- Lover of nature. Physicist. My scientific life used the Transmission Electron Microscopy as a tool to study defects in different semiconductors on atomic leveledit
ABSTRACT Explanted worn alumina orthopaedic hip replacements show characteristic wear regions, ranging from severe wear, dominated by intergranular fracture, to regions in which minimal damage has occurred during articulation. The surface... more
ABSTRACT Explanted worn alumina orthopaedic hip replacements show characteristic wear regions, ranging from severe wear, dominated by intergranular fracture, to regions in which minimal damage has occurred during articulation. The surface damage accumulation mechanisms are complex and not fully understood. This paper presents a detailed transmission electron microscopy (TEM) study of the surface damage accumulation mechanisms following in vitro tested worn alumina hip replacement prostheses. TEM of focused ion beam cross-section samples indicated extensive surface dislocation activity, which is restricted in the outer grain layer. Except for one example of basal slip, all slips were found to be on pyramidal planes. Both inter- and transgranular cracks were observed in regions of high wear. Grooves, largely associated with third-body abrasion, were generally associated with extensive dislocation activity. Three types of wear debris were seen from the worn surface, namely: granular wear debris, nanocrystalline wear debris and oblong wear debris. Wear debris were shown to arise from grain pull-out and severe plastic deformation at the surface. The observations allow a mechanistic model of the damage accumulations leading to wear and ultimately failure.
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ABSTRACTWe report on high quality GaN layers grown with the use of one intermediate layer. The defect analysis shows that the density of dislocation is only 8×107/cm2 in these layers, compared to over 1010/cm2 for layers grown without the... more
ABSTRACTWe report on high quality GaN layers grown with the use of one intermediate layer. The defect analysis shows that the density of dislocation is only 8×107/cm2 in these layers, compared to over 1010/cm2 for layers grown without the intermediate layer (IL). Electron microscopy on cross-section samples shows that deposition under certain specific conditions of a low- temperature IL directly benefits the quality of the subsequently deposited GaN layer. The growth of the GaN top layer appears to be similar to growth observed for lateral epitaxial overgrowth layers. This first time observation opens the possibility for using standard growth methods of GaN compounds to achieve a dislocation density comparable to that achieved with lateral overgrowth epitaxy.
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Gallium nitride is one of the most promising materials for ultraviolet and blue light-emitting diodes and lasers. Both Molecular Beam Epitaxy (MBE) and Metal-Organic Chemical Vapor Deposition (MOCVD) have recently made strong progress in... more
Gallium nitride is one of the most promising materials for ultraviolet and blue light-emitting diodes and lasers. Both Molecular Beam Epitaxy (MBE) and Metal-Organic Chemical Vapor Deposition (MOCVD) have recently made strong progress in fabricating high-quality epitaxial GaN thin films. In this paper, we review materials-related issues involved in MBE growth. We show that a strong understanding of the unique meta-stable growth process allows us to correctly predict the optimum conditions for epitaxial GaN growth. The resulting structural, electronic and optical properties of the GaN films are described in detail.
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A reply to the Comment on Evidence for superconductivity in low-temperature-grown GaAs is given. It is argued that the authors findings are clearly distinguished from the scope of the previous work.(AIP)
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Page 1. Journal of Electronic Materials, Vol. 22, No. 12, 1993 Special Issue Paper First Direct Observation of EL2-Like Defect Levels in Annealed LT-GaAs ND JAGER, **^ AK VERMA,* P. DRESZER,** N. NEWMAN,** Z. LILIENTAL ...
Research Interests: Materials Science, Arsenic, Electronic Materials, Photoionization, Molecular beam epitaxy, and 11 moreBand Structure, Electronic, Electronic properties, High Temperature, Photocurrent, Schottky diode, Excited states, Schottky Barrier, Photoemission, Low Temperature, and Electrical And Electronic Engineering
Research Interests: Materials Science, Solid State Physics, Crystallography, Electronic Materials, Raman Spectroscopy, and 15 moreSilicon, Transmission Electron Microscopy, Atomic Force Microscopy, Silicon Carbide, X ray diffraction, Cross Section, Microstructures, Epitaxy, High-Resolution X-Ray Diffraction, Film Thickness, Electrical And Electronic Engineering, Carbide, Defect Density, Root mean square, and Root mean square error
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... 2×10 4 cm −1 , respectively. The defects in the wing material were observed primarily at the bottom of the film where lateral growth of the GaN occurred from the AlN and the SiC. Plan view AFM also revealed different microstructures ...
