bluuebunny/crossref_metadata_2025 huggingface dataset:
Movpe Growth of High Quality AlxGa1−xN/GayIn1-yN (x>0, y<1) Heterostructures for Short Wavelength Light Emitter
Authors: Akasaki I. , Amano H.
Published: April 2011

High-quality AlGaN/GaN and AlGaN/GalnN DHs were fabricated by MOVPE using low-temperature deposited AlN buffer layer. We applied the newly designed dual-flow-channel reactor, by which high-quality and well-controlled AlGaN and GalnN alloys and their heterostructures have been grown. AlGaN/GaN-DH shows low-threshold stimulated emission by optical pumping at room temperature for both edge and surface modes. The peak wavelength of stimulated emission for edge mode was 369.5nm. The peak wavelength of stimulated emission was affected by the strain due to heterostructure as well as the many body effect under high excitation. The wavelength for stimulated emission can be widely changed by using GalnN as the active layer. AlGaN/GalnN DH with InN molar fraction of the active layer of 0.09 shows room temperature low-threshold stimulated emission for edge mode by optical pumping with peak wavelength of 402.5nm. A few mW-class symmetrical AlGaN/GaN DH LED and anti symmetrical AlGaN/GalnN/GaN DH LED using low energy electron beam irradiation (LEEB1) treated Mg-doped P-AlGaN cladding layer were fabricated. These results show that column-Ill nitrides are promising for the realization of practical short wavelength LED and LD.
Buffer Layer Thickness and the Properties of InN Thin Films on AIN- Seeded (00.1) Sapphire And (111) Silicon
Authors: Kistenmacher T. J. , Ecelberger S. A. , Bryden W. A.
Published: April 2011

Introduction of a buffer layer to facilitate heteroepitaxy in thin films of the Group IIIA nitrides has had a tremendous impact on growth morphology and electrical transport. While AIN- and self-seeded growth of GaN has captured the majority of attention, the use of AIN-buffered substrates for InN thin films has also had considerable success. Herein, the properties of InN thin films grown by reactive magnetron sputtering on AIN-buffered (00.1) sapphire and (111) silicon are presented and, in particular, the evolution of the structural and electrical transport properties as a function of buffer layer sputter time (corresponding to thicknesses from ∼50Å to ∼0.64 μm) described. Pertinent results include: (a) for the InN overlayer, structural coherence and homogeneous strain normal to the (00.1) growth plane are highly dependent on the thickness of the AIN-buffer layer; (b) the homogeneous strain in the AIN-buffer layer is virtually nonexistent from a thickness of 200Å (where a significant X-ray intensity for (00.2)AIN is observed); and (c) the n-type electrical mobility for films on AIN-nucleated (00.1) sapphire is independent of AIN-buffer layer thickness, owing to divergent variations in carrier concentration and film resistivity. These effects are in the main interpreted as arising from a competition between the lattice mismatch of the InN overlayer with the substrate and with the AIN-buffer layer.
Theoretical Studies of C(100) Surface Reconstruction and Reaction with CH2
Authors: Jing Z. , Whitten J. L.
Published: April 2011

The reconstruction of the C(100) surface and its reaction with CH2 are studied by a cluster model at several theoretical levels [1–13]. For the reconstruction ofthe C(100) surface, the calculated surface dimer bond length is found to be very sensitive to the level of theoretical treatment and the spin state. A single-determinant SCF treatment gives a closed-shell singlet state, higher in energy than the triplet state, and with a dimer length of 1.401 Å, 0.279 Å shorter than the triplet. The correct ground state is a singlet, but a multi-determinant wavefunction is required for its description. At the CI level, the surface dimer bond length in the ground state is found to be 1.508 Å and the energy decrease on dimer formation with respect to the ideal C(100)-lxl surface is 2.28 eV per dimer. For the reaction of CH2 with C(100), no barrier is found for the chemisorption of CH2on the surface and the reaction is highly exothermic. The surface is converted from C(100)-2×1 to C( 100)-1×1 upon CH2 chemisorption.
Electrical Characterization of Aluminum Nitride Films on Silicon Grown by Chemical Vapor Deposition
Authors: Khan A. H. , Meese J. M. , Stacy T. , Charlson E. M. , Charlson E. J. , Zhao G. , Popovici G. , Prelas M. A.
Published: April 2011

Aluminum nitride (AlN) films were grown on silicon (Si) substrates by chemical vapor deposition (CVD). The films were characterized by scanning electron microscopy (SEM) and x-ray diffraction (XRD). The refractive index of the AlN films was determined by ellipsometry. Current-voltage and current-temperature characteristics were performed on metal-AlN-p+ Si structures with Pt, Au and Al as metal electrodes. The characteristics showed that at high field and high temperature the carrier conduction mechanism in the film was dominated by Frenkel-Poole emission. The relative dielectric constant of the AlN films was estimated to be 9.66+0.3 from capacitance-voltage-frequency (C-V-f) measurements on Au-AlN-p+ Si.
Conductivity and Ftir Measurements of the Hydrogen Content of Heat Treated Diamond Films
Authors: Sung T. , Khasawinah S. , Popovici G. , Prelas M. A. , Spitsyn B. V. , Manning G. , Loyalka S. , Tompson R. V.
Published: April 2011

The content of bonded hydrogen in hot filament grown diamond films was determined by Fourier transform Infrared (FTIR) measurements before and after annealing. The quantity of bonded hydrogen was found to remain unchanged on annealing in diamond films with high amounts of microcrystalline diamond and amorphous carbon. The hydrogen content was found to decrease on annealing ∼9 times in diamond film of good crystalline quality. The change of the bulk hydrogen content did not seem to be linked to changes in resistivity of the samples.
Blue Light Electroluminescence From Doped μc-SiC prepared by Excimer (ArF) Laser Crystallisation
Authors: Lau S. P. , Marshall J. M. , Dyer T. E. , Hepburn A. R. , DaVies J. F.
Published: April 2011

