Formation characteristics and photoluminescence of Ge nanocrystals in HfO₂

Ge nanocrystals (NCs) are shown to form within HfO₂ at relatively low annealing temperatures (600-700 °C) and to exhibit characteristic photoluminescence (PL) emission consistent with quantum confinement effects. After annealing at 600 °C, sample implanted with 8.4× 10¹⁵ Gecm^-2 show two major PL peaks, at 0.94 and 0.88 eV, which are attributed to no-phonon and transverse-optical phonon replica of Ge NCs, respectively. The intensity reaches a maximum for annealing temperatures around 700 °C and decreases at higher temperatures as the NC size continues to increase. The no-phonon emission also undergoes a significant redshift for temperatures above 800 °C. For fluences in the range from 8.4× 1015 to 2.5× 10¹⁶ cm^-2, the average NC size increases from ∼13.5±2.6 to ∼20.0±3.7 nm. These NC sizes are much larger than within amorphous SiO₂. Implanted Ge is shown to form Ge NCs within the matrix of monoclinic (m) -HfO₂ during thermal annealing with the orientation relationship of [101] m -HfO₂ // [110] Ge NC.