Breakthroughs Enable Spin Electronics Of Semiconductors

Future information technology that uses the spin of electrons to process information could be used in quantum computers. Researchers have long strived to make spin-based information technology work at room temperature. Now, researchers from Sweden, Finland and Japan have designed a semiconductor component where information can be efficiently transferred between electron spins and light at higher temperatures.

Most people know that electrons have a negative charge, but they also have another property, namely spin. Electron spin has the potential to contribute to the development of information technology. Simplified, we can imagine spin as the electron rotating around its axis, much like the globe spins around its own axis. Spintronics is a promising candidate for future information technology, which utilizes this quantum property of electrons to store, process and transmit information. It brings several important advantages, such as higher speed and lower energy consumption compared to traditional electronics.

In recent decades, the development of spin electronics based on metals has been of great importance for the ability to store large amounts of data. But there would be several advantages to developing spin electronics based on semiconductor materials, in the same way that semiconductor technology is the backbone of today's electronics and photonics.

- An important advantage of spin electronics based on semiconductors is the potential to transform the information represented by the spin state and transmit it to light, and vice versa. Such technology is called opto-spin electronics. This would make it possible to integrate spin-based information processing and storage with optical information transfer, says Weimin Chen, professor at the Department of Physics, Chemistry and Biology (IFM) at Linköping University, who has led the study published in Nature Photonics .

The temperature sets it
One catch is that today's electronics are used at room temperature and warmer. A real obstacle on the way in the development of spin electronics has been that the electrons tend to randomly change spin direction when the temperature rises, so that the information encoded with the spin state of the electrons is lost or becomes unclear. A prerequisite for the development of spin electronics based on semiconductor materials is therefore that we can orient almost all electrons in the same spin state and keep them that way, ie that the electrons are spin-polarized at room temperature and warmer. Previous research has achieved a maximum of 60 percent electron spin polarization.

Now, researchers at Linköping University, Tampere University and Hokkaido University have succeeded in achieving over 90 percent electron spin polarization at room temperature. The spin polarization remains high up to 110 ° C. The basis for the progress is the nanostructure that the researchers have constructed from layers of different semiconductor materials (see description under the article). This opto-spin electronics structure contains nanoscale areas called quantum dots. Each quantum dot is around 10,000 times smaller than the thickness of a hair. When the quantum dot is struck by an electron, it emits light, or more specifically an individual photon whose state is determined by the electron's spin. Quantum dots are therefore considered to have great potential as an interface for transmitting information between electron spin and light in spin electronics, photonics and quantum computers.

Well-known materials
The quantum dots consist of indium arsenide (InAs) and a layer of gallium nitrogen arsenide (GaNAs) acts as a spin filter. Between them is a layer of gallium arsenide (GaAs). Similar structures are already used in optoelectronics based on gallium arsenide, and the researchers believe that it can facilitate the integration of spin electronics with existing electronic and photonic components.

- We are very pleased that our long-term efforts to increase the knowledge required to create well-controlled nitrogen-based semiconductors push the boundaries of spin electronics. So far, we have succeeded well in using such materials in optoelectronics, such as highly efficient solar cells and laser diodes. We now look forward to continuing this work and combining photonics and spintronics with a common platform for light-based and spin-based information technology, says Professor Mircea Guina, who leads the research group at Tampere University in Finland.

The research has been funded with support from, among others, the Swedish Research Council, the Foundation for Internationalization of Higher Education and Research (STINT), the government's strategic initiative Advanced Functional Materials at Linköping University, the European Research Council ERC, Academy of Finland and Japan Society for the Promotion of Science.