as expected for intersubband transitions between heavy hole states. A good agreement with photocurrent measurements is also found. © 2002 American Institute of Physics.
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78.67.De Quantum wells
78.60.Fi Electroluminescence
73.21.Fg Quantum wells
42.70.Hj Laser materials
68.65.Fg Quantum wells
72.40.+w Photoconduction and photovoltaic effects

Fabrication of an InGaN multiple-quantum-well laser diode featuring high reflectivity semiconductor/air distributed Bragg reflectors

Hailong Wang, Masami Kumagai, Takehiko Tawara, Toshio Nishida, Tetsuya Akasaka, Naoki Kobayashi, and Tadashi Saitoh

Appl. Phys. Lett. 81, 4703 (2002); http://dx.doi.org/10.1063/1.1530749 (3 pages) | Cited 3 times

Online Publication Date: 9 December 2002

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High-quality deeply-etched GaN-based semiconductor/air distributed Bragg reflectors (DBRs) have been fabricated. A 50% reduction relative to the value for reflectors of Fabry–Perot type in the threshold pump intensity was realized by the introduction of such DBRs at the ends of the laser cavity. The reflectivity of the grating was evaluated between 44% and 62%. Finite-difference time-domain simulation had earlier been used to obtain a design for the semiconductor/air DBRs, which provides high values for reflectivity despite a significant inclination from the vertical of the sidewalls of the structure. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.De Semiconductor-device characterization, design, and modeling
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
02.70.Bf Finite-difference methods

Second-harmonic generation in amorphous silicon nitride microcavities

S. Lettieri, S. Di Finizio, P. Maddalena, V. Ballarini, and F. Giorgis

Appl. Phys. Lett. 81, 4706 (2002); http://dx.doi.org/10.1063/1.1526171 (3 pages) | Cited 19 times

Online Publication Date: 9 December 2002

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We report an experimental observation of optical second-harmonic generation in an amorphous silicon–nitride based planar microcavity. The spectral dependence of the second-harmonic signal is investigated as a function of both wavelength and polarization state of the fundamental beam. The second-harmonic signal is enhanced by two orders of magnitude at the Fabry–Perot resonance. We ascribe the origin of the optical nonlinearity to surface second-harmonic generation occurring at the interfaces of the multilayered structure, where the resonant enhancement is due to the high intracavity fundamental light intensity and to the increase of the photonic density of states. Analysis of polarization dependence shows that interfacial second-order nonlinearity results from a distribution of dipoles directed perpendicularly to the plane of the film and distributed accordingly to an ∞mm point group symmetry. © 2002 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.82.Gw Other integrated-optical elements and systems

Optical switching of Mg-rich Mg–Ni alloy thin films

K. Yoshimura, Y. Yamada, and M. Okada

Appl. Phys. Lett. 81, 4709 (2002); http://dx.doi.org/10.1063/1.1530378 (3 pages) | Cited 76 times

Online Publication Date: 9 December 2002

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Mg–Ni alloy thin films were prepared by dc magnetron sputtering using Mg and Ni targets, and their optical switching property for hydrogen exposure has been investigated. Pd-capped MgNix (0.1<x<0.3) films show a good switchable mirror property. Optical transmittance of these Mg-rich Mg–Ni thin films in the hydride state is much improved compared with that of Mg2Ni thin film. We speculate that the variation of the ratio of Mg2NiH4 to MgH2 formed in the hydride state may cause this difference. Such a wide modulation range of optical switching is important for the application of this material to energy efficient smart windows. © 2002 American Institute of Physics.
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42.79.Wc Optical coatings
42.79.Ci Filters, zone plates, and polarizers
78.66.Bz Metals and metallic alloys
42.79.Bh Lenses, prisms and mirrors

Dislocation annihilation by silicon delta-doping in GaN epitaxy on Si

O. Contreras, F. A. Ponce, J. Christen, A. Dadgar, and A. Krost

Appl. Phys. Lett. 81, 4712 (2002); http://dx.doi.org/10.1063/1.1529309 (3 pages) | Cited 35 times

