Silicon nanoantenna designs for optical-frequency electronics

Electron photoemission is a physical phenomenon related to the interaction between light and matter. When an electromagnetic wave impinges on a material, it can transfer its energy to one of the electrons bound within the target. Considering light as a set of discrete energy packets called photons, if more than one photon is involved in the energy transfer process, the electron photoemission is said to be non-linear. In the non-linear regime, if the optical field is strong enough to bend the energy barrier between the material and the vacuum and to let the electron tunnel out, it is possible to generate sub-optical-cycle current pulses that are synchronized with the optical field waveform. Therefore, the photoemitted current will be dependent on the phase of the impinging pulse. This particular regime is called optical-field-driven tunneling emission and, thanks to the sub-optical-cycle temporal resolution of the current pulses, it has technological applications like time-domain field sampling, petahertz (PHz) optoelectronics, and carrier-envelope-phase (CEP) detection. In this work, the combination of two mechanisms (pulsed laser and Field Enhancement (FE)) is explored to access optical-field-driven tunneling emission regimes for planar devices and to overcome actual device limitations. Plasmonic devices based on gold can reach high FE but they suffer from degradation after irradiation. Nanoantennas provide an attractive means to obtain a local electric field above the optical-field-driven tunneling threshold in confined regions of space and time, thereby avoiding device damage. Nanoantennas are investigated in the non-linear regime due to their high degree of freedom in geometric design and in materials choice. The main objective of this master’s thesis is to investigate new geometrical designs and materials for nanoantennas in order to explore new physics behaviors and resonance mechanisms. In a previous work based on nanostructured silicon-tip array, an optical-field-driven tunneling emission regime has been demonstrated thanks to the material strength and the possibility to achieve FE even without plasmonic-based resonances. These two qualities make the silicon a good candidate to realize planar array devices able to exploit optical-field-driven tunneling. Through this work, I studied and designed planar silicon nanoantennas that rely on Fabry-Perot-like resonance. The magnitude of the FE achieved in silicon nanostructures is similar to the one achieved in gold devices, therefore the capability of planar silicon nanoantennas to detect the phase of the incident pulses is also investigated. The research begins by starting with finite element method (FEM) simulations. Different shapes and layouts will be simulated to evaluate the intensity of the field enhancement in the near-infrared and visible regions for silicon-based nanoantennas. The simulated data are then analyzed using suitable MATLAB® codes to evaluate the ex??pected device performance: CEP sensitivity and signal-to-noise ratio (SNR). These quantities are compared for different designs and different incident pulses, to check for which combination yields the best performance. In the last part of this master’s thesis multiple array devices are fabricated in a cleanroom facility to evaluate the feasibility of the geometry proposed in the design/simulation phase and to check the possibility of exploiting the optical-field-driven tunneling mechanism in silicon.