Fig. shows a representative top view SEM of a 20 nm InN film deposited on (0001) 4H-SiC. The contrast of the image is weak, indicating that our InN film is smooth and is free from the common surface non-homogeneities such as large crystal grains and In-rich droplets. It should be mentioned that non-optimal ALD growth condition will lead to rougher surface and In-rich clusters as observed in the literature. A smooth surface is further shown by the topographical atomic force micrograph of the InN surface (Fig. ). The root-mean square (RMS) roughness of the 20 nm thick InN film is 0.16 nm. For comparison, the root-mean square roughness of the bare 4H-SiC substrate is 0.13 nm. We find that the RMS roughness of InN is independent on the thickness of InN in this study. The surface stepping feature of 4H-SiC caused by the CMP process finished at the substrate supplier (insert in Fig. ), is duplicated by the InN film, showing the conformity of the InN growth at the nanometer-scale.