Chemicals Based Technologies - Ultra-Purification of Gallium

Introduction

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. The process has been developed at a scale of 2.5 kg/batch and can be scaled up as required.

Most of the ultrapure Gallium is imported at present. Gallium is obtained essentially as a by-product of aluminium and zinc industry. India has a well established aluminium industry which produces tones of commercial gallium as byproduct. In view of this, sufficient raw material is available indigenously for ultra-purification. Standardization of protocol by BARC may significantly reduce imports of ultra-pure gallium.

Ultrapurification of gallium

Main impurities present in commercial gallium are aluminum, silver, arsenic, bismuth, cadmium, cobalt, chromium, copper, iron, mercury, manganese, molybdenum, nickel, lead, tin, antimony, selenium, zinc and vanadium.

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 the gross impurities.

3. The sodium gallate solution on electro-winning with stainless steel electrodes yields ultra-pure 6N gallium (99.99999%).

The ultra-pure gallium is then sealed in high purity teflon bottles under argon to avoid contamination due to oxidation.

Analysis of Gallium ( >6N pure)

Analysis of purified gallium has been carried out by accredited national and international laboratories.

Applications of pure Gallium

Ultrapure Gallium is used in the manufacture of semiconductor materials such as GaAs, GaN, GaP, InGaAs, etc. which are used in high speed opto-electronic devices (light emitting diodes, Laser diodes, photovoltaics, etc.). It is also used as a dopant.

Infrastuctural Requirements

A. Clean room area (Class 10000) 15ft (w) x 15ft (I)
B. Clean benches (Class 100 - 3 nos.)
C. Fume hood (1 no.)
D. Skilled Man Power: B.Sc. (chemistry) graduate from a recognized university (2 nos.).

For further information please contact :

Head,
Technology Transfer & Collaboration Division,
Bhabha Atomic Research Centre, Trombay,
Mumbai - 400 085
Tel : 091-022-25505337/25593897
Fax : 091-022-25505151
E-mail : headttcd@barc.gov.in

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