Thermal conductivity and large isotope effect in GaN from first principles

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid-State Physics

Background:

• Lattice thermal conductivity is crucial for thermal management in electronic devices.
• Understanding phonon scattering mechanisms is key to designing materials with desired thermal properties.

Purpose of the Study:

• To investigate the lattice thermal conductivity of Gallium Nitride (GaN) using atomistic first-principles calculations.
• To compare the thermal properties of GaN with other III-V semiconductors like Gallium Phosphide (GaP), Gallium Arsenide (GaAs), and Gallium Antimonide (GaSb).
• To elucidate the underlying mechanisms responsible for the thermal conductivity and its enhancement in GaN.

Main Methods:

• Atomistic first-principles calculations were employed to determine lattice thermal conductivity.
• Phonon properties, including frequencies and coupling strengths, were analyzed.
• The impact of isotopic enrichment on thermal conductivity was simulated.

Main Results:

• Gallium Nitride (GaN) exhibits a substantial increase in lattice thermal conductivity (~65% at room temperature) upon isotopic enrichment.
• This enhancement is attributed to weak coupling between acoustic and optic phonons in GaN.
• Stiff atomic bonds and a large mass ratio between Gallium and Nitrogen atoms contribute to high phonon frequencies and a significant acoustic-optic phonon energy gap.

Conclusions:

• The weak phonon-phonon scattering in GaN is responsible for its high thermal conductivity and the notable enhancement with isotopic enrichment.
• The findings provide critical insights into the interplay of intrinsic phonon-phonon scattering and isotopic effects in determining thermal transport properties.
• This study highlights GaN as a material with significant potential for thermal management applications.