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Assessing atomically thin delta-doping of silicon using mid-infrared ellipsometry

Journal of Materials Research

Katzenmeyer, Aaron M.; Luk, Ting S.; Bussmann, Ezra B.; Young, Steve M.; Anderson, Evan M.; Marshall, Michael T.; Ohlhausen, J.A.; Kotula, Paul G.; Lu, Ping L.; Campbell, DeAnna M.; Lu, Tzu-Ming L.; Liu, Peter Q.; Ward, Daniel R.; Misra, Shashank M.

Hydrogen lithography has been used to template phosphine-based surface chemistry to fabricate atomic-scale devices, a process we abbreviate as atomic precision advanced manufacturing (APAM). Here, we use mid-infrared variable angle spectroscopic ellipsometry (IR-VASE) to characterize single-nanometer thickness phosphorus dopant layers (δ-layers) in silicon made using APAM compatible processes. A large Drude response is directly attributable to the δ-layer and can be used for nondestructive monitoring of the condition of the APAM layer when integrating additional processing steps. The carrier density and mobility extracted from our room temperature IR-VASE measurements are consistent with cryogenic magneto-transport measurements, showing that APAM δ-layers function at room temperature. Finally, the permittivity extracted from these measurements shows that the doping in the APAM δ-layers is so large that their low-frequency in-plane response is reminiscent of a silicide. However, there is no indication of a plasma resonance, likely due to reduced dimensionality and/or low scattering lifetime.

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TYPE Journal Article YEAR 2020
ScopusOSTIDOI

Photothermal alternative to device fabrication using atomic precision advanced manufacturing techniques

Proceedings of SPIE - The International Society for Optical Engineering

Katzenmeyer, Aaron M.; Dmitrovic, S.; Baczewski, Andrew D.; Bussmann, Ezra B.; Lu, Tzu-Ming L.; Anderson, Evan M.; Schmucker, S.W.; Ivie, J.A.; Campbell, DeAnna M.; Ward, D.R.; Wang, George T.; Misra, Shashank M.

The attachment of dopant precursor molecules to depassivated areas of hydrogen-terminated silicon templated with a scanning tunneling microscope (STM) has been used to create electronic devices with sub-nanometer precision, typically for quantum physics demonstrations, and to dope silicon past the solid-solubility limit, with potential applications in microelectronics and plasmonics. However, this process, which we call atomic precision advanced manufacturing (APAM), currently lacks the throughput required to develop sophisticated applications because there is no proven scalable hydrogen lithography pathway. Here, we demonstrate and characterize an APAM device workflow where STM lithography has been replaced with photolithography. An ultraviolet laser is shown to locally heat silicon controllably above the temperature required for hydrogen depassivation. STM images indicate a narrow range of laser energy density where hydrogen has been depassivated, and the surface remains well-ordered. A model for photothermal heating of silicon predicts a local temperature which is consistent with atomic-scale STM images of the photo-patterned regions. Finally, a simple device made by exposing photo-depassivated silicon to phosphine is found to have a carrier density and mobility similar to that produced by similar devices patterned by STM.

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TYPE Journal Article YEAR 2020
ScopusOSTIDOI

Creation of nanoscale magnetic fields using nano-magnet arrays

AIP Advances

Sapkota, Keshab R.; Eley, S.; Bussmann, Ezra B.; Harris, C.T.; Maurer, Leon M.; Lu, Tzu-Ming L.

We present the fabrication of nano-magnet arrays, comprised of two sets of interleaving SmCo5 and Co nano-magnets, and the subsequent development and implementation of a protocol to program the array to create a one-dimensional rotating magnetic field. We designed the array based on the microstructural and magnetic properties of SmCo5 films annealed under different conditions, also presented here. Leveraging the extremely high contrast in coercivity between SmCo5 and Co, we applied a sequence of external magnetic fields to program the nano-magnet arrays into a configuration with alternating polarization, which based on simulations creates a rotating magnetic field in the vicinity of nano-magnets. Our proof-of-concept demonstration shows that complex, nanoscale magnetic fields can be synthesized through coercivity contrast of constituent magnetic materials and carefully designed sequences of programming magnetic fields.

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TYPE Journal Article YEAR 2019
ScopusOSTIDOI
Results 26–50 of 95
Results 26–50 of 95