UCL / LCN Seminar: Measuring properties of single defects, dopants and quantum dots with nm spatial resolution – Prof. Peter Grütter, McGill University

UCL / LCN Seminar: Measuring properties of single defects, dopants and quantum dots with nm spatial resolution – Prof. Peter Grütter, McGill University Share on X

Peter is a visitor at the LCN until 5 June, so if you would like to meet him you can contact me, or him directly, please contact Neil Curson (n.curson@ucl.ac.uk).

Semiconductor interfaces often have isolated trap states which modify electronic properties. We have developed a framework to quantitatively describe a metal-insulator semiconductor (MIS) device formed out of a metallic AFM tip, vacuum gap, and semiconducting sample. This framework allows the measurement of local dopant concentration, bandgap and band bending timescales with nm scale resolution of different defects on semiconductors such as 2D MoSe₂, Si and pentacene monolayers [1].

Specifically, we have characterize individual defects at the Si-SiOx interface. We show that surface charge equilibration timescales, which range from 1−150 ns, increase significantly around interfacial states [2]. From this we conclude that dielectric loss under time-varying gate biases in metal-insulator-semiconductor capacitor device architectures is highly spatially heterogeneous over nm length scales. We have also analyzed two-state fluctuations localized at these interfacial traps, exhibiting bias-dependent rates and amplitudes. When measured as an ensemble, these observed defects have a 1/f power spectral trend at low frequencies [3]. Low-frequency noise due to two level fluctuations inhibits the reliability and performance of nanoscale semiconductor devices, and challenges the scaling of emerging qubits. The presented method and insights provide a more detailed understanding of the origins of 1/f noise in silicon-based classical and quantum devices, and could be used to develop processing techniques to reduce two-state fluctuations associated with defects.

Finally, I will demonstrate that properties can be measured with a time resolution limited only by the minimal energy (or force) detectable by AFM. We demonstrate this by mechanically detecting the intensity autocorrelation of a 100fs optical pulse and locally mapping the second order non-linear susceptibility c⁽²⁾. This opens the door to future atomically resolved spatio-dynamic characterization of exciton generation and recombination sites or the identification of defects in 2D materials suitable for emission of entangled photons.

References:

[1] M. Cowie, et al., Phys. Rev. Materials 6, 104002 (2022)
[2] M. Cowie, et al., Phys. Rev. Lett. 132, 256202 (2024)
[3] M. Cowie, et al., Proc. Natl. Acad. Sci. USA 121 (44) e2404456121 (2024)
[4] Z. Schumacher et al., Proc. Natl. Acad. Sci. USA 117, 19773 (2020)

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