Transient Pauli blocking in a InN film as a mechanism for broadband ultrafast optical switching

TL;DR

This paper demonstrates broadband ultrafast optical switching in InN thin films driven by transient Pauli blocking, with a theoretical model explaining the dynamics and enabling design of ultrafast photonic devices.

Contribution

It introduces a new understanding of Pauli blocking induced solely by electronic temperature rise for ultrafast optical switching in degenerate semiconductors.

Findings

Successful broadband switching from visible to near-infrared

Quantified electron-phonon coupling and electronic specific heat

Model accurately predicts spectral switching window

Abstract

The transient Pauli blocking effect offers a promising route for achieving ultrafast optical switching in semiconductors, enabling a rapid switching from an initially opaque state to a relatively transparent state upon photoexcitation. Herein, we demonstrate broadband ultrafast optical switching in degenerate InN thin films, spanning the visible to near-infrared spectral range, using pump-probe transient transmittance measurements. To elucidate the underlying physical mechanism, we perform probe-energy-resolved analysis for ultrafast dynamics, and develop a theoretical model based on a quasi-equilibrium Fermi-Dirac distribution. The model successfully captures the experimental transients and yields an electron-phonon coupling constant of $1.0\times10^{17}\,\mathrm{W\,m^{-3}\,K^{-1}}$, along with an electronic specific heat coefficient ranging from 1.52 to 2.02 $\mathrm{mJ\,mol^{-1}\,K^{-2}}$, which allow direct prediction of the spectral switching window. Notably, we demonstrate that the Pauli blocking effect can be induced solely by a laser-excitation driven rise in electronic temperature, without requiring significant carrier injection into the conduction band in degenerate semiconductors. These findings offer new insights for designing ultrafast optical modulators, shutters, and photonic devices for next-generation communication and computing technologies.