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11 Oct 2004

Volume 85, Issue 15, pp. 2999-3325

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 3241 (2004); http://dx.doi.org/10.1063/1.1805714 (3 pages)

Y. K. Liu, J. A. Zapien, C. Y. Geng, Y. Y. Shan, C. S. Lee, Y. Lifshitz, and S. T. Lee
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[110] Orientated lead salt midinfrared lasers

Z. Shi, X. Lv, F. Zhao, A. Majumdar, D. Ray, R. Singh, and X. J. Yan

Appl. Phys. Lett. 85, 2999 (2004); http://dx.doi.org/10.1063/1.1799240 (3 pages) | Cited 6 times

Online Publication Date: 19 October 2004

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A Lead salt midinfrared quantum-well (QW) laser on [110] orientation is proposed. Theoretical simulations of [110] QW edge-emitting lasers show a 70° temperature increase in continuous-wave operation compared to the conventional [100]-orientated lasers. This is because the gain on [100]-orientated QW structure is significantly increased. Among [100], [111], and [110] orientations, [110]-orientated QW structure offers the highest gain. PbSe∕PbSrSe QW structures were successfully grown on [110]-orientated BaF2 substrate by molecular-beam-epitaxy (MBE). Photoluminescence intensity of [110]-orientated samples was twice as high as that on [111]-orientated BaF2 substrates from the same MBE run.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.07.St Quantum wells
78.55.Hx Other solid inorganic materials
85.30.De Semiconductor-device characterization, design, and modeling
78.67.De Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Near-stoichiometric LiNbO3 optical waveguides fabricated using vapor transport equilibration and Ti co-diffusion

De-Long Zhang, W. H. Wong, and E. Y. B. Pun

Appl. Phys. Lett. 85, 3002 (2004); http://dx.doi.org/10.1063/1.1805700 (3 pages) | Cited 11 times

Online Publication Date: 19 October 2004

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Near-stoichiometric planar and strip LiNbO3 optical waveguides were demonstrated using vapor transport equilibrium process and co-diffusion of titanium metal. Optical confinement is better in z-cut substrates than in x-cut substrates, and the waveguides were characterized optically. Spectral measurements, such as OH− absorption, optical absorption near the fundamental edge, and Raman scattering, were carried out to examine the Li-composition and crystalline phase inside and outside the guiding layer. The results have shown that the vapor transport equilibration process has brought these waveguides toward stoichiometric composition, the Li content inside and outside the waveguide layer is essentially identical, and the LiNbO3 phase is still retained within the waveguide layer.
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42.79.Gn Optical waveguides and couplers
81.10.Bk Growth from vapor
66.30.J- Diffusion of impurities
61.66.Bi Elemental solids
61.66.Dk Alloys
78.30.Hv Other nonmetallic inorganics

Bottom-up soft-lithographic fabrication of three-dimensional multilayer polymer integrated optical microdevices

Yanyi Huang, George T. Paloczi, Joyce K. S. Poon, and Amnon Yariv

Appl. Phys. Lett. 85, 3005 (2004); http://dx.doi.org/10.1063/1.1802380 (3 pages) | Cited 9 times

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We develop a method to efficiently fabricate three-dimensional multilayer polymer microchips for integrated optical applications. This method uses soft lithography to mold the core structures on top of the cladding layers. By repeating the process, a three-dimensional multilayer integrated optical microdevice, which consists of several layers of individual planar optical devices, is fabricated. We demonstrate a dual-layer microring resonator optical filter device where the devices in the different layers show essentially identical transmission responses.
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42.81.Bm Fabrication, cladding, and splicing
85.60.Bt Optoelectronic device characterization, design, and modeling
42.70.Jk Polymers and organics
42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays
42.82.-m Integrated optics

Improvement in spatial resolution of plasma-enhanced quantum-well intermixing by stress-inducing dielectric mask

H. S. Djie, T. Mei, and J. Arokiaraj

Appl. Phys. Lett. 85, 3008 (2004); http://dx.doi.org/10.1063/1.1803912 (3 pages) | Cited 2 times

Online Publication Date: 19 October 2004

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We report the use of a stress-inducing dielectric mask to improve the spatial resolution of the proximity quantum-well intermixing process. Photoluminescence and Raman spectroscopy were used to study the band gap modification and the spatial resolution using Ar plasma in the InGaAs∕InGaAsP laser structure. A spatial resolution of 2.4 μm has been achieved with the presence of an SixNy annealing cap as a stress-inducing mask. The simple technique provides a promising approach of lateral band gap tuning with a high spatial resolution for high-density photonic integrated circuits.
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81.05.Ea III-V semiconductors
73.21.Fg Quantum wells
78.67.De Quantum wells
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors

Time response characteristics of an oxide-confined GaAs∕AlGaAs resonant cavity-enhanced photodetector

E. Estacio, C. Alonzo, A. Samson, A. Garcia, A. Somintac, and A. Salvador

Appl. Phys. Lett. 85, 3011 (2004); http://dx.doi.org/10.1063/1.1806267 (3 pages)

Online Publication Date: 19 October 2004

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This work compares the speed characteristics of a ∼135-μm-diam GaAs∕AlGaAs resonant cavity-enhanced (RCE) detector-emitter device with its laterally oxidized ∼80-μm-diam counterpart. The full width at half-maximum of the photocurrent spectrum exhibited no degradation in wavelength selectivity. Moreover, oxide confinement caused no current bottleneck that was inferred to adversely affect the device speed. The measured pulse responses were 65 and 75 ps for the unoxidized and oxidized devices, respectively. Oxide-confined RCE photodetectors show relevant application in concentric hybrid RCE vertical cavity laser devices, this work deals with the speed characteristics of laterally oxidized resonant cavity-enhanced devices.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
84.40.Az Waveguides, transmission lines, striplines
78.60.Fi Electroluminescence
72.40.+w Photoconduction and photovoltaic effects
78.47.-p Spectroscopy of solid state dynamics

Interband cascade lasers grown on GaAs substrates lasing at 4 microns

Cory J. Hill and Rui Q. Yang

Appl. Phys. Lett. 85, 3014 (2004); http://dx.doi.org/10.1063/1.1803952 (3 pages) | Cited 1 time

Online Publication Date: 19 October 2004

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Antimonide-based type II interband cascade lasers grown on GaAs substrates have been demonstrated at emission wavelengths longer than 4 μm at temperatures up to 270 K in pulsed-mode operation. Investigations by transmission electron microscopy, atomic force microscopy and x-ray diffraction are presented and discussed to gain insights into material issues such as defects and dislocations associated with device performance.
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42.55.Px Semiconductor lasers; laser diodes
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Ps Atomic force microscopy (AFM)
68.37.Lp Transmission electron microscopy (TEM)

Differential ellipsometric surface plasmon resonance sensors with liquid crystal polarization modulators

I. R. Hooper and J. R. Sambles

Appl. Phys. Lett. 85, 3017 (2004); http://dx.doi.org/10.1063/1.1806273 (3 pages) | Cited 17 times

Online Publication Date: 19 October 2004

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Differential ellipsometric interrogation of surface plasmon (SP) resonances is a technique that gives ultrahigh sensitivity to refractive index changes, and it may provide the basis for chemical and biological sensors. In this study, a liquid crystal polarization modulator has been developed to provide such a differential technique. A refractive index sensitivity of 2×10−7 refractive index units is demonstrated, which is at least as sensitive as more established SP sensing techniques. The use of a liquid crystal modulator allows for low-voltage signal modulation and also feedback locking to zero. Possibly more important, it leads to pixelization for array sensing and for potential imaging.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.Pw Imaging detectors and sensors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Hp Optical processors, correlators, and modulators
42.70.Df Liquid crystals
78.68.+m Optical properties of surfaces

Surface acoustic wave-driven planar light-emitting device

Marco Cecchini, Giorgio De Simoni, Vincenzo Piazza, Fabio Beltram, H. E. Beere, and D. A. Ritchie

Appl. Phys. Lett. 85, 3020 (2004); http://dx.doi.org/10.1063/1.1803936 (3 pages) | Cited 11 times

