Distribution by Scientific Domains

Terms modified by MBE

  • mbe growth

  • Selected Abstracts

    Interdiffusion phenomena in InGaAs/GaAs superlattice structures

    B. Sar, kavak
    Abstract We have studied structural properties of InGaAs/GaAs superlattice sample prepared by Molecular Beam Epitaxy (MBE) using high resolution X-ray diffractometer (HRXRD). Increasing strain relaxation and defect generations are observed with the increasing Rapid Thermal Annealing (RTA) temperature up to 775 °C. The higher temperatures bring out relaxation mechanisms; interdiffusion and favored migration. The defect structure and the defects which are observed with the increasing annealing temperature were analyzed. Firstly, the in-plane and out-of-plane strains after the annealing of sample were found. Secondly, the structural defect properties such as the parallel X-ray strain, perpendicular X-ray strain, misfit, degree of relaxation, x composition, tilt angles and dislocation that are obtained from X-ray diffraction (XRD) analysis were carried out at every temperature. As a result, we observed that the asymmetric peaks especially in asymmetric (224) plane was affected more than symmetric and asymmetric planes with lower polar or inclination angles due to c-direction at low temperature. These structural properties exhibit different unfavorable behaviors for every reflection direction at the increasing temperatures. The reason is the relaxation which is caused by spatially inhomogeneous strain distribution with the increasing annealing temperature. In the InGaAs superlattice samples, this process enhances preferential migration of In atoms along the growth direction. Further increase in the annealing temperature leads to the deterioration of the abrupt interfaces in the superlattice and degradation in its structural properties. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    The impact of SiC substrate treatment on the heteroepitaxial growth of GaN by plasma assisted MBE

    A. S. Brown
    Abstract We report on the impact of the preparation of the Si-face 4H-SiC(0001)Si substrate using a Ga flash-off process on the epitaxial growth of GaN by plasma-assisted molecular beam epitaxy. The nucleation, as well as the resultant structural and morphological properties of GaN grown directly on 4H-SiC(0001)Si are strongly influenced by the chemical and morphological modifications of the SiC surface induced by the Ga flash-off process. Herein we describe the impact of the specific concentration of Ga incident on the surface (quantified in terms of monolayer (ML) coverage): of 0.5 ML, 1ML and 2ML. The residual oxygen at the SiC surface, unintentional SiC nitridation and the formation of cubic GaN grains during the initial nucleation stage, are all reduced when a 2 ML Ga flash is used. All of the above factors result in structural improvement of the GaN epitaxial layers. The correlation between the SiC surface modification, the initial nucleation stage, and the GaN epitaxial layer structural quality has been articulated using x-ray photoelectron spectroscopy, x-ray diffraction, atomic force microscopy and spectroscopic ellipsometry data. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Nano vanadyl-phthalocyanine crystals fabricated on KBr substrate

    Suguru Mototani
    Abstract Vanadyl-phthalocyanine (VOPc) thin films deposited on a KBr substrate by molecular beam epitaxy (MBE) consist of nano-VOPc crystals epitaxially grown. The nano-VOPc crystals acquire a square shape as a result of annealing at 150°C. The size of the nano-crystals is controllable by changing the conditions of MBE deposition and thermal treatment. The growth processes of nano-crystals on the KBr substrate are elucidated experimentally and are shown to be closely related to strong interaction between the VOPc molecules and the KBr substrate. Their mechanisms can be explained in terms of surface diffusion of the VOPc molecules on the KBr substrate. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(2): 41,48, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20645 [source]

    M. Joy Lewis MBE 1930,2007

    David Matthews
    No abstract is available for this article. [source]

    Controlled Growth of High-Quality ZnO-Based Films and Fabrication of Visible-Blind and Solar-Blind Ultra-Violet Detectors

    ADVANCED MATERIALS, Issue 45 2009
    Xiaolong Du
    Abstract ZnO is a wide-bandgap (3.37,eV at room temperature) oxide semiconductor that is attractive for its great potential in short-wavelength optoelectronic devices, in which high quality films and heterostructures are essential for high performance. In this study, controlled growth of ZnO-based thin films and heterostructures by molecular beam epitaxy (MBE) is demonstrated on different substrates with emphasis on interface engineering. It is revealed that ultrathin AlN or MgO interfacial layers play a key role in establishing structural and chemical compatibility between ZnO and substrates. Furthermore, a quasi-homo buffer is introduced prior to growth of a wurtzite MgZnO epilayer to suppress the phase segregation of rock-salt MgO, achieving wide-range bandgap tuning from 3.3 to 4.55,eV. Finally, a visible-blind UV detector exploiting a double heterojunction of n-ZnO/insulator-MgO/p-Si and a solar-blind UV detector using MgZnO as an active layer are fabricated by using the growth techniques discussed here. [source]

