Relaxation processes of the light-induced giant injection magnetoresistance in semiconductor/granular-film heterostructures with cobalt nanoparticles

We have studied relaxation processes of the photocurrent and the light-induced giant injection magnetoresistance (${\mathrm{IMR}}^{(ph)}$) in ${\mathrm{SiO}}_{2}(\mathrm{Co})/\mathrm{GaAs}$ heterostructures, where the ${\mathrm{SiO}}_{2}(\mathrm{Co})$ structure is the granular ${\mathrm{SiO}}_{2}$ film with Co nanoparticles, and have found that the photocurrent is accompanied by relaxation oscillations. Relaxation oscillations are caused by transitions between the photocurrent and electrons on the highest level in the interface quantum well. The light-induced magnetoresistance ${\mathrm{IMR}}^{(ph)}$ reaches the maximum value in the avalanche onset region and has the local minimum at the higher voltage. It is found that the local minimum can been explained by delocalization of the highest level in the interface quantum well and by decrease of the probability of the backscattering process of injected electrons on deeper levels. ${\mathrm{SiO}}_{2}(\mathrm{Co})/\mathrm{GaAs}$ heterostructures are proposed to use as efficient fast-response magnetic sensors operating without hysteresis at room temperature.