Entire Range Of Growth Temperatures Research Articles

Photoluminescence Studies of Si-Doped Epitaxial GaAs Films Grown on (100)- and (111)A-Oriented GaAs Substrates at Lowered Temperatures

The electrical properties and photoluminescence features of uniformly Si-doped GaAs layers grown on GaAs substrates with the (100) and (111)A crystallographic orientations of the surface are studied. The samples are grown at the same As4 pressure in the growth temperature range from 350 to 510°C. The samples grown on GaAs(100) substrates possess n-type conductivity in the entire growth temperature range, and the samples grown on GaAs(111)A substrates possess p-type conductivity in the growth temperature range from 430 to 510°C. The photoluminescence spectra of the samples exhibit an edge band and an impurity band. The edge photoluminescence band corresponds to the photoluminescence of degenerate GaAs with n- and p-type conductivity. The impurity photoluminescence band for samples on GaAs(100) substrates in the range 1.30–1.45 eV is attributed to VAs defects and SiAs–VAs defect complexes, whose concentration varies with sample growth temperature. Transformation of the impurity photoluminescence spectra of the samples on GaAs(111)A substrates is interpreted as being a result of changes in the VAs and VGa defect concentrations under variations in the growth temperature of the samples.

Фотолюминесцентные исследования легированных кремнием эпитаксиальных пленок GaAs, выращенных на подложках GaAs с ориентациями (100) и (111)А при пониженных температурах

AbstractThe electrical properties and photoluminescence features of uniformly Si-doped GaAs layers grown on GaAs substrates with the (100) and (111)A crystallographic orientations of the surface are studied. The samples are grown at the same As_4 pressure in the growth temperature range from 350 to 510°C. The samples grown on GaAs(100) substrates possess n -type conductivity in the entire growth temperature range, and the samples grown on GaAs(111)A substrates possess p -type conductivity in the growth temperature range from 430 to 510°C. The photoluminescence spectra of the samples exhibit an edge band and an impurity band. The edge photoluminescence band corresponds to the photoluminescence of degenerate GaAs with n - and p -type conductivity. The impurity photoluminescence band for samples on GaAs(100) substrates in the range 1.30–1.45 eV is attributed to V _As defects and Si_As– V _As defect complexes, whose concentration varies with sample growth temperature. Transformation of the impurity photoluminescence spectra of the samples on GaAs(111)A substrates is interpreted as being a result of changes in the V _As and V _Ga defect concentrations under variations in the growth temperature of the samples.

Effect of the growth temperature and nitrogen precursor on the structural and electrical transport properties of SmN thin films

ABSTRACTWe report on the structural and electrical properties of epitaxial SmN thin films grown by molecular beam epitaxy. The effect of the growth temperature and nitrogen precursor, either pure molecular N2 or NH3 was investigated. The structural quality of SmN was assessed by X-ray diffraction and the epitaxial growth character is observed over the entire range of growth temperatures, from 300°C to 800°C, with both nitrogen precursors. The highest quality films are produced at a growth temperature of about 430°C by using N2 as a nitrogen precursor. Hall Effect and resistivity measurements establish that SmN films are heavily n-type doped semiconductors, suggesting the presence of nitrogen vacancies, a recurring phenomenon in rare earth nitride compounds.

Epitaxial and textured TiN thin films grown on MgO(1 0 0) by reactive HiPIMS: the impact of charging on epitaxial to textured growth crossover

Ultra-thin TiN films were grown on MgO(1 0 0) substrates by high power impulse magnetron sputtering at growth temperatures of C–C. Epitaxial TiN films were obtained when a metallic substrate holder is used, while only textured films were achieved for the films grown by HiPIMS using a substrate holder with a ceramic shadow mask. For the entire range of growth temperatures, the epitaxial films are denser and exhibit a higher growth rate compared to the textured films. Also, chemical composition analysis reveals that all the epitaxial TiN films are N-deficient sub-stoichiometric. As the growth temperature increases, the surface roughness of both epitaxial and textured films decreases, however the epitaxial films generally show less roughness than the textured films. In comparison to epitaxial films previously grown by dc magnetron sputtering, the HiPIMS grown epitaxial films are sub-stoichiometric and according to x-ray measurements, they are in a higher strain state whilst presenting higher film density and atomically smoother surfaces. A HiPIMS-induced negative charging of the TiN islands formed on top of the insulating mask is concluded to be the main reason for the growth mode transition from two dimensional Stranski–Krastanov to three dimensional Volmer–Weber when the shadow mask is used. Acceleration of the ionized species of the HiPIMS plasma including Ti+ , N+ , and Ti2+ toward the substrate when they approach the substrate holder is the reason for the observed changes in the film densities, growth rates, and surface roughness.

