Control of hot-carrier relaxation time in Au-Ag thin films through alloying

TL;DR

This study investigates how alloying Au with Ag in thin films affects hot-carrier relaxation times, revealing that small alloying changes can significantly extend carrier lifetimes, which is promising for plasmonic device optimization.

Contribution

It provides the first detailed analysis of how chemical composition influences hot-carrier relaxation dynamics in Au-Ag alloys using time-resolved spectroscopy.

Findings

Relaxation times vary up to 8x with composition changes.

Adding 2% Ag increases hot carrier lifetime by ~35%.

Relaxation time is inversely proportional to the imaginary permittivity.

Abstract

The plasmon resonance of a structure is primarily dictated by its optical properties and geometry, which can be modified to enable hot-carrier photodetectors with superior performance. Recently, metal-alloys have played a prominent role in tuning the resonance of plasmonic structures through chemical composition engineering. However, it has been unclear how alloying modifies the time dynamics of generated hot-carriers. In this work, we elucidate the role of chemical composition on the relaxation time of hot-carriers for the archetypal Aux Ag1-x thin-film system. Through time-resolved optical spectroscopy measurements in the visible wavelength range, we measure composition-dependent relaxation times that vary up to 8x for constant pump fluency. Surprisingly, we find that the addition of 2% of Ag into Au films can increase the hot carrier lifetime by approximately 35% under fixed fluence, as a result of a decrease in optical loss. Further, the relaxation time is found to be inversely proportional to the imaginary part of the permittivity. Our results indicate that alloying is a promising approach to effectively control hot-carrier relaxation time in metals.