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HL: Halbleiterphysik

HL 10: Halbleiterlaser II

HL 10.3: Vortrag

Montag, 24. März 2003, 15:45–16:00, BEY/81

Lasing properties of GaAs/(Al,Ga)As quantum-cascade lasers as a function of injector doping density — •Manfred Giehler, Rudolf Hey, Helmar Kostial, Swen Cronenberg, Tomohiko Ohtsuka, Lutz Schrottke, and Holger T. Grahn — Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin

Lasing properties of GaAs/Al_0.33Ga_0.67As quantum-cascade lasers (QCLs) are investigated as a function of injector doping concentration n_s between 3.5 and 10×10¹¹ cm⁻². Optimal lasing was observed for n_opt ≈ 6×10¹¹ cm⁻², where the threshold current exhibits a minimum and the characteristic temperature as well as the operating temperature show a maximum. Furthermore, at n_opt the QCLs display the highest lasing energy E₀ of 135 meV, whereas for QCLs with lower and higher doping levels E₀ is up to 20 meV red-shifted. The existence of an optimum value n_opt can be explained because an increasing n_s increases the current and therewith the gain, but also increases the losses due to the scattering of electrons from the injector back into the active region and due to free carrier absorption. The dependence of E₀ on n_s cannot be explained by the influence of n_s on the field distribution, it may be partly due to an occupation of levels above the upper laser level for high n_s values.