Czochralski technique

Question 1

What is the Czochralski technique?

Answer 1

~ alumina is melted in an iridium crucible in an argon atmosphere

~ a thin seed of sapphire with a precise orientation is dipped into the melt. It is withdrawn at a controlled rate, and crystal and crucible are rotated in opposite directions

~ as the seed is drawn upward, crystal layers are added to form a single crystal boule

~ nearly bubble free, low dislocation density crystals are formed. Growth can take up to two months

Question 2

What is the size of a boule?

Answer 2

~ boules up to 20cm diameter and 60cm in length are grown

Question 3

What are the applications for this technique?

Answer 3

~ used for ruby lasers (now have been mostly displaced by Nd-YAG lasers)

~ infrared windows (sapphire is transparent deeper into the infrared than fused silica)

~ infrared cameras, night vision goggles, or infrared pyrometer windows and high-temp process windows (more refractory than fused silica)