Indirect light absorption model for highly strained silicon infrared sensors

TL;DR

This paper models how tensile and compressive uniaxial strains up to 2% affect silicon's indirect light absorption, revealing significant shifts in absorption limits and potential for infrared sensor applications.

Contribution

It introduces a strain-inclusive model for silicon's indirect light absorption based on first-principles material properties, extending previous models to strained conditions.

Findings

Absorption limit shifts from 1.14 to 1.35 μm under 2% strain.

Absorption increases by a factor of 55 with 2% compressive strain.

Strain effects are mainly due to changes in bandgap and valence band effective mass.

Abstract

The optical properties of silicon can be greatly tuned by applying strain and opening new perspectives, particularly in applications where infrared is key. In this work, we use a recent model for the indirect light absorption of silicon and include the effects of tensile and compressive uniaxial strains. The model is based on material properties such as the bandgap, the conduction and valence band density-of-states effective masses, and the phonon frequencies, which are obtained from first principles including strain up to +2% along the [110] and [111] directions. We show that the limit of absorption can increase from 1.14 (1.09) to 1.35 $\mu$m (0.92 eV) under 2% strain and that the absorption increases by a factor of 55 for the zero-strain cutoff wavelength of 1.14 $\mu$m when a 2% compressive strain is applied in the [110] direction. We demonstrate that this effect is mainly due to the impact of strain on the electronic bandgaps of silicon, directly followed by the valence band density-of-states effective mass.