共查询到20条相似文献,搜索用时 15 毫秒
1.
Heon Song Seon-Ho LeeEun-Su Jang Dong-Wook KimR. Navamathavan Jin Soo KimCheul-Ro Lee 《Journal of Crystal Growth》2009,311(19):4418-4422
InxGa1−xN quantum dots (QDs) were grown on GaN/sapphire (0 0 0 1) substrates by employing nitridation of nano-alloyed droplet (NNAD) method using metal-organic chemical vapor deposition (MOCVD). In+Ga alloy droplets were initially formed by flowing the precursors TMIn and TMGa. Density of the In+Ga alloy droplets was increased with increasing precursors flow rate; however, the droplet size was scarcely changed in the range of about 100–200 nm. Two cases of InxGa1−xN QDs growth were investigated by varying the nitridation time and the growth temperature. It was observed that the InxGa1−xN QDs size can be easily changed by controlling the nitridation process at the temperature between 680 and 700 °C for the time of 5–30 min. Self-assembled InxGa1−xN QDs were successfully grown by employing NNAD method. 相似文献
2.
Toshiaki Asai Kensuke NagataToshiaki Mori Kentaro NagamatsuMotoaki Iwaya Satoshi KamiyamaHiroshi Amano Isamu Akasaki 《Journal of Crystal Growth》2009,311(10):2850-2852
The processes as in title of relaxation of the lattice mismatch and the recovery of crystalline quality in thick AlxGa1−xN on high-temperature-grown AlN were investigated. When x=0.3, rapid lattice relaxation occurred over a few microns, then the crystalline quality gradually recovered over 10 μm. In contrast, when x=0.7, relaxation of the lattice mismatch gradually occurred over 5 μm. 相似文献
3.
Phannee Saengkaew Armin DadgarJuergen Blaesing Thomas HempelPeter Veit Juergen ChristenAlois Krost 《Journal of Crystal Growth》2009,311(14):3742-3748
We present MOVPE-grown, high-quality AlxGa1−x N layers with Al content up to x=0.65 on Si (1 1 1) substrates. Crack-free layers with smooth surface and low defect density are obtained with optimized AlN-based seeding and buffer layers. High-temperature AlN seeding layers and (low temperature (LT)/high temperature (HT)) AlN-based superlattices (SLs) as buffer layers are efficient in reducing the dislocation density and in-plane residual strain. The crystalline quality of AlxGa1−xN was characterized by high-resolution X-ray diffraction (XRD). With optimized AlN-based seeding and SL buffer layers, best ω-FWHMs of the (0 0 0 2) reflection of 540 and 1400 arcsec for the (1 0 1¯ 0) reflection were achieved for a ∼1-μm-thick Al0.1Ga0.9N layer and 1010 and 1560 arcsec for the (0 0 0 2) and (1 0 1¯ 0) reflection of a ∼500-nm-thick Al0.65Ga0.35N layer. AFM and FE-SEM measurements were used to study the surface morphology and TEM cross-section measurements to determine the dislocation behaviour. With a high crystalline quality and good optical properties, AlxGa1−x N layers can be applied to grow electronic and optoelectronic device structures on silicon substrates in further investigations. 相似文献
4.
In this study, we have investigated the effect of substituting Mn for Fe on the crystallization kinetics of amorphous Fe73.5−xMnxCu1Nb3Si13.5B9 (x = 1, 3, 5, 7) alloys. The samples were annealed at 550 °C and 600 °C for 1 h under an argon atmosphere. The X-ray diffraction analyses showed only a crystalline peak belonging to the α-Fe(Si) phase, with the grain size ranging from 12.2 nm for x = 0 to 16.7 nm for x = 7. The activation energies of the alloys were calculated using Kissinger, Ozawa and Augis-Bennett models based on differential thermal analysis data. The Avrami exponent n was calculated from the Johnson-Mehl-Avrami equation. The activation energy increased up to x = 3, then decreased with increasing Mn content. The values of the Avrami exponent showed that the crystallization is typical diffusion-controlled three-dimensional growth at a constant nucleation rate. 相似文献
5.
