Low-temperature direct bonding of β-Ga2O3 and diamond substrates under atmospheric conditions

Surface-functionalized β-Ga2O3 and diamond substrates were directly bonded by annealing at 250 °C in atmospheric air. Prior to bonding, the β-Ga2O3 and diamond surfaces were OH-terminated by oxygen plasma irradiation and H2SO4/H2O2 cleaning, respectively. After contacting the OH-terminated surfaces with each other, direct bonding was formed by a thermal dehydration reaction. The annealed specimen had a shear strength of 14 MPa because of the generation of chemical bonds between β-Ga2O3 and diamond surfaces. The analysis of interface structures revealed that the β-Ga2O3 and diamond surfaces were atomically bonded without nano-voids, cracks, or any intermediate layer. The β-Ga2O3 and diamond substrates were bonded without any serious loss in crystallinity except for the outermost surfaces. We believe that the β-Ga2O3/diamond heterostructure can contribute to the high-power applications of β-Ga2O3 devices.