A Multiscale Model of the Si LPCVD Process

2004 ◽  
Vol 859 ◽  
Author(s):  
Maurizio Rondanini ◽  
Maurizio Masi ◽  
Sergio Carrà ◽  
Carlo Cavallotti ◽  
Politecnico di Milano
Keyword(s):  
Kinetic Monte Carlo ◽  
Morphological Evolution ◽  
Industrial Process ◽  
Chemical Vapor ◽  
Multiscale Model ◽  
Operating Conditions ◽  
Multiscale Approach ◽  
3 Dimensional ◽  
Growth Regime ◽  
Pressure Chemical

ABSTRACTThe Low Pressure Chemical Vapor Deposition of Si from SiH4 is an industrial process that can be used to deposit epitaxial Si at relatively low surface temperatures. Multiscale models are necessary in order to tune the operating conditions to optimize the quality of the deposited materials. In this work we present a multiscale approach meant to describe the film morphological evolution at different time and length scales. The reactor fluid dynamics and overall mass and temperature balances are solved with the finite element method. The morphological evolution of the film is investigated with 3D kinetic Monte Carlo. We have systematically investigated the dependence of the growth morphology from temperature, pressure and gas phase composition (SiH4/H2 ratio) with the aim of determining the operating parameters window that can lead to the best film morphology. We found that the presence of a significant amount of hydrogen on the surface can significantly influence the surface morphology. In particular hydrogen can be considered as the principal responsible of the transition from an order terrace step flow growth regime, which prevails at high temperatures, to a disordered 3 dimensional growth regime. It is also worth noting that our KMC simulations show that the hydrogen surface chemistry active at low temperatures is probably richer than expected, since the formation of a significant number of island on the surface dramatically increases the concentration of steps, and thus the variety of configurations by which two adsorbed H atoms can interact.

scholarly journals Direct Synthesis of Oxynitride Nanowires through Atmospheric Pressure Chemical Vapor Deposition

Nanomaterials ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 2507
Author(s):  
Babak Adeli ◽  
Fariborz Taghipour
Keyword(s):  
Solid Solution ◽  
Vapor Deposition ◽  
Atmospheric Pressure ◽  
Wide Spectrum ◽  
Direct Synthesis ◽  
Chemical Vapor ◽  
Building Blocks ◽  
Operating Conditions ◽  
Wide Range ◽  
Pressure Chemical

Binary and ternary oxynitride solid alloys were studied extensively in the past decade due to their wide spectrum of applications, as well as their peculiar characteristics when compared to their bulk counterparts. Direct bottom-up synthesis of one-dimensional oxynitrides through solution-based routes cannot be realized because nitridation strategies are limited to high-temperature solid-state ammonolysis. Further, the facile fabrication of oxynitride thin films through vapor phase strategies has remained extremely challenging due to the low vapor pressure of gaseous building blocks at atmospheric pressure. Here, we present a direct and scalable catalytic vapor–liquid–solid epitaxy (VLSE) route for the fabrication of oxynitride solid solution nanowires from their oxide precursors through enhancing the local mass transfer flux of vapor deposition. For the model oxynitride material, we investigated the fabrication of gallium nitride and zinc oxide oxynitride solid solution (GaN:ZnO) thin film. GaN:ZnO nanowires were synthesized directly at atmospheric pressure, unlike the methods reported in the literature, which involved multiple-step processing and/or vacuum operating conditions. Moreover, the dimensions (i.e., diameters and length) of the synthesized nanowires were tailored within a wide range.

scholarly journals Multiscale Simulations of Singlet and Triplet Exciton Dynamics in Disordered Molecular Systems based on Many-Body Green’s Functions Theory

2019 ◽  
Author(s):  
Jens Wehner ◽  
Björn Baumeier
Keyword(s):  
Diffusion Tensor ◽  
Kinetic Monte Carlo ◽  
Multiscale Model ◽  
Transport Processes ◽  
Triplet Exciton ◽  
Multiscale Approach ◽  
Molecular Materials ◽  
Many Body ◽  
Gw Approximation ◽  
Reorganization Energies

