Improved Quality of InN Thin Films Using a Thin InGaN Compressive Strain Gradient Layer

High-quality InN has significant opportunities for exciting and impactful electronic and photonic applications. These applications rely on growth techniques that produce high-quality InN thin films. To achieve the fabrication of InN semiconductor thin films with a low density of misfit and threading dislocations, we report on a growth technique that utilizes composition and strain gradients to limit the propagation of defects into InN grown on a GaN/sapphire substrate. The growth technique we have investigated utilizes a compressively strained gradient transition layer to limit the propagation of threading dislocations from the GaN buffer. Reflection high-energy electron diffraction, high-resolution X-ray diffraction, Raman spectroscopy, photoluminescence, and Hall measurements were employed to evaluate the effectiveness of the gradient transition layer to improve the quality of InN thin films. The outcome is that for InN films grown on partially graded InxGa1–xN (x → 0 to 29%), when compared with InN grown directly on a GaN substrate, we observed about a 40% decrease in edge dislocations, a 50% increase in photoluminescence, and a 20% increase in mobility. When compared to a sharp strain boundary, a linear strain gradient offers threading dislocations the opportunity to reduce the energy of the system more by leaving the system than by propagating into the strained region.