A group of scientists from Hong Kong University of Science and Technology; the University of California, Santa Barbara; Sandia National Laboratories and Harvard University were able to fabricate tiny lasers directly on silicon — a huge breakthrough for the semiconductor industry and well beyond.
For more than 30 years, the crystal lattice of silicon and of typical laser materials could not match up, making it impossible to integrate the two materials — until now.
As the group reports in Applied Physics Letters, from AIP Publishing, integrating subwavelength cavities — the essential building blocks of their tiny lasers — onto silicon enabled them to create and demonstrate high-density on-chip light-emitting elements.
To do this, they first had to resolve silicon crystal lattice defects to a point where 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 nearly defect free and quantum confinement of electrons within quantum dots grown on this template made lasing possible.
The group was then able to use optical pumping, a process in which light, rather than electrical current, “pumps” electrons from a lower energy level in an atom or molecule to a higher level, to show that 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 professor Kei May Lau, Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology.