bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion Implantation Induced Interdiffusion in Quantum Wells for Optoelectronic Device Integration
Authors: Fu L. , Tan H. H. , Cohen M. I. , Jagadish C. , Dao L. V. , Gal M. , Li Na , Li Ning , Liu X. , Lu W. , Shen S. C.
Published: April 2011

Ion implantation induced intermixing of GaAs/AlGaAs and InGaAs/AlGaAs quantum wells was studied using low temperature photoluminescence. Large energy shifts were observed with proton implantation and subsequent rapid thermal annealing. Energy shifts were found to be linear as a function of dose for doses as high as ∼5×1016 cm−2. Proton implantation and subsequent rapid thermal annealing was used to tune the emission wavelength of InGaAs quantum well lasers as well as detection wavelength of GaAs/AlGaAs quantum well infrared photodetectors (QWIPs). Emission wavelength of lasers showed blue shift whereas detection wavelength of QWIPs was red shifted with intermixing.
A Bowtie Antenna Coupled Tunable Photon-Assisted Tunneling Double Quantum Well (DQW) THz Detector
Authors: Khodier Majid M. , Christodoulou Christos G. , Simmons Jerry A.
Published: April 2011

The integration of a bowtie antenna with a double electron layer tunneling transistor (DELTT) device for the purposes of THz detection is investigated in this paper. The concept of THz detection, based on photon-assisted tunneling (PAT) between the two electron layers in a double quantum well (DQW) heterostructure, will be explained. The detector is expected to have narrowband, electrically tunable, fast response, and the possibility to operate at relatively high temperatures. Since the active area of the detector is very small, which is necessary to achieve fast response, it is not efficient in collecting THz radiation. Therefore, a broadband bowtie antenna is integrated with the detector to efficiently collect the THz radiation. Characteristics of different bowtie antenna geometries at THz frequencies were studied. An equivalent circuit model of the THz detector was developed, for the first time, to estimate the impedance characteristics at THz frequencies. Such a model is crucial for achieving impedance matching between the DELTT and the antenna to increase the overall coupling efficiency.
Fast Room Temperature Detection of State of Circular Polarization of Terahertz Radiation
Authors: Ganichev Sergey D. , Ketterl Hermann , Prettl Wilhelm
Published: April 2011

We report on a room temperature detector which allows to determine and monitor the state of polarization of terahertz radiation with picosecond temporal resolution. The detector is based on the circular photogalvanic effect recently observed in GaAs/AlGaAs quantum wells. The circular photogalvanic effect yields in response to elliptically polarized radiation a current signal proportional to the degree of circular polarization. The peak current signal occurs in unbiased samples for circular polarization, vanishes at linear polarization and changes sign by switching the helicity from right-handed to left-handed. The detector consists of a (113)A MBE grown p-GaAs/AlGaAs multiple quantum well structure. The response has been measured in the wavelength range between 76 μm and 280 μm at normal incidence of the radiation on the sample.
Scatterometry for Lithography Process Control and Characterization in IC Manufacturing
Authors: Kostoulas Yiorgos , Raymond Christopher J.
Published: April 2011

As modern circuit architecture features steadily decrease in size, more accurate tools are needed to meaningfully measure critical dimensions (CD). As a general rule, a metrology tool should be able to measure 1/10 of the product tolerance. An emerging technology for high speed, high accuracy CD measurement is scatterometry. This paper describes scatterometrybased measurements of metal features of 350 nm with a space of 450 nm (pitch of 800nm) on top of a complicated layer stack and compares them with the results of an atomic force microscope (AFM). We also looked into lithography cell monitoring and trending by measuring CDs on 3 daily litho cell monitors over a period of 40 days. Our long term results show excellent agreement with those of a scanning electron microscope (CD-SEM).
Influence of Er and O doses in Er-related emission in Al0.70Ga0.30As:Er
Authors: Uekusa Shin-ichiro , Arai Tomoyuki
Published: April 2011

Er ions with doses ranging from 1×1013 cm−2 to 1×1015 cm−2 were implanted into Al0.70Ga0.30As on GaAs substrates. at 800 °C. Photoluminescence (PL) intensity of Er-related emission around 1.54 μm was enhanced by co-implanted oxygen (O). The optimum dose of Er ion was 1×1014 cm−2 and O ion was 1×1015 cm−2, respectively. Furthermore, from the temperature dependence of the PL intensity of sample implanted with the optimum dose, we estimated the values of E1, E2, and E3, the activation energies in order to investigate the rapid thermal quenching of Er ion in Al0.70Ga0.30As. We found that PL intensity of Er-related emission, in addition to O dose, was enhanced approximately twenty two times at room temperature. And from the temperature dependence of the lifetime of the optimum dose of Er and O, the value 245meV of EA, the activation energy for the decrease of the lifetime, was nearly equal to the value 235meV of E3. Based on the result, the decrease of the lifetime confirms that the radiative efficiency is lower; therefore, we propose that rapid thermal quenching occurs at temperatures above 200 K due to the decrease of the radiative efficiency.
Intra-magnetoexciton transitions in semiconductor quantum wells
Authors: Barticevic Z. , Pacheco M. , Duque C. A. , Oliveira L. E.
Published: April 2011

