Carrier dynamics in self-organized quantum dots have been studied using temperature-dependent differential transmission spectroscopy and room temperature high-frequency electrical impedance measurements on quantum dot lasers. These results suggest the existence of a long relaxation time (∼100 ps) for the excited state carriers at higher temperatures with the dominant scattering mechanism being electron–hole scattering. The long relaxation time is exploited to realize far-infrared sources and detectors based on intersubband transitions in quantum dots. Quantum dot detectors with large detectivity ( D ∗ =(9–10) ×10 9 cm Hz 1/2/W) and responsivity ( R =100 mA/W ) have been reported at T =40 K . A unique unipolar intersubband quantum dot laser (13.3 μm) has also been reported at T =283 K , using the long intersubband relaxation time and the short interband recombination time to achieve population inversion between the ground and the excited states.