Strain induction on GE nanobeams by electrostatic actuation

Ayan, Arman
Germanium (Ge) is one of the most promising materials to accomplish the monolithic integration of optics and electronics on the same chip, mainly due to its compatibility with the existing silicon (Si) technology, high charge carrier mobility and high absorption coefficient in the near-infrared region. However, realization of efficient Ge light emitters requires techniques such as tensile strain induction, tin (Sn) incorporation and/or heavy n-type doping to alter its band gap enabling direct transitions. Among these techniques, low-threshold Ge laser has been demonstrated by strain induction. Yet, an integrated-circuit (IC) compatible method capable of tuning the strain dynamically is yet to be shown. In this thesis, a novel way of inducing strain on Ge nanobeams via electrostatic actuation is proposed, which offers simple fabrication and post-fabrication tunability. Ge nanobeam is modeled by finite element method, and the deflection and strain formation are discussed with inherent non-idealities. The maximum deflection is set to one third of the initial gap (g/3) distance between the Ge nanobeam and Si substrate to operate at a safe margin from pull-in. The effect of the dimensions on the required deflection and voltage to reach a predetermined strain is investigated at g/3 deflection. Moreover, possible electrical and mechanical failure mechanisms are discussed together with possible structural modifications to reduce the required voltages. Lastly, the electrical analysis of the nanobeam structures are analyzed and the results showed that non-uniform strain profile could outperform uniformly strained structures. This thesis shows that the required strain to observe direct band transition of Ge can be achieved via electrostatic actuation of Ge nanobeams. Therefore, the proposed Ge nanobeams could lead to a tunable and IC compatible Ge laser on Si that can serve as the key missing component of the monolithically-integrated chips


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Citation Formats
A. Ayan, “Strain induction on GE nanobeams by electrostatic actuation,” M.S. - Master of Science, Middle East Technical University, 2018.