Intrinsic thermal conductivities and size effect of alloys of wurtzite AlN, GaN, and InN from first-principles

Despite the fact the alloys of wurtzite AlN, GaN, and InN are widely used in electronics, the studies on their thermal conductivities (κ) are inadequate, and the intrinsic limits are still unknown. In this work, the intrinsic κ of alloys and their films are calculated from first-principles within the virtual crystal treatment. The κ of alloys are strongly suppressed even by a small amount of alloying. For instance, with only 1% alloying of Al or In, κ of GaN decreases about 60%. At relatively high alloying, with concentration between 0.2 and 0.8, the κ of alloys are not significantly changed. At room temperature, the minimal a-axis κ are about 18, 22, and 8 W m−1 K−1, while the minimal c-axis κ are about 22, 27, and 10 W m−1 K−1 for Al x Ga1− x N, In x Ga1− x N, and In x Al1− x N, respectively. The size effect in films can persist up to a few tens of micrometers, and κ can be reduced by half in about 100 nm thick films.