Thermal conductivity and phonon scattering of AlGaN nanofilms by elastic theory and Boltzmann transport equation

ABSTRACT

Aluminum gallium nitride (AlGaN) plays an essential role in deep ultra-violet light emitting diodes and high electron mobility transistors etc. For example, 2 nm - 5 nm AlGaN nanofilms consist of the quantum wells in ultra-violet light emitting diodes, which have been attracting extensive attention since the rise of COVID 2019. Since most photons and heat are generated in these AlGaN nanofilms, the thermal properties of AlGaN nanofilms are strongly influenced by the heat dissipation of devices. In this paper, utilizing elastic theory and the Boltzmann transport equation, the phonon dispersion relations, density of states, specific heat capacities and thermal conductivities of 2 nm Al (delta) Ga1-delta N nanofilms with various delta are theoretically calculated at different temperatures. The thermal conductivity of nanofilm is significantly smaller than that of its bulk counterpart. In contrast with bulk AlGaN, due to the dominance of boundary scattering and alloy disorder scattering, the thermal conductivity of Al (delta) Ga1-delta N exhibits a similar dependence on Al concentration to bulk Al (delta) Ga1-delta N. Meanwhile, since the screening of Umklapp scattering, the saturation temperature of thermal conductivity is delayed from 50 to 100 K in bulks to about 300 K in nanofilms. The shrinkage of nanofilms' thermal conductivity is also slower than for bulks. We believe that our work will be helpful in controlling the self-heating effect of devices based on AlGaN nanofilms.