A novel method has been developed to prepare highly conductive and wide band gap doped (B2H6/PH3) microcrystalline silicon carbide (μ-SiC) by excimer (ArF) laser crystallisation. Doped a-SiC:H films were prepared by Plasma Enhanced Chemical Vapour Deposition (PECVD), both with and without H2 dilution. After crystallisation, this material has Taue gap of around 2.0 eV and exhibits a dark conductivity as high as 20 (Ωcm)-1, more than ten orders of magnitude higher than before the laser irradiation. This is shown to be mainly due to the formation of SiC microcrystallites in the laser crystallised a-SiC:H.

In this paper, we report that this material can be utilised not only as the carrier injection layer in a-SiC:H based Thin Film Light Emitting Diodes (TFLEDs) but also as a luminescent layer. Blue light emission has been observed from a laser crystallised (LC) doped μc-SiC based electroluminescent device, the peak wavelength is around 490nm.

The simplicity of excimer (ArF) laser crystallisation and its capability to fabricate poly-Si TFTs, makes this a promising novel method to realise fully integrated Si large area multi-colour displays.
Investigation of Structural Defects in 4H SiC Wafers
Authors: Tuominen M. , Yakimova R. , Glass R. C. , Tuomi T. , Janzén E.
Published: April 2011

For high-power device applications SiC has better physical and electronic properties than the traditional semiconductor materials Si and GaAs. In this work, structural defects of 4H SiC wafers have been studied and partly compared with results from a previous study of 6H material. Optical microscopy, scanning electron microscopy, high-resolution X-ray diffraction and synchrotron X-ray topography were used for structural studies of 4H SiC.Optical micrographs show micropipes and larger specific defects - tubes and cracks. X-ray rocking curve peaks are broad and split revealing the mosaicity of the material. Synchrotron X-ray topographs show areas having a large number of defects, images of cracks and micropipes, and misorientated regions close to the micropipes.
A Dynamic Model of III-V Ternary Semiconductor Alloys in the Epitaxial Growth
Authors: Gu Bing-Lin , Yu Jing-Zhi , Hu Xiao , Ohno Kaoru , Kawazoe Yoshiyuki
Published: April 2011

A concentration wave method for several interpenetrating Bravais sublattices is presented by considering the intralayer and interlayer effective interactions and the difference between the surface layers and the deeper layers in III – V alloys. The ground state ordered structures of ternary III – V semiconductor alloys are deduced and a dynamic model is established.
GaInAs/GaInP Double Barrier Structures: Growth and Application in Tunneling Diodes
Authors: Reaves C.M. , Yen J.C. , Cevallos N A. , Mishra U.K. , DenBaars S.P.
Published: April 2011

We have fabricated resonant tunneling diodes (RTD's) containing a GaInAs quantum well and strained GaInP barriers. These diodes exhibit good characteristics at 80 K with a peak to valley current ratio of 1.34 which is comparable to other reports for RTD in this material system. Additional RTD's were made using a InAs rich well region to study the effect of strain compensation. To investigate the properties of these structures, transmission electron microscopy (TEM) and low temperature photoluminescence (PL) were performed. TEM shows that both RTD structures contain misfit dislocations. PL measurements indicate that the dislocations are not significantly affecting the GaInAs quantum well.
Chemical Beam Epitaxial Growth of GaP and InP Using Alternative, Safer Precursors
Authors: Sadwick L.P. , Kim C.W. , Ryu H.H. , Hill C.W. , Stringfellow G.B. , Gedridge R. W. , Jones A.C.
Published: April 2011

Phosphorus (P)-based alloys are important for applications in areas including optoelectronics and high speed electronics. Gas phase technologies such as organometallic vapor phase epitaxy (OMVPE) and chemical beam epitaxy (CBE) have traditionally used the extremely dangerous hydride, phosphine (PH3). Less hazardous alternatives need to be found. Three such alternative P-sources are: tertiarybutylphosphine (TBP), bisphosphinoethane (BPE) and trisdimethylaminophosphine (TDMAP). InP and GaP growth results using TBP, BPE, and TDMAP along with a brief discussion of the pyrolysis of these alternative P-sources are presented. InP has been grown using ethyldimethylindium and pre-cracked BPE with excellent surface morphology and strong 10 K photoluminescence with a half width of 4.8 meV. The residual doping level typically was in the high 1015 to low 1016 cm-3 range. GaP has been grown at a substrate temperature of 480°C without precracking the TDMAP.
Growth and Doping of AlAs by Mombe
Authors: Abernathy C. R. , Pearton S. J. , Wisk P. W. , Hobson W. S. , Ren F.
Published: April 2011

A comparison of dimethylethylamine alane (DMEAA) and trimethylamine alane (TMAA) as aluminum sources and CBr4 and CC14 as carbon doping sources for deposition of AlAs by metalorganic molecular beam epitaxy (MOMBE) has been carried out. DMEAA was found to produce the lowest oxygen levels in AlAs, 5 x 1017 cm-3 VS. 1021 cm-3 for TMAA, even at growth temperatures as low as 500°C. This reduction is likely due to the absence of oxygenated solvents used during synthesis of the DMEAA. Undoped films grown from either source were fully depleted as-grown. Through the use of CBr 4, hole concentrations up to 4.5x1019 cm-3 were achieved in AlAs layers grown fiom DMEAA. Attempts to increase the hole concentration beyond this level resulted in a decrease in the hole concentration even though SIMS analysis showed the carbon concentration to increase with increasing dopant flow. Though the carbon sources did not appear to introduce additional oxygen, they appear to introduce other impurities, such as Cl and Br. Also, due to parasitic etching reactions with the adsorbed halogen, the use of these sources reduces the Al incorporation rate.
Reflection High-Energy Electron Diffraction Study of Arsenic Incorporation in Metalorganic Molecular Beam Epitaxy of GaAs
Authors: Dong H. K. , Hung S. C. H. , Tu C. W.
Published: April 2011