    Missing data estimation for 1,6,h gaps in energy use and weather data using different statistical methods

    David E. Claridge
    Abstract Analysing hourly energy use to determine retrofit savings or diagnose system problems frequently requires rehabilitation of short periods of missing data. This paper evaluates four methods for rehabilitating short periods of missing data. Single variable regression, polynomial models, Lagrange interpolation, and linear interpolation models are developed, demonstrated, and used to fill 1,6,h gaps in weather data, heating data and cooling data for commercial buildings. The methodology for comparing the performance of the four different methods for filling data gaps uses 11 1-year data sets to develop different models and fill over 500 000 ,pseudo-gaps' 1,6,h in length for each model. These pseudo-gaps are created within each data set by assuming data is missing, then these gaps are filled and the ,filled' values compared with the measured values. Comparisons are made using four statistical parameters: mean bias error (MBE), root mean square error, sum of the absolute errors, and coefficient of variation of the sum of the absolute errors. Comparison based on frequency within specified error limits is also used. A linear interpolation model or a polynomial model with hour-of-day as the independent variable both fill 1,6 missing hours of cooling data, heating data or weather data, with accuracy clearly superior to the single variable linear regression model and to the Lagrange model. The linear interpolation model is the simplest and most convenient method, and generally showed superior performance to the polynomial model when evaluated using root mean square error, sum of the absolute errors, or frequency of filling within set error limits as criteria. The eighth-order polynomial model using time as the independent variable is a relatively simple, yet powerful approach that provided somewhat superior performance for filling heating data and cooling data if MBE is the criterion as is often the case when evaluating retrofit savings. Likewise, a tenth-order polynomial model provided the best performance when filling dew-point temperature data when MBE is the criterion. It is possible that the results would differ somewhat for other data sets, but the strength of the linear and polynomial models relative to the other models evaluated seems quite robust. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Improving Diagnostic Accuracy Using an Evidence-Based Nursing Model

    Rona F. Levin PhD
    Diagnósticos de enfermagem; prática baseada em evidências; precisão diagnóstica Exactitud diagnóstica; práctica basada en la evidencia; diagnósticos de enfermería PURPOSE. To propose an evidence-based model (EBM) to improve diagnostic accuracy in nursing. DATA SOURCES. Published literature, experience, and expertise of authors. DATA SYNTHESIS. Using an EBM directs clinicians on how to use the best available evidence from the literature to determine the best fit between cues and diagnoses, integrate this evidence with clinician expertise and patient preferences, and conduct a self-evaluation of the process. CONCLUSIONS. Use of an EBM to teach nurses how to ask relevant diagnostic questions and provide a framework for nurse educators to teach evidenced-based practice may lead to developing more competent diagnosticians and improving diagnostic accuracy in nursing. OBJETIVO. Propor um modelo baseado em evidências (MBE) para melhorar a precisão diagnóstica na enfermagem. FONTE DE DADOS. Literatura publicada, experiência e conhecimento das autoras. SÍNTESE DOS DADOS. A utilização de um BEM orienta as enfermeiras clínicas sobre como utilizar a melhor evidência disponível na literatura para determinar o melhor ajuste entre as pistas obtidas e os diagnósticos, integrando esta evidência com o conhecimento clínico da enfermeira e as preferências do paciente, e conduzindo a uma auto-avaliação do processo. CONCLUSÕES. O uso de um modelo de prática baseado em evidências para ensinar as enfermeiras a formular perguntas relevantes e oferecer aos educadores de enfermagem uma estrutura para o ensino da prática baseada em evidências pode levar ao desenvolvimento de dianosticadoras mais competentes e melhorar a precisão diagnóstica na enfermagem. PROPÓSITO. Proponer un modelo basado en la evidencia (MBE) para mejorar la exactitud diagnóstica en enfermería. FUENTES DE DATOS. Bibliografía publicada, experiencia y especialización de los autores. SÍNTESIS DE LOS DATOS. Utilizando un MBE guía a los clínicos en cómo utilizar la mejor evidencia disponible en la bibliografía para determinar el mejor encaje entre los datos y los diagnósticos, integrar esta evidencia con la especialidad clínica y las preferencias del paciente y llevar a cabo una auto-evaluación del proceso. CONCLUSIONES. El uso de un modelo de práctica basada en la evidencia para enseñar a las enfermeras cómo hacer preguntas diagnósticas pertinentes y proporcionar un marco de trabajo para que las enfermeras docentes enseñen la práctica basada en la evidencia, puede llevar a desarrollar mayor competencia al diagnosticar y mejoras en la exactitud diagnóstica. [source]

