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

Landau levels and shallow donor states in multiple GaAs/AlGaAs quantum wells (MQWs) are investigated by means of the cyclotron resonance at megagauss magnetic fields. Measurements of magneto-optical transitions were performed in pulsed fields up to 140 T and temperatures from 6–300 K. The ${\displaystyle 14\times 14}$ P${\displaystyle ·}$p band model for GaAs is used to interpret free-electron transitions in a magnetic field. Temperature behavior of the observed resonant structure indicates, in addition to the free-electron Landau states, contributions of magnetodonor states in the GaAs wells and possibly in the AlGaAs barriers. The magnetodonor energies are calculated using a variational procedure suitable for high magnetic fields and accounting for conduction band nonparabolicity in GaAs. It is shown that the above states, including their spin splitting, allow one to interpret the observed magneto-optical transitions in MQWs in the middle infrared region. Our experimental and theoretical results at very high magnetic fields are consistent with the picture used previously for GaAs/AlGaAs MQWs at lower magnetic fields.

Figure 1

Optical magnetotransmission (solid curves) and magnetic field intensity (dotted curves) versus time for three temperatures and laser wavelength ${\displaystyle {\lambda }_2=9.69\mu \mathrm{m}}$.

Figure 2

Resonance curves versus magnetic field for ${\displaystyle {\lambda }_2=9.69\mu \mathrm{m}}$ at three temperatures obtained at decreased magnetic field. Arrows indicate position ICR and CR peaks, dashed arrows indicate weakly pronounced peaks.

Figure 3

Resonance curves versus pulsed magnetic field recorded for ${\displaystyle {\lambda }_2=10.59\mu \mathrm{m}}$ at three temperatures obtained at decreased magnetic field. Arrows indicate positions of ICR and CR peaks, dashed arrows indicate weakly pronounced peaks.

Figure 4

Cyclotron resonance and MD cyclotron resonance transitions for both spin orientation. It is seen that for the LL number of 0 the $0-$ is higher as 0+ and in the case of LL number 1 is contrary the 1+ is higher as ${\displaystyle 1-}$.

Figure 5

Magneto-optical transition energies calculated including spin splitting according to theory presented in Sec. III and experimental data obtained at 6 K: full squares are our data, circles and crosses are data of Ref. [7].

Figure 6

Positions of resonance peaks at 70 K for wavelengths ${\displaystyle {\lambda }_1}$ and ${\displaystyle {\lambda }_2}$ and theoretical lines versus magnetic field.