Zone refining is the method used for obtaining highly pure silicon used as a semiconductor material.

Explanation:

1. Introduction:
Silicon is a widely used material in the semiconductor industry due to its excellent electrical properties. However, for many applications, high purity silicon is required to ensure optimal performance. The process of obtaining highly pure silicon involves several steps, one of which is zone refining.

2. Zone refining:
Zone refining is a technique that is used to purify silicon by removing impurities from the material. It is based on the principle of fractional crystallization, where impurities are selectively removed by melting and solidification.

3. Procedure:
The process of zone refining involves the following steps:
- A rod of impure silicon is taken and placed in a specially designed apparatus.
- The rod is heated at one end, creating a molten zone that moves along the length of the rod.
- As the molten zone moves, impurities are segregated towards the molten region.
- The molten zone is then allowed to solidify, resulting in a purified silicon crystal.
- The process is repeated multiple times, each time creating a new molten zone and refining the silicon further.
- With each repetition, the impurity concentration decreases, resulting in highly pure silicon.

4. Selective purification:
The principle behind zone refining is that impurities have different solubilities in molten silicon compared to solid silicon. As the molten zone moves along the rod, impurities with lower solubilities are left behind in the solid phase, resulting in their removal. This selective purification process allows for the production of highly pure silicon.

5. Advantages:
Zone refining offers several advantages for obtaining highly pure silicon:
- It allows for the removal of impurities with high precision, resulting in silicon with extremely low impurity concentrations.
- It is a continuous process, which allows for large-scale production of purified silicon.
- It is a relatively simple and cost-effective method compared to other purification techniques.

6. Conclusion:
In conclusion, zone refining is a method used for obtaining highly pure silicon used as a semiconductor material. It involves the selective purification of silicon by creating a molten zone that moves along the length of the material, removing impurities in the process. This technique is widely used in the semiconductor industry to ensure the high quality and performance of silicon-based devices.