Precise Alignment to Quantum Dots

May 12, 2008 By Miranda Marquit feature

“Precise lithographic alignment to site-controlled quantum dots is of major importance for numerous nano-photonic, nano-electronic and nano-spintronic devices,” Sven Höfling tells PhysOrg.com.

Höfling continues: “So far, most of the devices based on single quantum dots use a layer of self-organized quantum dots, where the dots are at random positions and a post-fabrication screening is employed to select devices with proper spectral and spatial alignment, for example, with respect to a cavity mode. After all, whether or not you can find a proper quantum dot is largely a matter of chance“

Höfling and his colleagues at Julius Maximilians University in Würzburg, Germany believe that they have come up with a scheme that would make it much easier to produce single dot-based devices to be used in the fabrication process of nano devices. The results from the team in Würzburg are reported in Applied Physics Letters: “Lithographic alignment to site-controlled quantum dots for device integration.”

“Previously used approaches were sufficient for the realization of single, research type devices, whose main purpose is the study of basic physics,” Höfling concedes, “but it does not allow for large scale device fabrication needed for widespread applications.” Right now, he points out, in many cases the yield of these nano devices is close to zero.

In order to usher in an era of widespread applications for nano devices, the Würzburg team combined two processes to produce single dot device with higher yield: a site-controlled quantum dot growth by pre-patterning and an accurate alignment technique. “People have pioneered this pre-patterned quantum dot growth before,” says Höfling. “Others have made accurate alignment. By combining them together, we are investigating a serious scheme that is scalable. This will significantly increase the yield of single quantum dot based devices.”

By using the accurate alignment, it is possible to know where the quantum dots are, allowing fabricators to pinpoint them and “use, for instance, a pulsed laser to excite them so that they emit single photons on demand,” Höfling says. “Before, it was guesswork. A random distribution of quantum dots would have to be used, shining light on it and hoping to find a proper located quantum dot in the device. Now, it’s much easier”.

Höfling does point out that the work needs to carry on further. “Right now, this work addresses spatial aspects only. We know in advance where the quantum dots are, but they can still have different properties. We also need to control better their properties, namely we need additionally a spectrally deterministic technology. That is what we are working on now, but site-control can here also be very useful to manipulate the properties of the quantum dots.”

Even without the spectral aspect, though, Höfling thinks that the work done by him and his peers has the potential to be very useful in the future. He says that single photon sources, single quantum dot lasers, electron memory devices, entangled photon pair emitters and the semiconductor building blocks for quantum information processing could all advance with help from this technology.

“Everything is decreasing in size,” Höfling points out, “and we need smaller and smaller devices. At some point, we are going to need to be able to produce single quantum dot based devices.”

“We have, in the meantime, succeeded to couple a single quantum dot spatially in a spatially deterministic way with a single photonic crystal mode,” he continues, “yielding a device which is capable of efficiently emitting single photons on demand.”

Copyright 2007 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

Explore further: Meet the high-performance single-molecule diode

Related Stories

Meet the high-performance single-molecule diode

July 29, 2015

A team of researchers from Berkeley Lab and Columbia University has passed a major milestone in molecular electronics with the creation of the world's highest-performance single-molecule diode. Working at Berkeley Lab's Molecular ...

Controlling interactions between distant qubits

July 23, 2015

A big part of the burgeoning science of quantum computation is reliably storing and processing information in the form of quantum bits, or qubits. One of the obstacles to this goal is the difficulty of preserving the fragile ...

New technique to synthesise nanostructured nanowires

July 16, 2015

Researchers have developed a new method for growing 'hybrid' crystals at the nanoscale, in which quantum dots – essentially nanoscale semiconductors – of different materials can be sequentially incorporated into a host ...

Recommended for you

Robotic insect mimics nature's extreme moves

July 30, 2015

The concept of walking on water might sound supernatural, but in fact it is a quite natural phenomenon. Many small living creatures leverage water's surface tension to maneuver themselves around. One of the most complex maneuvers, ...

The sound of music, according to physicists

July 30, 2015

Joshua Bodon is sick of hearing "Somewhere Over the Rainbow." More specifically, he's sick of hearing one 25-second clip of the song repeated more than 550 times.

New blow for 'supersymmetry' physics theory

July 27, 2015

In a new blow for the futuristic "supersymmetry" theory of the universe's basic anatomy, experts reported fresh evidence Monday of subatomic activity consistent with the mainstream Standard Model of particle physics.

0 comments

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.