Surface activated bonding of GaN and its application for optical devices

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Bonding of n-type GaN to gallium arsenide (GaAs) and polycrystalline Al was realized by surface activated bonding method at room temperature. The interface microstructure, bonding strength, and electrical characteristics of bonded interface junctions have been investigated through transmission electron microscopy (TEM), die-shear strength testing, tensile strength testing, and current-voltage (I-V) measurements. The silicon doped n-type GaN films used in this experiment were grown by metal organic chemical vapor deposition on (0001) sapphire substrates. For producing active surfaces, argon-fast atom beam (FAB) sputtering source (acceleration voltage and current of 1.5 kV and 15 mA) was used. The background pressure in the bonding chamber was in the range of 4×10^<-4>-6×10^<-7> Pa. The samples were brought into contact as quickly as possible at room temperature after surface activation. GaN films were successfully bonded to GaAs substrates and polycrystalline Al rods without any heat treatment. Cross-sectional TEM of GaN/Al samples bonded at room temperature showed a nearly continuous amorphous thin interlayer with a thickness of about 10 nm at the interface. The die-shear strength of GaN/GaAs was in the range of 1.5 -7 MPa. The tensile strength of GaN/Al was in the range of 14-19 MPa. The results of I-V measurements showed that the n-GaN/Al junctions without annealing were rectifying, and became ohmic after annealing in N_2 at 600℃. 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.