Negative magnetoresistance of Beδ-doped GaAs structures

Abstract

Magnetotransport properties of Be $\ensuremath{\delta}$-doped structures grown by molecular-beam epitaxy have been studied in the temperature range from $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ to room temperature. In the structure, an ultrathin low-temperature-grown GaAs layer or Se $\ensuremath{\delta}$-doped layer are placed in the vicinity of a Be $\ensuremath{\delta}$-doped layer, which results in a strong localization of holes at deep levels of the Be $\ensuremath{\delta}$-doped layer. With an applied magnetic field perpendicular to the $\ensuremath{\delta}$-doped layer, positive magnetoresistance is observed at all measured temperatures. With an applied magnetic field parallel to the $\ensuremath{\delta}$-doped layer, on the other hand, negative magnetoresistance occurs from room temperature to nearly $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, below which magnetoresistance changes into positive values. The negative magnetoresistance with a parallel magnetic field results from localized spins in the Be $\ensuremath{\delta}$-doped layer. Bumps of curves of magnetoresistance are observed with parallel magnetic fields in the temperature range from $50\phantom{\rule{0.3em}{0ex}}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which suggests the possibility of antiferromagnetic alignments of the spins in $\ensuremath{\delta}$-doped layer.