Population inversion by resonant tunneling in quantum wells

A terahertz quantum cascade laser based on a single quantum well active region is reported. It displays laser action at 3.74 THz with low threshold current densities around 30 A/cm(2). Analysis of the optical and electrical characteristics and their comparison with a transport model based on a density matrix approach clearly demonstrate the role of resonant tunneling for both injection and extraction of the electrons from the upper and lower states of the laser transition. (C) 2007 American Institute of Physics.