Matrix role in Ge nanoclusters embedded in Si_3N_4 or SiO_2

摘要

Ge nanoclusters (NCs), synthesized by ion implantation and annealing up to 900 ℃, result small (~2nm) and amorphous in Si_3N_4, crystalline and much larger in SiO_2. The NCs ripening and crystallization kinetics in Si_3N_4 is retarded by larger interfacial energy and lower diffusivity of Ge in comparison to SiO_2. Ge NCs absorb light more efficiently when embedded in Si_3N_4 than in SiO_2. A significant effect of the barrier height on absorption was evidenced, in agreement with effective mass theory predictions. The smaller bandgap of Ge NCs embedded in Si_3N_4 and their closeness is promising features for light harvesting applications.