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Surface pits in the form of v-shaped defects and resulting surface roughening, previously associated solely with InGaN films, were observed and investigated using atomic force microscopy on GaN films grown at 780°C via metalorganic vapor... more
Surface pits in the form of v-shaped defects and resulting surface roughening, previously associated solely with InGaN films, were observed and investigated using atomic force microscopy on GaN films grown at 780°C via metalorganic vapor phase epitaxy on conventionally and pendeo-epitaxially deposited GaN thin film templates. The density of the v-shaped defects was similar to the density of threading dislocations of ∼3×109cm−2 (that originate from the heteroepitaxial interface between the GaN template layer and the SiC substrate). Moreover, the v-defect density was diminished with decreases in the dislocation density via increases in the template layer thickness or the use of pendeo-epitaxial seed layers. A concomitant reduction in the full-width half-maxima of the X-ray rocking curves was also observed. A qualitative model is presented that describes the formation of v-shaped defects as a result of interactions between the movement of surface steps, screw-type dislocation cores, and clusters of atoms on the terraces that form under conditions of high surface undercooling.
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The controlled incorporation of excess As into GaAs grown by molecular beam epitaxy at low growth temperatures (LT-GaAs) is explored. The substrate temperature and the As/Ga flux ratio were systematically varied to investigate the... more
The controlled incorporation of excess As into GaAs grown by molecular beam epitaxy at low growth temperatures (LT-GaAs) is explored. The substrate temperature and the As/Ga flux ratio were systematically varied to investigate the influence of growth parameters on the formation of native defects and structural properties. Near infrared absorption, magnetic circular dichroism of absorption, and slow positron annihilation were applied to determine point defect concentrations of As antisites (AsGa) and Ga vacancies (VGa). Structural properties of as-grown and annealed LT-GaAs layers were investigated by x-ray diffraction and transmission electron microscopy. In a well defined parameter range the lattice expansion of the LT-GaAs layers correlates with the amount of AsGa. The VGa acceptor concentration can quantitatively account for the ionization of the AsGa donors.
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Typically only dilute (up to ∼10%) highly mismatched alloys can be grown due to the large differences in atomic size and electronegativity of the host and the alloying elements. We have overcome the miscibility gap of the GaN1−xAsx system... more
Typically only dilute (up to ∼10%) highly mismatched alloys can be grown due to the large differences in atomic size and electronegativity of the host and the alloying elements. We have overcome the miscibility gap of the GaN1−xAsx system using low temperature molecular beam epitaxy. In the intermediate composition range (0.10 < x < 0.75), the resulting alloys are amorphous. To gain a better understanding of the amorphous structure, the local environment of the As and Ga atoms was investigated using extended x-ray absorption fine structure (EXAFS). The EXAFS analysis shows a high concentration of dangling bonds compared to the crystalline binary endpoint compounds of the alloy system. The disorder parameter was larger for amorphous films compared to crystalline references, but comparable with other amorphous semiconductors. By examining the Ga local environment, the dangling bond density and disorder associated with As-related and N-related bonds could be decoupled. The N-rela...
