Semiconductor lasers

Abstract

At first glance, the semiconductor laser, or more precisely the semiconductor diode laser, is a special solid state laser, but for good reasons it is usually treated as a laser family of its own. Solid-state lasers in general are formed by a laser medium which is represented by a host material (of crystalline or glassy nature) doped by suitable ions (rare earths, transition elements). Generally, those dopants have clearly defined energy levels, which are more or less perturbed, i.e. broadened, by the binding fields of the host. However, in case of the semiconductor laser the lasing transitions take place between the valence and conduction bands as a consequence of the collective interaction processes of the electrons and the lattice as a whole. Therefore, the density of energy levels is extremely high in comparison to any other laser material. The excitation, represented by mobile electrons and holes, can be transported through the crystal to the recombination area which is called the active zone.