Seed layers on RABiTS tapes for Second-Generation HTS wires

Epitaxial films of CeO2 and Y2O3 on RABiTS metal tapes have been obtained by pulsed laser deposition. The dependence of the film crystal orientation on the temperature of synthesis has been studied. It is established that Y2O3 films grow with 100% (100) orientation, whereas a parasitic orientation is present in CeO2 films obtained in the entire range of growth temperatures. The texture sharpness in the substrate plane amounted to 8°. Electron-microscopic examination showed that an increase in the temperature of synthesis leads to the appearance of cracks on the surface of CeO2 films, while the surface of Y2O3 films remains continuous in the entire range of growth temperatures. Thus, Y2O3 films most fully obey the requirements to seed layers in (i) being epitaxial with 100% (100) crystal orientation, (ii) inheriting the substrate texture, and (iii) having a smooth crack-free surface.

Indium incorporation and emission wavelength of polar, nonpolar and semipolar InGaN quantum wells

InGaN quantum wells were grown by metal organic vapor-phase epitaxy on polar (0 0 0 1), nonpolar (1 0 0) and on semipolar (1 0 2), (1 1 2), (1 0 1) as well as (2 0 1) oriented GaN substrates. The room-temperature photoluminescence (PL) and electroluminescence (EL) emission energies for quantum wells grown on different crystal orientations show large variations of up to 600 meV. The following order of the emission energy was found throughout the entire range of growth temperatures: (1 0 1) < (1 1 2) = (0 0 0 1) < (2 0 1) < (1 0 0) = (1 0 2). In order to differentiate between the effects of strain, quantum-confined stark effect (QCSE) and indium incorporation the experimental data were compared to k.p theory-based calculations for differently oriented InGaN QWs. The major contribution to the shift between (1 0 0) and (0 0 0 1) InGaN quantum wells can be attributed to the QCSE. The redshift between (1 0 0) and the semipolar (1 0 2) and (2 0 1) QWs can be attributed to shear and anisotropic strain affecting the valence band structure. Finally, for (1 1 2) and (1 0 1) the emission energy shift could be attributed to a significantly higher indium incorporation efficiency.

Effects of photoperiod and temperature on growth and flowering in the annual (primocane) fruiting raspberry (Rubus idaeus L.) cultivar ‘Polka’

SummaryGrowth and flowering of the annual-fruiting raspberry (Rubus idaeus L.) cultivar ‘Polka’ were studied under controlled environment conditions in order to facilitate out-of-season production. Vegetatively-propagated plants originating from adventitious root buds were used. Height growth and the rate of leaf formation increased with increasing temperature, up to a broad optimum in the mid-20°C range. While elongation was consistently enhanced by long-day (LD) conditions, photoperiod had no effect on the rate of leaf formation. LD stimulation of growth thus resulted from increased internode length only. In agreement with earlier reports, it was found that, in contrast to biennial-fruiting cultivars, such annual-fruiting cultivars do not need low temperatures for flower initiation, nor do they appear to have a juvenile phase during which they are un-responsive to flower-inducing conditions. ‘Polka’ plants responded to inductive conditions as early as the 5-leaf stage, and flowered freely across the entire range of growth temperatures, even at 30°C. Flowering was advanced and the number of flowers increased with increasing temperature, up to an optimum at 27°C. Flowering was also consistently advanced and occurred at lower nodes under LD than under short-day (SD) conditions across the whole range of temperatures. Night interruption for 3 h in the middle of the night was also effective, demonstrating that this is a true photoperiodic response and not merely an effect of increased light integral in LD. It was also confirmed that a distinct vernalisation-type advancement of flowering took place when small, non-dormant plants were exposed to additional chilling at 6°C for several weeks. At low temperatures, a large proportion of the lateral buds were dormant, so that, at 12°C, the plants actually flowered only at their tips. Dissections also revealed that the dormant buds had initiated flowers; but, because of their dormant state, they needed several weeks of chilling before they could flower (biennial-fruiting behaviour). Both types of buds were initiated by the same environmental conditions. Practical applications of the findings are suggested.

