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The low thermal gradient Cz technique as a way of growing of dislocation-free germanium crystals
|Vitaly A. Moskovskih 1, Pavel V. Kasimkin 1, Vladimir N. Shlegel 2, Yan V. Vasiliev 2, Viktor A. Gridchin 1, Oleg I. Podkopaev 3|
1. Novosibirsk State Technical University (NSTU), K. Marx av., 20, Novosibirsk 630092, Russian Federation
Germanium is commonly used as a semiconductor material for optoelectronic and electronic applications. One of modern applications of Ge is a substrate for GaAs/Ge solar cells with high conversion efficiency more than 41% . For use as a substrate, material has to be dislocation-free or very low density of dislocations to avoid the negative impact of crystal defects on the quality of the growing epitaxial layers .
The obtaining of dislocation-free germanium single crystals is difficult. Formation of crystal defects, caused by thermoelastic stresses, is determined by the temperature field during the growth and cooling of the crystal. It is known that to decrease dislocation density it is necessary to reduce temperature gradients.
The aim of the work was a check of ability to grow single crystals of germanium with a low dislocation density by the low-thermal-gradient Czochralski technique (LTG Cz), which has been successfully used for the growth of oxide crystals . The use of conventional weighing control for the growth of semiconductors, in particular germanium, silicon and gallium arsenide, by the method LTG Cz is somewhat difficult because of so-called "anomalous" behavior of the weighted signal . For automatic control of the germanium crystals growth processes by LTG Cz we developed a method of obtaining information on the value of cross-sectional area of growing crystal based on modulation of pulling rate by the fast small measuring movements of the pulling rod, which cause weighing signal modulation by buoyancy forces.
Results of experiments on growing germanium crystals with a diameter of 45 mm from the graphite crucibles are presented. The crystals were grown in the directions , ,  with growth rate from 3.5 to 10 mm/h. Simulation of Cz by CGSim commercial package let estimate that the temperature gradients during growth process did not exceed 1.5 K/cm. Single crystals were grown with a dislocation density of Nd = 100-200 cm-2. Grown crystals are partially faceted, their cross-sections differ from the round.
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Presentation: Oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, Topical Session 5, by Vitaly A. Moskovskih
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17
Submitted: 2013-03-29 06:46 Revised: 2013-04-15 10:21