The germanium laser might be harder to implement than previously thought
The germanium laser might be harder to implement than previously thought lead image
“It was saluted as the holy grail of Silicon Photonics,” says physicist Giovanni Capellini, referring to the first laser built from layers of germanium grown on a silicon wafer back in 2010. The achievement was a giant leap toward moving data using light instead of electricity — a solution that would be faster and more energy-efficient. But researchers attempting to reproduce the laser have been unsuccessful. Capellini and his colleagues at IHP in Frankfurt and the University of Pisa came to believe that focusing on the impact of heavy doping on the non-radiative recombination time could be a key element. So, they investigated the laser active material and analyzed their results with new theoretical models, of which they report in the 28 June 2017 issue of the Journal of Applied Physics.
By analyzing photoluminescence spectra with the help of a self-consistent multi-valley effective mass numerical model, the team headed by Thomas Schroeder estimated that the non-radiative lifetime be 0.1 ns, while it was usually considered to be 10 to 100 times longer. The researchers found that an alternative non-radiative mechanism, namely the Shockley-Read-Hall recombination — where charges meet at defects in the lattice and recombine in such a manner that prevents the emission of light — was more significant than expected, thus quenching the optical emission.
“It’s not good news, but it’s something people must be aware of because we need to control this side effect,” says co-author Michele Virgilio. All in all, the team remains cautiously optimistic. Capellini, for example, notes that people must tackle this unexpected level of complexity, but is still hopeful that the technology will see light one day.
Source: “The impact of donors on recombination mechanisms in heavily doped Ge/Si layers,” by Michael R. Barget, Michele Virgilio, Giovanni Capellini, Yuji Yamamoto, and Thomas Schroeder, Journal of Applied Physics (2017). The article can be accessed at https://doi.org/10.1063/1.4986236
