LANDAU-LEVEL LIFETIMES IN AN INAS ALSB QUANTUM-WELL DETERMINED BY A PICOSECOND FAR-INFRARED PUMP-PROBE TECHNIQUE/

We present measurements of Landau level lifetimes in a doped quantum w ell structure of InAs/AlSb using a combination of pump-probe and satur ation spectroscopy measurements. The cyclotron resonance was studied u sing far-infrared radiation from a free-electron laser has yielded the energy relaxation lifetime as a function of applied magnetic field, i n the range h omega(c) = 14.5 to 18.5 meV. An energy of 15 meV corresp onds to the magnetophonon resonance Delta l h omega(c) = h omega(LO) w ith Delta l=2. The lifetime at this energy is at or below the resoluti on limit of the pump-probe measurement: which is 10 ps. The results bo th at T = 4 K and 80 K, show that the Landau level lifetime, tau is 50 +/- 5 ps off resonance. The so-called ''LO phonon bottleneck'' is evi dently important in quenching the relaxation away from resonance.