Question

Elemental silicon to be used as semiconductor is purified by: (a) Floatation (b) Electrolysis (c) Zone refining (d) Heating under vacuum

Short answer

Zone refining is used to purify silicon for semiconductors.

Step-by-step solution

Analyzing the Question

The exercise asks to identify the method used specifically for purifying silicon for use as a semiconductor. Silicon needs to be highly pure for semiconductor applications, which requires a special purification process.

Understanding Zone Refining

Zone refining is a technique based on the principle of fractional crystallization. It involves heating a rod of material to melt a small region, then slowly moving this molten zone along the rod. Impurities concentrate in the molten region and are moved to one end of the rod, leaving behind high-purity silicon.

Evaluating Other Methods

- **Floatation** is a method mainly used for separating minerals from ores based on differences in their surface properties. It is not suitable for purifying silicon. - **Electrolysis** involves the use of electric current to drive a non-spontaneous reaction, typically used in the purification of metals like aluminum but not common for silicon. - **Heating under vacuum** is a method used in general purification processes but does not effectively concentrate impurities for semiconductor-grade silicon.

Choosing the Correct Answer

Based on the analysis, the most applicable method for purifying elemental silicon for semiconductors is **Zone Refining** as it provides the necessary level of purity by removing impurities effectively through controlled crystallization.

Key concepts

Zone Refining

Zone refining is a highly effective purification method often used to achieve the ultra-high purity required for semiconductor materials like silicon. The process operates on the principle of fractional crystallization. During zone refining, a small section of a silicon rod is heated until it melts, creating a local molten zone. This zone is then gradually moved along the rod. As the molten zone migrates, impurities in the silicon are more soluble in the liquid phase than in the solid. Consequently, impurities concentrate in the molten region and are carried along until they become concentrated at one end of the rod.

This method is crucial for semiconductor manufacturing because even tiny amounts of impurities can significantly affect the electrical properties of silicon. By using zone refining, manufacturers can ensure that silicon meets the stringent purity standards required for use in electronic components. This makes it indispensable in the field of materials science focused on electronics.

Semiconductors

Semiconductors form the backbone of modern electronics. Made from materials like silicon, they exhibit a conducting ability that lies between that of conductors and insulators. This unique property makes them ideal for controlling electrical current in devices.

The performance of semiconductor devices, such as transistors, diodes, and integrated circuits, heavily relies on the purity of the silicon used. Impurities in the semiconductor can introduce unwanted electronic states within the material, affecting its ability to properly conduct electricity and perform its function within an electronic device.

For instance, in electronics, semiconductors are used to fabricate microchips that serve as the brains of computers and smartphones. Understanding the role of semiconductors in technology is vital for innovations in electronics and has continued to evolve significantly over the decades.

Fractional Crystallization

Fractional crystallization is a separation process that separates components based on differences in their solubility. In the context of zone refining, it plays a pivotal role by allowing silicon to be purified to a high degree of purity.

During the process, the molten zone's ability to dissolve more impurities compared to the solid phase allows silicon to crystallize out as a purer substance. The less soluble impurities remain in the molten phase and are transported along the silicon rod. Once the molten zone reaches the end of the rod, it solidifies, leaving behind a much purer silicon material.

This process is not only utilized in silicon purification but also in other materials science applications where high purity is required, making it an essential tool in refining and material preparation.

Materials Science

Materials science is an interdisciplinary field that focuses on understanding and manipulating the properties of materials to develop new technologies. It encompasses the study of metals, ceramics, polymers, and semiconductors.

In the case of semiconductors like silicon, materials science is critical to both the development and optimization of purification techniques such as zone refining. By deeply understanding the structure and behavior of materials on an atomic level, scientists and engineers can devise methods to produce materials with desired properties.

Furthermore, materials science plays a significant role in the innovation of new semiconductor devices, paving the way for advancements in technologies across numerous fields, including computing, renewable energy, and telecommunications. By exploring new material combinations and refining existing ones, materials science continues to drive technological progress and improve the efficiency and functionality of electronic components.