Metalorganic molecular beam epitaxy (MOMBE) of GaAs using triethylgallium (TEGa) and As4 has been studied by reflection high-energy electron diffraction (RHEED). The effect of varying the group-Ill flow rates and group-V beam flux on the growth rate has been investigated over a wide range of substrate temperatures. For a given arsenic flux, the GaAs growth rate first increases linearly as the TEGa flow rate increases. This linear relation extends up to a certain TEGa flow rate, where the growth rate reaches its maximum value. When the TEGa flow rate is increased above this critical value, the growth rate decreases and reaches a stabilized value. From a study of both group-Ill and group-V induced RHEED intensity oscillations, we find that the V/Ill incorporation ratio is unity at the transition point. Compared to conventional molecular beam epitaxy (MBE), MOMBE behaves differently when the V/Ill incorporation ratio is less than unity. The transition region between V/III>I and V/III<1 is gradual and no excess gallium accumulates on the surface during growth. The arseniccontrolled growth rate obtained from conventional group-V induced oscillations where excess Ga atoms are present is greater than the growth rate in the stabilization region where V/IIl<1.
ETCH Rate and Thickness Measurements of Layered GaAs, AlAs and AlGaAs Structures Using a Laser Reflectance Technique
Authors: Grober Louise H. , Hong M. , Grober R.D. , Mannaerts J.P. , Freund R.S.
Published: April 2011

Laser reflectometry has been shown to be a useful tool for etch depth measurements during etching of multiple layer structures. We have extended the use of laser reflectometry to accurately determine the etch rates of GaAs, Al0.4Ga0.6As and AlAs as a function of temperature and to verify layer thickness in-situ. By use of computer simulation we compare a theoretical model to actual data to determine layer thicknesses and accurate etch rates. We compare our data to previously published work for GaAs etching.
Cross-Sectional Scanning Tunneling Microscopy of III-V Heterostructures Grown by Molecular-Beam Epitaxy
Authors: Lew A.Y. , Yu E.T. , Chow D.H. , Miles R.H.
Published: April 2011

Cross-sectional scanning tunneling microscopy and spectroscopy have been used to characterize InAs/Ga1-x InxSb strained-layer superlattices grown by molecular-beam epitaxy. Atomic-resolution constant-current images of the epitaxial layers reveal monolayer roughness at the superlattice interfaces. An asymmetry in electronic structure between interfaces in which InAs has been grown on Ga1-x InxSb and those in which Ga1-x InxSb has been grown on InAs has also been observed in these images. Close inspection of the images reveals increased growthdirection lattice spacings in the Ga1-x InxSb layers compared to the InAs layers, as well as even larger lattice spacings at the InAs/Ga1-x InxSb interfaces. The latter is consistent with the formation of primarily InSb-like interfaces. Current-voltage spectra obtained while tunneling into the superlattice layers are found to be strongly influenced by extended superlattice electronic states.
High-Quality InAs/A1Sb Superlattices with AlAs and InSb Interfaces
Authors: Bennett Brian R. , Shanabrook B.V. , Glaser E.R. , Wagner R.J.
Published: April 2011

The presence of two species of both cations and anions permits the construction of InAs/AlSb heterostructures with either AlAs- or InSb-like interfaces. InAs/AlSb superlattices with both types of interfaces were grown using migration-enhanced epitaxial techniques. The layer quality and control of interfacial composition were confirmed by x-ray diffraction, Raman spectroscopy, and photoluminescence measurements. We demonstrate that high-quality superlattices with both InSb- and AlAs-bonded interfaces can be achieved with appropriate growth temperatures.
A Study of Traps in Semi-Insulating III-V Epitaxial Films by Zero Bias Transient Current Spectroscopy
Authors: Lau W. S. , Goo C. H. , Chong T. C. , Tan C. T.
Published: April 2011

Semi-insulating Al0.3Ga0.7AS epitaxial films grown by molecular beam epitaxy at 400°C have been characterised by a recently proposed technique known as zero quiescent bias voltage transient current spectroscopy (ZBTCS). Separated electron trap spectra and hole trap spectra are obtained by ZBTCS. From these spectra, a prominent hole trap with an activation energy of 1.01eV, a prominent electron trap with an activation energy of 0.86eV and a continuum of states are detected. The trap concentrations of the detected hole trap and electron trap are calculated to be about 3.6x1015cm−3 and 9.7x1015cm−3 respectively. The continuum of states is believed to be due to the surface states of the Al0.3Ga0.7AS film. By passivating the surface with (NH4)2S solution, the magnitudes of the continuums in the spectra reduce significantly. With the reduction of the surface states, hole injections that interfere the electron trap spectra are suppressed, and consequently electron trap spectra with more pronounced peaks are produced.
The Characteristics of the Lateral Thickness Modulation in Strained Layer GaxIn1-xAs Multiple Quantum Well Structures Grown by MOVPE
Authors: Zhou X. , Charsley P. , Smith A. D. , Briggs A. T. R.
Published: April 2011