Architecture of thermal adaptation in an Exiguobacterium sibiricum strain isolated from 3 million year old permafrost: a genome and transcriptome approach.

BackgroundMany microorganisms have a wide temperature growth range and versatility to tolerate large thermal fluctuations in diverse environments, however not many have been fully explored over their entire growth temperature range through a holistic view of its physiology, genome, and transcriptome. We used Exiguobacterium sibiricum strain 255-15, a psychrotrophic bacterium from 3 million year old Siberian permafrost that grows from -5°C to 39°C to study its thermal adaptation.ResultsThe E. sibiricum genome has one chromosome and two small plasmids with a total of 3,015 protein-encoding genes (CDS), and a GC content of 47.7%. The genome and transcriptome analysis along with the organism's known physiology was used to better understand its thermal adaptation. A total of 27%, 3.2%, and 5.2% of E. sibiricum CDS spotted on the DNA microarray detected differentially expressed genes in cells grown at -2.5°C, 10°C, and 39°C, respectively, when compared to cells grown at 28°C. The hypothetical and unknown genes represented 10.6%, 0.89%, and 2.3% of the CDS differentially expressed when grown at -2.5°C, 10°C, and 39°C versus 28°C, respectively.ConclusionThe results show that E. sibiricum is constitutively adapted to cold temperatures stressful to mesophiles since little differential gene expression was observed between 4°C and 28°C, but at the extremities of its Arrhenius growth profile, namely -2.5°C and 39°C, several physiological and metabolic adaptations associated with stress responses were observed.

Nitrogen incorporation into GaInNAs lattice-matched to GaAs: The effects of growth temperature and thermal annealing

We have studied the effects of growth temperature and subsequent thermal annealing on nitrogen incorporation into lattice-matched dilute Ga0.942In0.058NAs-on-GaAs epilayers, which were grown by the molecular-beam epitaxy method. The samples were studied experimentally by means of x-ray diffraction and Raman spectroscopy and theoretically by calculations within the density-functional theory. Over the entire range of growth temperatures applied (410–470°C), nitrogen appeared to be mainly located on substitutional sites in “short-range-order clusters” as N–Ga4 and, to a lesser extent, as N–Ga3In. There were also indications of the presence of nitrogen dimers NN, as suggested by Raman spectroscopy, in qualitative agreement with the calculations. An increase in growth temperature reduced the amount of substitutional nitrogen and decreased the number of N–Ga4 clusters relative to N–Ga3In. Postgrowth thermal annealing promoted the formation of In–N bonds and caused a blueshift in the optical band gap, which increased as the growth temperature was lowered.

The Effect of Growth Temperature On The Microstructure of Movpe AlN/Si (111)

AbstractThe epitaxy, defect structure, and heterointerface microstructure of MOVPE-grown AlN on &lt;111&gt; oriented Si were studied by transmission electron microscopy (TEM) in an investigation of the affects of the growth temperature (925°C–1 175°C) on the microstructure of low thickness (∼0.2 μm) films. A film grown at 1175°C was single crystalline with the following orientation relationship: (0001)AlN||(111)Si, &lt;1120&gt; and &lt;1010&gt;AlN||&lt;211&gt;Si. All AlN films grown at temperatures below 1100°C were wire-textured polycrystals with (0001)AlNlargely parallel to (111)siand some in-plane preferred orientation similar to that of 1175°C AlN epifilms. Columnar grains/domains with faceted top surfaces were observed for the entire growth temperature range. The mean column diameters decreased from 50 nm to 35 nm as the growth temperature decreased. The columnar grain/domain structure and the faceted tops resulted in peakto-valley surface roughness on the order of 20 nm. Sharp interfaces of AlN/Si were generally observed in all AIN films studied by HREM except for the 1075°C film where a transitional layer of approximately 15Å thick was observed at some interface regions. Defects typically encountered in large lattice mismatched heteroepitaxial systems were observed.

