Sapphire Substrates for Micro- and OptoelectronicsDetails
Kyropoulos method allows to grow the large sapphire crystals of any crystallographic orientation, with an extremely low dislocation density of less than 1000 cm-2.
Kyropoulos method has several advantages compared with other melt method:
• Kyropoulos method, as the Czochralski method refers to the free growth methods, when the growing crystal is not limited by the walls of the crucible;
• is a highly effective method that allows to obtain bulk crystals of optical quality (1 and 2 categories) with weight of a several tens of kilograms;
• because of the high vacuum in the growth chamber, there is an effective evaporation of impurities from the melt, so the grown crystals have high chemical purity of 99.996%.
Single crystals are grown directly in the melt by a smooth decrease in temperature at small temperature gradients, which makes it possible to grow crystals with low dislocation density.
There are series-produced growing facilities of the "Vodopad" and "Omega" types with weight sensors have been developed in Ukraine. "Vodopad" and "Omega-200MA" facilities allow the growing of crystals with the weight of 25-35 kg and diameter of 200 mm.
"Omega-300MA" facility allow the production of crystals with the weight up to 85 kg and diameter of 300 mm.
The advantage of Kyropoulos method lies in its technical simplicity and reliability. It is economically advantageous, since the effective screening of the growth zone, which reduces heat losses to a minimum is possible. Kyropoulos method allows to grow large sapphire single crystals with weight of 80 kg or more. The growth of the single crystals in the low-gradient temperature field allows to avoid the possible formation in the single crystals of various kinds of inclusions, blocks, low angle boundaries and high concentrations of dislocations.