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Why is highly purified arsenic useful in semiconductor technology?

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A labeled diagram of the periodic table entry for arsenic, showing its atomic number 33, symbol As, atomic weight 74.921595, electron configuration, and classification as an other nonmetal. Additional icons indicate arsenic is solid at room temperature, has a rhombohedral crystal structure, and weakly acidic oxides. — arsenic Properties of arsenic.

Highly purified arsenic is essential in semiconductor technology primarily because it acts as a dopant to modify the electrical conductivity of materials like silicon and germanium.31

Because arsenic is a pentavalent element—meaning it has five electrons in its outermost shell—it serves as a donor atom when introduced into a semiconductor crystal lattice. When an arsenic atom replaces a silicon atom in the lattice, four of its electrons form covalent bonds with neighboring silicon atoms, while the fifth electron becomes a free conduction electron. This process creates an n-type (negative) semiconductor, significantly increasing its ability to conduct electricity.12

Additionally, highly purified arsenic is used to manufacture gallium arsenide, a compound semiconductor utilized in the production of diodes, lasers, and transistors.3