Crack-free > 1-μm AlN layer on Si substrate using ductile interlayer for strain modification in epitaxial film

Growing crack-free, epitaxial ultrawide-bandgap semiconductor films on cost-effective, large-area substrates, such as AlN on Si, poses a significant challenge due to substantial lattice and thermal expansion mismatches. We introduce an approach to mitigate tensile strain or reverse strain signs between the substrate and the AlN layer, thereby suppressing crack formation during the heteroepitaxial growth of thick III-N films. This approach introduces ductile metallic interlayers, specifically Au, to change the strain state of AlN from in-plane tensile to compressive, without initiating cracks. Furthermore, the Au interlayer is grown epitaxially as a single crystal, which prevents the transfer of tensile strain into the AlN film, as confirmed by x-ray diffraction and transmission electron microscopy. We demonstrate crack-free AlN films exceeding 1 μm in thickness. These findings hold significant promise for advancing the field of ultrawide-bandgap semiconductor materials, with potential applications in electronic, optoelectronic, sensing, and energy device applications.