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

December 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: Quantum communication controlled by resonance in 'artificial atoms'

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).

Related Stories

An optical switch based on a single nano-diamond

October 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. The scientific ...

Squeezing transistors really hard generates energy savings

December 6, 2013

Transistors, the workhorses of the electronics world, are plagued by leakage current. This results in unnecessary energy losses, which is why smartphones and laptops, for example, have to be recharged so often. Tom van Hemert ...

Nontoxic quantum dot research improves solar cells

December 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

Physicists develop new technique to fathom 'smart' materials

November 26, 2015

Physicists from the FOM Foundation and Leiden University have found a way to better understand the properties of manmade 'smart' materials. Their method reveals how stacked layers in such a material work together to bring ...

Mathematicians identify limits to heat flow at the nanoscale

November 24, 2015

How much heat can two bodies exchange without touching? For over a century, scientists have been able to answer this question for virtually any pair of objects in the macroscopic world, from the rate at which a campfire can ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.