Negative magnetoresistance of Be δ -doped GaAs structures

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