Semiconductors are made up of all of the following materials except which?

• A. Silicon
• B. Germanium
• C. Gallium arsenide
• D. Copper wire

Answer: (D)

Semiconductors are materials whose ability to conduct electricity sits between that of metals and insulators, and this can be tuned by their electronic structure and by adding impurities. Silicon is the quintessential semiconductor because its crystal lattice and band gap allow precise control of current in devices. Germanium behaves similarly and has been used in early transistor technology. Gallium arsenide is a compound semiconductor with high electron mobility, useful for fast electronics and optoelectronics. Copper wire, however, is a metal with many free electrons and no practical band gap for controlled semiconductor behavior, so it’s used for wiring rather than as a semiconductor material.