Low effective electron mass InGaAs/InAlAs for high power terahertz quantum cascade lasers

• Published in: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) p. 1
• Main Authors: Kainz, M. A., Deutsch, C., Krall, M., Brandstetter, M., Bachmann, D., Schonhuber, S., Detz, H., MacFarland, D. C., Andrews, A. M., Strasser, G., Unterrainer, K.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.06.2017
• Subjects: Doping; Electron optics; Gallium arsenide; Lattices; Lenses; Power generation; Quantum cascade lasers
• DOI: 10.1109/CLEOE-EQEC.2017.8086429

Summary form only given. Quantum cascade lasers (QCLs) are powerful sources of coherent radiation covering the frequency range from mid-infrared to terahertz. In the terahertz frequency range the active region is normally realized using a GaAs/Al x Ga 1-x As semiconductor heterostructure. This material system enables a variable conduction band offset by changing the Al-content in the barrier layers without introducing a significant lattice mismatch between the barrier and well material. In comparison to the standard GaAs-based material system, active regions based on material systems with a lower effective electron mass are highly beneficial for the design of terahertz QCLs as the optical gain increases for a lower effective electron mass [1]. Promising material systems are based on InGaAs or InAs with an effective electron mass of 0.043 and 0.023, respectively, compared to that of GaAs (0.067) [2, 3].In this work we present a systematic study of growth related asymmetries for terahertz QCLs based on the InGaAs/InAlAs material system lattice matched on InP. A nominally symmetric active region enables the comparison of the positive and negative bias direction of the very same device [4]. With such bias dependent performance measurements asymmetries like dopant migration and interface roughness, which play a crucial role in this material system, are studied and result in a preferred electron flow in growth direction. A structure based on a three well optical phonon depletion scheme is optimized for this bias direction. Depending on the doping concentration the performance of the QCLs shows a trade-off between maximum operating temperatures and high output powers. While a peak output power of 151 mW is achieved for a sheet doping density of 7.3 x 1010 cm-2, the highest operation temperature of 155 K is found for 2 x 1010 cm-2. By further attaching a hyperhemispherical GaAs lens to a laser facet, the peak output power could be improved and reaches a record output power for double metal waveguide terahertz QCLs of almost 600 mW.