Negative magnetoresistance and electron localization in GaAs-AlAs superlattices

We report the negative magnetoresistance measured in GaAs-AlAs short-period superlattices. The samples were doped with silicon so that the electrical conductivity was controlled by the DX silicon donor. We take advantage of the metastable character of the DX states at low temperature to tune the conductivity by increasing the photoionization of the ground state DX- in the persistent photoconductivity regime. The magnetic correction is generally interpreted in terms of weak localization and electron-electron interaction according to the Kawabata and Altshuler theories of the magnetoresistance at low magnetic field in semiconductors. However, we find that these models, previously developed in pure 3D or 2D systems, cannot be strictly applied in superlattices showing anisotropic diffusion and low mobility. Conversely, we show that the self-consistent approach to electron localization recently proposed by Bryksin and Kleinert (BK) in anisotropic systems accounts properly for the experimental results.