Reversible Modulation of Spontaneous Emission by Strain in Silicon Nanowires

TL;DR

This study computationally demonstrates how uniaxial strain can reversibly modulate spontaneous emission in silicon nanowires through symmetry changes and bandgap transitions, enabling potential optoelectronic applications.

Contribution

It reveals two distinct mechanisms by which strain affects emission in silicon nanowires, a phenomenon not observed in bulk silicon, offering new avenues for device engineering.

Findings

Strain causes a 10-100x change in emission times.

Wave function symmetry alteration impacts optical dipole strength.

Bandgap transition from direct to indirect slows photon emission.

Abstract

We computationally study the effect of uniaxial strain in modulating the spontaneous emission of photons in silicon nanowires. Our main finding is that a one to two orders of magnitude change in spontaneous emission time occurs due to two distinct mechanisms: (A) Change in wave function symmetry, where within the direct bandgap regime, strain changes the symmetry of wave functions, which in turn leads to a large change of optical dipole matrix element. (B) Direct to indirect bandgap transition which makes the spontaneous photon emission to be of a slow second order process mediated by phonons. This feature uniquely occurs in silicon nanowires while in bulk silicon there is no change of optical properties under any reasonable amount of strain. These results promise new applications of silicon nanowires as optoelectronic devices including a mechanism for lasing. Our results are verifiable using existing experimental techniques of applying strain to nanowires.