Silicon Could Bring New Terahertz Technology

Silicon-based computing technology seems to have reached the maximum limit of miniaturization and everyone is waiting for its successor. Now, a team of researchers claim to be able to revive the veteran of computer chips and even improve its capabilities, in an effort to develop new terahertz systems.

Their solution involves using surface plasmon resonance on silicon, in the terhertz region. Weili Zhang, a professor at Oklahoma State University and his colleagues have demonstrated how the use of laser pulses can create a surface plasmon resonance from a photonic crystal effect. "This is the first time anyone has reported seeing this transition. This is a very interesting change," he says.

Surface plasmon resonance is already used in many applications, such as the detection of protein and DNA and are greatly improving the sensitivity of spectroscopy.

Unfortunately, the technique has a major drawback, in the fact that for the moment, only gold and silver best support surface plasmons. And as Zhang says, "Silver isn't always long lasting and gold can be too expensive."

The new approach involved transforming silicon into a metallic compound, since surface plasmons can only exist in a metal/dielectric interface. These plasmons are actually electromagnetic waves that run along that interface surface.

"What we wanted to do," said Zhang, "is start with a non-conductive material to see if we could excite surface plasmons in the terahertz region. We used ultra-fast laser pulses that resulted in photodoping." of the silicon they used, due to its properties as a semiconductor. "We see the photonic crystal signature disappear because the permittivity changes, the silicon becomes metallic, and the condition for surface plasmons is satisfied, thus the resonance changes."

Their findings could have applications in terahertz systems that would be made more efficient with this new method of generating the surface plasmon resonance.

"Terahertz systems always need some kind of filters to control operating frequencies and wavelengths," Zhang points out. "But with regular metals, once the structure is fixed, the operating frequencies are fixed. With this silicon process, these things can be changed. Both the frequencies and intensity can be controlled. This new way is more flexible and efficient."