Basic Concepts

Abstract

This chapter reviews some background material on semiconductor lasers and lays the theoretical foundation for the development of a theory for the gain media in these lasers. We begin with a brief summary of the historical background of semiconductor laser development in Sect. 1.1. Section 1.2 describes the basic laser structure and discusses how an inversion is created. Section 1.3 introduces the concept of heterostructures. Some basic aspects of the semiconductor band structure are presented in Sect. 1.4. A more detailed band-structure analysis including the modifications caused by quantum confinement and strain effects is presented in Chaps. 5, 6. Section 1.5 briefly discusses cgs and MKS units, both of which are used extensively in the semiconductor laser literature. The problem is that MKS has been used traditionally for lasers, while cgs is often used in semiconductor theory. Hence, the marriage of the fields requires a familiarity with both systems of units. Section 1.6 discusses the Fermi-Dirac distributions of the carrier probabilities. Section 1.7 introduces the concept of quantum confinement and Sect. 1.8 makes contact with the laser electric field by outlining a derivation of the slowly varying electromagnetic-field equations. This shows how the field amplitude and phase are influenced by an induced polarization of the medium. Section 1.9 begins our discussion of this induced polarization using a quantum mechanical description of the semiconductor medium.