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We present structural and electronic data which indicate that the dominant defects in GaAs grown at low temperatures (LT GaAs) by molecular beam epitaxy (MBE) are As antisites (AsGa) and Ga vacancies (VGa), with negligible amounts of As... more
We present structural and electronic data which indicate that the dominant defects in GaAs grown at low temperatures (LT GaAs) by molecular beam epitaxy (MBE) are As antisites (AsGa) and Ga vacancies (VGa), with negligible amounts of As interstitials (Asi). We show that the change of lattice parameter correlates with the concentration of AsGa, and that AsGa alone can account for the lattice expansion. We also show that the total concentration of AsGa has a characteristic second power dependence on the concentration of AsGa in the positive charge state for the material grown at different temperatures. This can be understood provided that VGa defects are the acceptors responsible for the carrier compensation. Our results are consistent with most experimental results and the theoretical expectation from the calculation of defect formation energies. We find that the conclusion may also be true in As-rich bulk GaAs.
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Transmission electron microscopy is applied to investigate the effect of annealing on misfit dislocations in an In0.2Ga0.8As/GaAs(001) heterostructure. In as-grown samples, an orthogonal array of 60° dislocations along 〈110〉 directions is... more
Transmission electron microscopy is applied to investigate the effect of annealing on misfit dislocations in an In0.2Ga0.8As/GaAs(001) heterostructure. In as-grown samples, an orthogonal array of 60° dislocations along 〈110〉 directions is observed in the interface. During annealing, the 60° dislocations along 〈110〉 directions are bent from 〈110〉 directions toward 〈100〉 directions. The process represents a new strain relaxation mechanism in semiconductor heterostructures. As the dislocation segments along 〈100〉 can relieve the strain more effectively than 60° dislocations, we propose that the dislocations move nonconservatively in or near the interface by diffusion along the dislocation cores or in the heterointerface.
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A simple procedure for the synthesis of an important standard, isotopically enriched methylmercury, which is not commercially available, has been established successfully. The isotopically enriched standard synthesized is utilized in... more
A simple procedure for the synthesis of an important standard, isotopically enriched methylmercury, which is not commercially available, has been established successfully. The isotopically enriched standard synthesized is utilized in conventional isotope dilution mass spectrometry (IDMS), as well as in speciated IDMS (SIDMS), for determination of the true concentration of methylmercury in environmental samples. The CH3201Hg+ standard has been synthesized from commercially available 201HgO and tetramethyltin. The synthesis time required is 1 h at 60°C. The product is highly pure, yielding more than 90% as 201Hg in CH3201Hg+. Hazardous dimethylmercury does not occur during this synthesis procedure. The product synthesized was analyzed using high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (ICP-MS) and ICP-MS alone in order to determine its concentration, isotopic composition and purity. The stability of the product was also evaluated for over 6 months and found to be stable at 4°C in the dark. The isotopically enriched methylmercury synthesized can be used in SIDMS and IDMS analyses as a standard. Copyright © 2003 John Wiley & Sons, Ltd.
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^74Ge and ^70Ge nanocrystals were synthesized in 500nm thick SiO2 layers on silicon substrates by multi-energy ion implantation followed by thermal annealing.[1] Raman spectroscopy(RS) and transmission electron microscopy (TEM) were used... more
^74Ge and ^70Ge nanocrystals were synthesized in 500nm thick SiO2 layers on silicon substrates by multi-energy ion implantation followed by thermal annealing.[1] Raman spectroscopy(RS) and transmission electron microscopy (TEM) were used to confirm the existence of nanocrystalline Ge. Raman spectra exhibited asymmetrically broadened line-shapes due to phonon confinement and the nanocrystals' size distribution, consistent with an average particle size between
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300-nm-thick AlN layers were grown directly on 6H-SiC(0001) with six Si–C bilayer-height (1.5 nm) steps by rf-plasma-assisted molecular-beam epitaxy (MBE). To avoid unintentional active-nitrogen exposure, AlN was grown just after the... more
300-nm-thick AlN layers were grown directly on 6H-SiC(0001) with six Si–C bilayer-height (1.5 nm) steps by rf-plasma-assisted molecular-beam epitaxy (MBE). To avoid unintentional active-nitrogen exposure, AlN was grown just after the nitrogen plasma ignition. By combining optimized Ga pre-deposition and no active-nitrogen exposure, layer-by-layer growth was realized from the first layer of AlN. Screw-type and edge-type threading dislocation densities in the AlN layer were reduced to 6×104 and 4×108 cm-2, respectively. Most of the edge-type dislocations were located at the step edge of the SiC substrate. The dislocation density of the AlN grown on the terrace of the SiC substrate was as low as 8×107 cm-2.
