Scientists from the Institute of Physics of the Czech Academy of Sciences, led by Zdeněk Hubička and Jiří Olejníček, have succeeded in developing an improved method for preparing thin films of zinc oxide (ZnO) that respond to vacuum ultraviolet radiation much faster than previously known films produced by other methods. We have previously written about the early benefits of this technology here. The key to the current shift has been the use of a new plasma deposition method based on electron cyclotron wave resonance, which has made it possible to significantly reduce the appearance of specific defects in the material. This led to the detection rate of the optical signal and the photosensitivity itself being increased several times. The results, which were published in the prestigious Scientific Reportsjournal, were contributed to also by colleagues from Japan, Kuwait and New Zealand.
Radiation that cannot be seen by the human eye, but which plays a key role in space exploration, surface sterilisation and microchip production. Meet vacuum ultraviolet (VUV) radiation. To detect it, scientists need extremely sensitive materials, often with a fast time response. A team of scientists with Czech participation has developed a new tool for this purpose – semiconductor films with exceptional properties.
Capturing VUV radiation is not easy. It is extremely energetic light with a very short wavelength (100–200 nm), which is invisible to the human senses. In order to detect it, the material must convert the photon into an electrical signal as sensitively, quickly and without interference as possible.
The result is extreme sensitivity and fast response times
The key to success has been thin films of ZnO, a material commonly used in optoelectronics. Scientists from the Institute of Physics of the Czech Academy of Sciences, led by Zdeněk Hubička and Jiří Olejníček, have been able to significantly reduce the number of a certain group of defects in the film using advanced plasma technology – specifically plasma produced by electron cyclotron wave resonance (ECWR). In doing so, they have removed obstacles that normally reduce the accuracy of measurements, such as spurious signals or the so-called dark current, a current that is generated even without the influence of light.
"By controlling the power of the plasma, we were able to influence the crystallinity, the concentration of a certain number of defects and the conductivity of the material so that we significantly improved its ability to respond to incident radiation. Eliminating other types of defects will be a task for further research," says Jiří Olejníček.
Czech technology with global reach
The creation of the material itself did not however mean the end of the research. The international team examined its properties in detail – Japanese laboratories carried out luminescence measurements that confirmed a significantly lower density of defects affecting these sensory properties. Another method was time-resolved microwave conductivity (TRMC), which showed that the charge carriers in the material were behaving as they should.
"The results of this research confirm that when leading experts across disciplines and continents come together, international collaboration can yield extremely powerful results," said Alexandr Dejneka, Head of the Division of Optics of the Institute of Physics.
In addition to their exceptional parameters, the new ZnO films have one practical advantage – they are compatible with conventional semiconductor manufacturing technologies. They can, therefore, be used in industrial detectors, in ionizing radiation research or in space applications. Czech laboratories thus introduce into the world technologies that help to see what is normally invisible.