TY - JOUR
T1 - Effect of steady ampoule rotation on radial dopant segregation in vertical Bridgman growth of GaSe
AU - Lee, Hanjie
AU - Pearlstein, Arne J.
N1 - Funding Information:
The authors gratefully acknowledge the comments, suggestions, and information provided by Drs. Nils C. Fernelius, Valeriy G. Voevodin, Kerim Allahverdiev, and the referee. The authors gratefully acknowledge support of the Microgravity Science and Applications Division of the National Aeronautics and Space Administration through Grant NAG3-1121 during the early stages of development of the code used herein, and thank the AFRL Window on Science program for sponsoring the visits of Drs. Voevodin and Allahverdiev. The computations were performed using the facilities of the National Center for Supercomputing Applications.
PY - 2002/5
Y1 - 2002/5
N2 - For vertical Bridgman growth of the nonlinear optical material GaSe in an ampoule sufficiently long that flow and dopant transport are not significantly influenced by the upper free surface, we show computationally that steady rotation about the ampoule axis strongly affects the flow and radial solid-phase dopant segregation. Radial segregation depends strongly on both growth rate U and rotation rate Ω over the ranges 0.25 μm s-1≤U≤3.0μm s-1 and 0≤Ω≤270 rpm. For each growth rate considered, the overall radial segregation passes through two local maxima as Ω increases, before ultimately decreasing at large Ω. Rotation has only modest effects on interface deflection. Radial segregation computed using a model with isotropic conductivity (one-third the trace of the conductivity tensor) predicts much less radial segregation than the "correct" model using the anisotropic conductivity, with the segregation decreasing monotonically with Ω. Consideration of a model in which centrifugal acceleration is deliberately omitted shows that, as Ω increases, diminution and ultimately disappearance of the "secondary" vortex lying immediately above the interface is due to centrifugal buoyancy, while axial distension of the larger "primary" vortex above is due to Coriolis effects. These results, which are qualitatively different from those accounting for centrifugal buoyancy, suggest that several earlier computational and analytical predictions of rotating vertical Bridgman growth are either limited to rotation rates sufficiently low that centrifugal buoyancy is unimportant, or are artifacts associated with its neglect. The overall radial segregation depends approximately linearly on the product of 1 - k̃ and the growth rate U for the conditions considered, where k̃ is the segregation coefficient.
AB - For vertical Bridgman growth of the nonlinear optical material GaSe in an ampoule sufficiently long that flow and dopant transport are not significantly influenced by the upper free surface, we show computationally that steady rotation about the ampoule axis strongly affects the flow and radial solid-phase dopant segregation. Radial segregation depends strongly on both growth rate U and rotation rate Ω over the ranges 0.25 μm s-1≤U≤3.0μm s-1 and 0≤Ω≤270 rpm. For each growth rate considered, the overall radial segregation passes through two local maxima as Ω increases, before ultimately decreasing at large Ω. Rotation has only modest effects on interface deflection. Radial segregation computed using a model with isotropic conductivity (one-third the trace of the conductivity tensor) predicts much less radial segregation than the "correct" model using the anisotropic conductivity, with the segregation decreasing monotonically with Ω. Consideration of a model in which centrifugal acceleration is deliberately omitted shows that, as Ω increases, diminution and ultimately disappearance of the "secondary" vortex lying immediately above the interface is due to centrifugal buoyancy, while axial distension of the larger "primary" vortex above is due to Coriolis effects. These results, which are qualitatively different from those accounting for centrifugal buoyancy, suggest that several earlier computational and analytical predictions of rotating vertical Bridgman growth are either limited to rotation rates sufficiently low that centrifugal buoyancy is unimportant, or are artifacts associated with its neglect. The overall radial segregation depends approximately linearly on the product of 1 - k̃ and the growth rate U for the conditions considered, where k̃ is the segregation coefficient.
KW - A1. Convection
KW - A1. Segregation
KW - A2. Bridgman technique
KW - B1. Gallium compounds
KW - B2. Nonlinear optical materials
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U2 - 10.1016/S0022-0248(02)00869-2
DO - 10.1016/S0022-0248(02)00869-2
M3 - Article
AN - SCOPUS:0036570775
SN - 0022-0248
VL - 240
SP - 581
EP - 602
JO - Journal of Crystal Growth
JF - Journal of Crystal Growth
IS - 3-4
ER -