How does the crystal structure of silicon help it function as a semiconductor?

Silicon functions as a semiconductor primarily due to its three-dimensional periodic crystal structure, where each atom is surrounded by four neighbors. Each silicon atom shares its four outer electrons with these neighbors, forming covalent bonds that hold the structure together.12

In this crystalline arrangement, the discrete energy levels of isolated atoms spread into energy bands. The highest filled band is the valence band, separated from the empty conduction band by a specific energy gap of 1.12 eV. At low temperatures, electrons are bound in the valence band, making the material an insulator. However, at higher temperatures, thermal vibrations can break covalent bonds, promoting electrons to the conduction band and leaving behind mobile, positively charged holes in the valence band. These free electrons and holes act as charge carriers, allowing the material to conduct electricity when an electric field is applied. Conductivity can be further enhanced through doping, which introduces impurities to create n-type or p-type semiconductors.123