Ultra-low-energy ion-beam-synthesis of Ge nanocrystals in thin ALD Al2O3 layers for memory applications

Structural and electrical properties of ALD-grown 5 and 7nm-thick Al"2O"3 layers before and after implantation of Ge ions (1keV, 0.5-1x10^1^6 cm^-^2) and thermal annealing at temperatures in the 700-1050^oC range are reported. Transmission Electron Microscopy reveals the development of a 1nm-thick SiO"2-rich layer at the Al"2O"3/Si substrate interface as well as the formation of Ge nanocrystals with a mean diameter of ~5nm inside the implanted Al"2O"3 layers after annealing at 800^oC for 20min. Electrical measurements performed on metal-insulator-semiconductor capacitors using Ge-implanted and annealed Al"2O"3 layers reveal charge storage at low-electric fields mainly due to location of the Ge nanocrystals at a tunnelling distance from the substrate and their spatial dispersion inside the Al"2O"3 layers.