    Using SWAT to Model Streamflow in Two River Basins With Ground and Satellite Precipitation Data,

    Kenneth J. Tobin
    Abstract:, Both ground rain gauge and remotely sensed precipitation (Next Generation Weather Radar , NEXRAD Stage III) data have been used to support spatially distributed hydrological modeling. This study is unique in that it utilizes and compares the performance of National Weather Service (NWS) rain gauge, NEXRAD Stage III, and Tropical Rainfall Measurement Mission (TRMM) 3B42 (Version 6) data for the hydrological modeling of the Middle Nueces River Watershed in South Texas and Middle Rio Grande Watershed in South Texas and northern Mexico. The hydrologic model chosen for this study is the Soil and Water Assessment Tool (SWAT), which is a comprehensive, physical-based tool that models watershed hydrology and water quality within stream reaches. Minor adjustments to selected model parameters were applied to make parameter values more realistic based on results from previous studies. In both watersheds, NEXRAD Stage III data yields results with low mass balance error between simulated and actual streamflow (±13%) and high monthly Nash-Sutcliffe efficiency coefficients (NS > 0.60) for both calibration (July 1, 2003 to December 31, 2006) and validation (2007) periods. In the Middle Rio Grande Watershed NEXRAD Stage III data also yield robust daily results (time averaged over a three-day period) with NS values of (0.60-0.88). TRMM 3B42 data generate simulations for the Middle Rio Grande Watershed of variable qualtiy (MBE = +13 to ,16%; NS = 0.38-0.94; RMSE = 0.07-0.65), but greatly overestimates streamflow during the calibration period in the Middle Nueces Watershed. During the calibration period use of NWS rain gauge data does not generate acceptable simulations in both watersheds. Significantly, our study is the first to successfully demonstrate the utility of satellite-estimated precipitation (TRMM 3B42) in supporting hydrologic modeling with SWAT; thereby, potentially extending the realm (between 50°N and 50°S) where remotely sensed precipitation data can support hydrologic modeling outside of regions that have modern, ground-based radar networks (i.e., much of the third world). [source]

    Obituary: John Harold West MBE

    Frank E. Whitehead
    No abstract is available for this article. [source]

    The Bar Examination and the Dream Deferred: A Critical Analysis of the MBE, Social Closure, and Racial and Ethnic Stratification

    LAW & SOCIAL INQUIRY, Issue 3 2004
    William C. Kidder
    In this article, the author applies social closure theory to help explain why more than a dozen states have recently enacted more stringent bar exam passing standards and why others are considering similar changes. While higher standards are usually advocated as a way to protect the public from lower student "quality," the author applies social closure theory and argues that changes in passing standards are a response to a perceived oversupply of lawyers, especially among solo practitioners. In the 1990s, crowding among solo practitioners reached record levels, and real earnings eroded substantially. The author then links this labor market analysis to a critical examination of the knowledge claims that justify the bar exam to the legal profession and the public at large. The article's conclusion is that the psychometric research sponsored by the National Conference of Bar Examiners consistently minimizes and obscures the disparate impact and unfairness of the bar exam for people of color. [source]

    Precipitable water vapour estimation on the basis of sky temperatures measured by a single-pixel IR detector and screen temperatures under clear skies

