High Performance Quantum Cascade Lasers and Their Applications Daniel Hofstetter and J´ erˆomeFaist Institute of Physics, University of Neuchˆatel, 2000 Neuchˆ atel, Switzerland Daniel.Hofstetter@unine.ch Jerome.Faist@unine.ch Abstract. This chapter describes our results on distributed feedback quantum cas- cade lasers in the wavelength range around 5 μm and around 10 μm. We present two different gain region designs; one with three quantum wells and one with a double phonon resonance. Several fabrication techniques are also presented and analysed in terms of fabrication simplicity, performance, yield, and reliability. We will out- line typical results for all devices and also show some interesting applications. In light of this, the chapter is organized as follows: We start with a brief introduc- tion; in Sect. 2, the advantages and drawbacks of the different gain regions are outlined; Sect. 3 deals with the fabrication technology which was required to build these lasers; in Sect. 4, we present the measurement results on the devices; and finally, Sect. 5 describes two examples of interesting applications in the fields of optical spectroscopy and optical data transmission. The chapter ends with a brief conclusion and an outlook. 1 Introduction The development of high-performance mid-infrared light sources has expe- rienced tremendous progress during the last couple of years. Pacemakers of this progress were the appearance and the subsequent improvements of the quantum cascade (QC) laser [1,2,3]. After the pioneering work of Kazarinov and Suris about transport and gain in superlattice structures in 1971 [4], it took 23 years to realize the first working QC laser. During this long pe- riod, researchers investigated many different aspects of intersubband transi- tions [5,6] and the nature of resonant tunneling effects in thin semiconduc- tors [7,8]. They also learned to control the growth of extremely thin semi- conductor layers by methods like molecular beam epitaxy (MBE) [9,10,11] and metalorganic vapor phase epitaxy (MOVPE) [12,13]. All these impor- tant developments were crucial milestones towards the realization of a mid- infrared semiconductor laser based on intersubband transitions. But this kind of preparative work done in the 1970s and the 1980s also paved the way for a rapid development of the QC laser once it was born. Only one year after the demonstration of the QC laser by Faist et al. at Bell Labs in 1994 [1], the first continuous wave (CW) QC laser was operating at cryogenic tem- peratures [14,15]; and in 1996, room temperature pulsed operation could be I. T. Sorokina, K. L. Vodopyanov (Eds.): Solid-State Mid-Infrared Laser Sources, Topics Appl. Phys. 89, 61–98 (2003) c  Springer-Verlag Berlin Heidelberg 2003