- The shape of the PL spectra are independent on anneal temperature and implantation dose, only their intensities change.
- Strong PL is obtained from SiO2 layers containing nanoclusters as well as from SiO2 layers containing no nanoclusters at all (small dose, moderate anneal temperature).
The PL is not due to quantum confinement effects.
Comparison with Ar-implanted and unimplanted silicon oxide layers:
- The PL of Ar-implanted and unimplanted SiO2 layers is much less than that of Si, Ge or Sn-implanted SiO2 layers.
The radiation damage alone is not sufficient; the excess of Si, Ge or Sn is necessary.
Energy level diagramm:
Possible defects in SiO2:
- common bond type in SiO2: Si-O-Si
- non-bridging oxygen hole center:
Possible luminescence centers in SiO2:
- neutral oxygen vacancy: Si-Si
- Si-Ge, Ge-Ge
- Si-Sn , Sn-Sn
- twofold coordinated Si, Ge or Sn:
.. .. ..
O-Si-O, O-Ge-O, O-Sn-O
The Substitution of on atom with an haevier, but isoelectronic atom increases the spin-orbit coupling of the forbidden T1-> S1 transition.
Predictions of the Heavy-atom-effect in the order of Si, Ge, Sn:
- The intensity of the T1-> S1 transition increases in respect of the S1-> S1 transition.
- The emission energy of the T1-> S1 transition shifts to higher energies.
The decay constant of the T1-> S1 transition reduces.