Nonequilibrium electron-phonon coupling across the interfaces between Al nanofilm and GaN

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Aluminum (Al) is crucial for source/drain contacts in Gallium Nitride (GaN)-based transistors.
• Effective energy transfer between electrons and phonons in Al/GaN is essential for device performance and thermal management.
• Existing models like the two-temperature model (TTM) have limitations in accounting for diverse electron-phonon interactions.

Purpose of the Study:

• To investigate the non-equilibrium electron-phonon (e-ph) coupling in pure Al and Al nanofilms on GaN substrates.
• To determine the thickness dependence of e-ph coupling in Al nanofilms.
• To analyze the coupling strengths between high-energy electrons and different phonon modes using advanced techniques.

Main Methods:

• Utilized time-domain thermoreflectance (TDTR) to measure non-equilibrium e-ph coupling.
• Employed a modified two-temperature model (MTTM) to analyze TDTR data and obtain coupling factors.
• Investigated pure Al and Al nanofilms of varying thicknesses on GaN substrates.

Main Results:

• Al nanofilms exhibit enhanced e-ph coupling coefficients compared to pure Al.
• The longitudinal acoustic (LA) phonon mode shows a significantly higher e-ph coupling factor than transverse acoustic (TA1, TA2) modes in Al.
• LA phonon mode dominates the electron relaxation process following ultrafast femtosecond laser excitation.

Conclusions:

• Al nanofilms on GaN substrates present stronger e-ph coupling, beneficial for thermal management in electronic devices.
• The dominance of the LA phonon mode in energy transfer provides insights into electron relaxation dynamics.
• Findings offer crucial experimental and theoretical guidance for laser processing and the design of advanced electronic devices.