Polarization is a characteristic reflecting how the vectors (propagation directions) of the electric and magnetic fields of a light wave are oriented in space. For instance, the light of a regular incandescent lamp is not polarized, since the field vectors are omnidirectional; however, if the light is passed through a special lens (polarizer), some of the multidirectional vectors will be cut off. The polarization effect in photography helps avoid lens flare; it is also used in devices for visualizing living tissue.
In order to create silicon-based optoelectronic devices, the material must become sensitive to polarization, which means being able to distinguish between polarized light and unpolarized light. This is usually achieved with semiconductor materials or expensive lithography methods, i.e., selective creation of sensitive areas on the silicon surface using photomasks.
A more affordable alternative has been offered by the scientists from the Institute of Automation and Control Processes RAS, who used ordinary silicon wafers as blanks for photodetectors. On their surface, the authors printed optically inhomogeneous silicon gratings, which interacted with light in different ways. This made the material sensitive to polarization.
The physicists tested the resulting photodetectors via light of varying polarization (polarized or unpolarized) and wavelengths (from 500 to 1600 nanometers, i.e., green, yellow, orange, red and infrared light). The experiment showed that silicon photodetectors can detect polarization in a wide range of wavelengths, from 700 to 1100 nanometers, which correspond to the red and infrared ranges. The efficiency of capturing incident light was 100%. Thanks to this, photodetectors can be used not only in solar energy, but also in medicine for the purpose of studying living tissue.
“The proposed technology can be used to create high-contrast photodetectors for medical and biological drugs and tissues. This approach can also be used to adapt a conventional silicon photodetector for fiber-optic communication lines that provide an Internet connection. As this development is based on silicon technology, which is well-known and quite advanced, this will significantly reduce the cost of its practical implementation and scaling,” Yulia Bondarenko, one of the authors of the study, is quoted as saying by the Russian Science Foundation.
