Kp. Dharmasena et Hng. Wadley, Modeling multifrequency eddy current sensor interactions during vertical Bridgman growth of semiconductors, REV SCI INS, 70(7), 1999, pp. 3125-3142
Electromagnetic finite element modeling methods have been used to analyze t
he responses of two ("absolute" and "differential") eddy current sensor des
igns for measuring liquid-solid interface location and curvature during the
vertical Bridgman growth of a wide variety of semiconducting materials. Th
e multifrequency impedance changes due to perturbations of the interface's
location and shape are shown to increase as the liquid/solid electrical con
ductivity ratio increases. Of the materials studied, GaAs is found best sui
ted for eddy current sensing. However, the calculations indicate that even
for CdTe with the lowest conductivity ratio studied, the impedance changes
are still sufficient to detect the interface's position and curvature. The
optimum frequency for eddy current sensing is found to increase as the mate
rial system's conductivity decreases. The analysis reveals that for a given
material system, high frequency measurements are more heavily weighted by
the interfacial location while lower frequency data more equally sample the
interface curvature and location. This observation suggests a physical bas
is for potentially measuring both parameters during vertical Bridgman growt
h. (C) 1999 American Institute of Physics. [S0034-6748(99)02306-0].