Suchergebnisse

Aluminum nitride (AlN) is a semiconductor with a wide range of applications from light-emitting diodes to high-frequency transistors. Electronic grade AlN is routinely deposited at 1000 degrees C by chemical vapor deposition (CVD) using trimethylaluminum (TMA) and NH3, while low-temperature CVD routes to high-quality AlN are scarce and suffer from high levels of carbon impurities in the film. We report on an atomic layer deposition-like CVD approach with time-resolved precursor supply where readsorption of methyl groups from the AlN surface is suppressed by the addition of an extra pulse, H-2, N-2, or Ar, between the TMA and NH3 pulses. The suppressed readsorption allowed deposition of AlN films with a carbon content of 1 at. % at 480 degrees C. Kinetic and quantum-chemical modeling suggests that the extra pulse between TMA and NH3 prevents readsorption of desorbing methyl groups terminating the AlN surface after the TMA pulse. ; Funding Agencies|Swedish Foundation for Strategic Research (SSF) through the project "time-resolved low temperature CVD for III-nitrides" [SSF-RMA 15-0018]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty grant SFO Mat LiU) [2009 00971]; Swedish Research Council (VR)Swedish Research Council

A comprehensive systematic method for chemical vapor deposition modeling consisting of seven well-defined steps is presented. The method is general in the sense that it is not adapted to a certain type of chemistry or reactor configuration. The method is demonstrated using silicon carbide (SiC) as a model system, with accurate matching to measured data without tuning of the model. We investigate the cause of several experimental observations for which previous research reports only have had speculative explanations. In contrast to previous assumptions, we can show that SiCl2 does not contribute to SiC deposition. We can confirm the presence of larger molecules at both low and high C/Si ratios, which have been thought to cause so-called step-bunching. We can also show that high concentrations of Si lead to other Si molecules other than the ones contributing to growth, which also explains why the C/Si ratio needs to be lower at these conditions to maintain high material quality as well as the observed saturation in deposition rates. Due to its independence of a chemical system and reactor configuration, the method paves the way for a general predictive CVD modeling tool. ; Funding Agencies|Swedish Foundation for Strategic Research project "SiC-the Material for Energy-Saving Power Electronics"Swedish Foundation for Strategic Research [EM11-0034]; Knut & Alice Wallenberg Foundation (KAW)Knut & Alice Wallenberg Foundation; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO Mat LiU) [2009 00971]; Swedish Research Council (VR)Swedish Research Council

Silicon carbide is a semiconductor material with ideal properties for high-temperature and high-power applications. The epitaxial layer fabrication Is usually performed using chemical vapor deposition (CVD) under a hydrogen rich atmosphere and high temperature. At such conditions the surface of the growing layer is expected to be passivatecl,by the abundantly present hydrogen. In this work, we use quantum chemical density functional theory (B3LYP and M06-2X) and transition state theory to study surface reactions related to the deposition of carbon on the (0001) surface of 4H-SiC. We show that it is unlikely for an adsorption to occur on a passivated, site unless the hydrogen termination is removed. We propose that unterminated sites can be effectively created during the CVD by an abstraction process. We provide details of the adsorption process of active carbon species, namely CH3, CH4, C2H2, and C2H4 gases, and their subsequent surface reactions such as desorption, abstraction of neighboring surface, hydrogens and dinner formation. The reaction rates and sticking coefficients are provided for the temperature range of 298-2500 K. Finally, entire reaction paths from adsorptions to stable surface products are presented and discussed. ; Funding Agencies|Swedish Foundation for Strategic Research; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials (AFM); Linkoping University

Chemical Vapor Deposition (CVD) is one of the technology platforms forming the backbone of the semiconductor industry and is vital in the production of electronic devices. To upscale a CVD process from the lab to the fab, large area uniformity and high run-to-run reproducibility are needed. We show by a combination of experiments and gas phase kinetics modeling that the combinations of Si and C precursors with the most well-matched gas phase chemistry kinetics gives the largest area of of homoepitaxial growth of SiC. Comparing CH4, C2H4 and C3H8 as carbon precursors to the SiF4 silicon precursor, CH4 with the slowest kinetics renders the most robust CVD chemistry with large area epitaxial growth and low temperature sensitivity. We further show by quantum chemical modeling how the surface chemistry is impeded by the presence of F in the system which limits the amount of available surface sites for the C to adsorb. ; Funding agencies: Knut & Alice Wallenberg Foundation (KAW) project Isotopic Control for Ultimate Material Properties; Swedish Foundation for Strategic Research project SiC - the Material for Energy-Saving Power Electronics [EM11-0034]; Swedish Government Strategic Research

