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: Study details laser pulse effects on behavior of electrons

add to favorites email to friend print save as pdf

Related Stories

New 2-D quantum materials for nanoelectronics

Nov 21, 2014

Researchers at MIT say they have carried out a theoretical analysis showing that a family of two-dimensional materials exhibits exotic quantum properties that may enable a new type of nanoscale electronics.

New terahertz device could strengthen security

Nov 21, 2014

We are all familiar with the hassles that accompany air travel. We shuffle through long lines, remove our shoes, and carry liquids in regulation-sized tubes. And even after all the effort, we still wonder if these procedures ...

Spiral laser beam creates quantum whirlpool

Nov 17, 2014

(Phys.org) —Physicists at Australian National University have engineered a spiral laser beam and used it to create a whirlpool of hybrid light-matter particles called polaritons.

Princeton team explores 3D-printed quantum dot LEDs

Nov 06, 2014

Some of the most important developments marking advances in the 3D printing industry are in the realm of material science, notes 3d Printing Industry. "The more materials we can print, the more useful the ...

On-demand conductivity for graphene nanoribbons

Nov 10, 2014

Physicists have, for the first time, explored in detail the time evolution of the conductivity, as well as other quantum-level electron transport characteristics, of a graphene device subjected to periodic ...

Recommended for you

Particles, waves and ants

16 hours ago

Animals looking for food or light waves moving through turbid media – astonishing similarities have now been found between completely different phenomena.

User comments : 0

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.