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

The dynamics of injected carriers and the conditions for intersubband gain and population inversion in ln(Ga)As-GaAs self-organized quantum dots have been studied. Direct femtosecond pump-probe spectroscopy as a function of t emperature 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(-1) are calculated in the dots. Far-infrared spontaneous emission centered around 13 mum is ob served in edge-emitting light-emitting diodes. Stimulated emission, with a distinct threshold around 1.1 kA/cm(2) in the light-current characteristics , is observed in plasmon-enhanced waveguide devices. The intersubband thres hold occurs after a threshold is observed for interband lasing (similar to1 mum) in the same device.