Similar phenomena associated with the lateral thickness modulation have been observed in two different types of GaxIn1-x strained layer multiple quantum well structures grown on InP by MOVPE. The thickness modulations were always quasi-periodic and developed anisotropically in the [110] direction. It has been found that lattice distortions were caused by such thickness modulations, resulting probably in overall surface elastic relaxation. Once the thickness modulation had started at some stage of the growth, it would continue in the subsequent layer with approximately the same modulation period and an amplified amplitude. This is attributed to the effect of the lattice deformation at the growth surface on the deposition rate of the subsequent layer. The effect of such factors as the magnitude of strain, the growth temperature and the V/III gas ratio on the onset of the thickness modulation is discussed.
Heterostructural Characterization of Pseudomorphic, Partially Strained, and Highly Mismatched Semiconductors Using Double Crystal X-Ray Diffraction, TEM, and SEM
Authors: Kim Hyung Mun , Kim Sang-Gi , Nahm Sahn , Park Hyung-Ho , Lee Hae-Kwon , Lee Jae-Jin , Cho Kyung-Ik , Choo Heung Ro , Kim Hong Man , Park Hyung Moo , Park Sin-Chong
Published: April 2011

Heterostructural properties of pseudomorphic (AlGaAs/GaAs), partially strained (GaInAs/GaAs), and highly strained (GaAs/Si) semiconductor systems have been studied using High Resolution Double-Crystal X-ray Diffraction (DXRD), Transmission Electron Microscopy (TEM), and Scanning Electron Microscopy (SEM). Using the high resolution DXRD with CuKα1 and two-reflection Si (220) monochromator, we obtained (004) symmetric and (115) or (224) asymmetric reflection rocking curves for samples grown by molecular beam epitaxy. With 0.5 μm thick samples, perpendicular and in-plane lattice mismatches were calculated using elastic theory and compared with each other. The different degree of relaxation for these samples was observed and correlated with the lattice mismatch, X-ray layer peak broadening (i.e., full width at half maximum), and SEM surface morphology. For a GaInAs/GaAs sample, the strain relaxation along one of the <110> directions was more than the other direction, that is, the strain relaxation is not isotrophic. Also we observed that the lines were mainly parallel in one direction, i.e., they did not form a cross-hatch pattern. TEM images from both cross-sectional and planar views of the samples will be presented.
Anisotropic Structural and Electronic Properties of InGaAs/GaAs Heterojunctions
Authors: Goldman R.S. , Rammohan K. , Raisanen A. , Goorsky M. , Brillson L.J. , Rich D.H. , Wieder H.H. , Kavanagh K.L.
Published: April 2011

We have investigated the structural and electronic properties of partially strain-relaxed InxGal-xAs/GaAs heterojunctions, grown by molecular beam epitaxy (MBE) on both misoriented and nominally flat (001) GaAs substrates. Mobility measurements using Hall bars aligned along the [110] and [110] in-plane directions reveal an asymmetry in bulk InGaAs electron mobility. This asymmetry is correlated with an anisotropic bulk strain relaxation and interfacial misfit dislocation density, determined from high-resolution x-ray rocking curves (XRC), as well as a polarization anisotropy in cathodoluminescence (CL).
Kinetic Monte Carlo Simulations of Ge Segregation During Epitaxial Growth of Si-SixGel-x Heterostructures
Authors: Deppe J. , Lill J. V. , Godbey D. J. , Hobart K. D.
Published: April 2011

The temperature dependence of germanium surface segregation during growth by solid source SiGe molecular beam epitaxy was studied by x-ray photoelectron spectroscopy and kinetic Monte Carlo (KMC) modeling. Germanium segregation persisted at temperatures 60ºC below that predicted by a two-state exchange model. KMC simulations, where film growth, surface diffusion, and surface segregation are modeled consistently, successfully describe the low temperature segregation of germanium. Realistic descriptions of MBE must follow the physical rates of the growth, surface diffusion, and surface segregation processes. A specific, step mediated exchange mechanism is also considered and shown to lead to surface segregation. While this model of Ge segregation seems possible, more work is necessary to obtain a consistent set of energy barriers.
Gas Source Molecular Beam Epitaxy of ZnSe on (In,Ga)P
Authors: Lu K. , Fisher P.A. , Ho E. , House J.L. , Petrich G.S. , Kolodziejski L.A.
Published: April 2011

The wide bandgap semiconductor ZnSe has been nucleated on epitaxial (In,Ga)P buffer layers (on GaAs substrates) having various In compositions, and hence various lattice constants. The III-V ternary alloy offers a wide range of lattice constants for the heteroepitaxy of a multitude of potential II-VI light emitting devices, such as blue pn injection lasers composed of the (Zn,Mg)(S,Se) material system. Since the II-VI and III-V layers are grown using gas source molecular beam epitaxy in separate dedicated reactors, the technique of amorphous As deposition is employed to passivate the (In,Ga)P surface prior to the ex situ transfer. High resolution double crystal x-ray diffraction measurements on the ZnSe/(In,Ga)P/GaAs heterostructures indicate that for In compositions of 50-52%, the buffer layers with a thickness of 4 μm were only partially relaxed on the GaAs substrates, with the residual mismatch remaining at the ZnSe/III-V heterointerface. The critical thickness of (In,Ga)P, with In concentrations near 52-56%, on GaAs greatly exceeds the predicted critical thickness from either the energy balancing or force balancing model. For an In composition of 56% (and a film thickness of 4 μm), the buffer layers contain an in-plane lattice constant equal to that of ZnSe, and therefore represent the lattice-matched condition, even though the film is not fully relaxed. For (In,Ga)P buffer layers lattice-matched to ZnSe, but mismatched to GaAs, the surface exhibits the expected cross-hatched surface morphology. The occurrence of the cross-hatched surface is significantly alleviated by the addition of a pseudomorphic layer of GaAs positioned between the ZnSe and (In,Ga)P layer.
Low Pressure MOVPE Photo-Assisted Growth of ZnxCd1-xS
Authors: Dumont Hervé , Fujita Shizuo , Fujita Shigeo
Published: April 2011

