Introduction to Nanomaterials and Devices

Chapter 4

Optical Properties

The optical properties of any material are the result of photon interaction with the constituents of the material. The aim of this chapter is to describe photon interaction with semiconductor materials, including nanoscale material systems, which leads to effects that are the basis for many technologies, such as detectors, emitters, optical communications, display panels, and optical oscillators. The interaction of photons with electrons in semiconductor materials is the most important interaction that gives rise to many phenomena. Electrons in semiconductor materials can absorb photons and be excited from the valence band to the conduction band. This transition is called interband transition. The inverse of this process occurs when electrons decay from a higher energy level, such as a conduction band, to a lower energy level, such as a valence band, and as a result photons are emitted. This is the basis for light-emitting diodes (LEDs) and laser diodes. Electrons can absorb photons and be excited from one state to another within a particular band, such as a conduction band. This transition is called an intraband transition. In nanoscale material systems, such as quantum wells, wires, and dots, electrons can be excited by photons and jump from one confined energy level to another. When the electrons are excited from one bound state to another in the conduction band of a quantum well, as an example, the transition is called an intersubband transition. ...