Enhancing sputtered GaN/Si film quality by adding AlGaN buffer layer in a continuous deposition process

In this work we demonstrate the achievement of significative improvements in the structural and morphological quality of wurtzite GaN films (approximately 250 nm thick) by introducing an initial growth step involving an AlGaN buffer layer on p-type Si (100) substrates through a continuous reactive sputtering process. We investigated the influence of using single and multiple AlxGa1-xN buffer layers with varying Al content (x ranging from 0.07 to 0.37) and different thicknesses (from 166 nm to 1 µm). The obtained samples underwent characterization through X-ray diffraction and scanning electron microscopy. The results reveal a slight increase in the c-axis preferred growth direction and grain sizes even with a single and thin (250 nm) Al0.07Ga0.93N buffer layer. Conversely, the use of a single Al0.37Ga0.63N buffer layer led to significant morphological changes and a remarkable improvement in the c-axis preferred orientation. The most favorable outcomes were observed with the implementation of a triple AlGaN buffer layer, featuring decreasing Al content from the substrate, indicating the attainment of a high-quality GaN top layer comparable to epitaxial GaN.