Bond orbital description of the strain induced second order optical susceptibility in silicon

TL;DR

This paper presents a bond-orbital model based on sp3 theory to describe strain-induced second-order optical susceptibility in silicon, enabling better simulation and optimization of nonlinear optical effects in strained silicon devices.

Contribution

It introduces a simple, parameterized formula for $ ext{chi}^{(2)}$ in silicon using strain gradients, advancing the theoretical understanding and practical modeling of nonlinear optical responses.

Findings

Validated the main claims about $ ext{chi}^{(2)}$ in strained silicon.

Provided estimates for the magnitude of $ ext{chi}^{(2)}$ in practical devices.

Developed a tool for optimizing nonlinear optical effects in silicon devices.

Abstract

We develop a theoretical model, relying on the well established sp3 bond-orbital theory, to describe the strain-induced $\chi^{(2)}$ in tetrahedrally coordinated centrosymmetric covalent crystals, like silicon. With this approach we are able to describe every component of the $\chi^{(2)}$ tensor in terms of a linear combination of strain gradients and only two parameters $\alpha$ and $\beta$ which can be estimated theoretically. The resulting formula can be applied to the simulation of the strain distribution of a practical strained silicon device, providing an extraordinary tool for optimization of its optical nonlinear effects. By doing that, we were able not only to confirm the main valid claims known about $\chi^{(2)}$ in strained silicon, but also estimate the order of magnitude of the $\chi^{(2)}$ generated in that device.