Landau levels and shallow donor states in GaAs/AlGaAs multiple quantum wells at mega-gauss magnetic fields

摘要

Landau levels and shallow donor states in multiple GaAs/AlGaAs quantum wells(MQWs) are investigated by means of the cyclotron resonance at mega-gaussmagnetic fields. Measurements of magneto-optical transitions were performed inpulsed fields up to 140 T and temperatures from 6 to 300 K. The $14\times14$\textbf{P}$\cdot$\textbf{p} band model for GaAs is used to interpretfree-electron transitions in a magnetic field. Temperature behavior of theobserved resonant structure indicates, in addition to the free-electron Landaustates, contributions of magneto-donor states in the GaAs wells and possibly inthe AlGaAs barriers. The magneto-donor energies are calculated using avariational procedure suitable for high magnetic fields and accounting forconduction band nonparabolicity in GaAs. It is shown that the above states,including their spin splitting, allow one to interpret the observedmagneto-optical transitions in MQWs in the middle infrared region. Ourexperimental and theoretical results at very high magnetic fields areconsistent with the picture used previously for GaAs/AlGaAs MQWs at lowermagnetic fields.