Direct wafer bonding of highly conductive GaSb/GaInAs and GaSb/GaInP heterojunctions prepared by argon-beam surface activation

The authors present a low-temperature wafer bonding process for the formation of electrically conductive n-GaSb/n-Ga_0.79In_0.21As and n-GaSb/n-Ga_0.32In_0.68P heterojunctions. The surfaces are deoxidized by sputter-etching with an argon-beam and bonded in ultrahigh vacuum. The sputtering behavior was investigated for each material, revealing a distinct selective sputtering characteristic for Ga_0.32In_0.68P. According to these findings, the settings for the bonding process were chosen. The mechanical and electrical properties of the wafer bonds were studied. Fully bonded 2 in. wafer pairs were found for both material combinations exhibiting high bond energies, which are comparable to the binding energies in the semiconductors. Furthermore, bond resistances below 5 mΩ cm² could be reached, which are in the range of the lowest resistances that have been reported for wafer bonded heterojunctions. This speaks, together with the high bond energies, for a high amount of covalent bonds at the interfaces. These promising bond characteristics make the integration of antimonides with arsenides or phosphides by wafer bonding attractive for various optoelectronic applications such as multijunction solar cells.