Short wavelength InAs-based QC Lasers Roland Teissier, Jan Devenson, Olivier Cathabard, and Alexei N. Baranov Abstract—We report on recent progress in the development of InAs/AlSb QCLs. The large conduction band offset of this material system allowed the fabrication of the first QCLs emitting below λ=3 µm. Devices operating at high temperature in the whole wavelength range from 3 to 5 µm are presented. Index Terms—Quantum cascade laser, mid-infrared, InAs, AlSb I. INTRODUCTION NP-based QCL is today a dominant technology for mid-IR semiconductor lasers. However, intrinsic material properties — namely, insufficient conduction band offset and lateral valleys position — makes difficult the realization of efficient lasers below λ~4 µm. For eight years, the shortest wavelength QCL emission was about 3.5 µm [1]. The year 2006 has seen remarkable breakthroughs with three different technologies approaching the wavelength mark of 3 µm: InGaAs/AlAsSb lattice matched on InP at University of Sheffield [2]; strained (Ga)InAs/Al(In)As heterostructures grown on InP at Humboldt University of Berlin [3]; and InAs/AlSb on InAs substrate at University of Montpellier [4]. Here, we present InAs/AlSb devices which push back the short wavelength frontier of QCLs well below 3 µm. We also demonstrate a new generation of InAs/AlSb QCLs operating in the spectral range of 3 to 5 µm with considerably improved performances. II. RECORD SHORT WAVELENGTH QCL We reported recently the first QCL below the wavelength of 3 µm [5], with an emission peak of 2.95 µm at cryogenic temperature. The InAs/AlSb heterostructures were grown on InAs substrates by solid source molecular beam epitaxy. The QCL employed a plasmon enhanced waveguide consisting in heavily doped InAs cladding layers separated from the active zone by short period InAs/AlSb superlattices. The active zone of the devices was based on a vertical transition in three active quantum wells (Fig.1). Authors are with Institut d’Électronique du Sud, CNRS and Université Montpellier 2, Montpellier, F-34095 France (e-mail: roland.teissier@ies.univ- montp2.fr ). Using a similar design with a suitable scaling of InAs layer thicknesses we obtained room temperature QCL emission below λ=3 µm and a new record laser emission at a wavelength of 2.75 µm at low temperature (Fig.2). 0 100 200 300 400 500 600 0 500 1000 1500 Energy (meV) Distance (Å) F=120 kV/cm e3 e2 Fig. 1. Typical active region of the short wavelength InAs/AlSb QCLs, designed for an emission at 3.1 µm. III. HIGH TEMPERATURE OPERATION OF SHORT WAVELENGTH QCLS Up to now, InAs/AlSb QCLs [4][6] did not exhibit performances at the level expected from the attractive intrinsic properties of theses materials which are: a high conduction band offset of 2.1 eV, a large Г-L separation of >0.73 eV and a small electron effective mass of 0.023 m 0 in InAs. Further than a much lower short wavelength limit, this should lead to I 0,0 0,5 1,0 1,5 0 5 10 15 20 25 0 100 200 300 2.6 2.7 2.8 2.9 Wavelength (μm) T=79K 130K 120K 110K 100K 80K Voltage (V) Current (A) 80K D391 100 ns / 1 kHz 12 μm x 3.48 mm T=80K Peak power (mW) Fig. 2. Voltage-current and light-current characteristics of a InAs/AlSb QCL emitting at a wavelength of 2.75 µm.