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ABSTRACTHigh quality growth of InSe on Si(111) was achieved by insertion of GaSe buffer layer. Rhombohedral polytypes were formed in both the InSe and GaSe layers. Twinning and stacking disorder was often detected in these materials due... more
ABSTRACTHigh quality growth of InSe on Si(111) was achieved by insertion of GaSe buffer layer. Rhombohedral polytypes were formed in both the InSe and GaSe layers. Twinning and stacking disorder was often detected in these materials due to their layered structure. Moreover, in samples with a thin GaSe layer, strong interdiffusion of indium into the GaSe layer was detected that resulted in the formation of an InxGaySe phase. The dominant threading defects present in these InSe/GaSe heterostructures were screw dislocations, which may act as nonradiative recombination centers.
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The structure of As implanted GaAs layers before and after annealing are described and the relation between the structural quality and carrier lifetime was determined. Subpicosecond carrier lifetimes were found already for as-implanted... more
The structure of As implanted GaAs layers before and after annealing are described and the relation between the structural quality and carrier lifetime was determined. Subpicosecond carrier lifetimes were found already for as-implanted layers, and this value changes only slightly after annealing in the temperature range up to 600°C. Annealing of As-implanted layers leads to the growth of As precipitates with a similar orientation relationship as those observed in low-temperature MBE-grown GaAs layers. However, it is still not clear whether point defects created by implantation or the As precipitates are responsible for the short carrier lifetime.
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ABSTRACTTransmission electron microscopy is applied to investigate the effect of post-annealing on misfit dislocations in an In0.2Ga0.8As/GaAs(001) heterostructure. An orthogonal array of 60º dislocations along [110] and [110] directions... more
ABSTRACTTransmission electron microscopy is applied to investigate the effect of post-annealing on misfit dislocations in an In0.2Ga0.8As/GaAs(001) heterostructure. An orthogonal array of 60º dislocations along [110] and [110] directions was observed in the interfaces of the samples grown by MBE at 520 ºC. When the as-grown samples were annealed at temperatures ranging from 600 to 800 ºC, the 60º dislocations were gradually reoriented by dislocation reactions occurring at the 90º intersections followed by nonconservative motion driven by dislocation line tension and the residual elastic misfit strain. The final result of this process was a dislocation array lying along [100] and [010] directions. The reoriented u=<100> dislocation has a Burgers vector , which is the same as that of 60º dislocation, but the edge component of its Burgers vector in the (001) interfacial plane is larger than that of 60º dislocation by a factor of , resulting in a greater contribution to elastic st...
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Bulk single crystals of GaN were used for epitaxial growth of GaN films by molecular beam epitaxy. Low temperature photoluminescence yields much higher intensity emission in the near bandedge region for epitaxial films with respect to the... more
Bulk single crystals of GaN were used for epitaxial growth of GaN films by molecular beam epitaxy. Low temperature photoluminescence yields much higher intensity emission in the near bandedge region for epitaxial films with respect to the situation in bulk crystals. Character of this luminescence changes also. Dominant band-to-band transitions in the bulk crystals are exchanged by bound exciton and/or donor-acceptor pair transitions observed in the epitaxial layers. We will compare the obtained results with the available data on the homoepitaxial samples grown by metalorganic chemical vapor deposition method and discuss the importance of establishing the basic information on energetic positions of excitonic transitions in stress free samples.
