Tuning gaps and phases of a two-subband system in a quantizing magnetic field

In this work we study the properties of a two-subband quasi-two-dimensional electron system in a strong magnetic field when the electron filling factor is equal to four. When the cyclotron energy is close to the intersubband splitting the system can be mapped onto a four-level electron system with an effective filling factor of two. The ground state is either a ferromagnetic state or a spin-singlet state, depending on the values of the inter-level splitting and Zeeman energy. The boundaries between these phases are strongly influenced by the inter-electron interaction. A significant exchange-mediated enhancement of the excitation gap results in the suppression of the electron-phonon interaction. The rate of absorption of non-equilibrium phonons is calculated as a function of Zeeman energy and inter-subband splitting. The phonon absorption rate has two peaks as a function of intersubband splitting and has a step-like structure as a function of Zeeman energy

Laser spectroscopy of semiconductor quantum wells

SIGLEAvailable from British Library Document Supply Centre- DSC:D92676 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Magnetic g-factor of electrons in GaAs/AlGaAs quantum wells

The magnitude and sign of the effective magnetic splitting factor g* for conduction electrons in GaAs/AlxGa(1-x)As quantum wells have been determined as a function of well width down to 5 nm. The experimental method is based on combined measurements of the decay time of photoluminescence and of the suppression of its circular polarization under polarized optical pumping in a magnetic field perpendicular to the growth axis (Hanle effect). Measurements as a function of hole sheet density in the wells reveal a transition from excitonic behavior with very small apparent g value for low density, to larger absolute values characteristic of free electrons at higher densities. For 20-nm wells g* for electrons is close to the bulk value (-0.44), and increases for narrower wells passing through zero for well width close to 5.5 nm. A theoretical analysis based on three-band k.p theory, including allowance for conduction-band nonparabolicity and for wave-function penetration into the barriers, gives a reasonable representation of the data, leading to the conclusion that g* in quantum wells has a value close to that of electrons in the bulk at the confinement energy above the band minimum

Optical Detection Of Charge Redistribution In A δ Modulation-doped Gaas-alxga1-xas Heterojunction

We have investigated magnetically-induced charge redistribution within a δ modulation-doped GaAs-AlxGa1-xAs heterojunction structure by studying the photoluminescence due to electrons from the two-dimensional (2D) electron system recombining with photoexcited holes. At well defined values of magnetic field, charge transfer occurs between this 2D electron system and the V-shaped potential well formed in the AlxGa1-xAs by Si δ modulation-doping. This redistribution of charge is observed as discontinuities in the photoluminescence energies. From these measurements we have derived the characteristic transfer time for electrons to move between these two wells. © 1998 Published by Elsevier Science Ltd. All rights reserved.1094267271Clark, R.G., High Magnetic Fields in Semiconductor Physics III (1992) Springer Series in Solid State Sciences, 101, p. 231. , edited by G. Landwehr, Springer-Verlag, Berlin and references thereinGoldberg, B.B., (1992) Surf. Sci., 263, p. 9. , and references thereinGoldys, E.M., (1992) Phys. Rev. B, 46, p. 7957. , and references thereinEllis, M.K., (1992) Phys. Rev. B, 45, p. 13765. , and reference thereinKukushkin, I.V., (1992) Phys. Rev. B, 45, p. 30. , and references thereinKukushkin, I.V., Von Klitzing, K., Ploog, K., Timofeev, V.B., (1989) Phys. Rev. B, 40, p. 7788Pulsford, N.J., Kukushkin, I.V., Hawrylak, P., Ploog, K., Haug, R.J., Von Klitzing, K., Timofeev, V.B., (1992) Phys. Stat. Sol., 173, p. 271Hayne, M., Usher, A., Plaut, A.S., Ploog, K., (1994) Phys. Rev. B, 50, p. 17208Domínguez-Adame, F., Méndez, B., Maciá, E., (1994) Semicond. Sci. Technol., 9, p. 263Dite, A.F., Kukushkin, I.V., Timofeev, V.B., Filin, A.I., Klitzing, V.K., (1991) Pis'ma Zh. Eksp. Teor. Fiz., 54, p. 393(1991) JETP Lett., 54, p. 389Aspnes, D.E., Kelso, S.M., Logan, R.A., Bhat, R., (1986) J. Appl. Phys., 60, p. 75