Shot Noise in Semiconductor Nanostructures

Quantum Shot Noise in Silicon CMOS Quantum Dot

Shot noise in quantum conductors reflects the granularity of charge transfers across the conductor, particularly their statistics. Measuring shot noise allows probing non-Markovian dynamics, where the transfer of one charge across a quantum conductor influences the transfer of the next charge. This peculiar correlated transport regime is associated with large current fluctuations (i.e. shot noise). This can be observed in quantum dots in the inelastic cotunneling regime, where single charge tunneling is prohibited by the large Coulomb energy of the dot, and second order processes involving two charges are dominant. Indeed, after each single inelastic cotunneling event, the quantum dot ends up in a different state, changing the conditions for the next cotunneling event.

We perform high-sensivity shot noise measurements in quantum dots realized in Silicon CMOS nonowires, in the foundry of CEA-LETI in Grenoble. This industrial-grade devices can have extremely small dimensions, below 15 nm in width, giving rise to remarkably stable Coulomb blockade features with very large energy scales. This allows us to observe very clear increase in the fluctuations with different amplitudes depending on the number of states involved in the transport.

This project is part of a collaboration between the Nanoelectronics group, the LATEQS laboratory in INAC-CEA Grenoble, and CEA-LETI in Grenoble

People: M. Seo, P. Roulleau, F. D. Parmentier

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Transmission electron microscope image of the cross-section of a 12 nm-wide CMOS Silicon nanowire, with an "Omega"-shaped gate surrounding it. The device is fabricated in LETI foundry in Grenoble.
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Fano factor (corresponding to the ratio between the measured shot noise and its expected Poissonian value) of a CMOS quantum dot as a function of gate and drain-source voltages.

Photon-Assisted Shot Noise Detection

Measuring the high frequency electromagnetic power radiated by a quantum conductor in a microwave circuit is challenging. The important mismatch between the quantum conductor impedance (h/e2) and the typical circuit impedance (50 Ω) makes for example the detection of the high frequency shot noise limited to few GHz. To circumvent this limitation, on-chip photon detectors have been developed using a second nearby quantum conductor and exploiting its photon detection ability. Examples are GaAs/AlGaAs 2D electron gas patterned quantum dots and Aluminium or Niobium SIS junctions.
These detectors have shown high sensitivity but need very low temperatures and lack of a universal photon-response. The
photon-response of quantum dots depends on an energy scale set by their geometry, that of superconducting junctions is limited by a characteristic energy gap and both systems show tunnel resistance variability. Regarding bolometric detectors their efficiency depends on the phonon relaxation time, requires low temperature and shows slow response time. We propose here to use the effect of Photon-Assisted Shot Noise (PASN) for on-chip radiation detection.
It is based on the low frequency current noise generated by the partitioning of photon excited electron and holes which are
scattered by the conductor. Remarkably, the resulting PASN noise provides a direct counting of the electron-hole pairs whose number is universally related to the incident radiation power. Up to a Fano factor, characterizing the type of scattering, the PASN response is independent on the nature and geometry of the quantum conductor used for detection. Ordered in temperature/frequency range, from few tens of milli-Kelvin and GHz frequency to several hundreds of Kelvin and THz, a wide range of conductors can be used like Quantum Point Contacts (this work), diffusive metallic or semi-conducting films, Graphene, Carbone nanotubes and other molecular conductors. PASN radiation detector are also expected very fast and only limited by
the electron dwell time in the scattering region of the conductor.

  • Harvesting dissipated energy with a mesoscopic ratchet, B. Roche, P. Roulleau, T. Jullien, Y. Jompol, I. Farrer, D.A. Ritchie and D.C. Glattli, Nature Communications 6, Article number: 6738 (2015)
  • Detecting noise with shot noise: a new on-chip Photon Detector, Y. Jompol, P. Roulleau, T. Jullien, B. Roche, I. Farrer, D.A. Ritchie and D.C. Glattli, Nature Communications 6, Article number: 6130 (2015)
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Scanning electron microscope view of the sample. Two lines defined by wet etching of the mesa are coupled via a coupling capacitance CC. On the upper line are patterned two QPCs in series: in red the QPC emitter, and in white a series resistor tuned on a plateau (therefore noiseless). On the lower line, the QPC detector is colored in blue.