Properties of nanocrystalline silicon probed by optomechanics

Daniel Navarro-Urrios,Laurent Bellieres,Jaakko Saarilahti,Clivia M Sotomayor-Torres,Tapani Makkonen,Teija Häkkinen,Arnaud Devos,Amadeu Griol,Jeremie Maire,Kestutis Grigoras,Guillermo Arregui,Emigdio Chávez-Ángel,Martín F Colombano,Alejandro Martínez,Jouni Ahopelto,Néstor E Capuj

doi:10.1515/nanoph-2020-0489

Abstract

Abstract Nanocrystalline materials exhibit properties that can differ substantially from those of their single crystal counterparts. As such, they provide ways to enhance and optimize their functionality for devices and applications. Here, we report on the optical, mechanical and thermal properties of nanocrystalline silicon probed by means of optomechanical nanobeams to extract information of the dynamics of optical absorption, mechanical losses, heat generation and dissipation. The optomechanical nanobeams are fabricated using nanocrystalline films prepared by annealing amorphous silicon layers at different temperatures. The resulting crystallite sizes and the stress in the films can be controlled by the annealing temperature and time and, consequently, the properties of the films can be tuned relatively freely, as demonstrated here by means of electron microscopy and Raman scattering. We show that the nanocrystallite size and the volume fraction of the grain boundaries play a key role in the dissipation rates through nonlinear optical and thermal processes. Promising optical (13,000) and mechanical (1700) quality factors were found in the optomechanical cavity realized in the nanocrystalline Si resulting from annealing at 950°C. The enhanced absorption and recombination rates via the intragap states and the reduced thermal conductivity boost the potential to exploit these nonlinear effects in applications including Nanoelectromechanical systems (NEMS), phonon lasing and chaos-based devices.

Highlights

Nanoscale optomechanical cavities (OMCs) [1] promise a route toward flexible, efficient and reliable interfaces to transfer classical and or quantum information between microwave and optical frequency domains in a single chip
Optical, mechanical and thermal properties and, especially, the dissipation rates of optomechanical nanobeams fabricated in nanocrystalline silicon (nc-Si)-on-insulator wafers have been investigated
The annealing temperature of the originally amorphous silicon films is found to have a strong effect on the material properties and, on the behavior of the optomechanical cavities

Summary

Introduction

Nanoscale optomechanical cavities (OMCs) [1] promise a route toward flexible, efficient and reliable interfaces to transfer classical and or quantum information between microwave and optical frequency domains in a single chip. It was demonstrated that nc-Si is an excellent and cost-competitive alternative to c-Si for optomechanical devices taking advantage of nonlinear effects while operating in ambient conditions [19]. Nonlinear dynamic functions, such as phonon lasing and chaos, were demonstrated with broader bandwidth than measured in equivalent SOI devices, as well as wafers [19]. The dynamic behavior depends on the optical and mechanical losses and on heat generation and extraction rates of the OMCs [4, 20] These properties can be tuned rather flexibly in nc-Si films by varying the processing parameters. The pristine nc-Si films own different nanocrystallite size distribution and tensile stress

Nanocrystalline silicon-oninsulator substrates

Optomechanical characterization of the nanobeams

Mechanical properties

Optomechanical and thermal properties

Conclusions