Internal radiative heat transfer in Czochralski growth of LiTaO 3 single crystal

Abstract

In order to investigate the effect of internal radiative heat transfer on growth behavior in the oxide Czochralski single crystal growth process, differently colored LiTaO 3 single crystals were grown in N 2 + 0.5 vol% O 2 and N 2 atmospheres. In the N 2 + O 2 atmosphere, transparent yellow crystals of 55 mm in diameter and 70 mm in length could easily be grown. The crystals have convex interfaces toward the melt. On the other hand, the crystals grown in the N 2 atmosphere are brown because of O 2 deficiency. The brown crystals have concave interfaces and it was difficult to grow long crystals by using the hot zone with the same structure as that used in the N 2 + O 2 atmosphere. From measurements of temperature gradient in the growth furnace, temperature changes around crystals in the crucible with O 2 introduction into the N 2 atmosphere and emitted spectra from growing crystals in the N 2 and N 2 + O 2 atmospheres, it is concluded that increase of the resistance to heat transfer due to the suppression of the internal radiative heat transfer in the colored crystals is responsible for the growth difficulties such as concave interfaces.