Nanobonding for Multi-Junction Solar Cells at Room Temperature

Abstract

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.

Fabrication of GaInP/GaAs//Si Solar Cells by Surface Activated Direct Wafer Bonding

“…Another technique is the surface activated wafer bonding where the surfaces are treated either with a reactive plasma [14] or with a beam of highly energetic ions or neutral atoms [15] prior bonding. Surface activated Si/GaAs bonds at room temperature after the argon fast atom beam treatment with high mechanical strength have been reported by different groups [16], [17]. Today wafer bonding is an established fabrication method for the integration of optoelectronic devices like lasers or photodetectors on Si integrated circuits and starts being used for the fabrication of high-efficiency solar cells [18], [19].…”

Fast Atom Beam Activated Wafer Bonds between n-Si and n-GaAs with Low Resistance

“…In this method the surfaces are deoxidized by sputtering with highly energetic argon atoms and bonded in a vacuum chamber. It was shown, that the argon bombardment leads to the formation of an amorphous interface layer 9,12 which disturbs the current transport over p-GaAs/n-Si 11,12 and n-GaAs/n-Si bond interfaces. 13 Current-voltage characteristics of fast atom beam activated n-GaAs/n-Si bonds were found to be diode-like 13 and the interface resistance leads to significant losses in multi-junction solar cells operating under high light intensities (50 W/cm 2 ).…”

Transport characteristics of minority electrons across surface-activated-bonding based p-Si/n-4H-SiC heterointerfaces

“…This view is consistent with frequently reported features in SAB-based interfaces that the thicknesses of amorphous layers formed at interfaces immediately after bonding are reduced upon annealing at temperatures lower than the eutectic points. 18,30) Irrespective of the mechanism underlying the enhanced current gain, the obtained β suggests that the intrinsic quality of SiC=Si bonding interfaces is favorable for the minority carriers to be injected across the interfaces with high efficiency at room temperature. HBTs with further improved device performances are likely to be achieved by optimizing the device structures and device fabrication process.…”