Fingerprints of spatial charge transfer in quantum cascade lasers

Abstract

We show that mid-infrared transmission spectroscopy of a quantum cascade laser provides clear-cut information on changes in charge location at different bias. Theoretical simulations of the evolution of the gain/absorption spectrum for a ϳ 7.4 m InGaAs/AlInAs/InP quantum cascade laser have been compared with the experimental findings. Transfer of electrons between the ground states in the active region and the states in the injector goes hand in hand with a decrease of discrete intersubband absorption peaks and an increase of broad, high-energy absorption toward the continuum delocalized states above the barriers.

Valence intersubband gain without population inversion

“…Detrimental cross absorption due to higher (empty) hole subbands is taken into account. Before proceeding further the following point should be highlighted: very good agreement with experiments has been obtained by considering electron-phonon and electron-impurity scattering as the main origin of dephasing in mid infrared systems [18][19][20]. Interface roughness scattering also plays a role even in THz systems, however this effect depends on sample quality [21,22] and the inclusion of sample quality considerations would be beyond the scope of this paper.…”

Intervalence transverse-electric mode terahertz lasing without population inversion

“…The current NEGF simulators for qcls do not take into account details of the interplay between manybody and band coupling effects and do not include carriercarrrier scattering. 15,24,25 Therefore, they cannot be used. Band coupling is required for two reasons.…”

Intersubband gain without global inversion through dilute nitride band engineering

“…Finally, absorption and gain are given by the solution of the integro-differential equation for ͑k , ͒ obtained from the carriers Green's function in linear response. 9,[22][23][24] The numerical matrix inversion technique used to solve this equation is similar to the interband method used in Ref. 25.…”