We demonstrate circular-shaped microcavity quantum-cascade lasers emitting in the THz region between 3.0 and 3.8 THz. The band structure design of the GaAs∕Al0.15Ga0.85As heterostructure is based on longitudinal-optical phonon scattering for depopulation of the lower radiative state. A double metal waveguide is used to confine the whispering gallery modes in the gain medium. The threshold current density is 900A∕cm2 at 5 K. Lasing takes place in pulsed-mode operation up to a heat-sink temperature of 140 K.
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Fasching et al. (2005) studied this question.
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