A Review on the Zone Refining Process Technology toward Ultra‐Purification of Gallium for GaAs/GaN‐based Optoelectronic Device Applications

Ultrapure gallium up to 99.9999%/ 99.99999% (6N/7N) purity level is a highly demanding material needed for the growth of gallium‐based group III–V semiconductor compounds and optoelectronic devices. However, general extraction of gallium from Bayer liquor contains high impurity content and ultra‐purification of the same cannot be accomplished by a single step. Thus, the purpose of this review is to assess various purification processes for the production of ultra‐pure gallium and to critically examine its applications in the optoelectronics industry. Through this research survey, it is found that zone refining of the zone melting process stands tall over other methods in purifying materials even up to 13N. Hence, scientists are adopting detailed mathematical models and simulation tools for designing unique zone refining systems for material purification. Current‐day technology even adopts intelligence methods such as machine learning, which sheds light on the importance of different zone refining parameters that influence the purification process. Here, the practical aspects of zone refining and how the feedback from the theoretical models or performance prediction through intelligence methods can be effectively incorporated into practice have also been emphasized This paper critically analyses different technologies for ultra‐purification of gallium required for high performing optoelectronic devices. Zone refining is found to be an effective technique for purifying materials in which vulnerable impurities can be reduced below parts per billion. Thus, different methodologies are discussed including intelligence method towards effectively utilizing zone refining apparatus in purifying gallium over 7N.