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The influence of Si doping on the structure of GaN grown by metal-organic chemicalvapor deposition (MOCVD) has been studied using transmission electron microscopy (TEM), x-ray diffraction and Raman spectroscopy. Undoped and low Si doped... more
The influence of Si doping on the structure of GaN grown by metal-organic chemicalvapor deposition (MOCVD) has been studied using transmission electron microscopy (TEM), x-ray diffraction and Raman spectroscopy. Undoped and low Si doped samples were compared with samples of increased dopant concentration. In addition, defect reduction due to different buffer layers (AIN and GaN) is discussed. Silicon doping improves surface morphology and influences threading dislocation arrangement. High doping leads to a more random distribution of dislocations. Based on this study it appears (for the same dopant concentration) that an AIN buffer layer can significantly reduce the number of threading dislocations, leaving the samples more strained. However, no significant reduction of threading dislocations could be observed in the samples with GaN buffer layer. These samples are the least strained.
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We have studied the photoluminescence spectra in both ordered and disordered phases of Ga0.5In0.5P alloy as a function of pressure. We found evidence of a pressure-induced conversion of Ga0.5In0.5P from a direct band gap semiconductor to... more
We have studied the photoluminescence spectra in both ordered and disordered phases of Ga0.5In0.5P alloy as a function of pressure. We found evidence of a pressure-induced conversion of Ga0.5In0.5P from a direct band gap semiconductor to an indirect band gap semiconductor owing to lowering of the X conduction band valleys relative to the minimum at the zone centre. Raman spectra
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ABSTRACTPresent hydride vapor phase epitaxial growth of GaN on Al2O3 can produce material of very high quality, especially in regions of the crystal far from the substrate/epilayer interface. In the present study, we characterize a... more
ABSTRACTPresent hydride vapor phase epitaxial growth of GaN on Al2O3 can produce material of very high quality, especially in regions of the crystal far from the substrate/epilayer interface. In the present study, we characterize a 248-μm-thick epilayer, which had been separated from its Al2O3 substrate and etched on top and bottom to produce flat surfaces. Temperature-dependent Hall-effect data have been fitted to give the following parameters: mobility μ(300) = 1320 cm2/V-s; μ(peak) = 12,000 cm2/V-s; carrier concentration n(300) = 6.27 × 1015 cm−3; donor concentration ND = 7.8 × 1015 cm−3; acceptor concentration NA = 1.3 × 1015 cm−3; and effective donor activation energy ED = 28.1 meV. These mobilities are the highest ever reported in GaN, and the acceptor concentration, the lowest. Positron annihilation measurements give a Ga vacancy concentration very close to NA, showing that the dominant acceptors are likely native defects. Secondary ion mass spectroscopic measurements show th...
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Results from electrical measurements, as well as lattice site determination, structural, and X-ray energy dispersive studies of Cu doping on InP, are presented. Hall measurements of carrier concentration as a function of inverse... more
Results from electrical measurements, as well as lattice site determination, structural, and X-ray energy dispersive studies of Cu doping on InP, are presented. Hall measurements of carrier concentration as a function of inverse temperature show that InP:Cu exhibits semi-insulating behavior after diffusion with Cu at temperatures exceeding 700°C. Similar measurements of carrier concentration and mobility show that samples exhibited properties
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ABSTRACTTransmission electron microscopy has been used to examine dislocations present in an epitaxial laterally overgrown (ELOG) sample of GaN grown on (0001)sapphire. Studies of both plan-view and cross-sectional samples revealed arrays... more
ABSTRACTTransmission electron microscopy has been used to examine dislocations present in an epitaxial laterally overgrown (ELOG) sample of GaN grown on (0001)sapphire. Studies of both plan-view and cross-sectional samples revealed arrays of dislocations present in the (11-20) boundary between the seed and the wing (overgrown) material and at the meeting front between adjacent wings, as well as dislocations in the form of half-loops extending into the wing regions. Both the boundary and half-loop dislocations had 1/3<11-20> Burgers vectors which were either perpendicular (boundary dislocations) or at 30°s (half-loops) to the boundary plane. Large angle convergent beam electron diffraction was used to show that the boundary dislocations and halfloops correlated respectively with tilts and twists of the wing material about (11-20). A model is proposed whereby the half-loops are generated from threading dislocations by shear stresses acting along the stripe direction. The origin,...
