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HL: Halbleiterphysik

HL 22: Halbleiterlaser

HL 22.2: Vortrag

Dienstag, 12. März 2002, 15:30–15:45, H13

Quantum cascade lasers with blocking barriers in the active regions — •C. Mann, Q. K. Yang, F. Fuchs, R. Kiefer, K. Köhler, and H. Schneider — Fraunhofer-Institut für Angewandte Festkörperphysik, Tullastrasse 72, D-79108 Freiburg, Germany

Quantum cascade lasers (QCLs) are unipolar mid- to far-infrared semiconductor lasers in which the laser transition occurs between quantized conduction-band states in a series of coupled quantum wells. Typically several tens of active regions connected by injectors are cascaded. In our contribution we report on a new design of QCLs improving the concept of Bragg reflectors by incorporating “blocking barriers” into the active region to significantly enhance the confinement of electrons in the initial state of the laser transition. We have kept all the advantages of λ∼ 5 µm QCLs (25 periods) employing the GaInAs/AlInAs/InP material system as published in [1] and substituted the AlInAs exit barrier by a triple layer sequence composed of AlAs (blocking barrier) sandwiched between equally thin AlInAs layers. To maintain the high tunneling probability out of the lower state the thickness of this triple layer was reduced appropriately. After growth (combining molecular beam epitaxy with metal-organic chemical vapor deposition) and processing of the wafers into ridge waveguide structures, lasers were cleaved and mounted substrate-side down on copper heat-sinks. The devices operate in pulsed mode up to 350 K with the threshold current density increasing exponentially from 1.6 kA/cm² at 77 K to 10.3 kA/cm² at 350 K. The maximum peak power per facet decreases from 900 mW to 2 mW.

[1] J. Faist et al., Appl. Phys. Lett. 68, 3680 (1996)