We have recently determined that anomalously low diffusion of high dose As implants in SiO2 is caused by phase separation. In an inert ambient, As segregates into spherical As-rich droplets of 50 to 500Å in diameter, which are essentially immobile when heated isothermally, even at 1405 °C. In a temperature gradient the droplets move toward the heat source.
The dependence of the segregation rate, drift, and diffusion on-the ambient and arsenic concentration is discussed here, and a new interpretation of the published arsenic diffusion data is provided.