A team of collaborating scientists from Hong Kong University of Science and Technology, the University of California, Santa Barbara, Sandia National Laboratories and Harvard University has discovered a new way to create tiny lasers directly on silicon. This new development could mean a major affect on the semiconductor industry, enabling next-gen microprocessors that run faster and consume less power.
For the past 30 years, the crystal lattice of silicon and typical laser materials could not match up, which made it impossible to integrate the two materials. But now the semiconductor challenge has been solved, propelling the integration of photonics with electronics on the silicon platform.
The team was able to achieve this merge by integrating subwavelength cavities, also known as the essential building blocks of tiny lasers, onto silicon, which allowed them to create and demonstrate high-density on-chip light-emitting elements.
The team first had to resolve silicon crystal lattice defects so that the cavities were essentially equivalent to those grown on lattice-matched gallium arsenide (GaAs) substrates. Nano-patterns created on silicon to confine the defects made the GaAs-on-silicon template almost defect-free, and quantum confinement of electrons within quantum dots grown on this template made this kind of lasing possible.
Next the group uses optical pumping, a process in which light “pumps” electrons instead of electrical current in order to show the devices work as lasers.
"Putting lasers on microprocessors boosts their capabilities and allows them to run at much lower powers, which is a big step toward photonics and electronics integration on the silicon platform," said Kei May Lau, Professor of Electronic and Computer Engineering, Hong Kong University of Science and Technology.
Traditional lasers used for commercial applications tend to be very large, around 1 mm x 1 mm, but it is the smaller lasers that tend to suffer from large mirror loss. The scientists were able to overcome this challenge by using “tiny whispering gallery mode lasers” that were only one micron in diameter, 1,000 times shorter in length and one million times smaller in area than ones that are currently used.
Whispering gallery mode lasers are seen as a great light source for on-chip optical communications, data processing and chemical-sensing applications in the field.
"Our lasers have very low threshold and match the sizes needed to integrate them onto a microprocessor," said Lau. "And these tiny high-performance lasers can be grown directly on silicon wafers, which is what most integrated circuits (semiconductor chips) are fabricated with."
The team now sees the tiny lasers on silicon being used in high-speed data communication applications and expects the technology will be on the market within the next 10 years.
"Photonics is the most energy-efficient and cost-effective method to transmit large volumes of data over long distances. Until now, laser light sources for such applications were 'off chip'—missing—from the component," said Lau. "Our work enables on-chip integration of lasers, an [indispensable] component, with other silicon photonics and microprocessors."
The team will also set out to work on electrically pumped lasers using standard microelectronics technology.