Highly sensitive optically detected resonance experiments have shown that magnetoexcitons in GaAs-(Ga,Al)As semiconductor quantum wells have discrete internal energy levels, with transition energies found in the far-infrared (terahertz) region. Here we are concerned with a theoretical study of the terahertz transitions of light-hole and heavy-hole confined magnetoexcitons in GaAs-(Ga,Al)As quantum wells, under a magnetic field applied in the growth direction of the semiconductor heterostructure. The various magnetoexciton states are obtained in the effective-mass approximation by expanding the corresponding exciton-envelope wave functions in terms of appropriate Gaussian functions. The electron and hole cyclotron resonances and intra-magnetoexciton transitions are theoretically studied by exciting the allowed electron, hole and internal magnetoexcitonic transitions with far-infrared radiation. Theoretical results are obtained for both the intra-magnetoexciton transition energies and oscillator strengths associated with excitations from 1s - like to 2s, 2p±, and 3p±- like magnetoexciton states, and from 2p- to 2s – like exciton states. Present results are in overall agreement with available optically detected resonance measurements and clarifies a number of queries in previous theoretical work.
Electron scattering in two-dimensional disordered heterostruetures
Authors: Gómez I. , Diez E. , Domínguez-Adame F. , Orellana P.
Published: April 2011

The main aim of this work is to study electron scattering in imperfect semiconductor heterostruetures. The source of unintentional disorder is the interface roughness at the heterojunctions occurring during growth. In order to achieve this goal we solve numerically the two–dimensional Ben Daniel–Duke equation for the electron scattering problem. Our model assumes open boundary conditions along the growth direction and periodic ones parallel to the heterojunctions. We then compute the reflection and transmission matrices that govern channel mixing due to interface roughness scattering. The knowledge of the mixing matrices allow us to calculate the transmission coefficient in any heterostruc-ture made of wide gap semiconductors. As an example, we compute the transmission coefficient in resonant tunneling devices based on double-barrier structures.
Sb-terminated InAs(001)-(2×4) and (2×8) studied using scanning tunneling microscopy and ab initio density functional theory
Authors: Barvosa-Carter William , Grosse Frank , Owen James H. G. , Zinck Jennifer J.
Published: April 2011

We have studied the structure of MBE-grown InAs(001)-(2×4) surfaces exposed to low Sb2 fluxes by scanning tunneling microscopy (STM) and ab initio density functional theory (DFT). Experimentally, we observe an Sb-terminated α2(2×4) phase over a wide range of temperatures (400–510 °C) for low Sb2 flux (<0.1 ML/s), whereas temperature and As2 flux must be carefully controlled to achieve the same As-terminated surface structure. At lower temperatures, we observe indications of an Sb-terminated (2×8) symmetry surface phase, and we report briefly on its proposed structure and stability, as well as its possible role in subsequent formation of the Sb-terminated (1×3) phase found at typical Sb2 fluxes used during heterostructure growth.
Asymmetric Hybrid Al(Ga)SbAs/InAs/Cd(Mg)Se Heterostructures for Mid-IR LEDS and Lasers
Authors: Ivanov S. V. , Kaygorodov V. A. , Solov'ev V. A. , Ivanov E. V. , Moiseev K. D. , Sorokin S. V. , Meltzer B. Ya. , Semenov A. N. , Mikhailova M. P. , Yakovlev Yu. P. , Kop'ev P. S.
Published: April 2011

A hybrid double heterostructure with large asymmetric band offsets, combining AlAsSb/InAs (as a III–V part) and CdMgSe/CdSe (as a II–VI part), has been proposed as a basic element of a mid-infrared laser structure design. The p-i-n diode structure has been successfully grown by molecular beam epitaxy (MBE) and exhibited an intense long-wavelength electroluminescence at 3.12 μm (300K). A II–VI MBE growth initiation with a thin ZnTe buffer layer prior to the CdMgSe deposition results in a dramatic reduction of defect density originating at the II–VI/III–V interface, as demonstrated by transmission electron microscopy. A less than 10 times reduction of electroluminescence intensity from 77 to 300K indicates an efficient carrier confinement in the InAs active layer due to high potential barriers in conduction and valence bands, estimated as ΔEC = 1.28 eV and ΔEV ∼ 1.6 eV. An increase in the pumping current results in a super-linear raising the EL intensity. The type of band line up at the coherent InAs/Cd1−xMgxSe interface is discussed for 0≤x≤0.2, using experimental data and theoretical estimations within a model-solid theory.
Airplane and Drop Experiments on Crystallization of InxGa1-xSb Semiconductor under Different Gravity Conditions
Authors: Balakrishnan Krishnan , Hayakawa Yasuhiro , Komatsu Hideki , Murakami Noriaki , Nakamura Tetsuo , Kimura Tadashi , Ozawa Tetsuo , Okano Yasunori , Miyazawa Masafumi , Dost Sadik , Dao Le. H. , Kumagawa Masashi
Published: April 2011

Melting and crystallization experiments of InGaSb were done under the reduced gravity condition (10–2G) in an airplane and at the normal gravity condition (1G) in the laboratory. Crystallized InGaSb was found to contain many needle crystals in both the cases. Reduced gravity condition was found to be more conducive for crystal growth than the normal gravity condition. Formation of spherical projections on the surface of InGaSb during its crystallization was in-situ observed using a high speed CCD camera in the drop experiment. Spherical projections showed dependence of gravity during its growth. Indium compositions in the spherical projections were found to vary depending on the temperature.
Characterization of LiInS2 and LiInSe2 single crystals for nonlinear optical applications
Authors: Isaenko Ludmila , Yelisseyev Alexander , Lobanov Sergei , Panich Alexander , Vedenyapin Vitaly , Smirnova Julia , Petrov Valentin , Zondy Jean-Jacques , Knippels Guido
Published: April 2011

