Light Emission and Laser

Abstract

In this chapter, physics of luminescence and laser oscillations are treated in detail. First the definition of Einstein coefficients is introduced to connect absorption with spontaneous emission and stimulated emission. Then the spontaneous and stimulated emission rates are derived from the perturbation theory. Absorption and emission rates are strongly affected by the density of states, The density of states in the presence of impurities are shown to result in the band tail effect, where Kane’s model is used. Using these results the gain of laser oscillations are discussed. The results are also used to explain various types of luminescence. Since semiconductor lasers are fabricated in heterostructures and light emission is confined by the heterointerfaces, we discuss optical wave guide analysis to reveal the importance of double heterostructure. Mode analysis of the waveguide is given in detail to explain TE and TM modes and confinement factor, in addition to Fabry–Perot analysis. Since most of the laser diodes (LDs) are fabricated in quantum well structures, confinements of electrons in the conduction band and holes in the valence bands play an important role in the laser mode and the gain. In order to obtain the quantized states in valence bands, we show how to solve $$6 \times 6$$ Luttinger Hamiltonian including strain effect. Final part of this chapter is devoted to the physics of GaN based lasers, where we show the strain effect plays an important role in the laser oscillations.