In the framework of a nonisothermal model it is shown that in the spot of cwCO2 laser of power P the
temperature of a small bare Si plate increases from T'=300[K] to an equilibrium temperature T0(P). The moment of
time t1(P) at which T0(P) is achieved, t0(P) at which the oxide layer of 1 nm is formed, the sample temperature at t0(P),
the oxide layer thickness at t1(P), the oxide layer growth rate at t0(P), and t1(P) are computed, for dry and wet oxidation
and for <100> and <111> oriented samples. How well the computed results are in agreement with the experimental
results depends on the magnitude of the effect of the processes which were not incorporated in the model. The advantage
of this analysis is the possibility to obtain explicit results from which the limits of the model can be specified and special
results can be gleaned. With this aim this study was undertaken.
The quality of the fiber depends to a considerable extent on homogeneity, i.e., on the distribution of both special added and detrimental impurities. A non-uniform distribution of such impurities along the fiber length and cross-section leads to non-uniform spatial, electrical and optical properties of the crystal. Variations of the concentration of impurities are determined by the processes that take place during the fiber manufacturing. In order to eliminate non-uniformities, crystal growth experts have concentrated on the analysis of the mass transport, heat transfer, impurity distribution and shape of the crystal-melt interface. In order to evaluate the dopant distribution, a stationary numerical model-including incompressible fluid flow in the Boussinesq approximation, heat and mass transfer, and surface tension-driven flows due to the temperature gradient along the liquid free surface (meniscus)-is developed using the finite element method. A two-dimensional axissymmetric model is implemented with COMSOL Multiphysics 3.3 software, and the Nd impurity distribution dependence on the pulling rate v0 and on the radius of the capillary channel Rcap in a LiNbO3 fiber grown from the melt by the EFG method is determined. Using this dependence, the optimal v0 and Rcap which assure the best impurity
distribution are chosen.
In this paper the dependence of the radius of a Nd:YVO4 cylindrical bar, grown in a low-gravity environment, on the pulling rate (v), melt temperature (T0) at the meniscus basis, pressure in the furnace (p) and die radius (r0e) is found. Those values of v, T0, p and r0e are determined for which the crystal radius variation, due to small uncontrollable variations of v, T0, p around some average values, cause minimal surface non-uniformity. Numerical results are given for a Nd:YVO4 cylindrical bar grown in a furnace in which the vertical temperature gradient is k=33 K/mm. Finally, the results obtained in low-gravity environment are compared to those obtained in terrestrial conditions.
In this paper the dependence of the crystal radius on the pulling rate (v), melt temperature (T0) at the meniscus basis, pressure in the furnace (p) and die radius (r0e) is found. This dependence is used to show in which kind the effect of the variation of one of these parameters can be compensated by varying an other one. Those values of v, T0, p and r0e are determined for which the crystal radius variations due to small uncontrollable variations of v, T0, p around some average values cause minimal surface non-uniformity. Numerical results are given for a Nd:YVO4 cylindrical bar grown in a furnace in which the vertical temperature gradient is k=33 K/mm.
In this paper a model for thermosolutal convection, thermotransport and mass transport is considered for a Bridgman-Stockbarger growth system. It is shown that if the growth process takes place in zero- gravity or in a low gravity environment and if at the moment when the bottom of the ampoule enters into the gradient zone the dopant concentration in the melt is given by a certain formula, then in the first 70% of the grown crystal the dopant concentration is almost equal to a prescribed concentration. In practice this means that the ampoule has to be filled with thin concentric rings, obtained by compacting powder, each of these rings having a constant concentration of dopant, given by the formula in function of the position of the ring in the ampoule. This ampoule is introduced into the hot zone of the furnace and the content is melted quickly so that the dopant diffusion during the melting process can be neglected. At the end of the melting process the translation of the ampoule begins. Numerical results are given to show the computed improvement obtainable in comparison to the experimental results.
In this paper we present the computed dopant field in the neighborhood of the melt/solid interface in the case of Bridgman-Stockbarger semiconductor crystal growth system in microgravity. The computation is made in quasi-steady state approximation for crystal and melt with thermophysical properties similar to those of gallium-doped germanium, using the 'precrystallization-zone' model. In the quasi- steady state approximation the translation of the ampoule is replaced by supplying melt into the ampoule with velocity V1 and removing crystal at the other end of the ampoule at the rate Vs equals V1. The 'precrystallization-zone' is considered to be a thin layer masking the crystal in which exists a periodical microstructure created by the periodical structure of the crystal which governs the arranging of the own atoms into a specific crystalline lattice. In fact, in this layer we have periodically distributed places which are not available for the dopant. Using this approximation and model, we find relevant radial segregation due to the precrystallization-zone. We also find that reducing the diameter of the rod a lower radial segregation appears. Therefore the influence of the precrystallization-zone is relevant even in microgravity and there is no reason to ignore this zone in general.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.