Room Temperature Layer by Layer Growth of GaN on Atomically Flat ZnO

We have grown GaN on atomically flat ZnO (000-1) substrates at room temperature with pulsed laser deposition (PLD). We have found that atomically flat surfaces of ZnO (000-1) substrates with a clear step and terrace structure have been obtained by annealing in a box made of ceramic ZnO. We have also found that GaN grows epitaxially even at room temperature on the step and terrace ZnO surface. Reflection high energy electron diffraction (RHEED) observations have revealed that the GaN film grows in the layer by layer mode from the early stage of the film growth. X-ray reflectivity measurements have revealed that the heterointerface between GaN and ZnO is quite abrupt and its roughness is less than 0.5 nm.