Atomic-Scale Investigation of the Lattice-Asymmetry-Driven Anisotropic Sublimation in GaN.

Thermal sublimation, a specific method to fabricate semiconductor nanowires, is an effective way to understand growth behavior as well. Utilizing a high-resolution transmission electron microscope (TEM) with in situ heating capability, the lattice-asymmetry-driven anisotropic sublimation behavior is demonstrated of wurtzite GaN: sublimation preferentially occurs along the [ 000 1 ¯ $000\bar{1}$ ] and [0001] directions in both GaN thin films and nanowires. Hexagonal pyramidal nanostructures consisting of six semipolar { 1 1 ¯ 01 } $\{ {1\bar{1}01} \}$ planes and one (000 1 ¯ $\bar{1}$ ) plane with the apex pointing to the [0001] direction are generated as a sublimation-induced equilibrium crystal structure, which is consistent with the lattice-asymmetry-driven growth behaviors in wurtzite GaN. These findings offer a new insight into the thermal stability of wurtzite GaN and provide essential background for tailoring the structure of III-nitrides for atomic-scale manufacturing.