Narrow-linewidth terahertz intersubband emission from three-level systems

Narrow-linewidth terahertz spontaneous emission resulting from interwell (o r diagonal) intersubband transition from an electrically pumped multiple-qu antum-well structure was observed. The center frequency of the emission pea k is at 2.57 THz, and its full width at half maximum is 0.47 THz. The emiss ion frequency is in good agreement with the calculated intersubband transit ion energy of 11.3 meV (corresponding to 2.7 THz) in a three-level system, which was designed to achieve population inversion between two radiative le vels. (C) 1999 American Institute of Physics. [S0003-6951(99)05345-0].