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Submitted on 31 May 2018
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Study of Pockels effect in strained silicon
Mathias Berciano, Pedro Damas, Guillaume Marcaud, Xavier Le Roux, Paul Crozat, Carlos Alonso Ramos, Daniel Benedikovic, Delphine Marris-Morini,
Eric Cassan, Laurent Vivien
To cite this version:
Mathias Berciano, Pedro Damas, Guillaume Marcaud, Xavier Le Roux, Paul Crozat, et al.. Study of Pockels effect in strained silicon. 2017 IONS Paris 2017, Jun 2017, Palaiseau, France. 2017. �hal- 01803058�
Study of Pockels effect in strained silicon
Mathias Berciano*, Pedro Damas, Guillaume Marcaud, Xavier Le-Roux, Paul Crozat, Carlos Alonso Ramos, Daniel Benedikovic, Delphine Marris-Morini, Eric Cassan and Laurent Vivien
Centre de Nanosciences et de Nanotechnologies, Bât 220, rue André Ampère – Université Paris-Saclay Centre scientifique d’Orsay, 91405 Orsay France
*mathias.berciano@c2n.upsaclay.fr
Optical modulation in silicon photonics is usually performed using plasma dispersion effect at the cost of high power consumption and a limitation of the modulation frequency due to the carrier inherent properties. In addition the centro-symmetry of silicon inhibits second order nonlinear effects such as Pockels effect, an ultra-fast electro-optic effect widely used in high speed and low-power consumption modulators for telecom and datacom applications. However it is possible to overcome this limitation by straining silicon using a stressed overlayer to break the crystal symmetry.
Pockels effect VS plasma dispersion effect
Crystal orientation dependence
Conclusion
• Straining the silicon crystal enables 2nd order nonlinear effects
Pockels effect is possible
Dependence on inhomogeneous strain
• Demonstration of linear E-O effect in strained silicon
Silicon waveguide strained by a SiN stress overlayer
Carriers play a big role in the electro-optic effect
Electro-optic modulation How to strain silicon
Effective index as a function of the voltage applied for different angle
orientations
High speed measurements
Pockels effect is fast compared to the plasma dispersion effect. RF measurements were performed in order to clearly seperate them.
ERC POPSTAR
Simulated η𝒙𝒙𝒚 and η𝒚𝒚𝒚 strain gradient distributions in the waveguide
𝑆𝑖 𝑆𝑖
𝑆𝑖𝑂2 𝑆𝑖𝑁
𝑆𝑖𝑂2 𝑆𝑖𝑁
𝑆𝑖𝑂2 𝑆𝑖𝑁
𝑀𝑒𝑡𝑎𝑙
𝑆𝑖
𝑉
𝑆𝑖 𝑠𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒
Cross-section view of the device
𝑬 𝑽
∆𝑵𝒆, ∆𝑵𝒉
∆𝒏𝑷𝒐𝒄𝒌𝒆𝒍𝒔 ∆𝒏𝑪𝒂𝒓𝒓𝒊𝒆𝒓𝒔
A highly stressed SiN is deposited by PECVD on the Si waveguides to break the cystal symmetry
with strain gradients
𝜑
Electrode
IN
OUT
Si waveguide
Straining silicon in different orientation change the efficiency of Pockels effect
Top view of angled Mach-Zehnder interferometers 𝑆𝑖𝑁
𝑆𝑖𝑂2
260 nm 400 nm
𝑥 𝑦
𝑧
Waveguide strained by a silicon nitride(SiN) stress layer 𝑆𝑖
𝑆𝑖 𝑠𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒
𝝈𝒊
Free carriers in silicon act as a parasitic effect for the correct
evaluation of Pockels effect
Influence of free carriers on Pockels effect
∆𝒏𝑷𝒐𝒄𝒌𝒆𝒍𝒔 = χ(𝟐)𝑬 2𝑛
𝑬
χ(𝟐) ≠ 𝟎
Electro-optic response
SiN straining overlayer
Coplanar electrodes to induce an electric
field TE single mode
waveguide
CV measurements
High frequency CV curve measured
Charges effect also exist at the SiN/Si interface:
•Fixed charges that create a constant potential barrier
•Interface traps due to defects
Cross-section view of a MIS capacitor with SiN used as insulator
𝑆𝑖 𝑠𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒 𝑆𝑖𝑁
𝑀𝑒𝑡𝑎𝑙
𝑀𝑒𝑡𝑎𝑙
𝑉
