MOSCOW, March 9. /TASS/ Researchers from the Center for Photonics and Quantum Materials at Skolkovo Institute of Science and Technology (Skoltech) have modeled electro-optical properties of two monolayer materials: black phosphorus and molybdenum disulfate, the Skoltech press office reported. The new materials can be used for creating efficient infrared photodetectors, as well as for solar cells.

"In our theoretical studies, from the very beginning we have computed the properties of two 2D-materials," stated Vasily Perebeinos, a Skoltech professor and the study’s supervisor. "Usually, such predictions fall fairly in line with reality and do not require additional experimental approvals. Therefore, our results provide a basis for engineers to upgrade the concept for real devices."

Why are 2D materials needed?

In recent years, 2D materials have attracted the attention of scientists from all over the world. They possess very special physical properties making them perspective for electronics and optoelectronics. Additionally, these material are usually cheaper that 3D conductors and semiconductors. There are a great variety of 2D materials but only a few of them are well studied. The most explored 2D material is graphene, made as flat sheets of carbon atoms.

Graphene displays unique mechanical and thermal characteristics but does not belong to the class of semiconductors which makes its application in electronics a complicated task.

"Graphene is a semi-metal," Perebeinos explained. "It’s something between a conductor and dielectric and therefore it is not very suitable for many electronic and microelectronic purposes. For instance, in the logic schemes of computers, we need to have switching elements which may pass and not pass the current. The metals and semimetals do not satisfy this requirement as they conduct the electricity." This motivated scientists to search for new 2D materials of a semiconductor nature.

Black phosphorus progress

In their first study, the researchers investigated flat material consisting of black phosphorus. They calculated how the mobility of electrons and some other electric characteristics of an ideally pure black phosphorus change during heating, which is unavoidable while a semiconductor is functioning. This material might find its application in sensitive infrared photodetectors.

Results on molybdenum disulfate

In the second study, the 2D material of molybdenum disulfate MoS2 was examined. Exposing this material to the photon of light triggers the appearance of excitons, the particles representing coupled pairs of electrons and holes, which under certain circumstances might be separated leading to the appearance of an electric current.

This principle is fundamental for modern solar cells. In molybdenum disulfate, the exciton’s binding energy is so large that to release electric current, scientists and engineers have to resort to some gimmicks - to deposit thin films of MoS2 on various surfaces which would affect the exciton’s stability.

Russian physicists have calculated that the exciton binding energy depends on the dielectric permittivity of medium (support), as well as the influence of external electric field.

"Our results show that the electric fields required for the separation of electrons and holes depend notably on the dielectric medium hosting the material," Perebeinos elaborated. "This opens the door to creating an electro-optic response in MoS2 which might be applied for solar energy generation and for photodetection."

Both studies by Russian physicists have been published in the journal Physical Review B.