The kinetic aspects of ordering in GaAs 1- xSb x grown by organometallic vapor phase epitaxy

Long range ordered structures have been studied in GaAs 1- x Sb x alloys with x ≈ 0.5 grown by organometallic vapor phase epitaxy (OMVPE). The emphasis of this paper is on the kinetic effects leading to the occurrence of ordering. In particular, the effects of growth temperature, growth rate, and substrate orientation are reported. The ordered simple tetragonal CuAu-I (L1 0) and the chalcopyrite (E1 1) structures were observed at the highest growth temperatures from 580 to 660°C on (100) oriented InP substrates with both high and low growth rates. The samples grown at lower temperatures, 550°C, on (100) oriented InP substrates were observed to have only the L1 0 ordered structure at a growth rate of 0.02 μm/min and principally the L1 0 ordered structure with a very small amount of E1 1 at a growth rate of 0.01 μm/min. A new superlattice structure with 3 times the normal zincblende periodicity along the [110] direction was observed for samples grown over the entire growth temperature range studied for GaAs 0.5Sb 0.5 on (100)InP substrates. Growth on (110) oriented substrates produced GaAs 0.5Sb 0.5 with only the L1 0 ordered structure. However, an additional superlattice structure with four times the normal periodicity along the [100] direction was observed for these samples. We also examined samples grown on (221) and (311) oriented InP substrates at 550°C. They showed very little ordering with only local observation of weak L1 0 superlattice electron diffraction spots. Photoluminescence measurements for the epilayers grown on (221) and (311) substrates showed much stronger intensities and narrower half-widths than for those grown on (100) and (110) oriented InP substrates, due perhaps to a higher degree of homogeneity in the absence of ordered phases.

Properties of high-purity AlxGa1−xAs grown by the metalorganic vapor-phase-epitaxy technique using methyl precursors

The metalorganic vapor-phase epitaxy (MOVPE) of AlxGa1−xAs most commonly employs the methyl precursors Al(CH3)3 and Ga(CH3)3. These precursors were used in the growth of AlxGa1−xAs over the entire range of alloy composition in a low-pressure horizontal MOVPE reactor. A complete chemical, electrical, and optical characterization of high-purity MOVPE AlxGa1−xAs grown over the entire range of growth temperatures (600–800 °C) was carried out in order to determine the relationship of the materials properties to the growth conditions. Carbon, the primary impurity in the layers, dominates the electrical properties of the epitaxial layers. A superlinear dependence of carbon incorporation on AlAs mole fraction is observed, along with a two-slope dependence on growth temperature. Photoluminescence spectra (2 K) were obtained from materials with AlAs mole fraction over the range 0≤x≤0.80. The photoluminescence intensity of the layers also exhibits a systematic dependence on alloy composition and growth temperature. The in situ gettering of oxygen by the growth reactants is necessary to achieve high luminescence intensity and low electrical compensation. The influence of the reactor design on this gettering process is modeled.

Influence of substrate temperature on the mobility of modulation-doped AlxGa1−xAs/GaAs heterostructures grown by molecular beam epitaxy

Single-period modulation-doped Al0.3 Ga0.7 As/GaAs heterostructures were grown by molecular beam epitaxy in a substrate temperature range of 580–750 °C. Excellent surface morphologies were routinely obtained throughout the entire range of growth temperatures. Highest mobilities (in dark) obtained were 8000, 90 000, and 196 200 at 300, 78, and 10 K, respectively. In room light, these figures improved to 9000, 110 000, and 250 000 cm2/Vs. The sheet carrier concentration yielding the best electron mobility was about 8×1011 cm−2. While the mobilities did not depend on the substrate growth temperature between 600 and 675 °C, some degradation was observed above 675 and below 600 °C.

Membrane phase behavior of a psychrotrophic and mesophilic bacillus

The phase properties of membranes isolated from the psychrotrophBacillus psychrophilus and the mesophileB. megaterium were examined using wide-angle X-ray diffraction. The temperature at which the transition from liquid-crystalline to crystalline (gel) phase occurred was below −30°C for both microorganisms, regardless of the temperature at which the microbial cells were grown. Thus the membranes for both microorganisms were exclusively liquid-crystalline over the entire growth temperature range. Indeed, the membrane was completely fluid at temperatures where growth of the psychrotroph ceases, thus indicating that the phase transition temperature is not the determinant of the minimum growth temperature.