Nonparabolic effective masses of conduction subbands in InGaAs/InAlAs quantum wells in normal and parallel directions

Nonparabolic effective masses of conduction electrons were comprehensively studied in two-dimensional InGaAs quantum wells (QWs) deeply confined within InAlAs barriers of the 0.52-eV band offset. Cause of nonparabolicity was attributed not to the penetration of wavefunctions into barriers but to the InGaAs bulk band structure of bandgap energy of 0.74 eV. Band calculations by a Kane's three-level model for narrow-gap semiconductors and a Zawadzki's model under Landau quantization modified for QW confinement were fairly compared with in-plane apparent cyclotron masses of electrons measured in a 10-nm-wide InGaAs QW. Simulation of optical transmittance through complex epitaxial wafer structures fit quite well with cyclotron resonance experiments. Masses normal to the QW plane were also determined from a series of eigen-energies observed in 20-nm-wide InGaAs QW. In-plane nonparabolicity was found to be several times larger than normal nonparabolicity.