Low-Temperature Bonding of GaN on Si Using a Nonalloyed Metal Ohmic Contact Layer for GaN-Based Heterogeneous Devices

A low-temperature integration process for GaN-based heterogeneous devices was demonstrated by low-temperature bonding with Cr/Au thin films. Nonalloyed Cr/Au ohmic contacts on n-type GaN were obtained by surface treatment with low-energy fast atom beams of Ar for 15 s prior to metal deposition on n-type GaN. The as-deposited Cr/Au (50/250 nm) contacts showed a smooth surface with a root-mean-square roughness of 1.8 nm. Au-Au surface-activated bonding was carried out at 150 degrees C in ambient air after surface activation by an Ar radio-frequency plasma. The GaN/Si samples bonded at a low temperature were so strong that bulk fracture was observed after the tensile test.