Influence of oxygen partial pressure on SrTiO3 bulk crystal growth from non-stoichiometric melts

Abstract

Cylindrical SrTiO₃ single crystals with diameters and lengths exceeding one inch were grown from non-stoichiometric melts below 1800 °C using the high temperature top-seeded solution growth (TSSG) method. Despite the large crystal diameter the quality has been improved compared to Verneuil grown crystals. Typical etch pit density (EPD) values are in the range between 2 × 10⁴ and 2 × 10⁵ cm⁻² for bulk crystals pulled in the <100> direction and using seeds with EPD values of 5 × 10⁵ cm⁻². So far pulling SrTiO₃ crystals from the melt suffers from growth instabilities like foot formation and subsequent spiraling. To avoid them an effective heat transport via the crystal is indispensable. Especially at elevated temperatures it requires a high optical transparency in the infrared region. In this paper we report the correlation between oxygen partial pressure, composition, IR-transmittance and coloration of the crystals. The growth at a sufficiently high oxygen partial pressure leads to an increase in the optical transparency of the crystals and can thereby suppress foot or spiral formation.