Online Publication Date: 19 October 2004

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Electroluminescence emission controlled by means of surface acoustic waves (SAWs) in planar light-emitting diodes (pLEDs) is demonstrated. Interdigital transducers for SAW generation were integrated onto pLEDs fabricated following the scheme which we have recently developed [Cecchini et al., Appl. Phys. Lett. 82, 636 (2003)]. Current-voltage, light-voltage, and photoluminescence characteristics are presented at cryogenic temperatures. We argue that this scheme represents a valuable building block for advanced optoelectronic architectures.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
43.38.Rh Surface acoustic wave transducers
78.55.Cr III-V semiconductors
62.65.+k Acoustical properties of solids
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Polarization-sensitive complex Fourier domain optical coherence tomography for Jones matrix imaging of biological samples

Yoshiaki Yasuno, Shuichi Makita, Takashi Endo, Masahide Itoh, Toyohiko Yatagai, Mari Takahashi, Chikatoshi Katada, and Manabu Mutoh

Appl. Phys. Lett. 85, 3023 (2004); http://dx.doi.org/10.1063/1.1804233 (3 pages) | Cited 16 times

Online Publication Date: 19 October 2004

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A polarization-sensitive Fourier domain optical coherence tomography (PS-FD-OCT) system is demonstrated. This OCT system is based on a spectral interferometer, does not require mechanical axial scanning, and enables phase information to be used in an OCT image. Owing to this phase information, the system requires only two measurements for determining the Jones matrix images and Müller images of biological samples. This system reveals the birefringence properties of the inner surface of a porcine esophagus.
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87.63.L- Visual imaging
78.20.Fm Birefringence

7 W average power, high-beam-quality green generation in MgO-doped stoichiometric periodically poled lithium tantalate

A. G. Getman, S. V. Popov, and J. R. Taylor

Appl. Phys. Lett. 85, 3026 (2004); http://dx.doi.org/10.1063/1.1806538 (3 pages) | Cited 5 times

Online Publication Date: 19 October 2004

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A periodically-poled MgO-doped stoichiometric lithium tantalate crystal is applied for single-pass, 67% peak-power efficient, 7.05 W average power second-harmonic generation of a single-mode Yb-doped all-fiber fundamental source. Reduced photorefraction and green-induced infrared absorption of the material allowed to maintain a low M2 value of the high-average-power 532 nm beam.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.30.Hv Other nonmetallic inorganics
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Loss characterization in microcavities using the thermal bistability effect

H. Rokhsari, S. M. Spillane, and K. J. Vahala

Appl. Phys. Lett. 85, 3029 (2004); http://dx.doi.org/10.1063/1.1804240 (3 pages) | Cited 17 times

Online Publication Date: 19 October 2004

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We demonstrate a powerful method based on the thermal bistability effect to characterize distinct loss mechanisms limiting the quality factor of microresonators. The relative importance of absorption and scattering losses are investigated in toroidal microcavities using this technique. Empirical results on thermal nonlinearity of these structures have been used to study the interaction of microtoroids with their ambient environment.
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42.25.Bs Wave propagation, transmission and absorption
42.25.Fx Diffraction and scattering

A grating-assisted resonant-cavity-enhanced optical displacement detection method for micromachined sensors

Wook Lee, Neal A. Hall, and F. Levent Degertekin

Appl. Phys. Lett. 85, 3032 (2004); http://dx.doi.org/10.1063/1.1804605 (3 pages) | Cited 3 times

Online Publication Date: 19 October 2004

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We present an integrated optical displacement sensing method for microscale sensors which is based on an asymmetric Fabry–Perot etalon structure with an embedded phase-sensitive diffraction grating. Analytical modeling of the structure shows that the etalon significantly improves the detection sensitivity as compared to a regular optical interferometer and the embedded diffraction grating enables integration of optoelectronics in a small volume. The efficacy of the method is experimentally validated on a surface micromachined diffraction-based opto-acoustic sensor fabricated on a quartz wafer. A 15 nm silver layer is used to form the bottom mirror of the etalon structure with a sensor membrane and embedded diffraction grating made of aluminum. Comparison of the results with and without the etalon shows an 8 dB increase in detection sensitivity with the etalon structure, which should be further enhanced with the use of low-loss dielectric mirrors.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.60.Ly Interferometers
42.79.Pw Imaging detectors and sensors
42.79.Dj Gratings

Origin of the green photoluminescence from zinc sulfide nanobelts

Changhui Ye, Xiaosheng Fang, Guanghai Li, and Lide Zhang

Appl. Phys. Lett. 85, 3035 (2004); http://dx.doi.org/10.1063/1.1807018 (3 pages) | Cited 70 times

