The quantum dots in the opto-spintronic nanostructure are made from indium arsenide; each quantum dot is around 10,000 times smaller than the thickness of a human hair. Image: Yuqing Huang.
The quantum dots in the opto-spintronic nanostructure are made from indium arsenide; each quantum dot is around 10,000 times smaller than the thickness of a human hair. Image: Yuqing Huang.

In the future, it may be possible to use electron spin to store, process and transfer information in quantum computers. To this end, it has long been the goal of scientists to use spin-based quantum information technology at room temperature.

A team of researchers from Sweden, Finland and Japan have now constructed a semiconductor component in which information can be efficiently exchanged between electron spin and light at room temperature and above. The researchers report their new method in a paper in Nature Photonics.

It is well known that electrons have a negative charge, but they also have another property, namely spin, which may prove instrumental in the advance of information technology. Spintronics – a promising candidate for future information technology – uses this quantum property of electrons to store, process and transfer information. This should bring important benefits, such as higher speed and lower energy consumption than traditional electronics.

Developments in spintronics in recent decades have been based on the use of metals, and these developments have proved highly significant for the possibility of storing large amounts of data. But there would be several advantages to using spintronics based on semiconductors, in the same way that semiconductors form the backbone of today's electronics and photonics.

"One important advantage of spintronics based on semiconductors is the possibility to convert the information that is represented by the spin state and transfer it to light, and vice versa," says Weimin Chen, professor at Linköping University, Sweden, who led the project. "The technology is known as opto-spintronics. It would make it possible to integrate information processing and storage based on spin with information transfer through light."

Electronics used today operates at room temperature and above. A serious problem in the development of spintronics has been that electrons tend to switch and randomize their direction of spin as the temperature rises, causing the information coded by the electron spin states to be lost or become ambiguous.

A necessary condition for the development of semiconductor-based spintronics is being able to orient all the electrons in a semiconductor to the same spin state, known as spin polarization, and maintain it at room temperature and higher. The highest electron spin polarization achieved to date is around 60% at room temperature, which is untenable for large-scale practical applications.

Researchers at Linköping University, Tampere University in Finland and Hokkaido University in Japan have now achieved an electron spin polarization greater than 90% at room temperature, with the spin polarization remaining at a high level up to 110°C. The researchers achieved this technological advance using an opto-spintronic nanostructure constructed from layers of semiconductor nanocrystals known as quantum dots.

When a spin-polarized electron impinges on a quantum dot, it emits light – to be more precise, it emits a single photon with a state (angular momentum) determined by the electron spin. Quantum dots are therefore considered to have great potential as an interface for transferring information between electron spin and light, as will be necessary in spintronics, photonics and quantum computing. In the Nature Photonics paper, the scientists show that it is possible to use an adjacent spin filter to control the electron spin of the quantum dots remotely, and at room temperature.

The quantum dots are made from indium arsenide (InAs), with a layer of gallium nitrogen arsenide (GaNAs) that functions as the spin filter and a layer of gallium arsenide (GaAs) sandwiched between the InAs and GaNAs. Similar structures based on GaAs are already being used in conventional optoelectronic technology, and the researchers believe this could make it easier to integrate spintronics with existing electronic and photonic components.

"We are very happy that our long-term efforts to increase the expertise required to fabricate highly-controlled N-containing semiconductors is defining a new frontier in spintronics," says Mircea Guina, head of the research team at Tampere University. "So far, we have had a good level of success when using such materials for optoelectronics devices, most recently in high-efficiency solar-cells and laser diodes. Now we are looking forward to continuing this work and to unite photonics and spintronics, using a common platform for light-based and spin-based quantum technology in Finland."

This story is adapted from material from Linköping University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.