X-ray structural analysis, nuclear magnetic resonance, optical spectroscopy and second harmonic generation were used to characterize the new nonlinear crystals LiInS2 and LiInSe2 which possess maximum band gap (3.59 and 2.86 eV at 300 K, respectively) among ternary chalcogenides. As grown crystals are only slightly colored while color change after annealing is due to native point defects.
Transmission Characterization of Drilled Alternating-Layer Three-Dimensional Photonic Crystals
Authors: Kuramochi Eiichi , Notomi Masaya , Yokohama Itaru , Takahashi Jun-ichi , Takahashi Chiharu , Kawashima Takayuki , Kawakami Shojiro
Published: April 2011

We propose a new three-dimensional photonic crystal structure or drilled alternating-layer photonic crystal (DALPC), which can be fabricated by a combination of the deposition of alternating layers of dielectric films and one-time dry etching. Our band calculation predicts that the DALPC has a photonic band gap (PBG) in all directions. We fabricated a Si/SiO2DALPC by electron beam lithography, bias sputtering, and fluoride-gas electron cyclotron resonance etching. We measured the light transmission of the DALPC sample in both the in-plane and vertical directions. We observed a transmission minimum around the 1.4-μm-wavelength for all measured directions and TE/TM polarizations, which demonstrated a potential of the DALPC as a three-dimensional PBG material.
Interference lithography for 3D photonic band gap crystal layer by layer fabrication
Authors: Feigel A , Kotler Z. , Sfez B. , Arsh A. , Klebanov M. , Lyubin V.
Published: April 2011

We present fabrication of 3D photonic band gap woodpile crystals from photosensitive chalcogenide glass with the help of interference lithography and layer by layer construction. The alignment method is described, which is scalable to extremely small feature sizes required for photonic crystals in the visible region.
Two Dimensional Photonic Crystal Modes and Resonances in Three-dimensional Structures
Authors: Fan Shanhui , Joannopoulos J. D.
Published: April 2011

We present three-dimensional analysis of two-dimensional guided resonances in photonic crystal slab structures. This analysis leads to a new understanding of the complex spectral properties of such systems. Specifically, we calculate the dispersion diagrams, the modal patterns, and transmission and reflection spectra of these resonances. From these calculations, a key observation emerges involving the presence of two temporal pathways for transmission and reflection processes. Using this insight, we introduce a general physical model that explains the essential features of complex spectral properties. Finally, we show that the quality factors of these resonances are strongly influenced by the symmetry of the modes, and the strength of the index modulation.
Artificial Second Order Non-Linearity in Photonic Crystals
Authors: Feigel A , Kotler Z. , Sfez B.
Published: April 2011

We describe a technique for obtaining effective second order non-linearity χ2 in non centro-symmetric Photonic Crystal made from centro-symmetric materials (e.g. glass, Ge or Si). The effect is based on the electric quadrupole transition, strong electromagnetic mode deformation and different contributions to the volume polarization from different parts of the photonic crystal1.
Profiling electric fields around dislocations in GaN
Authors: Cherns D. , Jiao C.G. , Mokhtari H.
Published: April 2011

Electron holography has been used to measure the electric potential around edge and screw dislocations in n-GaN viewed in a near end-on geometry. It is shown that the potential at edge dislocations is 2V below that in the bulk consistent with a negative charge of 2 electrons/c (c = 0.52nm). Preliminary results, which suggest that screw dislocations are also negatively charged, are discussed.
Band Gap Shift of GaN under Uniaxial Strain Compression
Authors: Peng H. Y. , McCluskey M. D. , Gupta Y. M. , Kneissl M. , Johnson N. M.
Published: April 2011

The band-gap shift of GaN:Mg epilayers on (0001)-oriented sapphire was studied as a function of uniaxial strain compression along the c-axis using time-resolved, optical absorption measurements in shock wave experiments. For longitudinal stresses ranging from 4 to 14 GPa, the band gap shift is approximately 0.026 eV/GPa. Combining this result with the known behavior of wurtzite GaN under hydrostatic pressure and biaxial stress, a new set of deformation potentials has been estimated: acz-D1 = -10.2 eV, act-D2 = -7.9 eV, D3 = 1.33 eV and D4 = -0.74 eV. A slow band gap shift is also observed following the immediate band gap increase upon impact. This phenomenon can be explained by a time-dependent screening of the piezoelectric field.
Improved Mobilities and Resistivities in Modulation-Doped P-type AlGaN / GaN Superlattices
Authors: Waldron Erik L. , Graff John W. , Schubert E. Fred , Dabiran Amir M.
Published: April 2011

P-type AlGaN / GaN superlattice structures have demonstrated higher acceptor activation due to a modulated valence band resulting from the superlattice as well as spontaneous and piezoelectric polarization fields. The polarization effects are due to the wurtzite structure of AlGaN and the strain present in AlxGa1-xN / GaN heterostructures. Variable temperature Hall effect studies of Mg doped Al0.20Ga0.80N / GaN superlattices reveal an improvement in resistivity and mobility for modulation-doped structures versus uniformly doped structures. Very low resistivities less than 0.1 & cm and hole mobilities ~ 36 cm2/V s are demonstrated. This improvement is attributed to a reduction of neutral and ionized impurity scattering for the two-dimensional hole gas present in the GaN layers of the modulation-doped superlattice. The improvement is greatest at temperatures below ~ 150 K. The doped regions of the superlattices have Mg concentrations of ~1019 cm-3. Two modulation-doped samples were grown by MBE: a standard scheme with dopants only in the AlGaN barriers, and a shifted scheme with dopants concentrated near the AlGaN / GaN interfaces. The standard sample has mobilities of 8.9 and 36 cm2/V s at 300 and 90 K, respectively. Resistivities of the standard sample are 0.21 and 0.068 Ω cm at 300 and 90 K, respectively. Carrier concentrations for this sample are 3.4 and 2.5 x 1018 cm-3 at 300 and 90 K, respectively. Capacitance-voltage profiling on the samples shows a clear indication of a two-dimensional hole gas as well as the periodicity of the superlattice.
High Efficiency UV-Emission at 345 nm from InAlGaN Light-Emitting Diodes
Authors: Kinoshita A. , Hirayama H. , Ainoya M. , Yamabi T. , Hirata A. , Aoyagi Y.
Published: April 2011

