Intersubband gain and stimulated emission in long-wavelength (/spl lambda/=13 /spl mu/m) intersubband In(Ga)As-GaAs quantum-dot electroluminescent devices

The dynamics of injected carriers and the conditions for intersubband gain and population inversion in In(Ga)As-GaAs self-organized quantum dots have been studied. Direct femtosecond pump-probe spectroscopy as a function of temperature and excitation density confirms earlier results and shows a long (>100 ps) electron relaxation time between the excited states and ground state in the dots. Intersubband gains as high as 170 cm/sup -1/ are calculated in the dots. Far-infrared spontaneous emission centered around 13 /spl mu/m is observed in edge-emitting light-emitting diodes. Stimulated emission, with a distinct threshold around 1.1 kA/cm/sup 2/ in the light-current characteristics, is observed in plasmon-enhanced waveguide devices. The intersubband threshold occurs after a threshold is observed for interband lasing (/spl sim/1 /spl mu/m) in the same device.