Abstract
In this study, radial crystallization purification method under induction was proposed for preparing 6N,7N ultra-high purity gallium crystal seed. The effect of cooling temperature on the morphology of the crystal seed, as well as the cooling water temperature, flow rate, and the addition amount of crystal seed on the crystallization process was explored, and the best purification process parameters were obtained as follows: temperature of the crystal seed preparation, 278 K; temperature and flow rate of the cooling water, 293 K and 40 L·h−1, respectively; and number of added crystal seed, six. The effects of temperature and flow rate of the cooling water on the crystallization rate were investigated. The crystallization rate decreased linearly with increasing cooling water temperature, but increased exponentially with increasing cooling water flow. The governing equation of the crystallization rate was experimentally determined, and three purification schemes were proposed. When 4N crude gallium was purified by Scheme I, 6N high-purity gallium was obtained, and 7N high-purity gallium was obtained by Schemes II and III. The purity of high-purity gallium prepared by the three Schemes I, II, and III was 99.999987%, 99.9999958%, and 99.9999958%, respectively.
Highlights
In the 1970s, compounds comprising gallium and Group IIIA elements were discovered to have excellent semiconductor properties
The appearance morphology of the seed crystal prepared at the cooling temperature in the range range 265–295 K is shown in Figure 2, indicating that at 265 K, the solidified structure comprised
When the solidified structure was removed, a large amount of liquid gallium was attached to the solidified structure was removed, a large amount of liquid gallium was attached to the surface, surface, resulting in an extremely irregular shape of crystal seed, because at 265 K, the growth rate resulting in an extremely irregular shape of crystal seed, because at 265 K, the growth rate of crystal of crystal nucleus increased after nucleation due to the large degree of supercooling, leading to the nucleus increased after nucleation due to the large degree of supercooling, leading to the emergence emergence of a large number of dendrites
Summary
In the 1970s, compounds comprising gallium and Group IIIA elements were discovered to have excellent semiconductor properties. According to the survey report of USGC in 2015 [8], the global demand for Ga was estimated to increase by 20 times in 2030, whereas with the development of semiconductor devices with higher performance, the demand of high impurity gallium has been increasing, because even very small amounts of impurities such as Cu, Pb, Fe, Mg, Zn, and Cr, which are always present in current large-scale commercial-quality gallium, can degrade or limit the electrical properties [9] Conventional refining methods such as electrolytic refining [10,11], regional melting [12], vacuum distillation [13], and drawn single crystal method [14] have been applied
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