Online Publication Date: 9 December 2002

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The addition of bursts of silicon has been observed to correlate with the reduction of threading screw dislocations during epitaxial growth of GaN on silicon by metalorganic chemical vapor deposition. The reduction is associated with bending of screw dislocations and “pairing” with equivalent neighboring dislocations with opposite Burgers vectors. This results in the formation of square dislocation loops. When the right type of dislocation is not available, the dislocation continues propagating in the original direction, leaving behind a kink at the silicon-rich position. These observations apply only to dislocations with a screw component. Edge dislocations are not affected by silicon delta-doping. A mechanism for the termination of threading screw dislocation is proposed, which involves pinning by the silicon impurities of the surface lattice steps associated with screw dislocations. © 2002 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
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Optically driven diffusion and mechanical softening in azobenzene polymer layers

N. Mechau, D. Neher, V. Börger, H. Menzel, and K. Urayama

Appl. Phys. Lett. 81, 4715 (2002); http://dx.doi.org/10.1063/1.1529081 (3 pages) | Cited 15 times

Online Publication Date: 9 December 2002

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A study of the thermally induced and photoinduced changes in the mechanical properties of thin azobenzene polymer layers utilizing electromechanical spectroscopy is presented. Upon illumination at room temperature, weak photoinduced plasticization is observed. This is well below the degree of softening induced by heating the layer above the glass transition temperature. At the same time, the polymer layer roughens, indicating light-induced diffusion of the macromolecules over micrometer distances. We propose an active photoinduced diffusion mechanism, in which free volume generated during the photoisomerization of one chromophore is reoccupied in the course of the photoinduced isomerization of an adjacent azobenzene molecule. © 2002 American Institute of Physics.
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82.35.Lr Physical properties of polymers
68.60.Bs Mechanical and acoustical properties
68.35.Fx Diffusion; interface formation
82.30.Qt Isomerization and rearrangement
42.70.Jk Polymers and organics
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
61.82.Pv Polymers, organic compounds
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.50.-m Photochemistry
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Vacancy trapping and annealing in noble-metal films grown at low temperature

C. E. Botez, K. Li, E. D. Lu, W. C. Elliott, P. F. Miceli, E. H. Conrad, and P. W. Stephens

Appl. Phys. Lett. 81, 4718 (2002); http://dx.doi.org/10.1063/1.1527988 (3 pages) | Cited 7 times

Online Publication Date: 9 December 2002

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We have used synchrotron x-ray diffraction to study the homoepitaxial growth on Cu(001), Ag(001), and Ag(111), at temperatures between 300 and 65 K. The growth on all of these surfaces exhibits a consistent trend towards a large compressive strain that is attributed to the incorporation of vacancies into the growing film below 160 K. In each case, the vacancy concentration is ∼ 2% at 110 K and we have measured the temperature dependence for incorporation on the (001) surfaces as well as the annealing behavior for Cu(001). These results, which suggest new kinetic mechanisms, have important implications for understanding epitaxial crystal growth. © 2002 American Institute of Physics.
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68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing

Dislocation effect on light emission efficiency in gallium nitride

Sergey Yu. Karpov and Yuri N. Makarov

Appl. Phys. Lett. 81, 4721 (2002); http://dx.doi.org/10.1063/1.1527225 (3 pages) | Cited 36 times

Online Publication Date: 9 December 2002

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We modify the model of nonradiative carrier recombination on threading dislocation cores [Z. Z. Bandić, P. M. Bridger, E. C. Piquette, and T. C. McGill, Solid-State Electron. 44, 221 (2000)] to estimate quantitatively the light emission efficiency in GaN as a function of the dislocation density and nonequilibrium carrier concentration. The model predictions are in good agreement with available data on the minority carrier diffusion length in GaN. The dislocation density must be reduced, at least, down to ∼ 107 cm−2 in order to provide a light emission efficiency close to unity. The n-type background doping is found to be favorable for the further efficiency improvement. © 2002 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Lk Linear defects: dislocations, disclinations

Depth profiling of Si nanocrystals in Si-implanted SiO2 films by spectroscopic ellipsometry

T. P. Chen, Y. Liu, M. S. Tse, P. F. Ho, Gui Dong, and S. Fung

Appl. Phys. Lett. 81, 4724 (2002); http://dx.doi.org/10.1063/1.1528286 (3 pages) | Cited 8 times

