Saturation spectroscopy of electronic states in a magnetic field in InAs / Al x Ga 1 ~ x Sb single quantum wells

We have carried out saturation spectroscopy of cyclotron resonance in a semiconducting InAs/Al Ga Sb single quantum well using the UCSB free electron laser and have extracted an effective Landau level lifetime using an n-level rate equation model. The effective lifetime shows strong oscillations ('an order of magnitude) with frequency. Minima are shifted to higher frequencies than those given by the simple parabolic magnetophonon resonance condition due to large nonparabolicity in the InAs conduction band. We have also used this technique to investigate the origins of two lines: the X-line and cyclotron resonance in a " semimetallic " InAs/Al Ga Sb single quantum-well structure. Results show that the two lines are of different origin. 1998 Elsevier Science B.V. All rights reserved. Saturation spectroscopy has been used in the last few years to determine Landau level (LL) lifetimes in various semiconductor systems [1,2,8]. Such investigations provide important information about fundamental energy loss mechanisms of carriers in high magnetic fields. The effective LL lifetime was found to depend inversely on the electron concentration in a GaAs/AlGaAs single heterostructure [3]. Recently, Vaughan et al. [2] have observed an oscillatory behavior of LL lifetime as a function of frequency (between 11 and 40 meV) in a semimetal-lic InAs/GaSb double heterojunction (40 nm InAs well). Minima occur approximately at the mag-netophonon resonance (MPR) condition, N " *-, N"1, 2 2 , and ". Here is the cyclotron resonance (CR) energy in the vicinity of the Fermi energy and *-is the LO-phonon energy (242 cm\) in InAs. Analysis is complicated in this case by the fact that the sample is semimetal-lic (the valence band in GaSb is higher in energy than the conduction band in InAs) and has low mobility. In addition, the duration of the laser