Improved electrical properties of wafer-bonded $p-GaAs/n-InP$ interfaces with sulfide passivation

Sulfide-passivated GaAs and InP wafers were directly bonded to explore the efficiency of sulfide passivation on the bonded interfacial properties. We find that the bonded GaAs/InP interfaces after sulfide passivation contain sulfur atoms and a decreased amount of oxide species relative to the pairs bonded after conventional acid treatment; however, the residual sulfur atoms have no effect on the bonding strength. The electrical properties of the bonded $p-GaAs/n-InP$ heterojunctions were studied for different acceptor concentrations in $p-GaAs$⁠. A reduced interfacial trap state density enhances the tunnel current flow across the depletion layer in the sulfide-passivated case. A directly bonded tunnel diode with a heavily doped $p-GaAs/n-InP$ heterojunction was achieved when the wafers were sulfide passivated and then bonded at temperatures as low as $300°C$⁠. This sulfide-passivated tunnel diode can be used for fabrication of lattice-mismatched multijunction solar cells in which subcells are integrated via direct bonding.