| 1. |
- Adolph, David, 1971, et al.
(författare)
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Growth of ZnO(0001) on GaN(0001)/4H-SiC buffer layers by plasma-assisted hybrid molecular beam epitaxy
- 2015
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 426, s. 129-134
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Tidskriftsartikel (refereegranskat)abstract
- Plasma-assisted molecular beam epitaxy was used to grow ZnO(0001) layers on GaN(0001)/4H-SiC buffer layers deposited in the same growth chamber equipped with both N- and O-plasma sources. The GaN buffer layers were grown immediately before initiating the growth of ZnO. Using a substrate temperature of 445 °C and an O2 flow rate of 2.5 standard cubic centimeters per minute, we obtained ZnO layers with statistically smooth surfaces having a root-mean-square roughness of 0.3 nm and a peak-to-valley distance of 3 nm as revealed by atomic force microscopy. The full-width-at-half-maximum for x-ray rocking curves obtained across the ZnO(0002) and ZnO(10 1¯ 5) reflections was 198 and 948 arcsec, respectively. These values indicated that the mosaicity of the ZnO layer was comparable to the corresponding values of the underlying GaN buffer layer. Reciprocal space maps showed that the in-plane relaxation of the GaN and ZnO layers was 82% and 73%, respectively, and that the relaxation occurred abruptly during the growth. Roomerature Hall-effect measurements revealed that the layers were inherently n-type and had an electron concentration of 1×1019 cm-3 and a Hall mobility of 51 cm2/V s.
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| 2. |
- Aguilar-Mamani, Wilson, et al.
(författare)
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Solution-mediated growth of NBA-ZSM-5 crystals retarded by gel entrapment
- 2018
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Ingår i: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 487, s. 57-64
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of flat tablet-shaped ZSM-5 crystals from a gel using metakaolin as aluminosilicate source and n-butyl amine as structure directing agent was investigated. The evolution inside the solid phase was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetry and mass spectrometry. A kinetic study indicated that the nucleation of the majority crystals occurred concurrently with the formation of the gel upon heating the starting liquid suspension. Microstructural evidences undeniably showed that the gel precipitated on ZSM-5 crystals and mineral impurities originating from kaolin. As a result, crystal growth was retarded by gel entrapment, as indicated by the configuration and morphology of the embedded crystals. The results presented herein are harmonized with a solution-mediated nucleation and growth mechanism. Our observations differ from the autocatalytic model that suggests that the nuclei rest inside the gel until released when the gel is consumed. Our results show instead that it is crystals that formed in an early stage before entrapment inside the gel that rest inside the gel until exposed at the gel surface. These results illustrate the limitation of the classical method used in the field to determine nucleation profiles when the crystals become trapped inside the gel.
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| 3. |
- Barrutia, Laura, et al.
(författare)
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Effect of Ge autodoping during III-V MOVPE growth on Ge substrates
- 2017
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 475, s. 378-383
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Tidskriftsartikel (refereegranskat)abstract
- During the MOVPE growth of III-V layers on Ge substrates, Ge atoms can be evaporated or etched from the back of the wafer and reach the growth surface, becoming incorporated into the epilayers. This is the so-called Ge autodoping effect, which we have studied through a set of growth experiments of GaInP and Ga(In)As layers lattice matched to Ge substrates, which have been characterized by Secondary Ion Mass Spectroscopy. The role of V/III ratio and growth rate on Ge autodoping has been studied and a MOVPE reactor pre-conditioning prior to the epitaxial growth of III-V semiconductor layers that mitigates this Ge autodoping has been identified. In addition, the use of 2-in. versus 4-in. Ge substrates has been compared and the use of a Si3N4 backside coating for the Ge substrates has been evaluated.
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| 4. |
- Chen, Jr-Tai, et al.