We will report the photo-assisted heteroepitaxial growth of Znx Cdl-xS by Metalorganic Vapor Phase Epitaxy (MOVPE). Sources materials were diethylzinc, dimethylcadmium and tertiaributylmercarptan. We have studied the effect of light intensity on the change of the Zn composition, crystalline quality and optical properties of epitaxial layers grown on (100) GaAs substrates. The Zn composition of the films could be increased by ≃ 15% by illuminating layers during the growth at 400°C. Concerning the characterization of epilayers, we observed a bright luminescence peak at E = 2.80 eV for x≃ 0.4. Epilayers with the best crystalline quality we could grown exhibited a full width at half maximum of ≃ 70 arsec by x-ray diffraction rocking curves when grown at 380°C.
Structural Characterization of InAlAs/InGaAs Layers Grown on InP Patterned Substrates
Authors: Peiro F. , Cornet A. , Morante J.R. , Zekentes K. , Georgakilas A.
Published: April 2011

In this work we present structural characterization by both Scanning and Transmission Electron Microscopy of InAlAs/InGaAs heterostructures grown on InP substrates. Our attention is devoted to study the two main problems limiting the application of these structures as devices: the presence of defects on the epilayer and the growth habit at theedges of the well. Our results show that a different faceting between the two <110> orthogonal directions develops during the growth and that a high density of defects is observed just at the intersection between the layers grown inside the windows and on the walls. Moreover, the presence of a polycrystalline layer developing over the mask indicates that a selective growth occurs.
Thermodynamic Calculations on Vapour Phase Species in Halogen Doped CDTE
Authors: Schwarz R. , Laasch M. , Benz K.W.
Published: April 2011

A thermodynamic analysis of the vapour phase species occurring in the undoped CdTe and doped CdTe:X (X = Cl, Br, I) systems is given. Calculations are performed using a Gibbs energy minimizer software (EPC), which offers the possibility of receiving relativly prompt results allowing for the change in experimental conditions as well as the consideration of even spurious species.

In each system, the dopant - transporting species are the cadmiumdihalogenides CdX2. Contrary, in the CdTe:I vapour phase two more species (Tel and I) have to be considered at the growing phase boundary afffecting transport and interface kinetics.
Electronic and Photonic Device Applications of In0.5Ga0.5P and In0.5Al0.5P Grown by Gas Source Molecular Beam Epitaxy
Authors: Kuo Jenn-Ming
Published: April 2011

Advances in gas-source molecular beam epitaxial (GSMBE) growth techniques have allowed the successful fabrication of electronic and photonic devices based on In0.5Ga0.5P and In0.5A10.5P heterostructures lattice matched to GaAs. Basically the interest in In0.5Ga0.5P and In0.5A10.5P derives from their unique material properties as well as their band alignment to GaAs. In this paper, we review the growth, fabrication, and performance of In0.5A10.5P/In0.2Ga0.8As pseudomorphic high electron mobility transistors (HEMT's), InO.5A10.5P/GaAs heterojunction bipolar transistors (HBT's), and In0.5Ga0.5P red light emitting diodes (LED's) grown on Ge/graded GexSil-x/Si substrates. The results provide a solid demonstration of the feasibility of using In0.5Ga0.5P and In0.5A10.5P prepared by GSMBE for manufacturing GaAs-based optoelectronic devices.
In-Situ Surface Photo-Absorption Study of Movpe Surface
Authors: Kobayashi Naoki
Published: April 2011

In-situ surface photo-absorption (SPA) method was applied to study the dynamic surface processes and the static surface structures during metal-organic vapor phase epitaxy (MOVPE). Observed spectra in near-ultaviolet and visible regions consist of an anisotropic dielectric response due to surface dimer-bonds as well as an isotropic response probably due to surface back-bonds. Time-resolved spectra showing dynamic changes of surface can be measured by the use of optical multichannel analyzer. The rate of surface decomposition of source molecule was measured as the change of reflectivity at a fixed wavelength. The decomposition of source molecule was characterized quantitatively, and various effects on the decomposition were studied. The style of decomposition and the activation energy depended on the substituent of source molecule and the rate of decomposition was affected by the surface potential and the strain.
Ag Films Deposited by Ionized Cluster Beam Deposition
Authors: Ren Zhong-Min , Du Yuan-Cheng , Ying Zhi-Feng , Xiong Xia-Xing , He Mao-Qi , Li Fu-Ming
Published: April 2011

Ionized cluster beam deposition (ICBD) technique has been used to deposit Ag films on both Si(111) and Si(100) substrates. Sizes of clusters in ionized cluster beam are found to distribute in a range of 100–600 atoms/cluster. X-ray diffraction (XRD), and α-step profile methods are used to analyze the properties of Ag films. As a comparison, Ag films deposited by conventional evaporation are also investigated. Highly textured Ag films with strong (111) orientation on Si (111) have been obtained at high accelerating voltage Va=4kV. The crystallinity and surface flatness of Ag films can be improved by ICBD at high accelerating voltages.
Segregation Effect and its Influence on Grain Boundary Diffusion in Thin Metallic Films
Authors: Aleshin A. N. , Bokstein B. S. , Egorov V. K. , Kurkin P. V.
Published: April 2011