    A. Maghrabi
    Abstract Precipitable water vapour (PWV) is an important component of the atmosphere, but remains difficult to measure with adequate spatial and temporal resolution under all weather conditions. Over the last four decades several techniques and methods have been developed to measure PWV more accurately, but each carries limitations preventing its widespread use. This paper presents preliminary results of a simple method for inferring PWV from the air temperature and infrared (IR) sky temperature under clear skies. Sky temperatures are measured using a broadband, single-pixel IR radiometer. A parametric model of the physical relationship between these three quantities was created using PWV data derived from a GPS receiver. By inverting the model, PWV estimates can be obtained from new temperature measurements. The measurements were taken between October 2002 and July 2004 in a coastal region of South Australia. The method was found to predict PWV quite accurately, with a mean bias error (MBE) of only , 0.009 mm and a root mean square error (RMSE) of 2.311 mm. The model was also compared to a set of 120 radiosonde-derived PWV values, resulting in a MBE and RMSE of 0.262 and 2.601 mm respectively. These preliminary results show that the clear sky PWV can be estimated accurately from sky temperatures obtained using a simple IR detector. Future work will extend the method to different sky and weather conditions. Copyright © 2009 Royal Meteorological Society [source]

    An Education Grounded in Biology: Interdisciplinary and Ethical Considerations

    MIND, BRAIN, AND EDUCATION, Issue 2 2009
    Howard Gardner
    ABSTRACT ABSTRACT,Work in the new area of Mind, Brain, and Education (MBE) raises epistemological and ethical issues. With respect to epistemology, the norms of the component disciplines must be honored and the resulting amalgam must be more than a mere sum of the parts. With respect to ethics, the roles of scientist, educator, and practitioner each raise ethical dilemmas and the MBE worker must be cognizant of each set of dilemmas and the possible strains among them. Only if both of these spheres are confronted can good work be achieved in MBE. [source]

    Photoluminescence properties of GaAs nanowire ensembles with zincblende and wurtzite crystal structure

    B. V. Novikov
    Abstract Self-standing III,V nanowires (NWs) are promising building blocks for future optoelectronic devices such as LEDs, lasers, photodetectors and solar cells. In this work, we present the results of low temperature photoluminescence (PL) characterization of GaAs NWs grown by Au-assisted molecular beam epitaxy (MBE), coupled with the transmission electron microscopy (TEM) structural analysis. PL spectra contain exci- ton peaks from zincblende (ZB) and wurtzite (WZ) crystal structures of GaAs. The peaks are influenced by the quantum confinement effects. PL bands corresponding to the exciton emission from ZB and WZ crystal phases are identified, relating to the PL peaks at 1.519 eV and 1.478 eV, respectively. The obtained red shift of 41 meV for WZ GaAs should persist in thin NWs as well as in bulk materials. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Highly conductive and optically transparent GZO films grown under metal-rich conditions by plasma assisted MBE

    H. Y. Liu
    Abstract We demonstrate a critical effect of a metal-to-oxygen ratio on the electrical, optical, and structural properties of ZnO films heavily doped with Ga (carrier concentration in the range of 1020,1021 cm,3) grown by plasma-assisted molecular beam epitaxy. The as-grown layers prepared under the metal-rich conditions exhibited resistivities below 3 × 10,4 , cm and an optical transparency exceeding 90% in the visible spectral range as well as a large blue shift of the transmission/absorption edge attributed to the Burstein,Moss shift of the Fermi level deep into the conduction band, indicating high donor concentration. In contrast, the films grown under the oxygen-rich conditions required thermal activation and showed inferior properties. Furthermore, electrical measurements point to the nonuniform depth distribution of free carriers. An oxygen-pressure-dependent surface disordering is suggested to be responsible for the drastic effect of the metal-to-oxygen ratio on the film properties. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Critical diameters and temperature domains for MBE growth of III,V nanowires on lattice mismatched substrates

    G. E. Cirlin
    Abstract We report on the growth properties of InAs, InP and GaAs nanowires (NWs) on different lattice mismatched substrates, in particular, on Si(111), during Au-assisted molecular beam epitaxy (MBE). We show that the critical diameter for the epitaxial growth of dislocation-free III,V NWs decreases as the lattice mismatch increases and equals 24 nm for InAs NWs on Si(111), 39 nm for InP NWs on Si(111), 44 nm for InAs NWs on GaAs(111)B, and 110 nm for GaAs NWs on Si(111). When the diameters exceed these critical values, the NWs are dislocated or do not grow at all. The corresponding temperature domains for NW growth extend from 320 °C to 340 °C for InAs NWs on Si(111), 330 °C to 360 °C for InP NWs on Si(111), 370 °C to 420 °C for InAs NWs on GaAs(111)B and 380 °C to 540 °C for GaAs NWs on Si(111). Experimental values for critical diameters are compared to the previous findings and are discussed within the frame of a theoretical model. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Optical anisotropy of A - and M -plane InN grown on free-standing GaN substrates

