Low-energy hydrogen ion bombardment is used to clean GaAs surfaces. The hydrogen ions produce contamination-free surfaces without changes in surface composition (stoichiometry) and surface roughness. The wafers were brought into contact at room temperature after cleaning under ultra-high vacuum (UHV), and bonded over the whole area (2 inches) without application of external mechanical pressure. After bonding, the p-GaAs/n-GaAs wafer pair was annealed at 200 °C for 30 min under UHV conditions (<5×10 mbar) to improve the interface bonding strength and to achieve a full-area wafer bonding.
Infrared (IR) imaging of the as-bonded wafers directly reveal the real bonding behaviour. High-resolution transmission electron microscopy images reveal that the wafers have been directly bonded without damage of the crystal lattice or intermediate layer and the interface is smooth. Current–voltage characterization shows near-ideal forward characteristics and the recombination in p–n junction space charge region.