The diffusion in Au-Cu and Pt-Cu thin films has been studied by Rutherford backscattering spectrometry (RBS) under the kinetic regime “B” (within the temperature interval of 175–290°C) and “C” (room temperature). The 1,5-2,0 MeV He+ RBS spectra were taken using 14–18 keV resolution. The RBS spectra were changed to depth-concentration profiles for both bulk and grain boundary (GB) diffusion. Under the kinetic regime “C” the absolute values of GB diffusion coefficients were obtained. Under the kinetic regime “B” the triple products δKDb, (δ is the GB width, Db is the GB diffusion coefficient, K is the enrichment ratio) were obtained using Whipple’s and Gilmer-Farrell’s models. The activation energies for both GB diffusion and bulk diffusion were determined for Au-Cu system as well as for Pt-Cu system. The comparison between the data on the GB diffusion for kinetics “B” extrapolated to room temperature and the data on the GB diffusion for the kinetics “C” enables one to derive the product δK and to separate the contribution of segregation into the parameters of GB diffusion for systems under study.
Liquid Metal Penetration along Grain Boundaries
Authors: Fradkov V. E.
Published: April 2011

Liquid metal grain boundary corrosion is discussed in terms of grain boundary etching profiles with equilibrium dihedral angles at the vertex of the grooves close to zero. It is shown that if the liquid solution is in equilibrium with the solid, then only grain boundary grooving occurs, producing small grooves growing in time as t½. However, if the equilibrium cannot be reached, a long liquid filled canal develops along the grain boundary, rapidly propagating with constant velocity. To stop such rapid grain boundary corrosion certain measures should be taken to reach the equilibrium state. This explains, for example, why removal of oxygen from the Nb(s)-Li(l) system prevents rapid grain boundary corrosion of Nb.
Scanning X-Ray Diffraction: A Technique With High Compositional Resolution for Studying Phase Formation in Co-Deposited Thin Films
Authors: Selinder T.I. , Miller D.J. , Gray K.E. , Beno M.A. , Knapp G.S.
Published: April 2011

Investigation of the formation of new metastable phases in alloy thin films requires ways of quickly determining the crystalline structure of samples with different compositions. We report a novel technique for acquiring structural information from films intentionally grown with a composition gradient. For example, binary metal alloy films were deposited using a phase-spread sputtering method. In this way essentially the entire composition range could be grown in a single deposition. By using a narrow incident x-ray beam and a translating sample stage combined with a position sensitive x-ray detector technique, detailed information of the metastable phase diagram can be obtained rapidly. Compositional resolution of the order of ±0.2% can be achieved, and is limited by the brightness of the x-ray source. Initial results from studies of phase formation in Zr-Ta alloys will be presented. Extensions of the analysis technique to ternary systems will be discussed.
Fine Structure of Sputtered Ni/Ti Multilayered Thin Films Studied by HREM
Authors: Casanove M. J. , Snoeck E. , Roucau C. , Hutchison J. L. , Jiang Z. , Vidal B.
Published: April 2011

Ni/Ti multilayered thin films can be efficient neutron guides and are therefore of great interest in neutron optics. Ni/Ti and NiC/Ti multilayers with various layer thicknesses were fabricated by magnetron sputtering and characterized by high resolution transmission electron microscopy (TEM). The TEM studies, performed on cross-sectional specimens, revealed that both kinds of layers were textured and snowed coherence in the growth direction. The presence of a 2 nra thick amorphous zone at the Ni/Ti interface in the carbon free thin films was also confirmed. On the contrary, sharp interfaces were obtained in NiC/Ti multilayers. The fine structure of the different layers will also be reported.
The Effect of Microstructure on the Magnetic Properties of Thin Film Magnetic Media
Authors: Yamashita T. , Ranjan R. , Chan L.H. , Lu M. , Ross C.A. , Chang J. , Tarnopolsky G.
Published: April 2011

Magnetic recording media used today are based on sputtered cobalt alloy films with thicknesses in the order of 50 nm. As recording density is increased, the microstructure of the film must be controlled with increasing level of sophistication to achieve the magnetic properties necessary for good recording performance. Recording density has been increasing at the compound annual rate of 30%, and in recent years at a higher rate. Already, 1 Gb/in2 has been achieved in the laboratory [1], and 10 Gb/in2 is being contemplated [2]. In order to achieve such densities, microstructural characteristics such as grain morphology, size distribution, crystallographic orientation, and grain separation must be controlled with great precision, and their relationship to magnetic properties must be understood. The paper will describe the effect of sputter process conditions and the selection of magnetic alloys on the film microstructure and describe what might be required to achieve high recording densities. Particular attention will be paid to grain size distribution and grain separation. Grain separation is important for low noise performance of the media. Alloy selection and sputtering conditions can be manipulated to achieve different levels of separation between the grains.
Effect of Ion Irradiation on the Artificial Structure and the Interlayer Coupling of Copper-Cobalt Multilayers
Authors: Bobo J-F. , Snoeck E. , Piecuch M. , Casanove M-J.
Published: April 2011

Structural defects like local ferromagnetic short-circuits are responsible for large reductions of the intrinsic interlayer coupling in the case of antiferromagnetically (AF) coupled multilayers (ML). We have investigated the role of such point defects in AF-coupled Cu-Co ML’s with tCu=8Å and tCo=12Å which have been irradiated with various doses of 200 keV xenon ions. A significant decrease of the giant magnetoresistance and of the saturation field is observed when the density of defects is increased. These results are compared with a micromagnetic model that takes into account local discontinuities of the AF coupling in an ideally AF-coupled ML. Evidence for the presence of such defects is investigated by TEM on cross-sectional specimens.
Thin Films of SrFeO2.5+x - Effect of Preferred Orientation on Oxygen Uptake
Authors: Sanders Brian W. , Yao Jianhua , Post Michael L.
Published: April 2011

