Experimental and theoretical studies of weak localization effects in superlattices

Abstract

Weak localization effects have been studied experimentally and theoretically in semiconductor superlattices. Low temperature parallel magnetotransport measurements of GaAs/AlGaAs multilayer periodic structures have revealed positive magnetoconductance. The magnitude of this effect, ascribed to weak localization phenomenon, has been found correlated with the superlattice miniband structure. Hence, the standard theory of weak localization in 2-D does not explain the experimental data. Consequently, a theory of weak localization in superlattices has been formulated and developed in order to quantitatively study the observed effects. This theory explicitly accounts for the highly anisotropic 3-D nature of semiconductor superlattices. It incorporates coherent transport through the superlattice potential barriers, electron wave function modulation, impurity distribution, and higher order effects of magnetic field. The experimental data of magnetoconductivity is reproduced very well by this theory. By fitting the theoretical curves to the data, the dephasing time is derived which follows the temperature dependence predicted for electron-electron scattering in 3-D anisotropic systems. Also, the temperature behavior of zero-field conductivity is self-consistently explained by the theoretical calculations. This analysis demonstrates the influence of the superlattice structure on parallel charge conduction. In addition, detailed studies of impurity distribution effects show that the theory provides the best explanation of the experiments if one assumes uniform distribution of short-range impurities rather than a nonuniform distribution corresponding to the doping profile of the measured superlattices. This is interpreted as a modification of weak localization by the weakly screened Coulomb scattering from ionized dopants and indicates the importance of long-range potential effects in this phenomenon.