Selenium is an insulator.

• A. True
• B. Not sure
• C. False
• D. Not an insulator

Answer: (C)

Electrical behavior of materials is described by conductor, insulator, and semiconductor categories. Semiconductors have moderate conductivity that can be controlled and tuned by temperature, impurities (doping), or external stimuli like light. Selenium fits this description: it’s a nonmetal with a band structure that allows charge carriers to be generated more easily than in an ideal insulator, and its conductivity increases noticeably under illumination. This photoconductivity is a hallmark of semiconductors, which is why selenium is used in photodetectors and early rectifier devices. Because its ability to conduct electricity can be activated or enhanced by light, selenium is not an insulator. The statement that selenium is an insulator is therefore not correct.