Novel quantum dot laser paves the way for lower-cost photonics

Mar 03, 2014
This is an Atomic Force Microscopy scan of the quantum dots over an area 1 micrometer (millionth of a meter) x 1 micrometer. Credit: Alan Liu

With the explosive growth of bandwidth demand in telecommunications networks, experts are continually seeking new ways to transmit increasingly large amounts of data in the quickest and cheapest ways possible. Photonic devices—which convert light to electricity and vice versa—offer an energy-efficient alternative to traditional copper network links for information transmission. Unfortunately, these devices are also almost always prohibitively pricey.

One way to bring those costs down is to make photonics compatible with the existing silicon microelectronics industry. A promising way to do that is by growing "quantum dot" lasers directly on silicon substrates, according to graduate student Alan Y. Liu of the University of California at Santa Barbara (UCSB) and his colleagues, who include UCSB professors John E. Bowers and Arthur C. Gossard. Although such quantum dot lasers have been grown on silicon before, their performance has not equaled that of quantum dot lasers grown on their native substrates, which are platforms made of similar materials as the quantum dot lasers themselves.

Now Liu and his collaborators in Bowers and Gossard's groups have demonstrated a novel quantum dot laser that not only is grown on silicon but that performs as well as similar lasers grown on their native substrates. The team will discuss its record-breaking results achieved using such lasers at this year's OFC Conference and Exposition, being held March 9-13 in San Francisco, Calif., USA.

The researchers believe the work is an important step towards large-scale photonic integration in an ultra low-cost platform.

This is an optical micrograph of the fabricated laser devices. Credit: Alan Liu

Currently, so-called "quantum well" lasers are used for data transmission. They consist of nanometers-thick layers of light-emitting material, representing the quantum well, sandwiched between other materials that serve to guide both the injected electrical current as well as the output light. A quantum dot laser is similar in design, but the sheets of quantum well materials are replaced with a high density of smaller dots, each a few nanometers high and tens of nanometers across. To put it in perspective, 50 billion of them would fit onto one side of a penny.

"Quantum wells are continuous in two dimensions, so imperfections in one part of the well can affect the entire layer. Quantum dots, however, are independent of each other, and as such they are less sensitive to the crystal imperfections resulting from the growth of laser material on silicon," Liu said.

"Because of this, we can grow these lasers on larger and cheaper silicon substrates. And because of their small size," Liu added, "they require less power to operate than quantum well lasers while outputting more light, so they would enable low-cost silicon photonics."

In their new work, the team grew quantum dots directly on silicon substrates using a technique known as molecular beam epitaxy, or MBE ("epitaxy" refers to the process of growing one crystal on top of another, with the orientation of the top layer determined by that of the bottom).

"The major advantage of epitaxial growth is that it enables us to exploit the existing economies of scale for silicon, which would drive down cost," Liu said. He added that "MBE is the best method for creating high-quality that are suitable for use in lasers" and that "the entire laser can be grown continuously in a single run, which minimizes potential contamination."

Explore further: Technique makes it possible to measure the intrinsic properties of quantum dot transistors

More information: Presentation W4C.5. titled "High Performance 1.3μm InAs Quantum Dot Lasers Epitaxially Grown on Silicon" will take place Wednesday, March 12 at 5:00 p.m. in room 121 of the Moscone Center. (

This work was recently published in Applied Physics Letters: Liu, A. Y., et al. "High performance continuous wave 1.3 μm quantum dot lasers on silicon." Applied Physics Letters, 104, 041104 (2014)

add to favorites email to friend print save as pdf

Related Stories

Quantum dots provide complete control of photons

Jan 31, 2014

By emitting photons from a quantum dot at the top of a micropyramid, researchers at Linköping University are creating a polarized light source for such things as energy-saving computer screens and wiretap-proof ...

Recommended for you

Mapping the optimal route between two quantum states

8 hours ago

As a quantum state collapses from a quantum superposition to a classical state or a different superposition, it will follow a path known as a quantum trajectory. For each start and end state there is an optimal ...

Spin-based electronics: New material successfully tested

12 hours ago

Spintronics is an emerging field of electronics, where devices work by manipulating the spin of electrons rather than the current generated by their motion. This field can offer significant advantages to computer technology. ...

Verifying the future of quantum computing

14 hours ago

Physicists are one step closer to proving the reliability of a quantum computer – a machine which promises to revolutionise the way we trade over the internet and provide new tools to perform powerful simulations.

A transistor-like amplifier for single photons

Jul 29, 2014

Data transmission over long distances usually utilizes optical techniques via glass fibres – this ensures high speed transmission combined with low power dissipation of the signal. For quite some years ...

User comments : 0