We study the magnetoresistance (MR) of the high-mobility 2D electron gas (2DEG) in a GaAs quantum well with AlAs/GaAs superlattice barriers [1] in linear and nonlinear regimes. The selectively doped structures under study were grown using molecular beam epitaxy (MBE) on (100) GaAs substrates. The width of the GaAs quantum well was 13 nm. It has been found that, as the measuring current I increases, the MR becomes negative in the range of classically strong magnetic fields. It has been shown that the observed negative MR is due to the transport of the 2DEG in the nonlinear regime. The current–voltage (I-V) characteristic for Hall bar devices becomes nonlinear as the magnetic field increases. In the presence of magnetic field, with an increase in I, the slope of the I-V characteristic becomes equal to the slope of the I-V characteristic in zero magnetic field. The I value above which the slope of the I-V characteristic becomes equal to one in zero magnetic field, is determined by the correlation length of the scattering potential [2]. We estimated the correlation length of the scattering potential in our samples as 5–10 nm. This estimates coincides by order of magnitude with the distance between the GaAs quantum well and delta-doped layers in our structures and it agrees with the generally accepted estimates of the correlation length of the scattering potential in high-mobility structures with modulated doping. Our results are consistent with the theory of the magnetotransport of the high-mobility 2DEG with large filling factors in the nonlinear regime [2]. Thus, it has been shown that the observed negative MR in the nonlinear regime can be used to find the correlation length of scattering potential in high-mobility modulated doping structures.
This work was supported by the RFBR, project no. 04-02-16789.

[1] K.-J. Friedland, R. Hey, et al., Phys. Rev. Lett. 77, 4616 (1996).
[2] M. G. Vavilov and I. L. Aleiner, Phys. Rev. B 69, 035303 (2004).

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