Optical and electrical properties of 340 nm-band bright UV-light emitting diodes (LEDs) were compared between In0.03Al0.20Ga0.77N and other active regions. Single peaked and high efficiency ultraviolet (UV) emission at 345 nm from In0.03Al0.20Ga0.77N LEDs is achieved under continuous current injection conditions. Any significant broadening and peak shift of the electroluminescence (EL) spectrum were not observed. We attribute such a good properties to using of high quality InAlGaN-quaternary active layer. The EL intensity of the InAlGaN quaternary-based LED showed more one order of magnitude higher intensity than that of AlGaN and GaN based LEDs. Additionally, The I-L characteristics of the InAlGaN quaternary-based LED showed a linearly increasing of intensity with increasing of injection current density, that is also observed for InGaN based LEDs. This shows the recombination efficiency of the InAlGaN-based LED is as much as that of InGaN based LEDs. From these results InAlGaN quaternary is expected to be a promising material for UV LEDs and LDs.
Growth of GaN epilayers on Si(111) substrates using multiple buffer layers
Authors: Hageman P.R. , Haffouz S. , Grzegorczk A. , Kirilyuk V. , Larsen P.K.
Published: April 2011

We present a study of the growth of high quality GaN films on Si(111) substrates by MetalOrganic Chemical Vapor Deposition technique. In order to improve the quality of the epitaxial films we introduced different nucleation or buffer layers and combinations of them. Our results obtained on an optimized AlN nucleation layer will serve as reference point. In order to improve the quality of the epitaxial films we introduced different combinations of nucleation and intermediate layers. The first combination consists of an optimized AlN nucleation layer followed by a 1 m-thick GaN film, on which we deposited SixNy/GaN intermediate layers. Based on the optimized AlN nucleation layer, we introduced AlGaN/GaN superlattices or AlN intermediate buffer layers. Additionally, we present results on the modification the Si(111) surface with NH3 to promote nucleation from selective GaN islands. In all experiments the total thickness of the GaN epilayers was 3 m m. X-ray diffraction, photoluminescence, Hall measurements and atomic force microscopy were used in order to elucidate the effectiveness of these growth processes. For the most successful deposition scheme, the one with the SixNy/GaN intermediate layers, the resulting GaN layers are of high quality as compared to the other methods. The donor bound exciton, which dominates the photoluminescence spectrum, showed a full width at half maximum (FWHM) of about 50 meV at room temperature and 10 meV at 4K. The FWHM of the symmetric (0002) rocking curves in w-scan is about 640 arcsec. The root-mean-square roughness, as measured by atomic force microscopy, does not exceed 10 Å.
V - III ratio effect on Cubic GaN Grown by RF Plasma Assisted Gas Source MBE
Authors: Sung Li-Wei , Lin Hao-Hsiung , Chia Chih-Ta
Published: April 2011

We report the investigation on the growth conditions and optical properties of cubic GaN films grown on (001) GaAs substrate by using RF plasma assisted gas source MBE. The cubic GaN films were deposited at different Ga to N flux ratios that were determined by deposition rates directly. Three growth regimes, namely, Ga droplet, intermediate Ga stable, and N stable regime, are defined in the growth diagram. Optical quality of these films was determined by using photoluminescence (PL). Micro-Raman scattering were performed to analyze the crystallinity of the films. Optimal growth condition of cubic GaN is on the boundary of intermediate Ga stable regime and Ga droplet regime at a growth temperature of Ts = 720°C.
Electroluminescence And Photoluminescence Studies Of A Nitride-Rich GaN1-XPx SQW Structure LED Grown By Laser-Assisted Metal-Organic Chemical Vapor Deposition
Authors: Kikawa Junjiroh , Yoshida Seikoh , Itoh Yoshiteru
Published: April 2011

We fabricated a light-emitting diode (LED) having a nitride-rich GaN1-xPx single quantum well (SQW) structure grown using laser-assisted metal-organic chemical vapor deposition (LA-MOCVD). The peak energy of the electroluminescence (EL) of the LED was 2.88 eV, which is in the vicinity of the energy due to the recombination of the bounding exciton by P atoms, known as an isoelectronic trap in GaN. We observed a blue shift of this peak by increasing the drive current. We also observed extra emission of band-to-band recombination at about 3.4 eV above a drive current of 32 mA, where the external quantum efficiency was already saturated.
Effect of Excimer Laser Annealing on Optical Properties of GaN Films Deposited by R.F. Magnetron Sputtering
Authors: Sung Man Young , Sung Woong-Je , Lee Yong-Il , Park Chun-Il , Choi Woo-Boem , Kim Sangsig
Published: April 2011

