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

Abstract

Fast atom beam activated direct wafer bonds can be used to combine GaAs and Si semiconductor structures and to achieve high bond strength and optical transparency. Some applications require a low ohmic resistance between the materials. Therefore, IV-characteristics of n-type wafer bonds between n-Si and n-GaAs were thoroughly investigated. n-Si/n-Si bonds showed ohmic resistance below 2.5 × 10−3 Ωcm2. However diode like IV-curves were found for both n-GaAs/n-GaAs and n-Si/n-GaAs bonds. This can be explained by the formation of a potential barrier at the interface, caused by carrier trapping in fast atom beam induced defects. Hall measurements of n-GaAs after fast atom beam treatment confirmed both, a reduction of the active carrier concentration, and the electron mobility. It was found that thermal annealing and higher bond temperatures can help reducing the potential barrier height at the n-Si/n-GaAs interface and thus lower the electrical bond resistance by healing crystalline defects. Highly conductive n-Si/n-GaAs wafer bonds with an interface resistance below 3.6 × 10−3 Ωcm2 were achieved after the optimization.

Investigation of room-temperature wafer bonded GaInP/GaAs/InGaAsP triple-junction solar cells

“…A wafer-bonding interface with a low resistance is an essential physical property of the semiconductor bond. [14~16] However, in conventional wafer-banding techniques, such as fast-atom-beam-activated wafer bonding [17,18] and fused bonding [14,16] , high-temperature or long annealing was generally required to achieve high mechanical strength and low electrical resistances. High temperature annealing would not only bring about wafer bending and void formation at a bonding interface owing to the difference in thermal expansion coefficients, but also cause the diffusion of dopants from heavily doped tunnel junctions between sub-cells, leading to the degradation of the tunnel junctions.…”

Status of Four-Junction Cell Development at Fraunhofer ISE

“…Bonding allows the combination of a wide range of different materials. Low resistance bonds between various materials have already been demonstrated including Si//GaAs, InP//GaAs and GaSb//GaInAs [19][20][21]…”

“…1.9eV and Al 0.03 Ga 0.97 As 1.47 eV) on GaAs while the second consists of an indiffused Ge cell (0.66 eV) with a metamorphic buffer structure and a Ga 0.81 In 0 19. As cell (1.15 eV).…”

III-V Multi-junction solar cells and concentrating photovoltaic (CPV) systems

“…Recently, a consortium of Fraunhofer ISE, Soitec, CEA-Leti, and Helmholtz Center Berlin investigated a fourjunction solar cell using wafer-bonding technology for terrestrial concentrator applications. Here, the challenge is to obtain a very low ohmic resistance at the wafer-bonding interface [45]. The structure consists of a GaInP/GaAs dualjunction wafer bonded to a GaInAsP/GaInAs dual junction.…”