Online Publication Date: 19 October 2004

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ZnS nanobelts with a pure wurtzite phase have been synthesized by a thermal evaporation method with the assistance of H2S in an Ar atmosphere. Photoluminescence band centered at about 535 nm has been observed under excitation in the range of 250–480 nm with decay rate as short as 860 ps. The origin of this intense photoluminescence is related to elemental sulfur species on the surface of the ZnS nanobelts. This assignment is substantiated by structural analysis by high-resolution electron microscopy, x-ray photoelectron spectroscopy, and photoluminescence and excitation technique. ZnS nanobelts with intense surface photoluminescence could be used as effective green light emitters, humid sensors, and UV light detectors.
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81.07.Bc Nanocrystalline materials
81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Polarization selection due to scattering losses in nonaxisymmetric vertical cavity surface emitting laser cavities

S. Riyopoulos and E. Nhan

Appl. Phys. Lett. 85, 3038 (2004); http://dx.doi.org/10.1063/1.1799239 (3 pages)

Online Publication Date: 19 October 2004

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A theoretical explanation is offered for the polarization pinning in vertical cavity surface emitting laser cavities with deliberately imposed lack of axisymmetry. The analytic computation of scattering losses shows that, for medium to small aperture sizes, differentiation in modal Q’s among the two polarizations is sufficient to overrule intrinsic near-degeneracies and maintain polarization throughout operation range. It is also shown that the prevailing polarization, the one with lowest round-trip losses, is aligned with the longest aperture dimension, in agreement with experiments.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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Production of ultrahigh-current-density ion beams by short-pulse skin-layer laser–plasma interaction

J. Badziak, S. Głowacz, S. Jabłoński, P. Parys, J. Wołowski, and H. Hora

Appl. Phys. Lett. 85, 3041 (2004); http://dx.doi.org/10.1063/1.1797557 (3 pages) | Cited 28 times

Online Publication Date: 19 October 2004

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We report experimental evidence, supported by a simple theory and numerical calculations, that the skin-layer subrelativistic interaction of a short (⩽1 ps) low-energy (<1 J) laser pulse with a thin preplasma layer in front of a solid target can produce a collimated fast ion flux of extremely high ion current density (⩾1010 A∕cm2 close to the target), comparable to those predicted for ballistically focused ion beams from relativistic laser–plasma interactions.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.-b Plasma properties
52.27.Ny Relativistic plasmas
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Amorphous-to-crystal transition of nitrogen- and oxygen-doped Ge2Sb2Te5 films studied by in situ resistance measurements

S. Privitera, E. Rimini, and R. Zonca

Appl. Phys. Lett. 85, 3044 (2004); http://dx.doi.org/10.1063/1.1805200 (3 pages) | Cited 72 times

Online Publication Date: 19 October 2004

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The amorphous-to-crystal transition has been studied through in situ resistance measurements in Ge2Sb2Te5 thin films doped by ion implantation with nitrogen or oxygen. The dependence of the electrical resistivity and structure on the annealing temperature and time has been investigated in samples with different dopant concentrations. Enhancement of the thermal stability and increase of the mobility gap for conduction have been observed in O- and N-doped amorphous Ge2Sb2Te5. Larger effects have been found in the case of nitrogen doping.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.61.Jc Amorphous semiconductors; glasses
61.72.up Other materials
61.72.S- Impurities in crystals
64.70.K- Solid-solid transitions
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments

Microphotoluminescence spectra of hillocks in Al0.11Ga0.89N films

W. C. Ke, C. S. Ku, H. Y. Huang, W. C. Chen, L. Lee, W. K. Chen, W. C. Chou, W. H. Chen, M. C. Lee, W. J. Lin, Y. C. Cheng, and Y. T. Cherng

Appl. Phys. Lett. 85, 3047 (2004); http://dx.doi.org/10.1063/1.1802379 (3 pages) | Cited 4 times

Online Publication Date: 19 October 2004

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The spatial variation of the optical properties of hillocks in Al0.11Ga0.89N films has been studied by using microphotoluminescence (μ-PL) microscopy. The μ-PL spectrum revealed a strong emission (IH) at 351 nm from the hillock, besides the near-band-edge emission (Inbe) at 341 nm. Moreover, the IH intensity increases significantly and its full width at half maximum decreases from ∼76 to ∼53 meV by probing across the hillock center. These indicated that the hillock structure is a strong emission center. The temperature-dependent μ-PL measurements showed that the IH also has the S-shape behavior with a transition temperature of ∼120 K which is lower than that of Inbe. The redshift of IH is also smaller than Inbe. Both indicated that the Al composition in hillocks is lower than the surrounding area.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.55.-a Thin film structure and morphology

