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 (similar to 100ps) 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)x 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 mum) 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.