A. Belousov S. Katrych J. Jun J. Zhang D. Günther Roman Sobolewski J. Karpinski B. Batlogg 《Journal of Crystal Growth》2009,311(16):3971-3974
We have successfully grown bulk, single crystals of AlxGa1−xN with the Al content x ranging from 0.5 to 0.9. Samples were grown from Ga melt under high nitrogen pressure (up to 10 kbar) and at high temperature (up to 1800 °C) using a gas pressure system. The homogeneity and Al content of the crystals were investigated by X-ray diffraction and laser ablation mass spectrometry. On the basis of the high-pressure experiments, the corresponding pressure–temperature (p–T) phase diagram of Al–Ga–N was derived. The bandgap of the material was determined by the femtosecond two-photon absorption autocorrelation method and is equal to 5.81±0.01 eV for the Al0.86Ga0.14N crystals. 相似文献
6.
The far-infrared spectra of Ge10Se90−xTex where x = 0, 10, 20, 30, 40, 50 glassy alloys were measured in the wavenumber region 50-650 cm−1 at room temperature. The results were explained in terms of the vibrations of the isolated molecular units. The addition of Te in Ge10Se90 has shown the appearance of GeTe2 and GeTe4 molecular units and vibrations of Se-Te bond as Se8−xTex mixed rings. The assignment of various absorption bands has been made on the basis of absorption spectra of pure Se, binary Ge-Se, Ge-Te, Se-Te and ternary Ge-Se-Te glassy alloys. The far-infrared transmission spectrum has been found to shift a little towards lower wavenumber side with the addition of Te content to Ge10Se90. The addition of Te to Ge-Se system replacing Se has found to reduce the Se-Se bonds and Ge-Se bonds and leads to the formation of Se-Te, Ge-Te and Te-Te bonds. 相似文献
7.
G.T. Thaler D.D. Koleske S.R. LeeK.H.A. Bogart M.H. Crawford 《Journal of Crystal Growth》2010,312(11):1817-1822
The thermal stability of ∼200-nm-thick InGaN thin films on GaN was investigated using isothermal and isochronal post-growth anneals. The InxGa1−xN films (x=0.08–0.18) were annealed in N2 at 600–1000 °C for 15–60 min, and the resulting film degradation was monitored using X-ray diffraction (XRD) and photoluminescence (PL) measurements. As expected, films with higher indium concentration showed more evidence for decomposition than the samples with lower indium concentration. Also for each alloy composition, decreases in the PL intensity were observed starting at much lower temperatures compared to decreases in the XRD intensity. This difference in sensitivity of the PL and XRD techniques to the InGaN decomposition suggest that defects that quench luminescence are generated prior to the onset of structural decomposition. For the higher indium concentration films, the bulk decomposition proceeds by forming metallic indium and gallium regions as observed by XRD. For the 18% indium concentration film, measurement of the temperature-dependent InGaN decomposition yields an activation energy, EA, of 0.87±0.07 eV, which is similar to the EA for bulk InN decomposition. The InGaN integrated XRD signal of the 18% film displays an exponential decrease vs. time, implying InGaN decomposition proceeds via a first-order reaction mechanism. 相似文献
8.
Calculation of phase diagrams in AlxIn1−xAs/InP,AsxSb1−xAl/InP and AlxIn1−xSb/InSb nano-film systems
The models for calculation of phase diagrams of semiconductor thin films with different substrates were proposed by considering the contributions of strain energy, the self-energy of misfit dislocations and surface energy to Gibbs free energy. The phase diagrams of the AlxIn1−xAs and AsxSb1−xAl thin films grown on the InP (1 0 0) substrate, and the AlxIn1−xSb thin films grown on the InSb (1 0 0) substrate at various thicknesses were calculated. The calculated results indicate that when the thickness of film is less than 1 μm, the strain-induced zinc-blende phase appears, the region of this phase extends with decreasing of the layer thickness, and there is small effect of surface energies of liquid and solid phases on the phase diagrams. 相似文献
9.
