Negative photoconductance in SiO2(Co)/GaAs heterostructure in the   avalanche regime
  In the avalanche regime we observed the negative photoconductance of heterostructures of silicon dioxide films containing cobalt nanoparticles grown on gallium arsenide, SiO2(Co)/GaAs. Light irradiation with the photon energy less than the bandgap energy of the GaAs creates holes trapped on defects within the GaAs bandgap, suppresses the avalanche feedback and causes a reduction of the current flowing in the SiO2(Co)/GaAs. 
L. V. Lutsev, V. V. Pavlov, P. A. Usachev, A. A. Astretsov, A. I.   Stognij, and N. N. Novitskii
cond-mat.mes-hall cond-mat.mtrl-sci