    P. Schley
    Abstract Wurtzite A - and M -plane InN films were grown by molecular beam epitaxy (MBE) on free-standing GaN substrates. Spectroscopic ellipsometry (SE) in the photon energy range from 0.56 up to 15,eV was applied in order to determine the ordinary and extraordinary complex dielectric function (DF) of InN. A distinct optical anisotropy was found over the whole energy range. The extraordinary absorption edge in comparison to the ordinary one is shifted to higher energies confirming previous studies. The investigations in the upper vacuum-ultraviolet (VUV) spectral range (9.5,15,eV) yielded transition energies for four critical points (CPs) of the band structure (BS) which have not been observed so far. [source]

    Three-dimensional ordering in self-organized (In,Ga)As quantum dot multilayer structures

    V. Kladko
    Abstract Molecular beam epitaxy (MBE) grown In0.5Ga0.5As/GaAs multilayer structures with quantum dots chains (QDs), obtained under different growth conditions, were investigated by high-resolution X-ray diffractometry (HRXRD) and AFM. It was determined that self-organized epitaxial growth of In0.5Ga0.5As/GaAs can lead to the formation of three-dimensional quantum-dot crystals with triclinic (distorted cubic) unit cell. The mechanisms of QDs ordering in dependence on As flux are analyzed. [source]

    Strain relaxation in AlN/GaN heterostructures grown by molecular beam epitaxy

    G. P. Dimitrakopulos
    Abstract The strain distribution and defects in a graded AlN/GaN heterostructure comprising AlN layers from 3 nm up to 100 nm grown by plasma-assisted MBE were studied using transmission electron microscopy techniques. Gradual strain relaxation was observed as well as strain partitioning between the GaN spacers and the thicker AlN layers. Elastic strain is retained even in the thicker layers of the heterostructure. Extensive introduction of threading and misfit dislocations is observed at and above the 7 nm AlN layer. The threading dislocations adopt inclined zig-zag line directions thus contributing to the relief of alternating compressive-tensile elastic strain across the the layers of the heterostructure. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Characterization of deep levels at GaAs/GaAs and GaAs/InAs interfaces grown by MBE-interrupted growth technique

    M. Kaniewska
    Abstract In order to find the origin of crystalline defects occurring in the preparation of InAs/GaAs quantum dots (QDs), their appearance was tracked through three different sample types designed as Schottky diodes. Specimens with a GaAs cap layer on a GaAs buffer layer as well as with an InAs wetting layer without QDs were grown by molecular beam epitaxy (MBE) using the interrupted growth technique. Deep level transient spectroscopy (DLTS) was used for comparison with structures containing InAs QDs. It was found that two main levels with thermal activation energies of 0.14,0.16 eV and 0.46,0.52 eV from the conduction band edge, respectively, are grown-in defects, which are characteristic of the growth interrupted interface occuring under an excess of As. Both these levels together with an additional level at 0.10,0.12 eV found in the InAs wetting layer structures were also present in those with QDs, probably resulting from strain or In penetration. All three defects were agglomerated close to the interface created by the interrupted growth. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    InGaAs/GaAs quantum wells and quantum dots on GaAs(11n) substrates studied by photoreflectance spectroscopy

    J. S. Rojas-Ramirez
    Abstract Pseudomorphic InGaAs/GaAs quantum wells (QWs) and self-assembled InAs quantum dots (QDs) were grown by molecular beam epitaxy (MBE) on GaAs(11n)A substrates. Photoreflectance spectroscopy was employed to investigate the transitions in the heterostructures. The transitions in QWs have two contributions, a blue shift due to the compressive strain, and a red shift due to the quantum confined Stark effect produced by the piezoelectric field. A traditional theoretical interpretation of the QWs transitions employing a simple well model with sharp interfaces shows discrepancies with the experimental results. In order to satisfactorily explain the transitions we proposed to include segregation effects of Indium at the wells interfaces. The matrix transfer method was implemented to numerically solve the Schrödinger equation taking into account In segregation effects by including an asymmetric potential well with a profile depending on the details of the In incorporation. With segregation effects included, the calculated transitions fit very well the PR spectra. On the other hand, the transitions in self-assembled QDs were obtained by fitting the PR spectra employing a first derivative line-shape function. For n = 2, 4, 5, two functions were required to fit the spectra. For n = 3 only one function was required, in agreement with the more uniform QDs size distribution observed by atomic force microscopy on GaAs(113)A. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Bismuth containing III,V quaternary alloy InGaAsBi grown by MBE

