Introduction to Semiconductors

Semiconductors have conductivity between conductors and insulators. Intrinsically, they're pure elements, notably silicon and germanium, with four valence electrons enabling unique electrical properties important in modern electronics.

Doping introduces impurities to intrinsic semiconductors, creating n-type or p-type materials. Donors add free electrons, while acceptors create holes. This process modulates electrical characteristics, permitting controlled conductivity.

In solids, energy levels form bands: valence and conduction. The energy gap between them defines semiconductor behavior. At absolute zero, this gap prevents electron flow; however, room temperature enables electron excitation, permitting conductivity.

Temperature, impurities, and light affect semiconductor conductivity. Increased temperature can excite more electrons into the conduction band, enhancing conductivity—an essential principle for thermistors and photoconductors.

A p-n junction forms by joining p-type and n-type semiconductors. This contact causes diffusion of charge carriers, leading to a built-in potential across the junction, foundational for diodes and transistors.

At the p-n junction, a depletion region emerges, devoid of free charge carriers. This space-charge region acts as an insulator until sufficient voltage is applied, which is critical for rectification and switching.

Quantum dots, semiconductor nanoparticles, exhibit quantum mechanical properties. Their size impacts their optical and electrical behaviors, promising advancements in displays, solar cells, and medical imaging.