Effect of strain-compensation in stacked 1.3 μm InAs∕GaAs quantum dot active regions grown by metalorganic chemical vapor deposition

N. Nuntawong, S. Birudavolu, C. P. Hains, S. Huang, H. Xu, and D. L. Huffaker

Appl. Phys. Lett. 85, 3050 (2004); http://dx.doi.org/10.1063/1.1805707 (3 pages) | Cited 16 times

Online Publication Date: 19 October 2004

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We have introduced tensile layers embedded in a GaAs matrix to compensate compressive strain in stacked 1.3 μm InAs quantum dot (QD) active regions. The effects of the strain compensation are systematically investigated in five-stack and ten-stack QD structures where we have inserted InxGa1−xP (x=0.30 or 0.36) layers. High-resolution x-ray diffraction spectra quantify the overall strain in each sample and indicate >35% strain reduction can be accomplished. Both atomic force and transmission electron microscope images confirm that strain compensation improves material crystallinity and QD uniformity. With aggressive strain compensation, room temperature QD photoluminescence intensity is significantly increased demonstrating a reduced defect density.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.05.cp X-ray diffraction
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)

Size effect and strain rate sensitivity in benzocyclobutene film

D.-L. Liu, T.-M. Lu, G.-C. Wang, and R. C. Picu

Appl. Phys. Lett. 85, 3053 (2004); http://dx.doi.org/10.1063/1.1805710 (3 pages) | Cited 3 times

Online Publication Date: 19 October 2004

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The mechanical properties of benzocyclobutene film are investigated at the nanoscale by nano-indentation using atomic force microscopy (AFM). The force versus indentation depth data were collected with two different AFM tips of radii ∼20 and ∼380 nm. A strong size effect of the plastic flow stress was observed as the radius of the indenter tip was reduced. More important, the material exhibited pronounced strain rate sensitivity when probed at the nanoscale, while it was rate insensitive at larger scales. These two size effects were quantified by analytic and finite element modeling.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Lm Deformation, plasticity, and creep
62.20.M- Structural failure of materials
62.20.F- Deformation and plasticity
68.37.Ps Atomic force microscopy (AFM)

Transition in growth mode by competing strain relaxation mechanisms: Surfactant mediated epitaxy of SiGe alloys on Si

M. Kammler and M. Horn-von Hoegen

Appl. Phys. Lett. 85, 3056 (2004); http://dx.doi.org/10.1063/1.1803914 (3 pages) | Cited 2 times

Online Publication Date: 19 October 2004

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Surfactant mediated epitaxy of Si(1−x)Gex alloys on Si(111) can, besides technological importance, clarify the influence of the lattice mismatch during surfactant mediated heteroepitaxial growth. For low Ge concentration we find an immediate layer-by-layer growth, whereas at high Ge concentration a roughening transition followed by relaxation of the lattice mismatch in a periodic dislocation network is preferred. This behavior can be explained by comparing the dislocation nucleation rate on a smooth surface with the island nucleation rate on a pseudomorphic film.
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81.05.Hd Other semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.Lk Linear defects: dislocations, disclinations
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Room-temperature synthesis of ultraviolet-emitting nanocrystalline GaN films using photochemical vapor deposition

Shunsuke Yamazaki, Takashi Yatsui, Motoichi Ohtsu, Taw-Won Kim, and Hiroshi Fujioka

Appl. Phys. Lett. 85, 3059 (2004); http://dx.doi.org/10.1063/1.1806271 (3 pages) | Cited 7 times

Online Publication Date: 19 October 2004

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We fabricated UV-emitting nanocrystalline gallium nitride (GaN) films at room temperature using photochemical vapor deposition (PCVD). For the samples synthesized at room temperature with V/III ratios exceeding 5.0×104, strong photoluminescence peaks at 3.365 and 3.310 eV, which can be ascribed to transitions in a mixed phase of cubic and hexagonal GaN, were observed at 5 K. A UV emission spectrum with a full width at half-maximum of 100 meV was observed, even at room temperature. In addition, x-ray photoelectron spectroscopy measurement revealed that the film deposited by PCVD at room temperature was well nitridized.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.55.Cr III-V semiconductors
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Vertical composition gradient in InGaAs∕GaAs alloy quantum dots as revealed by high-resolution x-ray diffraction