Abstract:GaN thin films on sapphire were grown by RF magnetron sputtering with ZnO buffer layer. The tremendous mismatch between the lattices of GaN and sapphire can be partly overcome by the use of thin buffer layer of ZnO. The dependence of GaN film quality on ZnO buffer layer was investigated by X-ray diffraction(XRD). The properties of the sputtered GaN are strongly dependent on ZnO buffer layer thickness. The optimum thickness of ZnO buffer layer is around 30nm. Using XRD analysis, we have found the optimal substrate temperature which can grow high quality GaN thin film. In addition, the effect of excimer laser annealing(ELA) on structural and electrical properties of GaN thin films was investigated. The surface roughness and images according to the laser energy density were investigated by atomic force microscopy(AFM) and it was confirmed that the crystallization was improved by increasing laser energy density.
Light emitters fabricated on bulk GaN substrates. Challenges and achievements.
Authors: Perlin Piotr , ski M. Leszczy , Prystawko P. , Czernecki R. , Nowak G. , Wisniewski P. , Dmowski L. , Teisseyre H. , Litwin-Staszewska E. , Suski T. , Grzegory I. , Porowski S. , Ivanov V.Yu. , Godlewski M. , Holst J. , Hoffman A.
Published: April 2011

We used high-pressure grown GaN single crystal substrates to fabricate dislocation free optoelectronic devices like light emitting diodes and laser diodes structures. The latter ones demonstrated laser action under optical pumping condition with the threshold of about 200 kW/cm2 at room temperature. In the present paper we would focus on the specific aspects of the homoepitaxial growth by MOVPE method including epi-ready substrate preparation and surface polarity choice. We believe that our results demonstrate clearly the feasibility of device fabrication based on high-pressure grown GaN bulk crystals.
Superior Structural Quality of Newly Developed GaN Pendeo-Epitaxial Layers.
Authors: Liliental-Weber Z. , Jasinski J. , Cherns D. , Baines M. , Davis R.
Published: April 2011

Transmission electron microscopy of plan-view and cross-section samples of pendeo-epitaxial layers is described. Samples grown with and without silicon nitride masks are compared. A large misorientation of the GaN grown above the mask was observed, with 2-3° tilt between wing and seed areas, caused by additional nucleation on the mask layer. Some misorientation was also observed between wing/wing areas of the sample. Samples grown without silicon nitride masks show much smaller misorientations and contain different types of defects.
Compositional and structural studies of amorphous GaN grown by ion-assisted deposition
Authors: Lanke U. D. , Koo A. , Ruck B. J. , Lee H. K. , Markwitz A. , Kennedy V. J. , Ariza M. J. , Jones D. J. , Rozière J. , Bittar A. , Trodahl H. J.
Published: April 2011

Amorphous GaN films have been deposited onto various substrates by ion-assisted deposition. The films were deposited at room temperature using nitrogen ion energies in the range 40-900 eV. Rutherford backscattering spectroscopy and nuclear reaction analysis show that the Ga:N atomic ratio is approximately one for films grown with ion energy near 500 eV; these films have the highest transparency. Films grown with ion energies below 300 eV are Ga rich, and show reduced transparency across the visible. Raman spectroscopy, x-ray diffraction, and transmission electron microscopy confirm the amorphous nature of the films. Annealing studies on a-GaN establish that the films begin to crystallise at a temperature of about 700 C. To investigate the local bonding environment of the Ga or N atoms, we have measured the extended x-ray absorption fine structure (EXAFS) of the transparent GaN films. The EXAFS results indicate that the films are dominated by heteropolar tetrahedral bonding, with a low density of homopolar bonds.
Study of High Nitrogen Compositions GaNAs and GaInNAs Material Quality by X-ray Diffraction and Photoluminescence
Authors: Ng T. K. , Yoon S. F. , Wang S. Z. , Loke W. K. , Fan W. J.
Published: April 2011

GaNAs and GaInNAs growths are subjects of considerable interest due to its technological importance in long wavelength lasers emitting within the optical-fiber communication wavelength window (1.31 – 1.55 m m). We study GaNAs and GaInNAs materials growth on (100) semi-insulating GaAs substrate with high nitrogen compositions (>2%) using a solid source molecular beam epitaxy (SSMBE) system in conjunction with a RF plasma source. GaNAs layer with high nitrogen compositions of 4.85% and 6% with good XRD peak intensities were successfully grown. GaInNAs quantum wells (QWs) were then grown with reference to the nitrogen compositions measured in the GaNAs materials to obtain nitrogen compositions > 2%. The photoluminescence (PL) peak positions of the GaInNAs QWs blueshifted after annealing at 840°C and 10min. It was found that the blueshift of PL peaks are highly dependent on nitrogen compositions.
Similarities in the Optical Properties of Hexagonal and Cubic InGaN Quantum Wells
Authors: Chichibu S. F. , Sugiyama M. , Onuma T. , Kuroda T. , Tackeuchi A. , Sota T. , Kitamura T. , Nakanishi H. , Ishida Y. , Okumura H. , Keller S. , Mishra U. K. , DenBaars S. P. , Nakamura S.
Published: April 2011

Optical properties of fully-strained wurtzite and zincblende InxGa1-xN/GaN multiple quantum well (MQW) structures were compared to discuss the origin of exciton localization. In contrast to the hexagonal InGaN MQWs, the photoluminescence (PL) peak energy of cubic InGaN MQWs showed a moderate blueshift with decreasing well thickness, L, and low-temperature PL decay time of the cubic MQWs did not depend strongly on L. The results imply that the wavefunction overlap in cubic InGaN MQWs was not reduced compared to the hexagonal ones, since they do not suffer from the electric field normal to the QW plane due either to spontaneous or piezoelectric polarization. Both MQWs exhibited a large and composition-dependent bandgap bowing, and time-resolved PL (TR-PL) signals showed a stretched-exponential decay even at room temperature. The exciton localization is considered to be an intrinsic property of InGaN.
Characterization of high-quality epitaxial AlN films grown by MOVPE
Authors: Shibata Tomohiko , Asai Keiichiro , Nagai Teruyo , Sumiya Shigeaki , Tanaka Mitsuhiro , Oda Osamu , Miyake Hideto , Hiramatsu Kazumasa
Published: April 2011

