Effect of High Al Content AlGaN Buffer Layer on the Properties of GaN-on-Silicon Materials

The lattice parameter and thermal expansion coefficient mismatch between the silicon substrate and GaN lead to high tensile stress, which makes the GaN epitaxial layer prone to cracking. Effective compensation of tensile stress on GaN to prevent cracking is an important issue in GaN epitaxial growth. In this work, GaN-on-silicon materials with different AlGaN buffer layer structures are prepared by metal-organic chemical vapor deposition (MOCVD). The GaN epitaxial material with a smooth and crack-free surface is fabricated by inserting 7 AlGaN buffer layers. The crystal quality of GaN is characterized using high resolution X-ray diffraction (HRXRD). The full-width half maximum (FWHM) value of GaN(002) and GaN(102) crystal plane is 398 and 780 arcsec, respectively. The surface root mean square (RMS) roughness of GaN material is 0.31 nm, and the vertical breakdown voltage (BV) of the epitaxial wafer reaches 918 V. The results show that high Al content of the AlGaN buffer layer can effectively reduce the tensile stress and dislocation density of the GaN layer when the entire AlGaN layer thickness remains constant. Suppressing the generation of surface cracks and improving the crystal quality can improve the vertical breakdown voltage and two-dimensional electron gas (2-DEG) characteristics of GaN epitaxial wafers. For the growth of GaN-on-Si materials, more AlGaN layers with high Al content help to resolve the mismatch of lattice parameters and thermal expansion coefficients between Si and GaN materials. 7-layer stepped AGaN buffer layer structure provides a good stress control and facilitates dislocation bending and annihilation, which improves the crystal quality and breakdown voltage of GaN epitaxial wafers.image (c) 2023 WILEY-VCH GmbH