Erbium Silicates as Advanced Optical Materials for Light Emission at
Telecommunicatios Wavelength in Silicon Photonics


Hiroo Omi and Takehiko Tawara*
Materials Science Laboratory, *Optical Science Laboratory

 Erbium silicates and erbium oxide, such as Er2SiO5 and Er2Si2O7, are promising materials as light emitters at the telecommunications wavelength and as optical amplifiers in the field of silicon photonics. In the erbium compounds, the density of erbium ions is 1022 atoms/cm3, which is orders of magnitude greater than that typically obtained by Er ion implantation in silicon substrate, allowing access to a large number of emitting centers. In this work, we combined real-time synchrotron radiation grazing incidence X-ray diffraction (GIXD) and PL experiments to optimize the structures and optical properties of erbium silicates on silicon substrate. We firstly studied the formation of the erbium silicates during annealing in Ar gas and O2/Ar mixture gases in real time. We determined the crystallographic structures and the temperature of crystallization, and assessed the possible reactions for the silicate formation. We secondly measured the photoluminescence (PL) from a sample annealed at 1060ºC [1].
 The 100-nm-thick erbium oxides were deposited on 100-nm-thick silicon oxide film grown on Si(001) substrates by reactive sputtering at room temperature. The samples are then annealed at up to 1300ºC in Ar and O2/Ar mixture gases. In micro-PL experiments, the samples were pumped by CW laser at the wavelength of 532 nm.
 The GIXD measurements show that erbium silicates and erbium oxide are formed by interface reactions between silicon oxide and erbium oxides deposited on silicon oxide by reactive sputtering in Ar gas and O2/Ar mixture gas ambiences. The erbium silicates are formed above 1060ºC in Ar gas ambience and above 1010ºC in O2/Ar gas ambience, and erbium silicides are dominantly formed above 1250ºC. The I15/2-I13/2 Er3+ PL from the erbium silicate exhibits abnormal temperature dependence (see Fig. 1). The PL intensity from the Er2SiO5 silicate exhibits abnormal temperature dependence of 1.529-µm Er3+ PL; the PL intensity decreases from 4 to 70 K and increases from 70 to 300 K. The increase of the PL intensity with increasing temperature observed at off-resonant excitation conditions can be explained by the phonon-assisted resonant absorption of the 532-nm excitation photons at the 2H11/2 levels of Er3+ ions in the erbium silicate films.

[1] H. Omi, T. Tawara, and M. Tateishi, AIP Advances 2 (2012) 012141.

Fig. 1. Photoluminescence from erbium silicates grown on Si substrate (a), Temperature dependence of
the PL intensity (b).

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