This paper presents the correlation between overall crystal mosaicities and dislocation behaviors of high-quality AlN epitaxial films grown on a C-plane sapphire substrate using a low-pressure metal organic vapor phase epitaxy (LP-MOVPE) method. Typical full width at half maximum (FWHM) values of x-ray rocking curves (XRC) for (0002) and (10-10) of the AlN are 80arcsec and 1800arcsec, respectively. From transmission electron microscopy (TEM) observations, edge-type dislocations thread the AlN layer, however, almost all screw-type dislocations disappear at an early AlN growth stage. The dislocation density of the AlN films in its surface region is as low as approximately 1x1010 cm-2. The distribution of the dislocations is considered to be caused by a large twisted mosaicity and a very small tilted mosaicity.
Helical-Type Surface Defects in GaN and InGaN Thin Films Epitaxially Grown on GaN Templates at Reduced Temperatures
Authors: Miraglia Peter , Preble Edward , Roskowski Amy , Einfeldt Sven , Davis Robert F.
Published: April 2011

The surface morphologies of GaN and InGaN films grown at 780°C by metalorganic vapor phase epitaxy were determined using atomic force microscopy. A qualitative model is presented to explain observed instabilities in the step morphology of these films, namely, the formation of hillock islands and v-defects that give rise to surface roughening. The latter are a result of a boundary dragging effect, where interactions occur between the movement of homogeneous and heterogeneous steps and the tendency to form atom clusters in the terrace in the transition in kinetic growth regime. The tendency to form v-defects was associated with dislocation density. A delay in the formation of v-defects in InGaN was observed and associated with the ammonia partial pressure and the interactions between hillock islands and pure screw or mixed dislocations. Hillock island formation was attributed to a transition in thermodynamic mode to three-dimensional island growth. Explanations for the foregoing observations are based on growth model theory previously developed by Burton, Cabrera, and Frank (BCF) and on changes in the surface kinetics with temperature, In composition, and gas phase composition.
Effect of Crystalization On Photoluminescence of ER2O3 Thin Films
Authors: Duan Xiaoman , Saini Sajan , Chen Keven , Lipson Michel , Michel Jurgen , Kimerling Lionel C.
Published: April 2011

The effect of microstructures on the photoluminescence of Er2O3thin films has been systematically studied in this paper. The Er2O3 film was fabricated via reactive sputtering of Er metal in an Ar/O2 atmosphere. The as-deposited thin film contained both amorphous and polycrystalline structures, which showed weak photoluminescence at 1.55 µm. Annealing at an elevated temperature from 650 to 1050 °C in O2 ambient significantly incorporated oxygen into the lattice and strongly promoted crystalline grain growth, which in turn dramatically induced the transaction of photoluminescence from 1.55 µm to 1.541 µm. The ideal large crystal Er2O3 structure with fcc-Er2O3 and bcc-Er2O3 precipitates was obtained by conducting a two-step annealing (650 °C for 5 hours followed by 1020 °C for 2 hours) which resulted in a sharp photoluminescence peak at 1.541 µm. Further significant enhancement of PL at 1.541 µm was achieved via RTA at 1050 °C for 30 seconds to introduce more fcc-Er2O3 precipitates into the bcc-Er2O3 matrix.
Optical Characterization of Cadmium Telluride Doped Heterostructured Opaline Photonic Crystal
Authors: Solovyev V. G. , Romanov S.G. , Torres C.M. Sotomayor , Gaponik N. , Eychmüller A. , Rogach A. L.
Published: April 2011

A double-layer photonic crystal (PhC) possessing incomplete photonic band gap (PBG) has been prepared by successive formation of one opaline film on top of another and subsequent impregnation with CdTe colloidal nanocrystals as the light source. Transmission, reflection and photoluminescence (PL) spectra of this nanocomposite have been measured from 1.8 to 2.5 eV at different angles of the light incidence and detection. The suppression of emission intensity has been found at both stop bands of the PhC heterostructure. Depending on the excitation power, either suppression or enhancement of the emission rate at the stop band has been observed.
Artificial Second Order Non-Linearity in Photonic Crystals.
Authors: Feigel A , Kotler Z. , Sfez B.
Published: April 2011

We describe a technique for obtaining effective second order non-linearity λ2in non centro-symmetric Photonic Crystal made from centro-symmetric materials (e.g. glass, Ge or Si). The effect is based on the electric quadrupole transition, strong electromagnetic mode deformation and different contributions to the volume polarization from different parts of the photonic crystal1.
Plastic Deformation of Thin Films – Bending
Authors: Nozaki T. , Kogure Y. , Doyama Masao
Published: April 2011

Widely accepted model of bending of a single crystal suggests that edge dislocations are introduced from both the compressed surface and extended surface. The present study examined this model by molecular dynamics using an embedded potential. Shockley partial dislocations are created on the compressed surface. Due to the characteristics of inter atomic potential, the stress on the compression surface is higher than that on the extended surface.
Stress-Strain Response of Free-Standing Nano-Crystalline Gold Thin-Films
Authors: Gudlavalleti Sauri , Kumar Sharvan , Anand Lallit
Published: April 2011

