Conduction electrons localized by charged magneto-acceptors A$^{2-}$ in GaAs/GaAlAs quantum wells

摘要

A variational theory is presented of A$^{1-}$ and A$^{2-}$ centers, i.e. of anegative acceptor ion localizing one and two conduction electrons,respectively, in a GaAs/GaAlAs quantum well in the presence of a magnetic fieldparallel to the growth direction. A combined effect of the well and magneticfield confines conduction electrons to the proximity of the ion, resulting indiscrete repulsive energies above the corresponding Landau levels. The theoryis motivated by our experimental magneto-transport results which indicate that,in a heterostructure doped in the GaAs well with Be acceptors, one observes aboil-off effect in which the conduction electrons in the crossed-fieldconfiguration are pushed by the Hall electric field from the delocalized Landaustates to the localized acceptor states and cease to conduct. A detailedanalysis of the transport data shows that, at high magnetic fields, there arealmost no conducting electrons left in the sample. It is concluded that onenegative acceptor ion localizes up to four conduction electrons.