Adapted from this Berkeley Lab ATAP press release
An international team of scientists including Foundry staff has used intense ion pules to form tiny artificial defects in silicon crystals that could allow information to be encoded in quantum bits. The work could lay the foundations for new devices for applications in quantum information science (QIS), an emerging field that promises to transform security, computing, and communications.
Microscopic defects in silicon crystals, called color centers, have long been known to form when the crystals are exposed to high-energy particles. Photon-emitting defects are attracting considerable attention because of their ability to connect photons and the spins states of electrons and nuclei. This ability makes them ideal candidates for quantum applications with single photon sources and for use in quantum networking—communication networks that securely interconnect quantum devices and systems.
Color centers can take different forms, such as W-centers, which are intrinsic defects in the crystal lattice comprised of three silicon interstitial atoms, G-centers, in which implanted pairs of carbon atoms bind to a silicon interstitial atom, and many others.
To create these color centers in silicon crystals, the researchers used the Berkeley Lab Laser Accelerator (BELLA) Center’s petawatt laser to form intense, high-powered laser pulses quadrillionths (a million-billionths) of a second in duration. They aimed these pulses at a microns-thick foil target, creating a dense plasma from the foil that released low-energy atoms. These atoms, initially implanted near the surface of the silicon, can diffuse into the silicon and form G-centers and other color centers following pre-heating by high-energy ions also emitted from the same laser-ion pulse.
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Without access to a high-quality laser like the one at the BELLA Center, which can deliver petawatt-level pulses at repetition rates up to 1 Hz, it would not have been possible to generate a series of many low- and high-energy ions pulses that are needed to reliably form and place the color centers in the crystalline lattice.
The team then used a suite of materials analysis techniques, including electron and helium ion microscopy to study the surface morphology of the silicon, secondary ion mass spectrometry, nuclear reaction analysis, and channeling Rutherford backscattering to measure the atomic composition and depth profile in the samples, as well as low-temperature photoluminescence to observe the optical properties of the color centers.
The work demonstrates a novel and effective method of “laser-ion doping” of materials and for creating color centers using ion pulses from a laser accelerator for direct local defect engineering and high-flux doping of semiconductors like silicon.
Thomas Schenkel, a Senior Scientist who heads ATAP’s Fusion Science & Ion Beam Technology Program and led the research, noted that the collaboration with Foundry staff scientist Liang Tan “enabled us to address critical aspects of color center theory, synthesis, and characterization, and was essential to completing the study.”
Read the full press release