Free-standing gold thin-film tension specimens of thicknesses in the range 500-700 nm were fabricated by e-beam deposition methods. The films have grains which have thicknesses essentially equal to the film thickness, and an in-plane grain-size distribution which is bi-modal, with a collection of small grains with an average size of 130 nm, and another collection of larger grains with an average size of 380 nm. The films possess a strong texture with the {111} crystallographic planes aligned with the plane of the film. The thin-film specimens have been tested in simple tension using a novel testing machine which enables measurement of the elastic-plastic stress-strain response of the films with high resolution. The experiments show that the gold thin-films have an initial yield strength of around 100 MPa, which is followed by rapid strain hardening to a stress level of 360 MPa at a strain of only ~1.2%, at which point the specimens fail abruptly. Transmission electron microscopy (TEM) investigations of the deformed films shows that the rapid strain hardening is attributable to extensive dislocation activity in the larger grains. The reason behind the low ductility in our gold specimens is still unclear, but it may be attributable to the observed lack of dislocation activity in the smaller grains, whose boundaries then serve as easier sites for alternative inelastic mechanisms such as grain boundary sliding and decohesion leading to low macroscopic strains to failure.
Effects of Surface Constraints on Stresses in Heteroepitaxial Films Grown on Compliant Substrates
Authors: Feng Zhaohua , Lovell Edward G. , Engelstad Roxann L. , Kuech Thomas F.
Published: April 2011

As films heteroepitaxially grow on substrates, lattice mismatch strain at the interfaces causes stresses in the films and substrates. These stresses can have deleterious effects on film quality. To facilitate an understanding of defect production and control during growth of films on compliant substrates, transient finite element models were developed to simulate the complete mechanical stress and strain fields. Effects of constraints between the template and handle wafer on the film stresses were examined. The investigation showed that different types of constraints caused stress variations over a large range. Other factors affecting the stresses, such as lattice mismatch strain, wafer radius, film and template thickness, were also assessed.
Structural Properties of Carbon Nitride Films Deposited by Reactive - Pulsed Laser Deposition Technique
Authors: Phani A.R. , Krzanowski J.E. , Nainaparampil J.J.
Published: April 2011

Carbon nitride films have been deposited by the reactive pulsed laser deposition technique by ablating carbon in a nitrogen atmosphere at different substrate temperatures and different background pressures of nitrogen. Si(111) and 440C steel substrates were used in the present investigation. Deposited films are uniform and show good adhesion to the substrates. The deposition rates depend on laser fluence, background pressure, and target-substrate distance. The nitrogen concentration in the deposited films increases with increasing background nitrogen gas pressure and laser fluence. Fourier transform infrared spectroscopy has been employed to evaluated CN bonds. X-ray photoelectron spectroscopy has been used to study the composition of the deposited films. X-ray diffraction and atomic force microscopy techniques revealed that the deposited films have an oriented microcrystalline structure after annealing at 900°C with smooth surface. Electronic, mechanical and tribological properties of these films have also been discussed.
Self-Formed Aluminum Nitride Microtubes that Exhibit a Large Bending Stress
Authors: Akiyama Morito , Shobu Kazuhisa , Xu Chao-Nan , Nonaka Kazuhiro
Published: April 2011

We have investigated the aluminum nitride microtubes made of aluminum nitride thin film. Aluminum nitride thin film deposited on aluminum foil forms microtubes of itself at room temperature when the aluminum foil is dissolved in hydrochloric acid solution. The aluminum nitride microtubes exhibit a large bending stress of 1100 94 megapascals. The bending stress is more than three times larger than the bending strength of aluminum nitride bulk. The diameter of the microtubes is proportional to the film thickness. The bending stress is independent of the film thickness and is fixed.
Postbuckled Square Thin Film Membranes Under Differential Pressure
Authors: Kramer Torsten , Paul Oliver
Published: April 2011

We report quantitative results on the load-deflection response of compressively prestressed square membranes under differential pressure. The membranes consist of 0.485 μm and 1.9 μm thick silicon nitride films. For these square membranes we observed a new symmetry transition of the deflection profile between a state without reflection symmetries at small loads to a state with reflection symmetries at sufficiently large loads. The load-deflection response was modeled by finite element simulations covering a wide range of prestrains e0 and pressures using various geometries. From the symmetry transition process, Young's modulus E = (150±5) GPa and the prestrain ε0 = (1.6±0.1) 10-3 of the membrane material was extracted.
Strain Rate Dependent Behavior of Pure Aluminum and Copper Micro-Wires
Authors: El-Deiry P. A. , Vinci R. P.
Published: April 2011

In order to shed light on the role that grain boundaries and dislocations play in anelastic relaxation of thin films and small-scale structures, we measured the effective elastic moduli of 99.99% pure Al and Cu 10 m m diameter micro-wires in the as-received (drawn and slight tempered) and annealed states. Moduli were determined using microtensile tests at various strain rates (6.7x10-6s-1, 1.3x10-5s-1, 2.6x10-5s-1, 4.5x10-5s-1, 2.5x10-4s-1, 4.5x10-4s-1). Focused-ion beam scanning electron microscopy was used for imaging grain sizes. Results from the as-received wires are compared with the annealed wires to illustrate the effects of grain size and dislocation density on effective moduli, which closely relates to grain boundary sliding and dislocation motion, respectively. We conclude that microstructure is more significant than scale in inducing anelasticity in small-scale wires and, by extension, thin films.
Void Intergranual Motion Under the Action of Electromigration Forces in Thin Film Interconnects with Bamboo Structure
Authors: Oren Ersin Emre , Ogurtani Tarik Omer
Published: April 2011

