**3. Basic material**

Apart from the oxygen, silicon is most commonly occurring element on the Earth. Silica is the dioxide from silicon and occurs mostly as quartz. Its synthesis has been familiar for many decades. It is extracted from (mainly) quartzite reduction with carbon in an arc furnace process [1]. The pulverized quartz and carbon are put in a graphite crucible. An arc causes them to melt at approximately 1800°C. Then, the reduction process takes place according to the formula:

$$\text{SiO}\_2 + 2\text{C} \blackheadrightarrow \text{Si} + 2\text{CO}\_{(\text{B})}\tag{1}$$

The liquid collected at the bottom of crucible can then be drawn off. Its purity can be approximately 97.9%. This is called metallurgic grade silicon (MG-Si). However, for silicon to be used in the semiconductor industry, the impurities must be removed almost completely by further processes. For such a high purity grade, multistage processes must be implemented.

**Figure 1.** *E(k) for the conduction and valence bands of silicon.*
