Aluminum Gallium nitride (AlGaN) plays an essential role in deep ultra-violet light emitting diode, high electron mobility transistor and etc. For example, 2 nm to 5 nm AlGaN nanofilms consist of the quantum wells in ultra-violet light emitting diodes, which are attracting extensive attention during nowadays COVID 2019. Since most photons and heat are generated in these AlGaN nanofilms, thermal properties of AlGaN nanofilms strongly influenced heat dissipation of devices. In this paper, utilizing elastic theory and Boltzmann transport equation (BTE), the phonon dispersion relations, density of states, specific heat capacities and thermal conductivities of 2 nm AlδGa1-δN nanofilms with various δ are theoretically calculated at different temperatures. The thermal conductivity of nanofilm is significantly smaller than that of bulk counterpart. In contrast with the bulk AlGaN, due to the dominance of boundary scattering and alloy disorder scattering, the thermal conductivity of AlδGa1-δN exhibits similar dependence on Al concentration with bulk AlδGa1-δN. Meanwhile, since the screening of Umklapp scattering, the saturation temperature of thermal conductivity is delayed from 50-100 K of bulks to about 300 K of nanofilms. The shrinkage of nanofilms’ thermal conductivity is also slower than the bulks. We believe that our work will be helpful in controlling the self-heating effect of devices based on AlGaN nanofilms.

Aluminum Gallium Nitride (AlGaN) nanofilms have been widely applied as active layers in ultra-violet (UV) opto-electronic devices and power electronics. Stress plays essential role in AlGaN based devices, especially in high electron mobility transistor (HEMT). Therefore, it is necessary to investigate the thermal properties of AlGaN nanofilms with various stresses. In this work, biaxial stressed [0001] oriented AlGaN nanofilms were studied. The phonon dispersion, density of states, velocity and heat capacity were simulated based on the elastic theory. Thermal conductivities of AlGaN nanofilms, which was found 1~2 orders of magnitude lower than the bulk materials, were then calculated by Boltzmann transport equation (BTE). Due to the modification of phonon dispersion and increasing of group velocity by tensile stress, the thermal conductivities of AlGaN nanofilms increase from compressive stress (-15 GPa) to tensile stress (+15 GPa). Moreover, a phonon energy gap appears in AlN nanofilm of -15 GPa, which disrupts the linear relation between thermal conductivity and stresses. Our work confirmed that the stress could be promising to tune the thermal conductivity of AlGaN nanofilms.