Trimodal island distribution of Ge nanodots on (001)Si

Abstract

Molecular beam epitaxy (MBE) grown Ge nanodots are found to come in a clear trimodal island distribution of huts, pyramids, and domes when grown on (001)Si at 550°C. The island types appear in this order as Ge coverage increases and for a certain coverage all three types are found to coexist at this growth temperature. Previously Ge nanodots have mostly been divided into huts and domes at growth temperatures below 600°C, or pyramids and domes above 600°C. The {105} faceted pyramidal and elongated huts and the multifaceted domes are well known, but a distinction has not previously been seen between huts and a separate size distribution of similarly {105}-faceted pyramidal nanodots twice the size of huts, at temperatures below 600°C. The 20–25nm wide huts also appear to be the smallest obtainable self-assembled Ge dots on (001)Si, in accordance with predictions based on Si1−xGex nanodots on (001)Si. They are about a factor of two too large for quantum dot applications.