The formation of faceted melt/crystal (m/c) interfaces takes place at crystal growth of many technologically important semiconductor materials. As is shown, for example in work [1, 2], the faceted interfaces must be morphologically more stable than nonfaceted ones as interfacial kinetics exerts a strong influence on the stability of the growing interface. Thus, crystal growth by the faceted mechanism enables to obtain perfect single crystals with higher dopant concentration than it is allowed by rough growth. However, theoretically and experimentally, the problem of facet stability at high dopant concentration is insufficiently investigated. To investigate this phenomenon more accurately it is necessary to know a kinetic dependence for facet at a high dopant concentration.

So, the aim of this work is to find the kinetic dependence V = V(dT), where V is crystal growth rate, dT is supercooling of singular facet 111 of Ge. To obtain data on V = V(dT) it is necessary to find dTi values that took place at different Vi values. The experimental data on dT were obtained from data on visualization of shape of m/c interface after etching longitudinal section of grown Ge crystal as follows. For a known value of the temperature gradient in the melt, gradTm, the value of the supercooling can be calculated from expression: dT = ∆×gradTm, where ∆ is the measured distance between the central part of the facet and the central part of the melting temperature isotherm as shown in Fig. 1. This approach of dT finding is based on fact that supercooling is negligible on nonfacetted regions of the interface.

Ge crystals were grown by AHP technique [3, 4]. The AHP method gives possibility to use a one dimensional model of a heat transfer to obtain data on V and gradTm. Thus, a set of data on dTi and correspond it data on Vi were obtained. Ge crystals were grown at 111 direction in 2 inch diameter graphite crucible.  Accuracy of crystallography orientation was 1 minute. Crystals were doped by Sb and it’s concentration in the melt was in the range of 9×10¹⁸ - 2×10²⁰ cm^-3. The dislocation density was in the range of 10⁴ – 10⁵/ cm². Crystal growth rate, at which the dT value was found, was in the range of 5 – 25 mm/hour. To make more a facet size the growth rate was increased and the temperature gradient was reduced before m/c interface marking. M/c interface marking was made by the AHP heater translation up to contact with the melt-crystal interface. After this procedure, the AHP heater was returned to its initial position and it was again fixed relative to the growth setup casing. The single crystal of Ge which was grown in this manner was cut into plates in the longitudinal direction. To visualize the melt-crystal interface and structure of a crystal, the Ge plate was etched by the method of anode etching in a 0.1 mole Na₂SO₃ per liter of H₂O.

 The obtained result on V = V(dT) dependence is presented in Fig. 2. V = V(dT) dependence has slightly squared relationship. This result corresponds to dislocations mechanisms of interfacial kinetic. One can see from Fig. 2 that as first approximation V = V(dT) dependence is linear dependence and the kinetic coefficient, b*,  is constant for Sb concentration in the range of  9×10¹⁸ - 2×10²⁰ cm^-3 and the crystal growth rate in the range of 5 – 25 mm/hour. One can see that dT value is big enough in spite of big density of dislocations and it must be taken into consideration for crystal growth rate more then 25 mm/hour and at small temperature gradient.

1. Abbaschian, R.; Coriell, S.; Chernov, A. In Solidification1999;
2. Hofmeister, W. H., Rogers, J. R., Singh, et al., Eds.; TMS: Warrendale, PA, 1999;pp 219-228.
3. E. Balikci, A. Deal, R. Abbaschian, et al, Crystal Growth & Design, 2004, vol. 4, No 2, pp. 377-381.
4. S.V. Bykova, V.D. Golyshev, et al, Journal of Crystal Growth, 275 (2005) 229 - 236

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1. Investigation of morphological stability of melt/crystal interface at CZT crystal growth by the AHP method under high pressure