Third-order optical nonlinearity and negative photoconductivity of Ge nanocrystals in Al2O3dielectric

Germanium (Ge) nanostructures embedded in Al 2 O 3 dielectric are synthesized by the vacuum electron-beam co-evaporation method. A clear blue-shift of the absorption edge and a large third-order nonlinear optical susceptibility are observed due to the quantum confinement effects. Current–voltage and capacitance–voltage characteristics of metal–insulator–semiconductor structures containing Ge nanocrystals are studied in the dark and under illumination. Negative photoconductivity due to the screening effects of the negatively charged Ge nanocrystals is experimentally demonstrated.