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The intersubband transition (IT) in GaAs/Alo3Ga07As multiple-quantum-well samples measured by the infrared-absorption technique at 5 K is studied as a function of the two-dimensional electron-gas density (cr) Ab. lueshift in the peak-position energy of the IT is observed as o increases. Single-particle calculations of the optical-absorption spectra, which are obtained by using the nonparabolic-anisotropic envelope-function approximation (EFA), indicate that the peakposition energy should show a redshift as cx is increased. %'e found that it is necessary to incorporate many-body corrections (in particular electron-electron intrasubband exchange and direct Coulomb interaction energies), depolarization, and excitonlike shifts in the EFA calculations in order to account for the experimental peak-position energy and blueshift as o. is increased.

Temperature and many-body effects on the intersubband transition in a GaAs/Alo 3Ga07As multiple quantum well are studied using the infrared-absorption technique and the envelope-functionapproximation method. In order to explain the measured peak position energy of the intersubband transition and its blueshift observed by decreasing temperature and/or increasing the two-dimensional electron-gas density, a theoretical model is developed which is based on a nonparabolic-anisotropic envelope-function-approximation (NAEFA) method. This model takes into account the many-body corrections, in particular, temperature-dependent electron-electron intrasubband and intersubband exchange and direct Coulomb interaction energies as well as the depolarization and excitonlike shifts within the framework of Zaluzny's implementation of Ando's formalism [Phys. Rev. B 43, 4511 11991)].Temperature-dependent effective masses, nonparabolicity, conduction-band offsets, the Fermi level, and line-shape broadening are also incorporated in the present NAEFA calculations. Our theory provides a qualitative explanation for the magnitude of the measured temperature blueshift. Additional support for many-body effects is obtained by utilizing the persistent photoeffect measurements.

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