Peter Friedli and Hans Sigg preparing the experiment at the Infrared Beamline at the SLS for determining the laser properties of Germanium. Photo: Frank Reiser, Paul Scherrer Institut |
Paul
Scherrer Institute (PSI) researchers have investigated how they could
make the semiconductor Germanium emit laser light. As a laser material, germanium together with Silicon could form the basis for innovative
computer chips in which information would be transferred partially in
the form of light. This technology would revolutionize data streaming
within chips and give a boost to the performance of electronics. The
researchers have demonstrated that germanium must be put under strain by
an external force in order to turn it into a laser material. The
decisive investigations were carried out by the scientists at the Swiss
Light Source (SLS) at PSI and their results have recently appeared in
the scientific journal Physical Review Letters. The research was
supported by the Swiss National Science Foundation (SNSF).
In
1965, Gordon Moore proposed a law stating that the surface density of
transistors in computer chips—and consequently their computing
power—would double every two years. This law has proved to be valid
since the beginning of the digital age; that is, since the introduction
of the first integrated circuits for micro-processors, in 1960. However,
in spite of the increasing number of transistors in computer chips, as
well as other progress which has been made, the overall performance of
processors has not been able to follow Moore’s Law for the past decade,
and specialists are now talking about ‘Moore’s Gap’. The reason for this
is that modern chips have more cores—individual processors—that can
only relatively slowly communicate with each other using current
technology.
“Actually,
we do know a way in which this gap can be closed. The key concept is
“optical data transfer” between the different cores on the chip,”
explains Hans Sigg, a PSI scientist. “This means partially transferring
information inside a chip with the aid of laser pulses, which would
significantly speed up the information exchange.”
In
order to do this, tiny lasers are needed which can be built into chips
to send out light pulses. These, however, have so far not been
available.
Tiny germanium lasers should make chips faster
Sigg’s
research team, together with colleagues from the ETH Zurich and the
Politecnico di Milano, has now been able to demonstrate that germanium,
under certain conditions, can function as a laser material.
“Germanium
lasers could make a break-through possible here, because germanium can
be readily combined with silicon, which is the basic material from which
chips are made. Silicon itself cannot emit light and can hardly be
combined with any available laser material,” points out Sigg.
Peter Friedli and Hans Sigg preparing the experiment at the Infrared Beamline at the SLS for determining the laser properties of Germanium. Photo: Frank Reiser, Paul Scherrer Institut |
In
their studies, which were performed at the Swiss Light Source (SLS) at
PSI, the researchers investigated those properties of germanium that are
important for the generation of laser light, and compared them with
those of currently available laser materials.
“We
stimulate the material by means of a powerful laser and simultaneously
observe the changes occurring using infra-red radiation from the SLS,”
elucidates the doctoral student Peter Friedli, who carried out the
decisive experiments together with scientist Lee Carroll. “To do this,
we used the fact that these light pulses are only 100 picosec (i.e.
0.1 billionths of a second) long, allowing us to follow the relevant
processes in the material; that is, the behavior of electrons at
different points in time.”
Germanium must be deformed
“Our
results are, on the one hand, encouraging, because Germanium behaves
similarly to traditional laser materials, and therefore the possibility
of it emitting light cannot be excluded,” says Sigg enthusiastically,
“but with the limitation that the balance between amplification and loss
is still so unfavorable in the Germanium layers investigated so far
that the material does not yet fulfill the condition for emitting laser
light.”
But
it has been demonstrated that this condition can be more closely
approached the more the germanium is put under strain using an external
force. The researchers hope to achieve the necessary conditions for the germanium in a follow-up project. For this, they will use a new
technology that allows the strain to be greatly increased.
This research project has been supported by the Swiss National Science Foundation (SNSF).
Source: Paul Scherrer Institute