Online Publication Date: 9 December 2002

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In this letter, we report an approach to depth profiling of Si nanocrystals embedded in SiO2 film based on spectroscopic ellipsometry. The SiO2 film is divided into many sublayers with equal thickness, and each sublayer is characterized by its nanocrystal concentration. In the spectral fittings, the effective dielectric function of each sublayer is obtained from an effective medium approximation by using the dielectric function of Si nanocrystal that is calculated with either the bond contraction or the phenomenological models for the band gap expansion of nanocrystals. The fittings yield the nanocrystal depth profiles and the nanocrystal sizes as well. The depth profiles from the two models are similar, and they are in good agreement with secondary ion mass spectroscopy analysis. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.20.Mq Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors
61.72.S- Impurities in crystals
81.70.Jb Chemical composition analysis, chemical depth and dopant profiling
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.Nq Composition and phase identification

Diffraction behavior of photorefractive molecular materials containing phenothiazine derivatives

Dong Hoon Choi, Kwang Yong Oh, Woong Gi Jun, Jae Hong Kim, and Suk-Ho Choi

Appl. Phys. Lett. 81, 4727 (2002); http://dx.doi.org/10.1063/1.1529080 (3 pages) | Cited 3 times

Online Publication Date: 9 December 2002

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We report the diffraction behavior of the photorefractive (PR) molecular materials that contain the phenothiazine derivatives. Diphenylhydrazine and malononitrile were reacted with N-alkyl substituted phenothiazinyl aldehyde to provide charge transporting and nonlinear optical (NLO) molecules, respectively. In the molecular materials prepared with phenothiazine derivatives, we observed very unusual complementary gratings formed by the space charge fields of two types of photocarriers, which can be explained based on a bipolar two-trap PR model. Adding the specific molecules to the host PR materials increased the trapped hole density during grating formation and erasing processes. © 2002 American Institute of Physics.
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42.70.Gi Light-sensitive materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.25.Fx Diffraction and scattering
42.79.Dj Gratings
42.70.Mp Nonlinear optical crystals

Fine structure of the trion triplet state in a single self-assembled semiconductor quantum dot

I. A. Akimov, A. Hundt, T. Flissikowski, and F. Henneberger

Appl. Phys. Lett. 81, 4730 (2002); http://dx.doi.org/10.1063/1.1527694 (3 pages) | Cited 39 times

Online Publication Date: 9 December 2002

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The emission from the charged biexciton is used to monitor the energy structure of the trion triplet state in a negatively charged CdSe/ZnSe quantum dot. The isotropic part of the electron–hole exchange interaction regroups the otherwise sixfold degenerated state in three Kramers doublets. The energy separation between the radiative pairs with total spin projection Fz = ±3/2 and ±1/2 is 1.6 meV. The anisotropic part mixes states with ΔFz = ±2 resulting in a partly linearly polarized transition dipole. Application of magnetic field lifts the degeneracy of the Kramers doublets. The g factors also manifest the anisotropic state mixing. © 2002 American Institute of Physics.
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73.21.La Quantum dots
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
71.70.Gm Exchange interactions
78.47.-p Spectroscopy of solid state dynamics

Change in photoluminescence from Er-doped TiO2 thin films induced by optically assisted reduction

Shuji Komuro, Tooru Katsumata, Hideki Kokai, Takitaro Morikawa, and Xinwei Zhao

Appl. Phys. Lett. 81, 4733 (2002); http://dx.doi.org/10.1063/1.1530733 (3 pages) | Cited 24 times

Online Publication Date: 9 December 2002

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Erbium-doped TiO2 (TiO2:Er) thin films with the anatase structure have been prepared on Si substrate by laser ablation. Sharp and intense Er-related emission in the visible region as well as in the IR region has been observed under over-band-gap excitation. The broad photoluminescence (PL) peaking at about 530 nm newly appears at low temperature. It has been understood that the broad PL is induced by an optically assisted reduction effect that is caused by both the H2O adsorption and the reduction process of TiO2 to Ti2O3 by UV illumination. In the IR region, Er-related emission consisted of one main peak located at 1.534 μm and many subpeaks located at around 1.54 μm can be observed even at room temperature. The drastic thermal quenching of the Er-related 1.54 μm emission is also considered due to the optically assisted reduction effect. © 2002 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
82.50.Hp Processes caused by visible and UV light
42.79.Wc Optical coatings
68.43.Mn Adsorption kinetics

Polymer scaffolding model for holographic polymer-dispersed liquid crystals

K. K. Vardanyan, J. Qi, J. N. Eakin, M. De Sarkar, and G. P. Crawford

Appl. Phys. Lett. 81, 4736 (2002); http://dx.doi.org/10.1063/1.1530750 (3 pages) | Cited 32 times

