Dresden 2003 – scientific programme

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HL: Halbleiterphysik

HL 10: Halbleiterlaser II

HL 10.4: Talk

Monday, March 24, 2003, 16:00–16:15, BEY/81

Subband population in GaAs/Al_0.33Ga_0.67As quantum-cascade structures — •Lutz Schrottke, Rudolf Hey, Helmar Kostial, Tomohiko Ohtsuka, and Holger T. Grahn — Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin

For a detailed understanding of quantum-cascade lasers (QCLs), an independent experimental determination of their basic processes is necessary. We have determined the population of the laser levels using interband photoluminescence (PL) spectroscopy. In these experiments, photoexcited holes serve as a probe for the electrically injected electrons in the conduction subbands. From the characteristic times for the hole transfer through the barriers, which have been estimated from time-resolved PL studies on double-quantum-well superlattices, we conclude that in the QCL structures the holes quickly relax into the ground state of the widest quantum well in the optically active region. Therefore, the PL spectra reflect only transitions from the two laser levels and the lowest conduction subband into the hole ground state of the widest well. Surprisingly, the occupation of the laser levels appears to be correlated with a bistable behavior of the current.