Recent progress in interband cascade lasers with separate confinement layers

Abstract

ABSTRACT Interband cascade lasers are efficient and compact semiconductor mid-infrared (3-6 P m) light sources with low-power consumptions. We report our recent prog ress in the development of interband cas cade lasers with separate confinement layers. Broad-area (0.1mm x1mm) lasers have been operated in cw m ode at temperatures up to 213K near 3.36 P m. For narrow ridge-waveguide (0.01mm x1.5mm) lasers, cw operation has been achieved at temperatures up to 266K near 3.43 P m, 260K near 3.7 P m, and 238K near 4.04 P m. The results on both broad-area and narrow-ridge IC lasers are discussed in comparison with previous regular IC lasers without separate confinement layers. Keywords: mid-infrared, lasers, semiconductors, quantum wells 1. INTRODUCTION Interband cascade (IC) lasers [1] are efficien t semiconductor laser sources in mid-IR (3-6 P m) wavelength region for practical applications owing to their unique features. Similar to intraband quantum cascade (QC) lasers [2], each electron is reused for generating multip le photons in IC lasers with high quantum efficiency, as shown in Fig. 1. Consequently, the carrier concentration required for threshold is lower than in conventional diode lasers, due to many serially connected stages with uniform carrier injection over every stage. However, unlike intraband QC lasers, IC lasers use optical transitions between the conduction and valence bands with opposite dispersion curvatures (as shown in Fig. 1) without involving fast phonon scattering. Furthermore, based on type-II quantum well (QW) structures with possibly suppressed Auger recombination, non-radiative losses are reduced in IC lasers, making it possible to significantly lower threshold current density. Additionally, due to a large conduction-band offset and type-II band-edge alignment in the nearly lattice-matched InAs/GaSb/AlSb III-V material system that is used, excellent carrier confinement can be achieved in IC lasers and their emission wavelengths can be tailored in a wide wavelength range, in principle from the mid-IR (as short as 2.5 P m) to the far-IR. Following the proposal of IC lasers in 1994 [1] and be ing stimulated by the theoretically projected high performance of IC lasers [3-4] and remarkable early successes in developing intraband QC lasers [5-6], significant progress has been achieved in the development of IC lasers with the use of molecular beam epitaxy