Online Publication Date: 9 December 2002

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A polymer scaffolding model is proposed to describe the electro-optic performance parameters of holographic polymer-dispersed liquid crystals (H-PDLC). Using a simple phenomenological approach to model the interaction between the liquid crystal and polymer scaffolding, the observed increase in critical field and reduced dynamic response times are well described, and the molecular interaction energy is deduced to be ∼ 10−4 J/m2. © 2002 American Institute of Physics.
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42.70.Df Liquid crystals
61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems
61.30.Cz Molecular and microscopic models and theories of liquid crystal structure
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
78.20.Jq Electro-optical effects
42.70.Ln Holographic recording materials; optical storage media
42.40.-i Holography

Carbon-nanotube-reinforced Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass composites

Zan Bian, Ming Xiang Pan, Yun Zhang, and Wei Hua Wang

Appl. Phys. Lett. 81, 4739 (2002); http://dx.doi.org/10.1063/1.1530371 (3 pages) | Cited 43 times

Online Publication Date: 9 December 2002

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Carbon-nanotube (CNT) reinforced Zr-based bulk metallic glass composites are prepared by the conventional die cast method. A large amount of CNTs still keep their seamless cylindrical morphology in the glassy matrix, even though some CNTs react with Zr, resulting in the formation of ZrC phase. Investigation shows that the elastic moduli, Vicker’s hardness, density, and Debye temperature of the composite are markedly changed by introducing CNTs into the glass. Our results suggest that CNTs are promising materials for preparing reinforced, lightweight bulk metallic glass composites with improved mechanical and physical properties relative to the undoped glass. © 2002 American Institute of Physics.
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81.05.Pj Glass-based composites, vitroceramics
61.46.-w Structure of nanoscale materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.25.-g Mechanical properties of nanoscale systems
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
81.07.De Nanotubes
61.43.Fs Glasses
62.20.D- Elasticity
62.20.Qp Friction, tribology, and hardness
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions

Acoustic cavity polariton in multilayer piezoelectric structures

Jing Chen and Jacob B. Khurgin

Appl. Phys. Lett. 81, 4742 (2002); http://dx.doi.org/10.1063/1.1530742 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2002

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Coupling between the transverse electromagnetic mode of the coplanar strips and transverse acoustic phonon mode in the multilayer piezoelectric structures is considered. It is shown that it leads to the formation of a coupled entity—acoustic cavity polariton, whose frequency and velocity can be adjusted within a very broad range by the proper design of the piezoelectric cavity. The acoustic cavity polaritons can be used in filters, delay lines, and solid-state traveling wave devices for frequencies of up to 100 GHz. © 2002 American Institute of Physics.
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68.35.Ja Surface and interface dynamics and vibrations
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
84.40.Az Waveguides, transmission lines, striplines
77.65.-j Piezoelectricity and electromechanical effects

Influence of strain on diffusion at Ge(111) surfaces

Vasily Cherepanov and Bert Voigtländer

Appl. Phys. Lett. 81, 4745 (2002); http://dx.doi.org/10.1063/1.1530730 (3 pages) | Cited 7 times

Online Publication Date: 9 December 2002

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The measurement of the density of two-dimensional islands by scanning tunneling microscopy after submonolayer growth is used to determine the strain dependence of surface diffusion. Templates of strained and relaxed Ge surfaces with the same surface reconstruction are prepared for comparison. The diffusion barrier for Ge and Si adatoms is found to increase with increasing compressive strain of the Ge(111) substrate. When the strain increases from relaxed Ge to Ge strained to the Si lattice constant, the diffusion barrier is estimated to increase by ∼ 60 meV. © 2002 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
68.35.Gy Mechanical properties; surface strains
81.05.Cy Elemental semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.43.Fg Adsorbate structure (binding sites, geometry)
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties

Magnesium segregation and the formation of pyramidal defects in p-GaN

Stephan Figge, Roland Kröger, Tim Böttcher, Peter L. Ryder, and Detlef Hommel

Appl. Phys. Lett. 81, 4748 (2002); http://dx.doi.org/10.1063/1.1527981 (3 pages) | Cited 21 times

