| 1. |
- Gunnarsson, Svante, 1959-, et al.
(författare)
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Reflections about reflections
- 2023
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Ingår i: Proceedings of the 19th CDIO International Conference. - : NTNU SEED. - 9788230361863 ; , s. 56-66
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Konferensbidrag (refereegranskat)abstract
- A case study of the use of reflections within the Applied physics and electrical engineering program at Linköping University is presented. Reflections have been used for several years and they are done at four stages in the program, in terms of reflections at the end of the Introductory course in year one, design-implement experiences in year three and five, and a reflection document that is the last component of the Master’s thesis. In the first three stages a project model is used to support the planning and execution of the project, and in the project model the project work ends with a reflection. In the reflection document connected to the Master’s thesis the student reflects upon both the thesis work itself and the entire education program, according to the sections and subsections of the CDIO Syllabus. The paper describes how the reflections are integrated in the program. Experiences from student perspective are collected in a small-scale study via interviews with students from year one and year five.
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| 2. |
- Huang, Jing-Jia, 1990-, et al.
(författare)
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Growth of silicon carbide multilayers with varying preferred growth orientation
- 2022
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 447
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Tidskriftsartikel (refereegranskat)abstract
- SiC multilayer coatings were deposited via thermal chemical vapor deposition (CVD) using silicon tetrachloride (SiCl4) and various hydrocarbons under identical growth conditions, i.e. at 1100 °C and 10 kPa. The coatings consisted of layers whose preferred growth orientation alternated between random and highly 〈111〉-oriented. The randomly oriented layers were prepared with either methane (CH4) or ethylene (C2H4) as carbon precursor, whereas the highly 〈111〉-oriented layers were grown utilizing toluene (C7H8) as carbon precursor. In this work, we demonstrated how to fabricate multilayer coatings with different growth orientations by merely switching between hydrocarbons. Moreover, the success in depositing multilayer coatings on both flat and structured graphite substrates has strengthened the assumption proposed in our previous study that the growth of highly 〈111〉-oriented SiC coatings using C7H8 was primarily driven by chemical surface reactions.
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| 3. |
- Huang, Jing-Jia, 1990-
(författare)
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Surface-Controlled Chemical Vapor Deposition of Silicon Carbide
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polycrystalline cubic silicon carbide, 3C-SiC, has long been investigated in the field of hard coating materials. The typical synthesis method for 3C-SiC coatings is thermal chemical vapor deposition (CVD) using either multicomponent precursors, e.g. methyltrichlorosilane, or a combination of single component precursors, e.g. silane and propane. In this thesis, the fabrication of polycrystalline SiC coatings has been explored from the new aspects on the basis of thermal CVD utilizing silicon tetrachloride (SiCl4) and various hydrocarbons, i.e. toluene (C7H8), methane (CH4) and ethylene (C2H4) as the precursors. The goal of this thesis is to control the surface chemistry in the SiCl4-based SiC CVD and has been accomplished by the following three different approaches: In the first approach to control the surface chemistry of SiC CVD, the difference in the adsorption energy of aromatic and aliphatic hydrocarbons on different SiC crystal planes was utilized. Under identical deposition conditions, a highly <111>-oriented 3C-SiC coating was deposited using C7H8 as the carbon precursor, whereas using CH4 resulted in a randomly oriented 3C-SiC. The results from quantum chemical calculation showed that the active film forming carbon species, i.e. C6H6 in the C7H8 process and CH3 in both C7H8 and CH4 processes, behaved differently when they adsorbed on the 3C-SiC (111) and (110) planes. CH3 is strongly chemisorbed on both planes, while C6H6 is chemisorbed on the (111) plane, but only physiosorbed on the other. The significant difference in the adsorption energy of CH3 and C6H6 on the (111) and (110) planes therefore explains the resulting highly <111>-oriented 3C-SiC from the C7H8 process. Furthermore, the ability to deposit 3C-SiC coatings with alternating highly <111>- and randomly oriented layers by merely switching the carbon precursor between C7H8 and CH4 or C2H4 in a single CVD deposition has further proven that the effect of aromatic hydrocarbons on the preferred growth orientation of 3C-SiC was controlled primarily by the surface chemistry. The second approach to the surface-controlled SiC CVD was based on the reduction of surface reaction probability (β) for conformal film growth via low-temperature, low-pressure CVD, which was originally proposed by Abelson and Girolami. Their strategies in reducing β, including lowering the temperature and increasing the precursor partial pressure, were successfully adapted to the SiC CVD growth using SiCl4 and C2H4 as the precursors in this thesis, where an elevated temperature and a moderate pressure were used. Moreover, the addition of Cl species as a growth inhibitor to the process further reduced the β, leading to a superconformal SiC growth. The third approach employed in this thesis for the SiC growth was pulsed CVD. Instead of a continuous and simultaneous SiCl4 and C2H4 flow, the precursors were pulsed alternately into the chamber with each precursor pulse being separated by a H2 purge. In this precursor delivery mode, the gas phase reactions between SiCl4 and C2H4 were avoided and hence the SiC growth was mostly controlled by the surface chemistry. Altering the pulse durations of the precursors led to a variation of growth per cycle (GPC), which was explained by a two-step mechanism. During the SiCl4 pulse, a thin layer of Si is deposited, which is carburized by carbon species produced during the C2H4 pulse. Additionally, the separation of precursor pulses should lead to a large increase in the surface coverage of Cl species, further enhancing the inhibition effect and resulting in a superconformal SiC growth. By using this approach, superconformal SiC coatings were achieved at temperatures where conventional CVD only yielded nonconformal SiC coatings. The observed decline in coating conformality with an elongated purge implied that more surface Cl species were replaced by H during the H2 purge and consequently the inhibition effect was diminished.