(författare)
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Low thermal resistance of a GaN-on-SiC transistor structure with improved structural properties at the interface
- 2015
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 428, s. 54-58
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Tidskriftsartikel (refereegranskat)abstract
- The crystalline quality of AlGaN/GaN heterostructures was improved by optimization of surface pretreatment of the SiC substrate in a hot-wall metal-organic chemical vapor deposition reactor. X-ray photoelectron spectroscopy measurements revealed that oxygen- and carbon-related contaminants were still present on the SiC surface treated at 1200 °C in H2 ambience, which hinders growth of thin AlN nucleation layers with high crystalline quality. As the H2 pretreatment temperature increased to 1240 °C, the crystalline quality of the 105 nm thick AlN nucleation layers in the studied series reached an optimal value in terms of full width at half-maximum of the rocking curves of the (002) and (105) peaks of 64 and 447 arcsec, respectively. The improvement of the AlN growth also consequently facilitated a growth of the GaN buffer layers with high crystalline quality. The rocking curves of the GaN (002) and (102) peaks were thus improved from 209 and 276 arcsec to 149 and 194 arcsec, respectively. In addition to a correlation between the thermal resistance and the structural quality of an AlN nucleation layer, we found that the microstructural disorder of the SiC surface and the morphological defects of the AlN nucleation layers to be responsible for a substantial thermal resistance. Moreover, in order to decrease the thermal resistance in the GaN/SiC interfacial region, the thickness of the AlN nucleation layer was then reduced to 35 nm, which was shown sufficient to grow AlGaN/GaN heterostructures with high crystalline quality. Finally, with the 35 nm thick high-quality AlN nucleation layer a record low thermal boundary resistance of 1.3×10-8 m2 K/W, measured at an elevated temperature of 160 °C, in a GaN-on-SiC transistor structure was achieved.
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| 5. |
- Forsberg, Kerstin M., et al.
(författare)
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The influence of hydrofluoric acid and nitric acid on the growth kinetics of iron(III) fluoride trihydrate
- 2015
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 423, s. 16-21
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Tidskriftsartikel (refereegranskat)abstract
- The influence of hydrofluoric acid and nitric acid concentration on the growth rate of beta-FeF3 center dot 3H(2)O crystals has been studied in different hydrofluoric acid (4.7-10.7 mol/(kg H2O)) and nitric acid (2.1-4.6 mol/(kg H2O)) mixtures at 50 degrees C. Seeded desupersaturation experiments were performed and the results were evaluated by considering the chemical speciation using two different speciation programs. The growth rate at 50 degrees C at a supersaturation ratio of 2, expressed in terms of free FeF3, was found to be in the range of (0.4-3.8) x 10(-11) m/s. The growth rate order was found to be two or higher in all experiments. The low growth rate and high growth rate order indicate that the growth rate is governed by the surface integration step. The growth rate was found to be independent of variations in acid concentrations: this is in accordance with the assumption of a surface integration controlled growth rate.
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| 6. |
- Garcia, Gustavo, et al.
(författare)
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Selective synthesis of FAU-type zeolites
- 2018
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Ingår i: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 489, s. 36-41
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, parameters influencing the selectivity of the synthesis of FAU-zeolites from diatomite were studied. The final products after varying synthesis time were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and gas adsorption. It was found that high concentrations of NaCl could completely inhibit the formation of zeolite P, which otherwise usually forms as soon as maximum FAU crystallinity is reached. In the presence of NaCl, the FAU crystals were stable for extended time after completed crystallization of FAU before formation of sodalite. It was also found that addition of NaCl barely changed the crystallization kinetics of FAU zeolite and only reduced the final FAU particle size and SiO2/Al2O3 ratio slightly. Other salts containing either Na or Cl were also investigated. Our results suggest that there is a synergistic effect between Na+ and Cl-. This is attributed to the formation of (Na4Cl)3+ clusters that stabilize the sodalite cages. This new finding may be used to increase the selectivity of syntheses leading to FAU-zeolites and avoid the formation of undesirable by-products, especially if impure natural sources of aluminosilica are used.
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| 7. |
- Ghasemi, Masoomeh, et al.
(författare)
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Thermodynamic assessment and binary nucleation modeling of Sn-seeded InGaAs nanowires
- 2017
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 478, s. 152-158
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Tidskriftsartikel (refereegranskat)abstract
- We have performed a thermodynamic assessment of the As-Ga-In-Sn system based on the CALculation of PHAse Diagram (CALPHAD) method. This system is part of a comprehensive thermodynamic database that we are developing for nanowire materials. Specifically, the As-Ga-In-Sn can be used in modeling the growth of GaAs, InAs, and InxGa1−xAs nanowires assisted by Sn liquid seeds. In this work, the As-Sn binary, the As-Ga-Sn, As-In-Sn, and Ga-In-Sn ternary systems have been thermodynamically assessed using the CALPHAD method. We show the relevant phase diagrams and property diagrams. They all show good agreement with experimental data. Using our optimized description we have modeled the nucleation of InxGa1−xAs in the zinc blende phase from a Sn-based quaternary liquid alloy using binary nucleation modeling. We have linked the composition of the solid nucleus to the composition of the liquid phase. Eventually, we have predicted the critical size of the nucleus that forms from InAs and GaAs pairs under various conditions. We believe that our modeling can guide future experimental realization of Sn-seeded InxGa1−xAs nanowires.