Transient thermoreflectance (TTR) technique is employed to study the thermal conductivity of beta-Ga2O3 and high Al-content AlxGa1-xN semiconductors, which are very promising materials for high-power device applications. The experimental data are analyzed with the Callaways model taking into account all relevant phonon scattering processes. Our results show that out-of-plane thermal conductivity of high Al-content AlxGa1-xN and (-201) beta-Ga2O3 is of the same order of magnitude and approximately one order lower than that of GaN or AlN. The low thermal conductivity is attributed to the dominant phonon-alloy scattering in AlxGa1-xN and to the strong Umklapp phonon-phonon scattering in beta-Ga2O3. It is also found that the phonon-boundary scattering is essential in thin beta-Ga2O3 and AlxGa1-xN layers even at high temperatures and the thermal conductivity strongly deviates from the common 1/T temperature dependence. ; Funding Agencies|Swedish Governmental Agency for Innovation Systems (VINNOVA) under the Competence Center Program [2016-05190]; Swedish Research Council VRSwedish Research Council [2016-00889, 2017-03714]; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research [FL12-0181, RIF14-055, EM16-0024]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University, Faculty Grant SFO Mat LiU [2009-00971]; NSFNational Science Foundation (NSF) [CBET-1336464, DMR-1506159]

4H-silicon carbides deposited by diamond films have wide applications in many fields such as semiconductor heterojunction, heat sink and mechanical sealing. Nucleation plays a critical role in the deposition of the diamond film on 4H-silicon carbides. Nevertheless, as a typical polar material, the fundamental mechanism of diamond nucleation on different faces of 4H-silicon carbides has not been fully understood yet. In this contribution, nucleation of diamond was performed on the carbon- and silicon-faces of 4H-silicon carbides in a direct current chemical vapor deposition device. The nucleation density on the carbon-face is higher by 2-3 orders of magnitude compared to the silicon-face. Transmission electron microscopy verifies that there are high density diamond nuclei on the interface between the carbon-face and the diamond film, which is different from columnar diamond growth structure on the silicon-face. Transition state theory calculation reveals that the unprecedented distinction of the nucleation density between the carbon-face and the silicon-face is attributed to different desorption rates of the absorbed hydrocarbon radicals. In addition, kinetic model simulations demonstrate that it is more difficult to form CH2(s)-CH2(s) dimers on silicon-faces than carbon-faces, resulting in much lower nucleation densities on silicon-faces. (C) 2019 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. ; National Key Research and Development Project 2017YFE0128600 Ningbo 3315 Innovation Team 2019A-18-C Science and Technology Innovation 2025 Major Project of Ningbo 2018023 National Defense Key Laboratory Fund 6142807180511 Innovation Funding of State Oceanic Administration NBHY-2017-Z3 Ningbo Industrial Technology Innovation Project 2016B10038 '13th Five-Year' Equipment Pre-research Sharing Project E1710161 'Key Talents' Senior Engineer Project of Ningbo Institute of Materials Technology and Engineering CONICYT in the project Fondecyt 11180121 VID U-IniciaUI 013/2018 Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO Mat LiU) 2009 00971 Swedish Research Council

4H-silicon carbides deposited by diamond films have wide applications in many fields such as semiconductor heterojunction, heat sink and mechanical sealing. Nucleation plays a critical role in the deposition of the diamond film on 4H-silicon carbides. Nevertheless, as a typical polar material, the fundamental mechanism of diamond nucleation on different faces of 4H-silicon carbides has not been fully understood yet. In this contribution, nucleation of diamond was performed on the carbon- and silicon-faces of 4H-silicon carbides in a direct current chemical vapor deposition device. The nucleation density on the carbon-face is higher by 2-3 orders of magnitude compared to the silicon-face. Transmission electron microscopy verifies that there are high density diamond nuclei on the interface between the carbon-face and the diamond film, which is different from columnar diamond growth structure on the silicon-face. Transition state theory calculation reveals that the unprecedented distinction of the nucleation density between the carbon-face and the silicon-face is attributed to different desorption rates of the absorbed hydrocarbon radicals. In addition, kinetic model simulations demonstrate that it is more difficult to form CH2(s)-CH2(s) dimers on silicon-faces than carbon-faces, resulting in much lower nucleation densities on silicon-faces. (C) 2019 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved. ; Funding Agencies|National Key Research and Development Project [2017YFE0128600]; Ningbo 3315 Innovation Team [2019A-18-C]; Science and Technology Innovation 2025 Major Project of Ningbo [2018023]; National Defense Key Laboratory Fund [6142807180511]; Innovation Funding of State Oceanic Administration [NBHY-2017-Z3]; Ningbo Industrial Technology Innovation Project [2016B10038]; 13th Five-Year Equipment Pre-research Sharing Project [E1710161]; Key Talents Senior Engineer Project of Ningbo Institute of Materials Technology and Engineering; CONICYT in the project Fondecyt [11180121]; VID [U-IniciaUI 013/2018]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO Mat LiU) [2009 00971]; Swedish Research Council (VR)Swedish Research Council