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Semiconductor Wafer Fusion Bonding and Single Photon Detectors |
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Single photon detectors that feature high quantum efficiency, low dark counts, photon number resolving capability and small timing jitter are indispensible requirement for various quantum communication protocols. Visible light photon counters (VLPCs) have demonstrated much of these properties in the visible (400-1000 nm) range. Extending the operation of these detectors to the ultraviolet (300-400 nm) and the infrared (1300-1600 nm) is critical for ion trap quantum information processing and long-distance quantum communication experiments. The MIST group has extensive experience in working with VLPCs. We have a cryostat optimized for operating VLPCs, with low temperature broadband amplifiers and optimal fiber coupling of input fields. Leveraging our expertise, we have been exploring modifications to VLPCs in collaboration with Dr. Henry H. Hogue at DRS Technologies. In an effort to fabricate the variants of VLPCs that operate beyond the normal absorption range of silicon, we constructed Schottky diode photodetectors to enhance the operation in the UV and fusion-bonded InGaAs absorption layers onto VLPC gain layers for the operation in the IR. The Schottky diode demonstrated dramatic improvement of VLPC’s quantum efficiency comparable to those achievable in conventional PMTs. The fusion bonding of Si and InGaAs revealed a crucial issue in the band alignment between the two semiconductor materials, which seems to critically depend on the chemistry of the interface as the materials are fused together. |
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· Kyle S. McKay |
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Project Participants: |
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· Air Force Office of Scientific Research |
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Project Sponsor: |
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· Dr. Henry H. Hogue, DRS Technologies · Prof. Scott Wolter, ECE, Duke University |
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Project Collaborators: |
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Traditionally, heterojunctions were grown in-situ and therefore strictly constrained by the lattice mismatch between the two materials that can be epitaxially grown on top of the other. Fusion bonding of dissimilar semiconductor materials removes this constraints as long as the crystallographic defects are confined at the fused interfaces and do not propagate into the material. However, the required surface preparation prior to fusion bonding puts constraints on the chemistry at the interface, which dominates the relative band alignment of the two material systems. In order to study this effect, we are constructing a UHV wafer fusion bonding system, which will provide us with the ultimate flexibility in the creation of heterojunctions. The figure shows the UHV fusion bonding system we are currently putting together. The fusion bonding chamber will be connected to an existing UHV system with separate chambers for sputter deposition of metals, XPS and UPS analysis, and optical ellipsometry analysis. This system allows us to prepare and analyze the surface of the semiconductor interfaces prior to fusion bonding in-situ. |
