Raman and photoluminescence characterization of Ge nanocrystals in co-sputtered Ge+SiO2 system

Raman and photoluminescence (PL) results of Ge nanocrystals prepared from c o-sputtered Ge + SiO2 samples under rapid-thermal annealling (RTA) with dif ferent annealing conditions are presented. The Raman results showed a trans ition from amorphous to nanocrystalline Ge when the samples were annealed a t a temperature higher than 700 degreesC for longer than 300 s. The Raman s pectrum of sample annealed at 1000 degreesC is very similar to that of the as-deposited amorphous sample. However, when the annealing duration is redu ced to less than 50 s, clear Raman signals can be seen for samples annealed at 1000 degreesC. Transmission electron micrographs showed that uniform Ge nanocrystals were obtained for samples annealed at 800 degreesC for 300 s or 1000 'C for 50 s, and nanocrystals with multiple twinned structure (of d iameter similar to 200 Angstrom) were observed near the Si-SiO2 interface ( 1000 degreesC for 300 s). PL results showed that maximum intensity of the 1 .9 and 3.0 eV peaks was obtained from samples annealed at 800 degreesC for 20 s or transiently to 1000 degreesC at 30 degreesC/s. These results sugges t that a critical thermal budget is required for the formation of uniform n anocrystals and for maximum PL emission. (C) 2001 Elsevier Science B.V. All rights reserved.