    G. Feng
    Abstract InGaAsBi epilayers were created on InP substrates by molecular beam epitaxy for the first time. The high crystalline quality of the InGaAsBi epilayer with smooth interface was confirmed by high resolution X-ray diffraction measurements. Up to 2.5% Bi was incorporated in the film based on Rutherford back scattering (RBS) results. The RBS channeling spectra give clear evidence that the Bi atoms were substitutionally located in the InGaAs zinc-blende lattice sites. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Projective techniques for the growth of compound semiconductor nanostructures

    T. Schallenberg
    Abstract We investigate the geometric deposition of compound semiconductors through shallow shadow masks as a means to obtain 3D nanostructures in situ. A high spatial resolution in the order of 10 nm and good material quality are achieved by epitaxy with directed molecular beams through stationary masks. Based on our study of growth dynamics new processes were tailored for the deposition of compound semiconductors. These expand the degrees of freedom of directional shadow growth. We would like to give an overview of this alternative technology, and present late results from experiments with an optimised molecular beam epitaxy (MBE) set-up. Projective techniques are demonstrated with sample structures. We discuss their respective potential and limitations. An outlook shows the perspective of further increase of the complexity of feasible structures by increasing the complexity of the masks (3D nanostructured). [source]

    Magnetotransport and magnetic properties of p -Zn1, xMnxTe:N , Carrier-induced ferromagnetism

    K.-T. Nam
    Abstract The magnetic properties of nitrogen-doped p -Zn1, xMnxTe grown by MBE were studied through the magnetotransport measurements. In a sample of p -Zn1, xMnxTe with x = 0.034 and p = 4.7 × 1019 cm,3, a hysteresis loop was observed below 2.5 K in the Hall resistance and the magnetoresistivity, which indicates the ferromagnetic transition. From the plot of (RHall/Rsheet)2 against B/(RHall/Rsheet) at several temperatures, which corresponds to the so-called Arrott plot, we can estimate the Curie temperature (Tc) of the sample as about 3 K, suggesting that this sample has the higher Tc than ever reported. We also demonstrated, by means of light irradiation, that the strength of ferromagnetic interactions can be controlled by changing the hole concentration. An increase of the ferromagnetic behaviours such as a small increase of the coercive field was observed under light irradiation. This result strongly supports that the ferromagnetic transition in Zn1, xMnxTe is the carrier-induced one. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    The effect of Gallium gallium adsorbate on SiC(0001) surface for GaN by MBE

    K. Jeganathan
    Abstract The adsorption of Gallium gallium (Ga) (Ga) on SiC(0001) reveals a well-ordered , R30° and 3 × 3 surface reconstructions with respect to different Ga adatom coverage. The GaN nucleation behaviours on R30° and 3 × 3 surfaces are significantly different. The GaN nucleates randomly in three-dimensional 3D islands on the R30° surface due to unoccupied surface states of dangling bonds. In contrast the 3 × 3 surface was found to be highly suitable for two-dimensional (2D) GaN nuclei which promotes a step-flow growth subsequently. The GaN growth kinetics is found to depend on the Ga atomistic process of SiC (0001). (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Hg(1-x)CdxTe from short to long wave infrared on Si substrates grown by MBE

    M. F. Vilela
    Abstract In this paper, we show the power of using molecular beam epitaxy (MBE) for the growth of the mercury cadmium telluride (HgCdTe) system. Abrupt composition profiles, changes in doping levels, or switching doping types are easily performed. It is shown that high quality material is achieved with Hg(1- x)CdxTe grown by MBE from a cadmium mole fraction of x =0.15 to x =0.72. Doping elements incorporation as low as 1015 cm -3 for both n-type and p-type material as well as high incorporation levels >1018cm -3 for both carrier types were achieved. Secondary ion mass spectrometry (SIMS) data, x-ray data, Hall data, the influence of doping incorporation with cadmium content and growth rate, etch pit density (EPD), composition uniformity determined from Fourier transform infrared (FTIR) transmission spectroscopy, and surface defect maps from low to high x values are presented to illustrate the versatility and quality of HgCdTe material grown by MBE. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Growth kinetics of AlxGa1,xN layers (0 < x < 1) in plasma-assisted molecular beam epitaxy

