Transport Properties in Semiconductors: Charge Dynamics and Conductivity

This lecture discusses the transport properties of semiconductors, focusing on charge dynamics and conductivity. It begins with an overview of intrinsic and doped semiconductors, explaining the balance of free electrons and holes. The instructor describes how the Fermi energy varies in intrinsic, p-type, and n-type semiconductors. The effects of external influences, such as electric and magnetic fields, on charge distribution are examined, including the formation of accumulation and depletion zones. The lecture also covers the concepts of drift currents and the relationship between electric fields and charge carrier mobility. The instructor explains the thermal motion of electrons and the average free path between collisions, leading to the derivation of drift velocity. The distinction between mobility and conductivity is clarified through analogies and examples, emphasizing the importance of charge carrier density in determining conductivity. Finally, the lecture concludes with a discussion on resistivity in semiconductors, highlighting the need to sum the contributions of different charge carriers to obtain accurate measurements.