Current–voltage and spectral-response characteristics of surface-activated-bonding-based InGaP/GaAs/Si hybrid triple-junction cells

Abstract

We measured the current-voltage (I-V) and spectral-response characteristics of InGaP/GaAs/Si hybrid triple-junction cells that were fabricated by using surface-activated bonding methods. We found by spectral response measurements that the current generated in the Si-based bottom cell was lower than those in the top and middle cells under the conditions of an air mass of 1.5G and one sun. Furthermore we observed a discrepancy between the short-circuit current, which was obtained by subtracting the estimated contribution of Si ledges surrounding InGaP/GaAs mesas to the I-V characteristics, and the results of spectral response measurements. One possible model for explaining the discrepancy was discussed on the basis of the electrical coupling scheme between subcells. The intrinsic conversion efficiency of a 5 ' 5 mm 2 triple-junction cell was crudely estimated to be >26% by compensating for the shadow loss as well as subtracting the contribution of Si ledges.

Electrical properties of GaAs//indium tin oxide/Si junctions for III–V-on-Si hybrid multijunction cells

“…Using SAB, dissimilar semiconductor substrates with different lattice constants and thermal expansion coefficients can be directly bonded to each other without heating. Previously, SAB-based InGaP=Si, 12) GaN=Si, 13) and InGaP=GaAs= Si 14,15) multijunction solar cells were reported by the present authors.…”

Intrinsic microstructure of Si/GaAs heterointerfaces fabricated by surface-activated bonding at room temperature

“…Alternatively, surface-activated bonding (SAB) at room temperature, 11) in which surfaces of substrates are activated before bonding by creating dangling bonds via the removal of contaminants under an energetic particle bombardment in high vacuum, is applied to form tough Si=III-V heterointerfaces without macro defects. 12) InGaP=GaAs==Si hybrid multijunction cells with a high efficiency up to 26% are demonstrated using the SAB method, 13,14) even though the estimated efficiency is still lower than the theoretical one of about 40%. 15) In the SAB method, it is believed that an amorphous-like intermediate layer, less than 7-8 nm in thickness, is formed on the surfaces in the surface activation process.…”

Mapping of Si/SiC p–n heterojunctions using scanning internal photoemission microscopy

“…9) As a next generation of development, recently, bonding interfaces have been used as active parts in the devices, typically seen in hybrid tandem solar cells. 10) It is notable that the reported conduction band discontinuities in Si=SiC heterojunctions fabricated by a conventional bonding method are largely scattered between 0.21 and 1.9 eV. 5,11) This suggests that the electrical properties of the Si=SiC heterojunctions largely vary with surface wet chemical treatment and possible interface states.…”