Heat capacity and phonon mean free path of wurtzite GaN

TL;DR

This study measures the heat capacity and phonon mean free path of bulk hexagonal GaN across a wide temperature range, revealing temperature-dependent phonon scattering mechanisms and providing key thermal properties for material applications.

Contribution

It provides new experimental data on GaN's heat capacity and phonon mean free path, with a detailed analysis of phonon scattering processes and temperature dependence.

Findings

Heat capacity fitted with Debye and Einstein models with 3% accuracy.

Phonon mean free path follows a T^{-2} dependence between 10-100 K.

Umklapp processes limit phonon mean free path above 100 K.

Abstract

We report on lattice specific heat of bulk hexagonal GaN measured by the heat flow method in the temperature range 20-300 K and by the adiabatic method in the range 5-70 K. We fit the experimental data using two temperatures model. The best fit with the accuracy of 3 % was obtained for the temperature independent Debye's temperature $\theta_{\rm D}=365$ {\rm K} and Einstein's temperature $\theta_{\rm E}=880$ {\rm K}. We relate these temperatures to the function of density of states. Using our results for heat conduction coefficient, we established in temperature range 10-100 K the explicit dependence of the phonon mean free path on temperature $\it{l}_{\rm ph}\propto T^{-2}$. Above 100 K, there is the evidence of contribution of the Umklapp processes which limit phonon free path at high temepratures. For phonons with energy $k_{\rm B}\times 300 $ {\rm K} the mean free path is of the order 100 {\rm nm}