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We summarize structural properties of thick HVPE GaN templates from the point of view of their application as substrates for growth of nitride layers. This is followed by the results of optical and structural studies, mostly transmission... more
We summarize structural properties of thick HVPE GaN templates from the point of view of their application as substrates for growth of nitride layers. This is followed by the results of optical and structural studies, mostly transmission electron microscopy, of nitride layers grown by MOCVD on top of the HVPE substrates. The results indicate high structural quality of these layers with a low density of threading dislocations (in the range of 10ⶠcmâ»Â²). Convergent beam electron diffraction studies showed that the MOCVD GaN films have Ga-polarity, the same polarity as the HVPE GaN substrates. Structural studies of an InGaN layer grown on top of the MOCVD GaN film showed the presence of two layers, which differed in lattice parameter and composition. The upper layer, on the top of the structure had a c-lattice parameter about 2% larger than that of GaN and contained 10.3 {+-} 0.8% of In. Values measured for the thinner, intermediate layer adjacent to the GaN layer were about 2 .5 ...
We demonstrate a data read-back scheme based on electron-beam induced current in a data storage device that utilizes thermal recording onto a phase-change medium. The phase-change medium is part of a heterojunction diode whose local... more
We demonstrate a data read-back scheme based on electron-beam induced current in a data storage device that utilizes thermal recording onto a phase-change medium. The phase-change medium is part of a heterojunction diode whose local charge-collection ef- ciency depends on the crystalline or amorphous state of a bit. Current gains up to 65 at 2 keV electron beam energy have
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Using low temperature molecular beam epitaxy (LT‐MBE) technique we have overcome the miscibility gap of GaAs and GaN alloys and successfully synthesized GaN1‐xAsx alloys in the whole composition range on crystalline (sapphire and silicon)... more
Using low temperature molecular beam epitaxy (LT‐MBE) technique we have overcome the miscibility gap of GaAs and GaN alloys and successfully synthesized GaN1‐xAsx alloys in the whole composition range on crystalline (sapphire and silicon) and amorphous (Pyrex glass) substrates. On the N‐rich side we found an increased incorporation of As with decreasing growth temperature. At high enough As content the films lose their crystallinity and become amorphous. On sapphire substrate, the alloys are amorphous in the composition range of 0.17
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The relation between structural perfection and optical properties of InGaN with 10% In are discussed. Transmission Electron Microscopy, X‐ray diffraction and Rutherford backscattering spectrometry measurements show that only strained... more
The relation between structural perfection and optical properties of InGaN with 10% In are discussed. Transmission Electron Microscopy, X‐ray diffraction and Rutherford backscattering spectrometry measurements show that only strained layers with a thickness not exceeding 100 nm are defect free and In concentration is lower than the nominal value. Extension of layer thickness leads to layer sequestration into sublayers with different In contents and the formation of planar defects as a result of layer relaxation. In concentration in such sublayers reach and in some cases exceed the nominal concentration. A single band edge photoluminescence peak is observed only for the thinnest layer. Samples with larger film thickness showed multiple PL peaks corresponding to layers with different In content. Much higher In content would be required to explain the presence of some PL peaks, suggesting that some PL peaks originate from the defective areas of the film. This was confirmed by cathodolu...
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Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.
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Research Interests: Condensed Matter Physics, Materials Science, Crystallography, High Pressure, Crystal Growth, and 15 moreSurface Roughness, Doping, Molecular beam epitaxy, Magnesium, MOCVD, Gallium nitride, Dislocations, CVD, Dopant, Epitaxy, Structural Properties, Growth rate, Heterojunctions, Hydride vapor phase epitaxy, and perpendicular
We present a systematic investigation on the formation of the highly mismatched alloy GaNxAs1−x using N+-implantation followed by a combination of pulsed laser melting and rapid thermal annealing. Thin films of GaNxAs1−x with x as high as... more
We present a systematic investigation on the formation of the highly mismatched alloy GaNxAs1−x using N+-implantation followed by a combination of pulsed laser melting and rapid thermal annealing. Thin films of GaNxAs1−x with x as high as 0.016 and an activation efficiency of the implanted N up to 50% have been synthesized with structural and optical properties comparable to films grown by epitaxial deposition techniques with similar substitutional N content. The effects of N+ implantation dose, laser energy fluence, and rapid thermal annealing temperature on the N incorporation as well as optical and structural properties of the GaNxAs1−x films are discussed.