    A. M. Mizerov
    Abstract Comparative study of growth kinetics of the AlxGa1-xN (x = 0-1) layers of different polarity, grown by plasma assisted molecular beam epitaxy (PA MBE) under different growth conditions (substrate temperature, group III to activated nitrogen and Al to Ga flux ratios) and on different buffer layers, is presented. The 60 °C higher temperature stability of N-face AlGaN layers is detected. The strong influence of elastic stress on growth kinetics of metal-polar AlxGa1-xN (x > 0.2) layers is observed and discussed. It was found that two-dimensional growth of AlGaN films of the same composition on different buffer layers at TS = 700 °C can be achieved at different group III surface enrichment, the AlGaN(0001)/c-Al2O3 films exhibiting the atomically smooth surface at group III to activated nitrogen flux ratio FIII/FN *gradually increased from 1.3 to 2 with the x variation from 0.1 to 0.8. In this case the alloy composition is controlled by the variation of Al flux only (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Structural and optical properties of ZnSe-based diluted magnetic semiconductor quantum-well wire arrays by wet chemical etching

    Tsutomu Muranaka
    Abstract The ZnSe-based mesa structures with well-defined and smooth facets were successfully demonstrated by using molecular beam epitaxy (MBE) and wet chemical etching. The ZnSe structures were found to be bound by (111) and (-1-11) facets along the [-110] direction, and bound by (1-11) and (-111) facets along the [110] direction, respectively. The intensities of the non-polarized PL peaks from the [-110]- and [110]-oriented QWW structures were almost proportional to the unetched region and additional decreases were not observed. The PL peaks from the QWW structures were found to be highly polarized when the polarization angle was aligned parallel to the wire direction. The degrees of the linear polarization were 18% for the [-110]-oriented QWW structure and 26% for the [-110]-oriented QWW structure, respectively. The results of the PL and magneto-PL measurements show no process-induced damage to degrade magneto-optical performance of the DMS structures by using this method. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    The microstructure and properties of InN layers

    P. Ruterana
    Abstract A series of InN layers grown by different techniques has been investigated by transmission electron microscopy, photoluminescence and Raman spectroscopy. The polarity is shown to be determined by the underlying GaN template. In these In polar layers, the c -screw dislocations density is low and that of a -type dislocations is in the high-109 cm -2 range. The dislocation density tends to decrease towards the surface. Along the first 0.5 ,m, and particularly in the samples grown by hydride vapour epitaxy, we observe a large number of stacking faults, which probably contribute to the dislocation density reduction. The optical band gap in MBE and MOVPE samples is between 0.6 and 0.7 eV, but that of the HVPE templates is above 1 eV. Estimations from Raman data show that this behaviour correlates well with the residual carrier concentration. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Non-polar cubic AlGaN/GaN HFETs grown by MBE on Ar+ implanted 3C-SiC (001)

    Elena Tschumak
    Abstract The growth of cubic group III-nitrides is a direct way to eliminate polarization effects, which inherently limit the fabrication of normally-off heterojunction field-effect transistors (HFETs) in GaN technology. HFET structures were fabricated of non-polar cubic AlGaN/GaN hetero layers grown by plasma assisted molecular beam epitaxy (MBE) on free standing 3C-SiC (001). The electrical insulation of 3C-SiC was realised by Ar+ implantation before c-AlGaN/GaN MBE. The structural properties of the epilayers were studied by high-resolution x-ray diffraction (HRXRD). HFETs with normally-off and normally-on characteristics were fabricated of cubic AlGaN/GaN. Capacitance-voltage (CV) characteristics of the gate contact were performed to detect the electron channel at the c-AlGaN/GaN hetero interface. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Laplace DLTS of molecular beam epitaxy GaAs grown on (100) and (211)B substrates

    R. H. Mari
    Abstract Deep Level Transient Spectroscopy (DLTS) and Laplace DLTS (LDLTS) techniques have been employed to study defects in n-type GaAs grown by MBE on (100) and (211)B GaAs planes. The DLTS spectra were different for the two GaAs substrate orientations. Five and four defect states are found in samples grown on (100) and (211)B GaAs planes, respectively with activation energies ranging from 0.054 eV to 0.570 eV. For all of the traps observed in our samples we obtained small activation energies as compared to the previous data published in literature on n-GaAs samples grown by MBE. This can be explained by the fact that the emission of the carriers depends on the applied electric field and temperature dependence of the carrier concentration. These two phenomena seem to explain the small trap energies seen in our samples. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]