LixFePO4 glasses have been prepared by fast-quenching method in the whole range of composition 0 ? x ? 1. The amorphous state of glassy materials is confirmed by X-ray diffraction. Information concerning the local environment of Li and Fe cations and the configuration of (PO4)3− oxo-anions is obtained by Fourier transform infrared (FTIR) spectroscopy. While the LiFePO4 crystalline materials undergo a transition from the paramagnetic to the antiferromagnetic ordering at 52 K, no magnetic ordering is observed in the vitreous samples that realize random field systems, so that a spin glass-like freezing is observed at low temperature. The paramagnetic Curie temperature of LixFePO4 is independent of x and shifted to θ = −60 K in the glassy state, due to a significant distortion of the FeO6 octahedra that alters the superexchange path inside the atomic FeO4 layers of the crystallized structure. On another hand, the PO4 tetrahedra are not significantly distorted in the glassy phase. The results are compared with highly disordered, but nanocrystallized LiFePO4 recently obtained at the early stage of synthesis by solid state reaction at 300 °C. In this latter case, the lack of long-range antiferromagnetic ordering is due to substitutional disorder among the cationic sublattice. 相似文献
10.
First-principles molecular dynamics (MD) simulations are performed to study the structure and dynamics of liquid Al1−xSix (x = 0.0, 0.12, 0.2, 0.4, 0.6, 0.8) at the temperature of 1573 K. The composition dependence of static structure factors, pair correlation functions, and diffusion constants are investigated. We found that the structure of the liquid Al1−xSix alloys is strongly dependent on the composition. From our simulation and analysis, we can see that although liquid Al1−xSix is metallic, there are some degrees of covalent tetrahedral short-range order in the liquid. The degree of tetrahedral short-range order increases linearly as the Si concentration in the liquid increased. The diffusion coefficients of both Al and Si atoms in liquid Al1−xSix alloys at 1573 K are not very sensitive to the composition. 相似文献
11.
Pulok Pattanayak 《Journal of Non》2008,354(32):3824-3827
The composition dependence of different thermal parameters such as glass transition temperature, non-reversing enthalpy, thermal diffusivity etc., of bulk As45Te55−xIx chalcohalide glasses (3 ? x ? 10), has been evaluated using the temperature modulated Alternating Differential Scanning Calorimetry (ADSC) and Photo Thermal Deflection (PTD) studies. It is found that there is not much variation in the glass transition temperature of As45Te55−xIx glasses, even though there is a wide variation in the average coordination number . This observation has been understood on the basis that the variation in glass transition temperature of network glasses is dictated by the variation in average bond energy rather than . Further, it is found that both the non-reversing enthalpy (ΔHnr) and the thermal diffusivity (α) exhibit a sharp minimum at a composition x = 6. A broad hump is also seen in glass transition and crystallization temperatures in the composition range 5 ? x ? 7. The results obtained clearly indicate a sharp thermally reversing window in As45Te55−xIx chalcohalide glasses around the composition x = 6. 相似文献
12.
S.V. Novikov C.R. Staddon A.V. Akimov R.P. Campion N. Zainal A.J. Kent C.T. Foxon C.H. Chen K.M. Yu W. Walukiewicz 《Journal of Crystal Growth》2009,311(13):3417-3422
We have studied the low-temperature growth of gallium nitride arsenide (GaN)As layers on sapphire substrates by plasma-assisted molecular beam epitaxy. We have succeeded in achieving GaN1−xAsx alloys over a large composition range by growing the films much below the normal GaN growth temperatures with increasing the As2 flux as well as Ga:N flux ratio. We found that alloys with high As content x>0.1 are amorphous and those with x<0.1 are crystalline. Optical absorption measurements reveal a continuous gradual decrease of band gap from ∼3.4 to ∼1.35 eV with increasing As content. The energy gap reaches its minimum of ∼1.35 eV at x∼0.6–0.7. The structural, optical and electrical properties of these crystalline/amorphous GaNAs layers were investigated. For x<0.3, the composition dependence of the band gap of the GaN1−xAsx alloys follows the prediction of the band anticrossing model developed for dilute alloys. This suggests that the amorphous GaN1−xAsx alloys have short-range ordering that resembles random crystalline GaN1−xAsx alloys. 相似文献
13.