Pulsed laser ablation has been used to deposit thin films of SrFeO25+x (x = 0 to ≈0.5). Previous work has shown that the orientation of the films, determined by powder x-ray diffraction depended strongly upon the deposition temperature. Films grown below 770 K showed little or no orientation. A growth temperature of 900 K resulted in films oriented (200). Growth temperatures of > 1000 K produced films oriented predominantly (110). At 673 K in an oxygen atmosphere, oriented films readily converted from the oxygen deficient brownmillerite form (x=0) to the oxygen rich cubic (or distorted cubic) perovskite form (x≈0.3). Films which exhibited no initial orientation did not react with oxygen under these conditions. Cycling non-oriented films between 230 and 800 ppm of oxygen in 101.3 kPa of nitrogen at 673 K resulted in weak (110) orientation. Once oriented, the films reacted readily with oxygen and exhibited measurable resistance changes. The conversion from oxygen deficient to oxygen rich form was monitored by x-ray diffraction and the DC resistance of the films.
Low Dielectric Constant, High Temperature Stable Copolymer Thin Films by Room Temperature Chemical Vapor Deposition
Authors: Gaynor Justin F. , Desu Seshu B.
Published: April 2011

Polyxylylene thin films grown by the chemical vapor deposition (CVD) process have long been utilized to achieve uniform, pinhole-free conformal coatings. They have recently been cited as possible low dielectric constant films for intermetal layers in high-speed ICs. Homopolymer films are highly crystalline and have a glass transition temperature around room temperature. We have demonstrated that room temperature copolymerization with previously untested comonomers can be achieved during the CVD process. Copolymerizing chloro-p-xylylene with perfluorooctyl methacrylate results in the dielectric constant at optical frequencies being lowered from 2.68 to 2.19. Copolymerizing p-xylylene with vinylbiphenyl resulted in films which increase the temperature at which oxidative scission occurs from 320 to 450C. Copolymerizing p-xylylene with 9-vinylanthracene resulted in a brittle, yellow film.
Asymptotic Behavior in Grain Growth
Authors: Wu David T.
Published: April 2011

Hillert’s model of grain growth consists of a drift term in size space that leads asymptotically to a distribution function and a growth exponent not often observed. Later theories introduce a diffusion term that is either assumed to dominate the drift term or a correction to it. This paper shows that the lower order drift term alone determines asymptotic grain growth behavior. A possible conclusion is that experimental results may need to be reinterpreted.
Elastic Properties of FeNi/Cu and FeNi/Nb Metallic Superlattices Investigated by Brillouin Light Scattering
Authors: Carlotti G. , Socino G. , Xia Hua , Hu An , Jiang S. S.
Published: April 2011

The Brillouin light scattering technique has been exploited in order to investigate the elastic properties of periodic superlattices consisting of alternating layers of Fe20Ni80 (permalloy) and either Cu or Nb. These multilayers, with total thicknesses ranging between 0.2 and 0.7 mm and with periods of typically 3-5 nm, present a polycrystalline structure with (110) texture for the Nb layers and (111) texture for both the FeNi and Cu layers. Measurement of the frequency position of the Brillouin peaks corresponding to the Rayleigh and Sezawa acoustic modes allowed the effective elastic constants of these structures to be determined. The values obtained are compared with those calculated from the elastic constants of the bulk materials, taking into account the polycrystalline nature of the superlattices and the crystallographic orientation of the layers.
Nucleation and Growth of Polycrystalline Silicon Films in an Ultra high Vacuum Rapid Thermal Chemical Vapor Deposition Reactor Using Disilane and Hydrogen
Authors: Violette Katherine E. , Öztürk Mehmet C. , Harris Gari , Sanganeria Mahesh K. , Lee Archie , Maher Dennis M.
Published: April 2011

A study of Si nucleation and deposition on SiO2 was performed using disilane and hydrogen in an ultra high vacuum rapid thermal chemical vapor deposition reactor in pressure and temperature ranges of 0.1 – 1.5 Torr and 625 – 750°C. The film analysis was carried out using scanning electron microscopy, transmission electron microscopy and atomic force microscopy. At lower pressures, an incubation time exists which leads to a retardation in film nucleation. At 750°C, the incubation time is 10s at 0.1 Torr and decreases to less than Is at 1.5 Torr. The nuclei grow and form three dimensional islands on S1O2, and as they coalesce, result in a rough surface morphology. At higher pressures, the inherent selectivity is lost resulting in a higher nucleation density and smoother surface morphology. For ˜ 2000 Å thick films, the root-mean-square surface roughness at 750ÅC ranges from 110Å at 0.1 Torr to 40Å at 1.5 Torr. Temperature also strongly influences the film structure through surface mobility and grain growth. At 1 Torr, the roughness ranges from 3Å at 625°C to 60Å at 750°C. The grain structure at 625°C/1Torr appears to be amorphous, whereas at 750°C the structure is columnar. The growth rate at 625°C/1.5 Torr is 1200 Å/min provides a surface roughness on the order of atomic dimensions which is comparable to or better than amorphous silicon deposited in LPCVD furnaces.
Characterization of the Substrate Interface of Excimer Laser Crystallized Polycrystalline Silicon Thin Films
Authors: Anderson G. B. , Boyce J. B. , Fork D. K. , Johnson R. I. , Mei P. , Ready S. E.
Published: April 2011

