Jan 20, 2020

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

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.

Source:IOPscience

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Jan 13, 2020

Wafer-scale layer transfer of GaAs and Ge onto Si wafers using patterned epitaxial lift-off

We have developed a wafer-scale layer-transfer technique for transferring GaAs and Ge onto Si wafers of up to 300 mm in diameter. Lattice-matched GaAs or Ge layers were epitaxially grown on GaAs wafers using an AlAs release layer, which can subsequently be transferred onto a Si handle wafer via direct wafer bonding and patterned epitaxial lift-off (ELO). The crystal properties of the transferred GaAs layers were characterized by X-ray diffraction (XRD), photoluminescence, and the quality of the transferred Ge layers was characterized using Raman spectroscopy. We find that, after bonding and the wet ELO processes, the quality of the transferred GaAs and Ge layers remained the same compared to that of the as-grown epitaxial layers. Furthermore, we realized Ge-on-insulator and GaAs-on-insulator wafers by wafer-scale pattern ELO technique.

Source:IOPscience


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Jan 7, 2020

Interfacial and mechanical characterization of wafer-bonded GaSb/amorphous α-(Ga,As)/GaAs structure for GaSb-on-insulator applications

In this study, the feasibility of using wafer-bonding technology to fabricate a GaSb semiconductor on GaAs substrates for potentially creating a GaSb-on-insulator structure has been demonstrated. A GaSb wafer has been bonded on two types of GaAs substrates: (1) a regular single crystal semi-insulating GaAs substrate and (2) the GaAs wafers with pre-deposited low-temperature amorphous α-(Ga,As) layers. The microstructures and interface adhesion studies have been carried out on these wafer-bonded semiconductors. It has been found that the GaSb-on-α-(Ga,As) wafers have shown enhanced interface adhesion and lower temperature bonding capability.

Source:IOPscience

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Electrical Conductivity of Direct Wafer-Bonded GaAs/GaAs Structures for Wafer-Bonded Tandem Solar Cells

Wafer bonding of GaAs using an ammonium sulfide (NH4)2S treatment is investigated for various structures. The effect of the wafer offcut angle on the electrical conductivity of III-V solar cell devices using n-GaAs/n-GaAs wafer-bonded structures is studied. High resolution x-ray diffraction is used to confirm the misorientation of the bonded samples. Additionally, we compare the electrical properties of epitaxially grown p-n junctions on GaAs to n-GaAs/p-GaAs wafer-bonded structures. High resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) are used to compare the interface morphology across the range of relative misorientations after a 600 {degree sign}C RTP. The ratio of well-bonded crystalline regions to amorphous oxide inclusions is consistent across all bonded samples, indicating that the degree of misorientation does not affect the level of interface recrystallization at high temperatures.

Source:IOPscience

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