Integrated circuits, assemblies of transistors that are the building blocks for all electronic devices, currently use electrons to ferry the signals needed for computation. But almost all communications devices use light, or photons, to send signals. The need to convert the signalling language from electrons to photons limits the speed of electronic devices.
Leonid Butov, a professor of physics at UCSD, and his colleagues at UCSD and UC Santa Barbara have built several exciton-based transistors that could be the basis of a new type of computer, they report this week in an advance online version of the journal Science. The circuits they have assembled are the first computing devices to use excitons.
"Our transistors process signals using exitons, which like electrons can be controlled with electrical voltages but unlike electrons transform into photons at the output of the circuit,” Butov said. “This direct coupling of excitons to photons bridges a gap between computing and communications."
Excitons are created by light in a semiconductor such as gallium arsenide, which separates a negatively charged electron from a positively charged “hole.” If the pair remains linked, it forms an exciton. When the electron recombines with the hole, the exciton decays and releases its energy as a flash of light.
Butov and his colleagues have used a special type of exciton where the electron and its hole are confined to different “quantum wells,” separated by several nanometers. This configuration creates an opportunity to control the flow of excitons using voltage supplied by electrodes.
These voltage gates create an energy bump that can halt the movement of excitons or allow them to flow. Once that energy barrier is removed, the exciton can travel to the transistor output and transform to light, which could be fed directly into a communication circuit, eliminating the need to convert the signal. "Excitons are directly coupled to photons, which allows us to link computation and communication," Butov said.
Others involved in the discovery were Alex High and Ekaterina Novitskaya at UC San Diego, and Micah Hanson and Arthur Gossard at UC Santa Barbara.
The scientists created simple integrated circuits by joining exciton transistors to form several types of switches that accurately direct signals along one or several pathways. Because excitons are fast, the switches can be flipped quickly. Switching times on the order of 200 picoseconds have been demonstrated so far. (A picosecond is one trillionth of a second). While exciton computation itself may not be faster than electron-based circuits, the speed will come when sending signals to another machine, or between different parts of a chip that are connected by an optical link.
The circuits Butov and his colleagues have created demonstrate that excitons could be used for computing, but practical applications will require the use of different materials. The gallium arsenide excitonic circuits will only work at frigid temperatures - below 40 degrees Kelvin (or -390 degrees Fahrenheit), a limit determined by the binding energy of the excitons. (Warmer than that, and the electrons won't bind with their holes to form excitons in this structure). The operating temperature can be increased by choosing different semiconductor materials, the scientists said.
Their research was funded by the Army Research Office, the Department of Energy and the National Science Foundation.
Contact: Leonid Butov (858) 822-0362, email@example.com
Susan Brown | newswise
Robots as Tools and Partners in Rehabilitation
17.08.2018 | Albert-Ludwigs-Universität Freiburg im Breisgau
Low bandwidth? Use more colors at once
17.08.2018 | Purdue University
New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference
Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...
Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.
Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...
17.08.2018 | Event News
08.08.2018 | Event News
27.07.2018 | Event News
17.08.2018 | Physics and Astronomy
17.08.2018 | Information Technology
17.08.2018 | Life Sciences