Observation of nonparabolic conduction subbands in InGaAs/InAlAs multi-quantum wells by very-high-field pulse cyclotron resonance

Observation of nonparabolic conduction band is rather difficult because ele ctrons normally occupy near the bottom of conduction band. Use of two-dimen sional electron gas and Landau quantization made it possible to scan equiva lent electron energy by a magnetic field. We report a cleat evidence of a n on-parabolic conduction subband in 5-10 nm wide InGaAs quantum wells in InG aAs/InAlAs multi- quantum well structures. Infrared optical transitions due to cyclotron resonance take place under pulsed high magnetic fields up to 100 T. In experiments, electron absorption is discriminated by a circular p olarized light of a carbon dioxide laser. Water and methanol vapor lasers w ere also used to measure the mass of low-energy electrons. Measurements wer e made near 30 K. (C) 2001 Elsevier Science B.V. All rights reserved.