Electrical study of memory effects in InAs quantum dots embedded in SiO2 on silicon substrates

Memory structures based on InAs nanocrystals directly grown by molecular beam epitaxy (MBE) on SiO₂ have been studied. The nanocrystals have a typical diameter of 5 nm and the density is about 2 times 10¹¹ cm^-2. High resolution TEM measurements have shown high crystalline quality and low size dispersion. Using these 7 nm-quantum dots, a test structure with a 3.5 nm-thick SiO2 tunnel oxide and a 10 nm-thick control oxide has been processed for data retention measurements. We have observed that 80 % of the initial injected electrons are still stored after three months. These results for the retention time of electrons in InAs nanocrystals are much better than comparable structures with silicon or germanium quantum dots. Finally, we demonstrate that an optimized structure with 3.5 nm-thick tunnel oxides, 10 nm-in diameter nc-InAs and 7 nm-thick control oxides could fill the industrial requirements for nonvolatile memories in terms of W/E time, W/E operating voltage and data retention.