Optical Properties of Semiconductors: Understanding Absorption and Transitions

This lecture covers the optical properties of semiconductors, focusing on the absorption coefficient and the differences between direct and indirect semiconductors. It begins with an introduction to the absorption coefficient and its significance in semiconductor physics. The instructor explains the Tauc plot, which is used to determine the band gap of semiconductors. The lecture also discusses optical phenomena in real crystals, including the Urbach tail and the differences between amorphous and crystalline materials. The wave-particle duality of light is introduced, along with the spectral range relevant to semiconductors. The lecture further delves into the mechanisms of light absorption and propagation in semiconductors, highlighting the role of excitons and the conservation of energy during photon absorption. The differences in absorption processes between direct and indirect semiconductors are examined, along with practical exercises to estimate band gaps and identify semiconductor types based on experimental data. Overall, the lecture provides a comprehensive overview of the fundamental concepts related to the optical properties of semiconductors.