Nanobonding for Multi-Junction Solar Cells at Room Temperature

Direct nanobonding of p-Si/n-GaAs wafers based on surface activation that uses an Argon (Ar)-fast atom beam at room temperature has been investigated. The bonding strength of the interface was 14.4 MPa at room temperature, and remained nearly constant after annealing up to 600 °C. An amorphous layer with a thickness of 11.5 nm was found across the interface without annealing. After annealing, the electrical current-voltage (I-V) characteristics were improved and the amorphous layer was diminished across the interface. The thermal stability of the interfacial properties of Si/GaAs indicates its potential use on the fabrication of multi-junction solar cells with Si substrate to lower the cost while improving the solar cells' efficiency. The thickness dependence of p-Si/n-Si interfacial I-V characteristics using COMSOL simulation indicates the decrease of breakdown voltage and current with the increase of the junction thickness.