SPONTANEOUS FAR-IR EMISSION ACCOMPANYING TRANSITIONS OF CHARGE-CARRIERS BETWEEN LEVELS OF QUANTUM DOTS

The spontaneous emission of far-infrared radiation (lambda congruent t o 10-20 mu m) from diode structures with vertically coupled InGaAs/AlG aAs quantum dots is observed. This emission is due both to transitions of holes and electrons between size-quantization levels in quantum do ts and to transitions from the continuum to a level in a quantum dot. It is observed only when accompanied by lasing at short wavelengths (l ambda congruent to 0.94 mu m) and, like the short-wavelength emission, it exhibits a current threshold. The spontaneous emission of long-wav elength radiation is also observed in InGaAs/GaAs quantum-well laser s tructures. This radiation is approximately an order of magnitude weake r than that from quantum-dot structures, and it has no current thresho ld. (C) 1998 American Institute of Physics.