Room temperature GaN-GaAs direct bonding by argon-beam surface activation

A room temperature direct bonding using surface activation by argon (Ar)-beam sputtering was applied to the bonding between gallium nitride (GaN) and gallium arsenide (GaAs). The silicon doped n-type GaN films used in this experiment were grown by metal organic chemical vapor deposition on (0001) sapphire substrates. The GaN film thickness is 3 μm with a surface roughness of approximately 0.22 nm (Ra) as measured by atomic force microscopy. The silicon doped n-type GaAs (100) wafers with a surface roughness of approximately 0.34 nm (Ra) were used as GaAs substrates. The GaN and GaAs samples were cleaned by sputtering with a 1.5 keV Ar-fast atom beam with 15 mA in the vacuum chamber (background pressure: 1.3×10-5~4.0×10-4 Pa). Then, the samples were brought into contact as quickly as possible with a load of 735 N at room temperature. After this process, GaN films were successfully bonded to GaAs substrates without any heat treatment. Cross-sectional scanning electron microscopy showed that most of the interface area was well bonded. The bonding strength was evaluated by die-shear tests. Although all samples were visibly separated from the interface rather than in the bulk region after die-shear tests, the estimated die-shear strength of GaN/GaAs structures was 1.5 -7 MPa. The advantage of our process is free from the various problems caused by the large thermal expansion mismatch during heat treatment in the conventional fusion bonding.

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