Friday, July 10, 2015

2-D-semiconductor of phosphorus and arsenic as an alternative to silicon

Chemists at the Technische Universitaet Muenchen (TUM) have developed a two-dimensional semiconductor, in which individual phosphorus atoms are replaced by arsenic. Within the framework of international cooperation they built it together with American colleagues first field-effect transistors.

For many decades, silicon is the basis of modern electronics. So far could produce ever smaller transistors, the silicon technology for smaller and smaller devices, the size of silicon transistors is gradually beginning to their physical limit. Silicon is also hard and brittle, but would consumers like to flexible devices, devices that can be incorporated into clothing and much more. All this has a race for new materials triggered that could replace silicon one day.

Such a material could be arsenic-containing black phosphorus. As the graph consisting of a single layer of carbon atoms, it forms thin layers. The range of its applications ranging from transistors, sensors to mechanical-flexible semiconductor devices. Unlike the graph whose electronic behavior is similar to that of metals, it behaves like a semiconductor.

Phosphors instead of graph

In a cooperation between the Technical University of Munich and the University of Regensburg on the German side and the American Universities University of Southern California (USC) and Yale field effect transistors of arsenic-containing black phosphorus have now been produced for the first time. The compounds synthesized Marianne Kopf laboratory of the department for synthesis and characterization of innovative materials at the TU Munich. The field effect Trasistoren were built and measured in the group of Professor Zhou and Dr. Liu.

Developed at TU Munich new method makes it possible to synthesize black arsenic-phosphorus without high pressure. This requires less energy and is cheaper. About the arsenic content, the gap between valence and conduction bands can be precisely adjusted. "This allows us to produce materials with previously unattainable electronic and optical properties in an energy window that was previously inaccessible," says Professor Tom Niges, head of the department for synthesis and characterization of innovative materials.

Detectors for infrared

In an arsenic content of 83%, the material has a band gap of 0.15 eV only. For such a material, for example sensors can be constructed that detect wavelengths in the far infrared. In this area, for example, LiDAR sensors operate (Light Detection and Ranging). They are used inter alia in cars as distance sensors. Another application is the measurement of dust particles and trace gases in the environmental monitoring.

Another interesting aspect of this new two-dimensional semiconductors are their anisotropic electronic and optical properties. The material can be peeled off in layers. The thinnest layers were reached so far only two atomic layers thick.

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