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| 4. |
- Mpofu, Pamburayi, et al.
(författare)
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Thermal atomic layer deposition of In2O3 thin films using a homoleptic indium triazenide precursor and water
- 2022
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 51:12, s. 4712-4719
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Tidskriftsartikel (refereegranskat)abstract
- Indium oxide (In2O3) is an important transparent conducting material widely used in optoelectronic applications. Herein, we study the deposition of In2O3 by thermal atomic layer deposition (ALD) using our recently reported indium(iii) triazenide precursor and H2O. A temperature interval with self-limiting growth was found between similar to 270 and 385 degrees C with a growth per cycle of similar to 1.0 angstrom. The deposited films were polycrystalline cubic In2O3 with In : O ratios of 1 : 1.2, and low levels of C and no detectable N impurities. The transmittance of the films was found to be >70% in visible light and the resistivity was found to be 0.2 m omega cm. The high growth rates, low impurities, high optical transmittance, and low resistivity of these films give promise to this process being used for ALD of In2O3 films for future microelectronic displays.
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| 5. |
- Rouf, Polla, 1993-
(författare)
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Time-resolved CVD of Group 13-Nitrides
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Group 13 nitrides (AlN, GaN and InN) and their alloys are semiconductor materials with a wide bandgap span covering from UV down to IR range. Their excellent electronic properties make them extremely attractive materials for light emitting diodes (LEDs) and different kind of transistor structures, especially high electron mobility transistors (HEMTs). These materials are routinely deposited by chemical vapor deposition (CVD) at high temperatures. The most sought-after material among the group 13 nitrides is InN due to its high electron mobility making it extremely useful in transistor structures. InN needs to be deposited at low temperatures as it decomposes at high temperatures. This does not only limit the deposition temperature for InN growth but also for all the other materials that will be deposited on top of InN. In this thesis the deposition of group 13 nitrides is investigated by low temperature atomic layer deposition (ALD) via both a thermal and plasma route. This was conducted by both process development and by improving the deposition chemistry by developing new precursors. Carbon impurities is one of the greater challenges when using the standard aluminum precursor trimethylaluminum (TMA) in ALD due to the strong Al–C bonds in the molecule. An in-situ removal of carbon impurities was investigated by introducing a cleaning pulse, after the TMA pulse. The cleaning pulse consisted of an H2, N2 or Ar gas pulse perpendicular to the surface. The introduction of the cleaning pulse reduced the carbon impurity in the AlN film from 3 at% down to under 1 at%. This made it possible to deposit AlN at higher temperature to obtain better crystalline quality and on the same time reduce the impurity levels. Kinetic simulations showed that the cleaning pulse cleans the surface from desorbed methyl groups resulting in a suppressed reabsorption pathway. To further reduce carbon impurities, the strong M–C bonded precursors was replaced with a M–N bonded one. The precursor used were tris(dimethylamido)gallium together with ammonia (NH3) plasma to deposit GaN. The precursor showed ALD behavior and the resulting GaN film possessed significantly lower carbon impurities compared to M-C bonded precursor at low deposition temperatures. This precursor could also produce epitaxial GaN directly on 4H-SiC without a need of a seed layer. To further investigate the precursor impact on deposition chemistry and ultimately the film quality, three indium precursors were evaluated, indium(III)guanidinate, indium(III)amidinate and indium(III)formamidinate. All three precursors have more or less the same structure, only difference being the size of the substituent on the endocyclic carbon position (-NMe2, -Me and -H respectively). Experimental results showed that smaller groups on the endocyclic carbon position improved the InN film quality in terms of crystallinity, morphology, stoichiometry and optical properties. Density functional theory (DFT) calculations showed that smaller moieties on the endocyclic position will lead to less surface and steric repulsion with the exocyclic position. As the size is decreased the exocyclic groups can fold up closer towards the endocyclic position leading to elongated metal-ligand bonds which will result in easier removal of the ligand for the upcoming NH3 plasma pulse. From these results a new ligand was developed to further improve the deposition chemistry where the endocyclic carbon atom in the ligand backbone of the foramidinate ligand was replaced by a N atom to form a triazenide ligand (iPr–N–N=N–iPr). The triazenide ligand possess no moiety on the endocyclic position compared to the ligands used previously and hence should result in improved material quality if extrapolated from our previous study. The ligand was placed on indium and gallium forming In(III)triazenide and Ga(III)triazenide respectively. Both precursors showed excellent thermal properties making them good ALD precursors. Their use for depositing InN and GaN was investigated with NH3plasma. The resulting films showed excellent quality where no carbon could be detected for either InN nor GaN using XPS and ERDA. Both InN and GaN showed epitaxial growth behavior on 4H-SiC at deposition temperature of 350 °C, a factor of three lower deposition temperature compared to CVD. Interestingly, several linear growth regimes (ALD windows) upon changing the temperature were observed, two and three for InN and GaN respectively. This indicated that the precursors decomposed upon increasing the temperature to form smaller fragments which increased the growth rate but on the same time the smaller precursor fragments saturated the surface. This was further confirmed by DFT calculations. The In(III)triazenide and Ga(III)triazenide was further used to deposit the ternary InGaN phase. A new method was developed where both precursors were mixed in the bubbler and co-sublimed into the reactor via a single pulse. The composition of the films could be tuned via bubbler temperature, deposition temperature and premixed ratio of the precursors in the bubbler. Near In0.5Ga0.5N could be obtained at low deposition temperatures confirmed by both XPS, ERDA and bandgap measurement. Deposition at 350 °C on 4H-SiC resulted in epitaxial In1-xGaxN without a need of a seed layer.
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