Thermal transport in heavy-ion irradiated GaN: The effect of static and dynamic annealing

The suppression of thermal transport in semiconducting materials due to ion irradiation has recently garnered wide attention. In particular, heavy gold ions (Au2+) have been shown to induce ultralow thermal conductivity (κ) in gallium nitride (GaN), down to ∼1 W m−1 K−1 at room temperature (RT). Although the repairing effect of thermal annealing on various structural defects has long been recognized, the impact on thermal transport remains largely unexplored, especially for semiconductors irradiated by heavy ions. Here, we prepare Au2+-irradiated single-crystalline GaN samples under five different ion fluences from 1011 to 1015 cm−2 and investigate how κ varies with both static and dynamic annealing. Compared to the as-irradiated samples, κ consistently increases as the static annealing temperature rises from 573 to 773 K and then 973 K, up to about 50% (5.8 × 1011 cm−2 fluence) of the value for pristine GaN and a factor of 6 at intermediate fluences (5.8 × 1012 and 5.8 × 1013 cm−2). Moreover, the recovered κ is always smaller at higher fluences, suggesting an increasing number of defects that cannot be readily repaired. Upon dynamic annealing (5 × 1014 cm−2), κ first decreases from 1.4 (irradiation at RT) to 1.2 W m−1 K−1 (573 K) and then rises to 7.8 W m−1 K−1 (973 K). This non-monotonic trend is attributed to the varying competition between the generation and annihilation of lattice defects at different temperatures. These findings expand our understanding of how annealing changes thermal transport in heavy ion-irradiated semiconductors and may facilitate their applications in harsh environments with intense radiation and high temperatures.