Excimer laser crystallized Si thin films on fused silica substrates exhibit a peak in the average grain size as a function of laser energy density. The average grain size increases with increasing laser fluence until a maximum value , approximately 10 microns for a 100 nm thick Si film, is achieved. The peak in grain size is accompanied by a peak in the electron Hall mobility. Further increases in the laser fluence result in a decrease in the Si grain size and an increase in the intragranular defects. A small energy range of 40 mJ/cm2 exists in which this peak in grain size can be achieved. Cross section TEM has shown that when the peak laser fluence is exceeded, the fused silica substrate can be as rough as 17 nm. Atomic force microscopy. performed on the substrate surface after the Si has been etched off, also shows that the magnitude and spatial frequency of the roughness increases when the critical laser fluence is exceeded. This degradation of the interface may also produce sites for stacking faults to form during the solidification of the Si. This result and results of simulations of the temperature of the interface during crystallization suggests that the peak energy range exists after the complete melting of the Si thin film and before the silica substrate starts to soften.
Characterization of Sputtered Ge Film
Authors: Cho Jaeshin , Theodore N. David
Published: April 2011

The electrical resistivity and microstructure of sputtered germanium film were characterized as a function of anneal temperature from 400 to 700°C. The as-deposited sputtered Ge film had an amorphous structure with resistivity of 165 Ω-cm which was maintained after annealing up to 540°C. After annealing above 550°C, the resistivity dropped by almost four orders of magnitude to ∼0.027 Ω-cm. The sharp transition of resistivity at 550°C is believed to be due to the recrystallization of Ge film from the as-deposited amorphous structure. The ohmic contact property on Ge films was also evaluated using sputtered tungsten. Low resistance ohmic contacts were obtained both on as-deposited and annealed Ge films, with typical ohmic contact resistance of 0.05 ± 0.008 Ω-mm on annealed Ge films. The W contacts were thermally stable after annealing up to 650°C.
Computational and Experimental Studies Of Grain Growth
Authors: Ngo Tue T. , Ahmadi Reza , Talin Alec A. , Williams R. Stanley
Published: April 2011

This paper addresses the validity of the single particle growth law rn-r0n=Kt in describing the formation of 3D grains during the vapor deposition of thin metal films, especially with respect to the value of the exponent n. Computer simulations based on the Huygen’s construction showed that the grain size distribution at full surface coverage did not depend significantly on the specific model chosen for initiating growth from nuclei. The particle size distributions obtained experimentally by STM measurements of thin Au films deposited on glass substrates agreed very well with the simulation results for n=2.
Evolution Of Crystalline Microstructure in GeTe Thin Films for Optical Storage Applications
Authors: Libera M.
Published: April 2011

The bit-erase process in phase-change optical storage is based on the amorphous to crystalline transformation. While there has been significant progress developing compositions and multilayered media for phase-change applications, quantitative studies of the crystallization kinetics and microstructural development are generally lacking. This paper describes work quantifying crystallization in GeTe thin films. Microstructural changes during isothermal annealing are measured usingin-situhot-stage optical microscopy. This technique measures the fraction crystallized, the number of crystallites, and crystallite radii as a function of time. These data are sufficient to deconvolute the individual contributions of nucleation and growth. We find an Avrami exponent of ∼4, consistent with time-resolved reflection/transmission studies. This exponent is due to 2-D growth at a constant rate plus transient nucleation. The data are used in a kinetic model to simulate non-isothermal crystallization during focused-laser heating characteristic of the bit-erase process.
Hydrogenation Mechanism of Top-Gated Polysilicon Thin Film Transistors
Authors: Ha Yong-Min , Han Jung-In , Han Chul-Hi , Kim Choong-Ki
Published: April 2011

Hydrogen diffusion paths in top-gated polysilicon thin-film transistors have been investigated by measuring the current-voltage characteristics of the transistors with various sizes after hydrogenation. Hydrogenation has been performed in ECR plasma sysytem. It is noted that hydrogen is introduced through three main paths instead of one predominant path. The hydrogen from different paths affects the device parameters differently.
Degradation Phenomena of low-temp. poly-Si TFT's Under Electrical Stress Before and After Hydrogenation
Authors: Kim Y. S. , Choi K. Y. , Jun M. C. , Han M. K.
Published: April 2011

The degradation mechanism in hydrogen passivated and as-fabricated poly-Si TFT's are investigated under the various electrical stress conditions. It is observed that the charge trapping in the gate dielectric is the dominant degradation mechanism in poly-Si TFT's which was stressed by the gate bias alone while the creation of defects in the poly-Si film is prevalent in gate and drain bias stressed devices. The degradation due to the gate bias stress is dramatically reduced with hydrogenation time while the degradation due to the gate and drain bias stress is increased a little. From the experimental results, it is considered that hydrogenation suppress the charge trapping at gate dielectrics as well as improve the characteristics of poly-Si TFT's.
Optically Controlled Alignment Of Liquid Crystals
Authors: Gibbons Wayne M. , Shannon Paul J. , Sun Shao-Tang
Published: April 2011

Optically controlled homogeneous-to-homogeneous alignment of liquid crystals using polarized light is reviewed. Application of this technology to liquid crystal display manufacturing is discussed. Important processing parameters such as tilt angle and optical energy density will be addressed.
A New Type TFT With Unique Operation And Simple Fabrication Process
Authors: Hattori Reiji , Tanida Yukinobu , Shirafuji Junji
Published: April 2011

A thin film transistor (TFT) with a new structure and a unique operation principle has been pioposed. This TFT has Schottky barrier contacts at source and drain, and employs electron tunneling through the Schottky barrier. The first feature of this TFT is simplification of the production process because a self-aligned technique is applicable and an ion-implantation process is not necessary. These advantages are promising for low-cost production of active-matrix liquid crystal displays (AM-LCDs). In this letter, we propose of new type TFT and carry out 2-D device simulation on a simplified structure to show the fundamental characteristics of this transistor and to optimize impurity density, channel thickness, and barrier height.