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| 8. |
- Gray, Ciaran, et al.
(författare)
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Growth of isotopically enriched ZnO nanorods of excellent optical quality
- 2015
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Ingår i: Journal of Crystal Growth. - : ELSEVIER SCIENCE BV. - 0022-0248 .- 1873-5002. ; 429
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Tidskriftsartikel (refereegranskat)abstract
- We have produced isotopically enriched ZnO nanorods using Zn-enriched ZnO source powder by vapour phase transport on silicon substrates buffer coated with unenriched ZnO seed layers. SEM and XRD data confirm successful growth of high quality, dense, c-axis aligned nanorods over a substantial surface area. Raman. data show a shift of greater than 1 cm(-1) in the peak position of the Raman scattered peaks due to the E-2(low) and E-2(high) phonon modes when the Zn isotope is changed from Zn-64 to Zn-68, consistent with previous work, thus confirming successful isotopic enrichment. SIMS data provides additional confirmation of enrichmenr. The optical qualiry (as dererrninecl by phoLoluminescence feature inrensiLy and line width) is excellenr. Samples with Zn isoLopic enrichmenr ranging from (ZnO)-Zn-64 to (ZnO)-Zn-68 display a shift in recombinarion energy of the bound excirons al. the band edge (3.34-3.37 eV) of similar to 0.6 meV. This blue-shift is also consisren d. with previously published data, further confirming both the excellen d. oprical qualiry and successful isoLopic subsfiLurion of ZnO nanorods using this relarively simple growth method. (c) 2015 Elsevier B.V. All rights reserved.
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| 9. |
- Haggren, Tuomas, et al.
(författare)
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InP nanowire p-type doping via Zinc indiffusion
- 2016
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 451, s. 18-26
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Tidskriftsartikel (refereegranskat)abstract
- We report an alternative pathway for p-type InP nanowire (NW) doping by diffusion of Zn species from the gas phase. The diffusion of Zn was performed in a MOVPE reactor at 350–500 °C for 5–20 min with either H2 environment or additional phosphorus in the atmosphere. In addition, Zn3P2 shells were studied as protective caps during post-diffusion annealing. This post-diffusion annealing was performed to outdiffuse and activate Zn in interstitial locations. The characterization methods included photoluminescence and single NW conductivity and carrier concentration measurements. The acquired carrier concentrations were in the order of >1017 cm−3 for NWs without post-annealing, and up to 1018 cm−3 for NWs annealed with the Zn3P2 shells. The diffused Zn caused redshift to the photoluminescence signal, and the degree of redshift depended on the diffusion process.
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| 10. |
- Hirasaki, Takahide, et al.
(författare)
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Growth of thick and high crystalline quality InGaN layers on GaN (000(1)over-bar) substrate using tri-halide vapor phase epitaxy
- 2016
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Ingår i: Journal of Crystal Growth. - : ELSEVIER SCIENCE BV. - 0022-0248 .- 1873-5002. ; 456, s. 145-150
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Tidskriftsartikel (refereegranskat)abstract
- The growth of thick InGaN layers on free-standing GaN (000 (1) over bar substrates was studied using tri-halide vapor phase epitaxy. It was found that high-indium-content InGaN can be grown under higher InCl3 input partial pressure at higher growth temperature, which allows the fabrication of a high crystalline quality InGaN layer with a smooth surface morphology. Using the growth conditions of high InCl3 input partial pressure and high growth temperature, crack- and droplet-free InGaN layers with a thickness of over 10 mu m and with an indium fraction of 0.05 were successfully grown. Although the surface showed many hillocks, the number of hillocks was reduced upon growth of thicker InGaN layers. Photoluminescence measurements confirm that thick InGaN layers could be successfully grown without degradation of the crystalline quality. (C) 2016 Elsevier B.V. All rights reserved.
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