<div>We present a multiscale model based on Many-Body Green’s Function Theory in the GW approximation and the Bethe-Salpeter Equation (GW-BSE) for the simulation singlet and triplet exciton transport in molecular materials. Dynamics of coupled electron-hole pairs is modeled as a sequence of incoherent tunneling and decay events in a disordered morphology obtained at room temperature from Molecular Dynamics. The ingredients of the rates associated to the events, i.e., reorganization energies, site energies, lifetimes, and coupling elements, are determined from a combination of GW-BSE and classical polarizable force field techniques. Kinetic Monte Carlo simulations were then employed to evaluate dynamical properties such as the excitonic diffusion tensor and diffusion lengths. Using DCV5T-Me(3,3), a crystalline organic semiconductor, we demonstrate how this multiscale approach provides insight into the fundamental factors driving the transport processes.</div><div>Comparing the results obtained with different calculation models, we investigate in particular the effects of charge-transfer mediated high exciton coupling and the influence of internal site energy disorder due to conformational variations. We show that a small number of high coupling elements indicative of delocalized exciton states does not impact the overall dynamics perceptively. Molecules with energies in the tail of the excitonic density of states dominate singlet decay, independent of the level of disorder taken into account in the simulation. Overall, our approach yields singlet diffusion lengths on the order of 10 nm as expected for disordered molecular materials.</div>

scholarly journals Multiscale Simulations of Singlet and Triplet Exciton Dynamics in Disordered Molecular Systems based on Many-Body Green’s Functions Theory

2019 ◽  
Author(s):  
Jens Wehner ◽  
Björn Baumeier
Keyword(s):  
Diffusion Tensor ◽  
Kinetic Monte Carlo ◽  
Multiscale Model ◽  
Transport Processes ◽  
Triplet Exciton ◽  
Multiscale Approach ◽  
Molecular Materials ◽  
Many Body ◽  
Gw Approximation ◽  
Reorganization Energies

<div>We present a multiscale model based on Many-Body Green’s Function Theory in the GW approximation and the Bethe-Salpeter Equation (GW-BSE) for the simulation singlet and triplet exciton transport in molecular materials. Dynamics of coupled electron-hole pairs is modeled as a sequence of incoherent tunneling and decay events in a disordered morphology obtained at room temperature from Molecular Dynamics. The ingredients of the rates associated to the events, i.e., reorganization energies, site energies, lifetimes, and coupling elements, are determined from a combination of GW-BSE and classical polarizable force field techniques. Kinetic Monte Carlo simulations were then employed to evaluate dynamical properties such as the excitonic diffusion tensor and diffusion lengths. Using DCV5T-Me(3,3), a crystalline organic semiconductor, we demonstrate how this multiscale approach provides insight into the fundamental factors driving the transport processes.</div><div>Comparing the results obtained with different calculation models, we investigate in particular the effects of charge-transfer mediated high exciton coupling and the influence of internal site energy disorder due to conformational variations. We show that a small number of high coupling elements indicative of delocalized exciton states does not impact the overall dynamics perceptively. Molecules with energies in the tail of the excitonic density of states dominate singlet decay, independent of the level of disorder taken into account in the simulation. Overall, our approach yields singlet diffusion lengths on the order of 10 nm as expected for disordered molecular materials.</div>

Growth of hematite on (0001) and {1102} sapphire substrates

1990 ◽  
Vol 48 (4) ◽  
pp. 376-377
Author(s):  
Lisa A. Tietz ◽  
Scott R. Summerfelt ◽  
C. Barry Carter
Keyword(s):  
Imaging Techniques ◽  
Chemical Vapor ◽  
Interface Energy ◽  
Dark Field ◽  
Cation Sublattice ◽  
Sapphire Substrates ◽  
Dark Field Imaging ◽  
Weak Beam ◽  
Pressure Chemical ◽  
Interface Structures

Defects in thin films are often introduced at the substrate-film interface during the early stages of growth. The interface structures of semiconductor heterojunctions have been extensively studied because of the electrical activity of defects in these materials. Much less attention has been paid to the structure of oxide-oxide heterojunctions. In this study, the structures of the interfaces formed between hematite (α-Fe2O3) and two orientations of sapphire (α-Al2O3) are examined in relationship to the defects introduced into the hematite film. In such heterojunctions, the oxygen sublattice is expected to have a strong influence on the epitaxy; however, defects which involve only the cation sublattice may be introduced at the interface with little increase in interface energy.Oxide heterojunctions were produced by depositing small quantities of hematite directly onto electrontransparent sapphire substrates using low-pressure chemical vapor deposition. Prior to deposition, the ionthinned substrates were chemically cleaned and annealed at 1400°C to give “clean”, crystalline surfaces. Hematite was formed by the reaction of FeCl3 vapor with water vapor at 1150°C and 1-2 Torr. The growth of the hematite and the interface structures formed on (0001) and {102} substrates have been studied by bright-field, strong- and weak-beam dark-field imaging techniques.

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