New materials will make locally flexible diodes possible

Diodes allow directional current. Without them, modern electronic devices would be unthinkable. Until now, they had to be made from two materials with different properties. A team at the Technical University of Munich (TUM) has now discovered a material that can make a diode with a simple temperature change.

Producing a diode usually involves combining two Semiconductor materials with different attributes. In most cases, these are modified forms of silicon to which various elements are added to produce the desired properties. This process is called doping.

Doping with phosphorus, arsenic or antimony, adding more free electrons into the material, called n-type doping. The letter n refers to electrons that carry a negative charge. In contrast, boron, aluminum, and gallium bind electrons from silicon, creating positively charged holes. The material is doped with p. Combining the two materials creates a diode that allows current to flow in only one direction.

Material properties change temperature

“We have now found a material where we can make n- or p-conductors just by varying the temperature,” says Tom Nilges, professor of Synthesis and Characterization of Innovative Materials at TUM. . The researchers were able to show that a temperature change only a few degrees is enough to bring about this effect — and a working diode can be made with a temperature gradient within the material.

“When the material is in room temperature, we have a perfectly normal p conductor. Professor Nilges explains: “If we then apply a temperature gradient, we can create a concurrent n conductor in the heated regions. just a few degrees is enough — in our case between 22 and 35 °C.”

For Nilges, the elimination of the need for doping is not the only advantage: “Every diode produced is always there. Not so with our material: with the temperature gradient, the diode also disappears. if need return. , it’s enough to make a temperature gradient. If we think about the scope of application for diodesexample in solar battery or in every kind of electronic component, the potential of this invention becomes clear. “

Complex ingredients

The search for the perfect material involved 12 years of work, now culminating in the discovery of the mint metal halide chalcogenide.₁₈Cu₃Te₁₁OLD_l3. It consists of the elements silver, copper, tellurium and chlorine. Researchers came across this type of compound while exploring thermoelectric materials, which generate electricity from heat. One material they studied showed the pn switching effect. However, this is only observed over a temperature range of about 100°C, which is not suitable for practical applications.

After extensive analysis and testing, in Ag₁₈Cu₃Te₁₁OLD_l3 Researchers have discovered a material that displays the desired effect and is also suitable for applications at normal temperatures. “Other research groups have also detected this switching effect in materialbut so far no one has been able to convert it to a specific application,” explains Nilges.

The study was published in Advanced Materials.

As a next step, the researchers plan to demonstrate that their material can be used to make transistors through changes in temperature.