Impact ionization in high resistivity silicon induced by an intense terahertz field enhanced by an antenna array

Abebe T Tarekegne,Maksim Zalkovskij,Peter U Jepsen,Andrew C Strikwerda,Krzysztof Iwaszczuk

doi:10.1088/1367-2630/17/4/043002

Abebe T Tarekegne, Maksim Zalkovskij + Show 3 more

Open Access

https://doi.org/10.1088/1367-2630/17/4/043002

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Abstract

We report on the observation of ultrafast impact ionization and carrier generation in high resistivity silicon induced by intense subpicosecond terahertz transients. Local terahertz peak electric fields of several MV cm−1 are obtained by field enhancement in the near field of a resonant metallic antenna array. The carrier multiplication is probed by the frequency shift of the resonance of the antenna array due to the change of the local refractive index of the substrate. Experimental results and simulations show that the carrier density in silicon increases by over seven orders of magnitude in the presence of an intense terahertz field. The enhancement of the resonance shift for illumination from the substrate side in comparison to illumination from the antenna side is consistent with our prediction that the back illumination is highly beneficial for a wide range of nonlinear processes.

Highlights

Impact ionization is a carrier multiplication mechanism where energized conduction band electrons collide with bound electrons to generate new electron-hole pairs [1,2,3]
To obtain the transmission spectrum of the antenna array, we divide the Fourier transform of the transmitted THz transient through the sample by that of a bare high resistivity (HR) Si reference
We note here that we do not observe any measurable change of transmission through bare HR Si even at highest available field strengths

Summary

Introduction

Impact ionization is a carrier multiplication mechanism where energized conduction band electrons collide with bound electrons to generate new electron-hole pairs [1,2,3]. Employing ultrashort electric field pulses for impact ionization enables switching of the conductivity of semiconductors on an ultrafast time scale. The investigation of such an immense carrier generation potential has been limited in silicon to theoretical simulations with experimental verifications based on strong static electric fields [2, 5,6,7]. A pure optical, noncontact and ultrafast impact ionization technique enables a better understanding of ultrafast carrier dynamics in silicon and it increases its functionality. We foresee applications of such ultrafast carrier multiplication in integrated circuit technology, metamaterial and antenna design

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