Synthesis of Germanium Nanocrystals and Its Possible Application in Memory Devices

A novel method of synthesizing and controlling the size of germanium nanocrystals was developed. A tri-layer structure comprising of a thin (~5nm) SiO2 layer grown using rapid thermal oxidation (RTO), followed by a layer of Ge+SiO2 of varying thickness (6 20 nm) deposited using the radio frequency (r.f.) co-sputtering technique and a SiO2 cap layer (50nm) deposited using r.f. sputtering, was investigated. It was verified using TEM that germanium nanocrystals of sizes ranging from 6 – 20 nm were successfully fabricated after thermal annealing of the tri-layer structure under suitable conditions. The nanocrystals were found to be well confined by the RTO SiO2 and the cap SiO2 under specific annealing conditions. The electrical properties of the tri-layer structure have been characterized using MOS capacitor test devices. A significant hysteresis can be observed from the C-V measurements and this suggests the charge storage capability of the nanocrystals. The proposed technique has the potential for fabricating memory devices with controllable nanocrystals sizes.