Chapter 3 Semiconductor Lasers with Wavelengths Exceeding 2 μm

Abstract

Semiconductor lasers with wavelengths exceeding 2 μm are at a very early stage in their development. This chapter summarizes semiconductor materials and laser fabrication technology appropriate for laser diodes having emission wavelengths exceeding 2 μm, including those with lattice-matched double heterostructure configurations. Narrow-gap semiconductor lasers suffer from excessive loss mechanisms—such as those due to tunneling current, Auger recombination, and free-carrier absorption. These raise threshold currents and limit the highest temperature for laser oscillation. The chapter discusses the factors determining threshold current density and compares the lasers fabricated from different semiconductor materials. Unlike the development of lasers with AlGaAs/GaAs and InP/InGaAsP double heterostructures, which has been stimulated by progress in optical fibers, semiconductor lasers with wavelengths exceeding 2 μm are now only at a very early stage in their development. Most recently, much attention has been paid to ultra-low-loss optical fiber materials in the near- and middle-infrared regions, such as thallium bromide and chalcogenide glass materials.