Negative photoconductivity and memory effects of germanium nanocrystals embedded in HfO 2 dielectric

A metal-insulator-semiconductor (MIS) structure containing an HfO 2/SiO 2 stack tunnel layer, isolated Germanium (Ge) nanocrystals, and an HfO 2 capping layer, was obtained by an electron-beam evaporation method. A high-resolution transmission electron microscopy (HRTEM) study revealed that uniform and pronounced Ge nanocrystals had formed after annealing. Raman spectroscopy provided evidence for the formation of Ge-Ge bonds and the optimal annealing temperature for the crystallization ratio of the Ge. The electric properties of the MIS structure were characterized by capacitance-voltage (C-V) and current-voltage (I-V) measurements at room temperature. Negative photoconductivity was observed when the structure was under a forward bias, which screened the bias voltage, resulting in a decrease in the current at a given voltage and a negative shift in flat band voltage. A relatively high stored charge density of 3.27×10 12 cm -2 was also achieved.