Technique makes it possible to measure the intrinsic properties of quantum dot transistors

Dec 20, 2013
Figure 1: Structure of a transistor based on a quantum dot. One at a time, electrons flow from the source to the drain through the quantum dot, depending on the potential of the gate electrode. The properties of such a transistor are strongly affected by the presence of stray quantum dots in the transistor channel.

Transistors are one of the most important devices in electronics and lie at the heart of modern computing. The progressive miniaturization of transistors is rapidly approaching the atomic scale, where even the tiniest imperfection can have a significant effect on performance. Keiji Ono and colleagues from the RIKEN Low Temperature Physics Laboratory have now developed a method for measuring the operational characteristics of single-atom 'quantum dot' transistors without the influence of surrounding imperfections.

When a pure material is implanted with isolated atoms of another element, the impurity atom can behave like a quantum dot, with properties quite different to its host matrix. Quantum dots can form the basis of transistor operation—switching an output on or off, depending on the state of an input—and can facilitate the transport of electrons through the transistor even when electron transport through the surrounding material, usually silicon, is blocked. In this configuration, while all electrons pass through the quantum dot, they can do so only one at a time. This makes the quantum-physical properties of the quantum dots dominant in the transistor's operation, producing a characteristic diamond shape in the measured current–voltage relationship.

Single-electron transport through the transistor, however, is very sensitive to external perturbations. Impurities in other parts of the transistor can cause stray electrical fields that act as quantum dots and thus influence the electrical behavior of the transistor and the appearance of the diamond shape in the electrical curves.

To counter such effects, Ono and his colleagues developed a measurement technique that allows them to quantify the effects of these 'stray' quantum dots so that the true properties of the main quantum dot can be isolated. The method is based on measurements of the transistor performance at various electrical voltages, which are analyzed using an electron transport model that incorporates the electrical effects of stray quantum dots. Among many uses, this information helps researchers to understand what voltages need to be applied to the in order to optimize the single-electron transport regime.

Although the quantum properties of through quantum dot transistors only appear at low temperatures, understanding the processes involved is also important for the optimization of regular transistors at room temperature, which are known to be affected by the presence of single defects in the transistor channel, says Ono. "We know quite a lot about . Applying quantum dot physics to commercial transistors is challenging but could have very useful implications."

Explore further: An optical switch based on a single nano-diamond

More information: Ono, K., Tanamoto, T. & Ohguro, T. Pseudosymmetric bias and correct estimation of Coulomb/confinement energy for unintentional quantum dot in channel of metal-oxide-semiconductor field-effect transistor. Applied Physics Letters 103, 183107 (2013). dx.doi.org/10.1063/1.4827817

Related Stories

An optical switch based on a single nano-diamond

Oct 15, 2013

A recent study led by researchers of the ICFO (Institute of Photonic Sciences) demonstrates that a single nano-diamond can be operated as an ultrafast single-emitter optical switch operating at room temperature. ...

Nontoxic quantum dot research improves solar cells

Dec 11, 2013

Solar cells made with low-cost, nontoxic copper-based quantum dots can achieve unprecedented longevity and efficiency, according to a study by Los Alamos National Laboratory and Sharp Corporation.

Recommended for you

Study sheds new light on why batteries go bad

Sep 14, 2014

A comprehensive look at how tiny particles in a lithium ion battery electrode behave shows that rapid-charging the battery and using it to do high-power, rapidly draining work may not be as damaging as researchers ...

Moving silicon atoms in graphene with atomic precision

Sep 12, 2014

Richard Feynman famously posed the question in 1959: is it possible to see and manipulate individual atoms in materials? For a time his vision seemed more science fiction than science, but starting with groundbreaking ...

Researchers create world's largest DNA origami

Sep 11, 2014

Researchers from North Carolina State University, Duke University and the University of Copenhagen have created the world's largest DNA origami, which are nanoscale constructions with applications ranging ...

Excitonic dark states shed light on TMDC atomic layers

Sep 11, 2014

(Phys.org) —A team of Berkeley Lab researchers believes it has uncovered the secret behind the unusual optoelectronic properties of single atomic layers of transition metal dichalcogenide (TMDC) materials, ...

User comments : 0