E.A. El-Sayad 《Journal of Non》2008,354(32):3806-3811
Thin films of Sb2Se3−xSx solid solutions (x = 0, 1, 2, and 3) were deposited by thermal evaporation of presynthesized materials on glass substrates held at room temperature. The films compositions were confirmed by using energy dispersive analysis of X-rays (EDAX). X-ray diffraction studies revealed that all the as-deposited films as well as those annealed at Ta < 423 K have amorphous phase. The optical constants (n, k) and the thickness (t) of the films were determined from optical transmittance data, in the spectral range 500-2500 nm, using the Swanepoel method. The dispersion parameters were determined from the analysis of the refractive index. An analysis of the optical absorption spectra revealed an Urbach’s tail in the low absorption region, while in the high absorption region an indirect band gap characterizes the films with different compositions. It was found that the optical band gap energy increases quadratically as the S content increases. 相似文献
14.
Daisuke Iida Kenta Tamura Motoaki Iwaya Satoshi Kamiyama Hiroshi Amano Isamu Akasaki 《Journal of Crystal Growth》2010,312(21):3131-3135
The electrical and optical properties of Mg-doped a- and c-plane GaN films grown by metalorganic vapor phase epitaxy were systematically investigated. The photoluminescence spectra of Mg-doped a- and c-plane GaN films exhibit strong emissions related to deep donors when Mg doping concentrations are above 1×1020 cm−3 and 5×1019 cm−3, respectively. The electrical properties also indicate the existence of compensating donors because the hole concentration decreases at such high Mg doping concentrations. In addition, we estimated the ND/NA compensation ratio of a- and c-plane GaN by variable-temperature Hall effect measurement. The obtained results indicate that the compensation effect of the Mg-doped a-plane GaN films is lower than that of the Mg-doped c-plane GaN films. 相似文献
15.
Electrical switching studies on bulk Ge10Se90−xTlx (15 ? x ? 34) glasses have been undertaken to examine the type of switching, composition and thickness dependence of switching voltages. Unlike Ge-Se-Tl thin films which exhibit memory switching, the bulk Ge10Se90−xTlx glasses are found to exhibit threshold type switching with fluctuations seen in their current-voltage (I-V) characteristics. Further, it is observed that the switching voltages (VT) of Ge10Se90−xTlx glasses decrease with the increase in the Tl concentration. An effort has been made to understand the observed composition dependence on the basis of nature of bonding of Tl atoms and a decrease in the chemical disorder with composition. In addition, the network connectivity and metallicity factors also contribute for the observed decrease in the switching voltages of Ge10Se90−xTlx glasses with Tl addition. It is also interesting to note that the composition dependence of switching voltages of Ge10Se90−xTlx glasses exhibit a small cusp around the composition x = 22, which is understood on the basis of a thermally reversing window in this system in the composition range 22 ? x ? 30. The thickness dependence of switching voltages has been found to provide an insight about the type of switching mechanism involved in these samples. 相似文献
16.
