Which one of the following is not a semiconductor?

Semiconductors are materials with electrical conductivity between that of a conductor and an insulator. Silicon (Si) and Germanium (Ge) are the most frequently used single-crystal semiconductors [1]. Gallium arsenide (GaAs) is a prominent compound semiconductor widely used for high-frequency and photovoltaic applications due to its high electron mobility [3]. In contrast, Quartz is a crystalline form of silicon dioxide (SiO2) [4]. While silicon is a semiconductor, its oxide form, silicon dioxide (quartz), is an excellent insulator with high dielectric strength and a wide band gap. Quartz is primarily valued for its piezoelectric and optical properties rather than semiconducting behavior [4]. Therefore, while silicon, germanium, and gallium arsenide are standard semiconductor materials, quartz functions as an insulator or dielectric material in electronic devices.

Sources

1. [1] https://bmsce.ac.in/Content/IT/Diode_introduction.pdf
2. [2] https://en.wikipedia.org/wiki/List_of_semiconductor_materials
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > 13.5. Some Rock-Forming Minerals > p. 175
4. [4] https://www.sciencedirect.com/topics/computer-science/silicon-dioxide-sio2