Effect of N2/H2 plasma on the growth of InN thin films on sapphire by hollow-cathode plasma-assisted atomic layer deposition

In this work, we have studied the influence of N2/H2 plasma gas flow rates on the hollow-cathode plasma-assisted atomic layer deposition (HCPA-ALD) growth of indium nitride (InN) films. The influence of N2/H2 plasma gas flow rates on crystallinity, lattice distortion, phonon properties, and bandgap was analyzed. We found that the strain can be relieved fully or partially through the incorporation of H2 in plasma. We present Raman scattering measurements on HCPA-ALD grown InN films. We found that the E2-high phonon relaxation time increases with decreasing H2 plasma flow. Atomic force microscopy (AFM) topography measurements revealed high surface roughness for InN films deposited with N2/H2. The spectroscopic ellipsometry analysis revealed that InN surface layers are thick and contain large void structures with the incorporation of H2 in N2 plasma. Combining the AFM surface morphology analysis with spectroscopic ellipsometry analysis, we propose a possible surface reaction mechanism for hydrogen incorporation on an InN surface. A clear shift of the absorption edge and a decrease in the absorption coefficient were observed when H2 was introduced into N2 flow. These results may provide a useful guide for understanding the HCPA-ALD growth mechanism of InN and In-rich nitrides.