ULTRA-PURIFICATION OF GALLIUM

Ultrapure gallium (7N) finds extensive application in electronics industry as III-V compound semiconductors and as a dopant. Gallium (7N pure) at present is not manufactured in India and needs import. BARC has standardized a protocol for producing 7N (99.99999%) pure gallium from commercially available metal (99.3%). The product quality obtained is equal to or better than imported.

Process Salient Features

Purification of gallium is carried out in clean rooms in three steps as described below to bring impurities down to ppb level.
1. Commercial gallium is heated at high temperature under dynamic vacuum (10-4 torr) to remove volatile impurities.
2. The gallium obtained (from step 1) is converted to sodium gallate solution after a series of chemical treatments to remove gross impurities.
3. The sodium gallate solution on electro-winning with stainless steel electrodes yields ultra-pure 7N gallium (99.99999%). 
The ultra-pure gallium is then sealed in high purity teflon bottles under argon to avoid contamination due to oxidation.

Applications

Ultrapure gallium is used in the manufacture of semiconductor materials such as gallium arsenide, gallium nitride, gallium phosphide, etc. which are used in high speed opto-electronic devices (gun diodes, laser diodes, light emitting diodes, etc). These applications have created an increased demand for high purity gallium in recent years.