M. Hanke, D. Grigoriev, M. Schmidbauer, P. Schäfer, R. Köhler, R. L. Sellin, U. W. Pohl, and D. Bimberg

Appl. Phys. Lett. 85, 3062 (2004); http://dx.doi.org/10.1063/1.1803938 (3 pages) | Cited 6 times

Online Publication Date: 19 October 2004

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Shape and composition profiles of self-organized In0.6Ga0.4As∕GaAs quantum dots (QDs) were investigated using diffuse x-ray scattering of a fivefold QD stack. To reveal the QD morphology, numerical scattering simulations of QDs with different morphologies were performed based on three-dimensional strain fields calculated by the finite element methods. Comparing our simulations to the data, we proved that the In concentration increases from the wetting layer to the top of the quantum dots. Moreover, we conclude that the In concentration of the wetting layers is significantly lower than the average value in the QDs.
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81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)

High-resolution diffuse x-ray scattering from threading dislocations in heteroepitaxial layers

S. Daniš, V. Holý, Z. Zhong, G. Bauer, and O. Ambacher

Appl. Phys. Lett. 85, 3065 (2004); http://dx.doi.org/10.1063/1.1806279 (3 pages) | Cited 9 times

Online Publication Date: 19 October 2004

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Diffuse x-ray scattering from epitaxial layers with screw dislocations perpendicular to the surface is calculated assuming correlated dislocation positions. The resulting intensity distribution was compared with a reciprocal-space map measured in a symmetric diffraction from a hexagonal GaN(0001) layer, and a good correspondence was achieved. From the fit, both the dislocation density and their correlation length were determined.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.70.Ck X-ray scattering
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Well width dependence of disorder effects on the optical properties of AlGaN∕GaN quantum wells

I. Friel, C. Thomidis, and T. D. Moustakas

Appl. Phys. Lett. 85, 3068 (2004); http://dx.doi.org/10.1063/1.1804253 (3 pages) | Cited 5 times

Online Publication Date: 19 October 2004

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We report on a temperature-dependent photoluminescence study of disorder effects on the optical properties of Al0.2Ga0.8N∕GaN multiple quantum wells as a function of the well width. It is found that the disorder-induced inhomogeneous broadening of the excitonic density of states increases with decreasing well width. A nonmonotonic temperature variation of the photoluminescence peak energy is observed, and interpreted as a crossover from a thermal to a nonthermal (trapped) distribution of recombining excitons amongst the band-tail states. The luminescence is quenched by two thermally activated mechanisms, and the dependence of the activation energies with well width is accounted for.
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81.05.Ea III-V semiconductors
73.21.Fg Quantum wells
78.67.De Quantum wells
73.20.At Surface states, band structure, electron density of states
78.55.Cr III-V semiconductors

Layered compound Nb3SiC2 predicted from first-principles theory

A. Grechnev, S. Li, R. Ahuja, O. Eriksson, U. Jansson, and O. Wilhelmsson

Appl. Phys. Lett. 85, 3071 (2004); http://dx.doi.org/10.1063/1.1791734 (3 pages) | Cited 18 times

Online Publication Date: 19 October 2004

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Show Abstract
A previously unobserved ternary carbide, Nb3SiC2, belonging to the family of the so-called Mn+1AXn or MAX phases is predicted from first-principles calculations. It has a theoretical bulk modulus of 269 Gpa, which is much higher than that of Ti3SiC2. The new phase is metastable with a formation energy of +0.02 eV∕atom. We suggest that the phase may possibly be synthesized using thin film technology. The chemical binding of Nb3SiC2 is investigated using the balanced crystal orbital overlap population indicator and it is found to be dominated by the formation of Nb 4d–C 2p covalent bonds.
Show PACS
61.50.Lt Crystal binding; cohesive energy
73.20.At Surface states, band structure, electron density of states
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
81.30.Dz Phase diagrams of other materials
61.66.Fn Inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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