Research Interests: Information Systems, Engineering, Materials Science, Laser, Kinetics, and 14 moreIII-V Semiconductors, Applied Physics, Pulsed Laser Deposition, Mathematical Sciences, Ultraviolet, Applied, Info, Thin Film, Physical sciences, Optical Properties, Alloy, Infrared Radiation, Epitaxy, and Structural Properties
Both the hexagonal and cubic GaN phases were synthesized in GaAs (001) by 50 keV N ion implantation at 380 °C and subsequent furnace annealing at 850–950 °C for 10 min–2 h. For a fluence of 1.5×1017 cm−2, transmission electron microscopy... more
Both the hexagonal and cubic GaN phases were synthesized in GaAs (001) by 50 keV N ion implantation at 380 °C and subsequent furnace annealing at 850–950 °C for 10 min–2 h. For a fluence of 1.5×1017 cm−2, transmission electron microscopy revealed that cubic GaN epitaxially crystallizes as precipitates in the GaAs matrix. A cubic-to-hexagonal GaN phase transition was observed for extended thermal anneals. By increasing the N fluence to 3×1017 cm−2, a continuous buried layer of randomly oriented hexagonal-GaN nanocrystals was produced.
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Al-polarity inversion domains formed during AlN layer growth on (0001) sapphire were identified using transmission electron microscopy (TEM). They resemble columnar inversion domains reported for GaN films grown on (0001) sapphire.... more
Al-polarity inversion domains formed during AlN layer growth on (0001) sapphire were identified using transmission electron microscopy (TEM). They resemble columnar inversion domains reported for GaN films grown on (0001) sapphire. However, for AlN, these columns have a V-like shape with boundaries that deviate by 2°±0.5° from the c axis. TEM identification of these defects agrees with the post-growth surface morphology as well as with the microstructure revealed by etching in hot aqueous KOH.
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Research Interests: Engineering, Materials Science, Microscopy, Transmission Electron Microscopy, Materials Science and Engineering, and 13 moreAtomic Force Microscopy, Molecular beam epitaxy, Physical sciences, Dislocation, Diffraction, Surface Morphology, High Temperature, Sapphire, CHEMICAL SCIENCES, Dislocation Density, Low Temperature, Surface Defects, and Defect Density
ABSTRACTV-like columnar inversion domains with a divergence angle of about 4.5° ± 1° grown in AlN films with N-polarity were studied using transmission electron microscopy (TEM) and atomic force microscopy. Such domains emerge at the... more
ABSTRACTV-like columnar inversion domains with a divergence angle of about 4.5° ± 1° grown in AlN films with N-polarity were studied using transmission electron microscopy (TEM) and atomic force microscopy. Such domains emerge at the surface forming a small islands in form of hexagonal, truncated pyramids. A model of such pyramid was proposed. TEM studies indicate a displacement of c/2 along the [0001] direction at the inversion domain boundary. A boundary itself is composed of long segments located on the {1100} planes, which are alternated by short segments on some inclined planes.
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ABSTRACT We use transmission electron microscopy to study orientation-patterned GaAs layers very attractive for applications in terahertz and infrared frequency conversion devices. We observe regularly distributed inversion domains... more
ABSTRACT We use transmission electron microscopy to study orientation-patterned GaAs layers very attractive for applications in terahertz and infrared frequency conversion devices. We observe regularly distributed inversion domains separated by inversion boundaries, together with undesirable microtwin defects originating at these boundaries. Atomic resolution aberration-corrected scanning transmission electron microscopy allowed us to resolve the GaAs dumbbells leading to a direct determination of the growth polarity of particular domains and determination of the alternating Ga-Ga and As-As bonds at the {110}-type antiphase boundary planes. We also determined observed microtwins as rotation twins called orthotwins, the defect that can cause optical losses.