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

• Published in: Optics express Vol. 28; no. 22; pp. 33528 - 33537
• Main Authors: Memarzadeh, Sarvenaz, Palm, Kevin J., Murphy, Thomas E., Leite, Marina S., Munday, Jeremy N.
• Format: Journal Article
• Language: English
• Published: 26.10.2020
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.406093

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 the generated hot-carriers. In this work, we elucidate the role of chemical composition on the relaxation time of hot-carriers for the archetypal Au x Ag 1−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 8× 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.