Physics and applications of IV-VI compound semiconductor lasers

Abstract

Lasers made of lead salt compounds have proven to be best suited for coverage of the mid-infrared region from 3 to 30 mu m. Nowadays double-heterostructure (DH) lasers are the standard, using as active layers PbEuSSe for the short-wavelength region below 4 mu m, PbEuTeSe or PbEuSe for the 4-8 mu m range and PbSnTe or PbSnSe for wavelengths beyond 8 mu m. Originally liquid phase epitaxy but now molecular beam and hot wall epitaxy techniques are most commonly used to produce a wide variety of laser structures. While simple DH lasers with contact or mesa stripes for lateral confinement prevail in commercial devices, highly sophisticated prototypes with buried layer, corrugated distributed Bragg reflector (DBR) and distributed feedback (DFB) and single- and multi-quantum-well structures have been successfully manufactured. Gas spectroscopy has remained the main field of application where mode quality and tuning properties of the emitted radiation are most important. The dominant development goal has been the increase of the operating temperature to make the use of simple cooling equipment possible. Theoretical models for threshold current calculations have been established; however, the reliability of the results has been impaired by the fact that basic material properties of the ternary and quaternary compounds are not well know. In the course of this paper the state of the art and the development trends of lead salt lasers are described. The various fields of applications are summarised. Two examples-one dealing with car exhaust monitoring, the other with clinical isotopic ratio measurements of the exhaled breath-are discussed in some detail.