C.F. Johnston M.J. KappersM.A. Moram J.L. HollanderC.J. Humphreys 《Journal of Crystal Growth》2009,311(12):3295-3299
This work assesses the relative effectiveness of four techniques to reduce the defect density in heteroepitaxial nonpolar a-plane GaN films grown on r-plane sapphire by metalorganic vapour phase epitaxy (MOVPE). The defect reduction techniques studied were: 3D–2D growth, SiNx interlayers, ScN interlayers and epitaxial lateral overgrowth (ELOG). Plan-view transmission electron microscopy (TEM) showed that the GaN layer grown in a 2D fashion had a dislocation and basal-plane stacking fault (BSF) density of (1.9±0.2)×1011 cm−2 and (1.1±0.9)×106 cm−1, respectively. The dislocation and BSF densities were reduced by all methods compared to this 2D-grown layer (used as a seed layer for the interlayer and ELOG methods). The greatest reduction was achieved in the (0 0 0 1) wing of the ELOG sample, where the dislocation density was <1×106 cm−2 and BSF density was (2.0±0.7)×104 cm−1. Of the in-situ techniques, SiNx interlayers were most effective: the interlayer with the highest surface coverage that was studied reduced the BSF density to (4.0±0.2)×105 cm−1 and the dislocation density was lowered by over two orders of magnitude to (3.5±0.2)×108 cm−2. 相似文献
17.
L.Y. Zhu 《Journal of Non》2009,355(1):68-207
ZrxTi1−xO2 (x = 0.1-0.9) fibers were prepared by the sol-gel dry-spinning method. Polyacetylacetonatozirconium (PAZ) and tetrabutyl titanate (C16H36O4Ti) were used as raw materials. The green fibers were obtained from the amorphous spinnable solution and then heat-treated to convert into polycrystalline fibers. The main phase changes from TiO2 to zirconium titanate (ZT) and then tetragonal ZrO2 with increasing ZrO2 content. The crystallization temperature varied with the molar ratio of Zr:Ti. The heat-treated fibers at 1050 °C have few pores and no cracks with diameters of 10-20μm and lengths of 1-5 cm. 相似文献
18.
M. Moret B. Gil S. Ruffenach O. Briot Ch. Giesen M. Heuken S. Rushworth T. Leese M. Succi 《Journal of Crystal Growth》2009,311(10):2795-2797
We have performed a detailed investigation of the photoluminescence features taken at 2 K on a series of GaxIn1−xN alloys grown by metal-organic vapour-phase epitaxy through the whole composition range. The evolution of the photoluminescence lineshape of GaInN alloys in the indium-rich region is dominated by doping effects rather than by band-gap tailing effects correlated to existence of random chemical crystal inhomogeneities. The lineshape of the photoluminescence indicates a residual electron concentration of about 1018–1019 cm−3 in the bulk part of the epilayers. The value we get for the bowing parameter is b=2.8 eV. 相似文献
19.
A. Gouyé O. Kermarrec A. Halimaoui Y. Campidelli D. Rouchon M. Burdin P. Holliger D. Bensahel 《Journal of Crystal Growth》2009,311(13):3522-3527
Si homo-epitaxial growth by low-temperature reduced pressure chemical vapor deposition (RPCVD) using trisilane (Si3H8) has been investigated. The CVD growth of Si films from trisilane and silane on Si substrates are compared at temperatures between 500 and 950 °C. It is demonstrated that trisilane efficiency increases versus silane's one as the surface temperature decreases. Si epilayers from trisilane, with low surface roughness, are achieved at 600 and 550 °C with a growth rate equal to 12.4 and 4.3 nm min−1, respectively. It is also shown that Si1−xGex layers can be deposited using trisilane chemistry. 相似文献
20.
In the present paper, the effect of carbon on the microstructural evolution of Zr66.7−xNi33.3Cx (x = 0, 1, 3) alloys during mechanical alloying has been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that these three alloys undergo similar amorphization and crystallization processes, and the final milling product is a metastable fcc-Zr66.7−xNi33.3Cx phase. The carbon addition can shorten the milling time for the complete amorphization reaction and enhance the stability of the formed amorphous alloy, which can suppress the mechanically induced amorphous-crystalline phase transformation with further increasing milling time. 相似文献