The rigorous formulation of the internal entropy production, and the generalized forces and conjugate fluxes associated with the virtual displacement of a triple junction are presented in multi-component systems. Extensive computer simulations are performed on the void configurational evolution during the intergranual motion; under the actions of capillary and electromigration forces in thin film metallic interconnects with bamboo structure having various grain textures. The texture studies in this work show clearly that there are two different and very distinct modes, namely: the grain boundary carving or tearing mode, and the interconnect edge cutting mode by the oblique slit formation (about 450) on the wind-side of the grain boundary.
Mechanical Behavior of Contact Aluminum Alloy
Authors: Read David T. , Cheng Yi-Wen , McColskey J. David , Keller Robert R.
Published: April 2011

We report the results of tensile tests of thin films of Al-0.5 % Cu deposited on bare silicon. This material was subjected to the complete CMOS fabrication process, including a high-temperature heat treatment. Contact metal makes the electrical connection between the metal wiring and the silicon transistors in a chip. Room-temperature values of yield strength, ultimate tensile strength, and elongation were all lower than the corresponding values found previously for pure electron-beam-evaporated aluminum films. The strengths and elongation decreased slightly as the specimen temperature was raised from 25 to 150°C. The slopes of the stress-strain curves from unloading-reloading runs were lower than the accepted Young's modulus of bulk polycrystalline aluminum. The results are interpreted with the help of scanning and transmission electron microscopy.
Magnetoresistive, Mechanically Hard Superlattices of CrN, NbN, TiN Multilayers Deposited on Monocrystalline Si Wafers
Authors: Wolkenberg Andrzej , Wrzesinska Hanna , Bochenek Andrzej , Tokarz Adam , Nitkiewicz Zygmunt , Przeslawski Tomasz , Ratajczak Jacek , Dluzewski Piotr
Published: April 2011

Hardness measurements on thin films have to face the problem of the effect of the substrate hardness on the obtained result. Also the method of hardness measurement exerts a considerable influence on the experimental data. Some models, which take such effects into account, are presented. We describe experimental results of hardness measurements made with the Vickers 5g probe. Nitride layers (CrN, TiN, NbN), superlattices composed of these nitrides and thin metal films deposited either on the monocrystalline Si or metallic substrates such as steel or copper have been investigated.

We also present measurements of the magnetoresistivity (MR) effect. on superlattices, which consist of the multilayers TiN/NbN deposited on Si substrates. Layers of different thickness of TiN and NbN obtained by the reactive sputtering method with different superlattice period values (L) and number have been studied. The composite hardness of the structures (superlattice on Si) was found to reach 80 GPa and MR value in the best probes was ~80% (for fields from some Gs to kGs). When the supporting thin metallic layer was present, then its influence on the composite hardness was also observed.
Epitaxial Island Growth and the Stranski-Krastanow Transition
Authors: Cullis A.G. , Norris D.J. , Walther T. , Migliorato M.A. , Hopkinson M.
Published: April 2011

The way in which the Stranski-Krastanow epitaxial islanding transition can be controlled by strain due to elemental segregation within the initially-formed flat ‘wetting’ layer is examined in detail. Experimentally measured critical ‘wetting’ layer thicknesses for the InxGa1−xAs/GaAs system (x = 0.25 - 1) are demonstrated to show good agreement with values calculated using a segregation model. The strain energy associated with the segregated surface layer is determined for the complete range of deposited In concentrations using atomistic simulations. The segregation-mediated driving force for the Stranski-Krastanow transition is considered to be important also for all other epitaxial systems exhibiting the transition.
Composition and Structure of Epitaxial CaF2 Layers at the First Stages of Their Growth on Si(111)
Authors: Würz R. , Bohne W. , Fuhs W. , Röhrich J. , Schmidt M. , Schöpke A. , Selle B.
Published: April 2011

CaF2 films with thicknesses in the monolayer range (<20 Å) were grown on Si(111) by evaporation from a CaF2 source at UHV conditions. They were characterized ex-situ by Heavy-Ion Elastic Recoil Detection Analysis (HI-ERDA), RBS/Channeling, X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM). The F/Ca ratio of the films was found to depend on the growth temperature Ts and to deviate appreciably from the stoichiometric composition (F/Ca=2). Due to an interface reaction which leads to a CaF-interface layer a change from polycrystalline to epitaxial growth occurs at Ts=450°C. At higher temperature film growth started with a closed layer of CaF on top of which CaF2 layers with an increasing fraction of pinholes were formed. By means of a two-step process at different temperatures, the amount of pinholes could be strongly reduced. It was found, that buffer layers of CaF2 with a CaF interface layer introduced in Au/p-Si contacts enhance the barrier height by as much as 0.36eV to values of 0.64eV.
Evolution of Stress and Relaxation of Strain of Ge and SiGe Alloy Films on Si(001)
Authors: Koch R. , Schulz J. J. , Wassermann B. , Wedler G.
Published: April 2011

We report on real time stress measurements by a sensitive cantilever beam technique of Ge and SiGe Alloy Films on Si(001) in combination with structural investigations by in situ STM (scanning tunneling microscopy) and ex situ AFM (atomic force microscopy). Characteristic features in the stress curves provide detailed insight into the development and relief of the misfit strain as well as the respective growth mode. For the Stranski-Krastanow system Ge/Si(001) the strain relaxation proceeds mainly in two steps: (i) by the formation of 3D islands on top of the Ge wetting layer and (ii) via misfit dislocations in larger 3D islands and upon their percolation. Co-deposition of Si influences the stress behavior drastically. The growth mode changes from Stranski-Krastanow to a kinetic 3D island mode at Si concentrations of about 20% leading to the so far smallest quantum dots of the Ge/Si system.