Germanium made compatible for lasers

April 22, 2013 by Maja Schaffner, ETH Zurich
Germanium made compatible
Light emitting bridges of germanium can be used for communication between microprocessors. Credit: Hans Sigg, PSI

(Phys.org) —Good news for the computer industry: a team of researchers has managed to make germanium suitable for lasers. This could enable microprocessor components to communicate using light in future, which will make the computers of the future faster and more efficient.

Researchers from ETH Zurich, the Paul Scherrer Institute (PSI) and the Politecnico di Milano have jointly developed a manufacturing technique to render the semiconductor germanium -compatible through high tensile strain. In their paper recently published in Nature Photonics, they reveal how they can generate the necessary tensile strain efficiently. The scientists demonstrate that they can use their method to effectively alter the of germanium, which is unsuitable for lasers as such: "With a strain of three per cent, the material emits around twenty-five times more photons than in a relaxed state," explains Martin Süess, a doctoral student at the Laboratory for Nanometallurgy headed by Ralph Spolenak and the EMEZ at ETH Zurich. "That's enough to build lasers with," adds his colleague Richard Geiger, a at the Laboratory for Micro- and at the PSI and the Institute for at ETH Zurich under Jérôme Faist.

High tension through microbridges

In order to bring the germanium into a laser-compatible, stretched form with the new method, the researchers use the slight tension generated in germanium when it evaporates on silicon, strengthening this prestrain with so-called microbridges: they score exposed germanium strips, which remain attached to the silicon layer at both ends, in the middle on both sides. The two halves of the strip thus remain connected solely by an extremely narrow bridge, which is precisely where, for physical reasons, the strain of the germanium grows so intense that it becomes laser-compatible.

"The tensile strain exerted on the germanium is comparable to the force exerted on a pencil as two lorries pull upon it in opposite directions," says Hans Sigg, the project manager at the PSI, explaining the feat on a micrometre scale in everyday proportions. The material properties change because the individual atoms move apart a little through the expansion of the material, which enables the electrons to reach energy levels that are favourable for the generation of light particles, so-called photons.

Germanium laser for the computer of the future

The interdisciplinary research team's method could increase the performance of future computer generations considerably. After all, in order to improve computer performance, computer chips have constantly been made smaller and more densely packed. However, this approach will eventually hit a brick wall in the foreseeable future. "In order to increase performance and speed further, the individual components need to be linked more closely and communicate with each other more efficiently," explains Süess. This requires new transmission paths that are faster than today, where the signals are still transmitted via electricity and copper cables.

"The way to go in future is light," says Geiger. In order to be able to use this to transfer data, however, first of all light sources are needed that are so small as to fit onto a chip and react well to silicon, the base material of all computer chips. Silicon itself is not suitable for the construction of laser light, which is also the reason why it is so important for the researchers to make germanium laser-compatible: "Germanium is perfectly compatible with silicon and already used in the in the production of silicon chips," explains Geiger. If it is possible to build tiny lasers out of germanium using the new method, a system change is within reach. "We're on the right track," says Süess. The international team of researchers is currently in the process of actually constructing a laser with the new method.

Explore further: Silicon nanowires under extreme tensile strain may lead to more efficient transistors

More information: Süess MJ, et al. Analysis of enhanced light emission from highly strained germanium microbridges. Nature Photonics. 2013. Published online: 14 April 2013 doi:10.1038/nphoton.2013.67

Related Stories

First germanium laser brings us closer to 'optical computers'

February 4, 2010

(PhysOrg.com) -- MIT researchers have demonstrated the first laser built from germanium that can produce wavelengths of light useful for optical communication. It’s also the first germanium laser to operate at room temperature. ...

Recommended for you

Walking crystals may lead to new field of crystal robotics

February 23, 2018

Researchers have demonstrated that tiny micrometer-sized crystals—just barely visible to the human eye—can "walk" inchworm-style across the slide of a microscope. Other crystals are capable of different modes of locomotion ...

Recurrences in an isolated quantum many-body system

February 23, 2018

It is one of the most astonishing results of physics—when a complex system is left alone, it will return to its initial state with almost perfect precision. Gas particles, for example, chaotically swirling around in a container, ...

Seeing nanoscale details in mammalian cells

February 23, 2018

In 2014, W. E. Moerner, the Harry S. Mosher Professor of Chemistry at Stanford University, won the Nobel Prize in chemistry for co-developing a way of imaging shapes inside cells at very high resolution, called super-resolution ...

Hauling antiprotons around in a van

February 22, 2018

A team of researchers working on the antiProton Unstable Matter Annihilation (PUMA) project near CERN's particle laboratory, according to a report in Nature, plans to capture a billion antiprotons, put them in a shipping ...

Urban heat island effects depend on a city's layout

February 22, 2018

The arrangement of a city's streets and buildings plays a crucial role in the local urban heat island effect, which causes cities to be hotter than their surroundings, researchers have found. The new finding could provide ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

Guy_Underbridge
not rated yet Apr 22, 2013
I had a hard time reconciling the title until I realized it didn't say 'Geranium'

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.