Online Publication Date: 9 December 2002

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Magnesium doping of GaN was found to generate extended defects with a pyramidal shape. Transmission electron micrographs of layers with different doping levels typically showed a defect-free region at the start of doping and a modulation of the defect density in the subsequent film. We developed a rate equation model based on the segregation of Mg to explain the formation process of these defects. The model explains the dependence of the defect-free thickness on the doping level and yields a criterion to avoid the defect formation. Hall measurements show a significant reduction of the free hole concentration for samples grown at doping levels beyond defect formation. © 2002 American Institute of Physics.
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64.75.-g Phase equilibria
61.72.Nn Stacking faults and other planar or extended defects
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ey III-V semiconductors
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Microstructural dependence of electron and hole transport in low-temperature-grown polycrystalline-silicon thin-film solar cells

Takuya Matsui, Riza Muhida, Tomohiro Kawamura, Toshihiko Toyama, Hiroaki Okamoto, Tsutomu Yamazaki, Shinya Honda, Hideyuki Takakura, and Yoshihiro Hamakawa

Appl. Phys. Lett. 81, 4751 (2002); http://dx.doi.org/10.1063/1.1527979 (3 pages) | Cited 11 times

Online Publication Date: 9 December 2002

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Carrier transport properties of undoped polycrystalline silicon (poly-Si) thin films prepared by SiH4–H2 plasma at low temperature have been investigated. The ac-conductivity measurement technique has been applied to poly-Si i layers with an n-i-n junction structure in order to characterize the electron conductivity along the growth direction. Furthermore, the hole conductivity has been measured with p-i-p junction structures. The temperature dependence of ac conductivity reveals that poly-Si films with relatively low crystalline volume fraction (Xc ∼ 50%) exhibit intrinsic character, while the poly-Si films with high Xc (>50%) exhibit n-type character with activation energies less than 0.15 eV. Based on these results, the relationship among microstructure, carrier transport, and photovoltaic performance of poly-Si solar cells is discussed. © 2002 American Institute of Physics.
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84.60.Jt Photoelectric conversion
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Electronic properties of GaN induced by a subsurface stressor

P. Waltereit, A. E. Romanov, and J. S. Speck

Appl. Phys. Lett. 81, 4754 (2002); http://dx.doi.org/10.1063/1.1524300 (3 pages) | Cited 4 times

Online Publication Date: 9 December 2002

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The influence of the strain field originating from a subsurface point source of dilatation (point stressor) on the electronic properties of nitride semiconductors is investigated. In the far field, real quantum dots can be viewed as such point stressors. The material surrounding the stressor was considered either to be a uniform GaN matrix or GaN matrix with an (In,Ga)N quantum well which is grown pseudomorphically between the stressor and the free surface. Isotropic elasticity was used to find the strain field around the stressor. A k⋅p perturbation theory approach was then applied to examine the shifts of the conduction and valence band edges caused by the stressor. We find lateral confinement for electrons and holes, which can be utilized to realize a strain-induced quantum dot in the quantum well. © 2002 American Institute of Physics.
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73.21.La Quantum dots
73.20.At Surface states, band structure, electron density of states
73.63.Kv Quantum dots
71.15.-m Methods of electronic structure calculations

Investigation of trap-assisted tunneling current in InAs/(GaIn)Sb superlattice long-wavelength photodiodes

Q. K. Yang, F. Fuchs, J. Schmitz, and W. Pletschen

Appl. Phys. Lett. 81, 4757 (2002); http://dx.doi.org/10.1063/1.1529306 (3 pages) | Cited 24 times

Online Publication Date: 9 December 2002

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Trap centers with an energy level positioned 1/3 of the band gap below the effective conduction band edge are observed in the electroluminescence spectra of InAs/(GaIn)Sb superlattice photodiodes with a cutoff wavelength of 11 μm. The trap centers are recognized by simulating the low-temperature current–voltage characteristics of the diodes. Excellent quantitative agreement on both, the I–V characteristic and the differential resistance between the experimental data and the theoretical prediction is achieved. The quantitative simulation of the I–V characteristics shows, that the 77 K performance of InAs/(GaIn)Sb photodiodes is dominated by generation-recombination processes even at long wavelengths. Above 50 K, tunneling currents are not of importance. © 2002 American Institute of Physics.
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73.61.Ey III-V semiconductors
85.60.Dw Photodiodes; phototransistors; photoresistors
78.60.Fi Electroluminescence
71.55.Eq III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
73.21.Cd Superlattices
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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