The Core Technology for Ultrafast Silicon Device

THE core technology that enables the realization of the fastest, nearly massless electrons has been successfully devised by a research team led by Professor Han Woong Yeom, Director of the Center for Atomic Wires and Layers at POSTECH. This achievement may lead to a breakthrough in the development of a truly new technology for semi-conductor devices.

Professor Yeom’s team successfully developed a core technology that will enhance the speed of a silicon device by several ten-folds through utilizing the interface, which is the boundary between two non-miscible materials, of metal film and silicon. The speed of the semiconductor device depends on the effective mass of the electron that transmits the electric signal, which means the smaller the effective mass of the electron, the faster the movement of the electron inside the semiconductor and thus the speed of the device. However, the effective mass of the electron is an intrinsic property of materials, and the academic world has been assuming that it is technically almost impossible to manipulate it on purpose. That was why industries such as the telecommunications sector chose to use expensive compound semiconductors, which have much smaller effective masses, instead of silicon.

Previously, an electron that moves as fast based on a small effective mass has been detected from graphene, a single layer of honeycomb lattice made of carbon atoms. Although this discovery has attracted a great amount of attention from the academic and industrial communities, it has been difficult to commercialize the discovery due to arising complications when attempting to incorporate it into the existing technology of semiconductors.

But the core technology that has been developed this time stands as an entirely new method, because it decreases the size of the effective mass largely by one twentieth of what it was before based on conventional semiconductor materials. Professor Yeom has revealed through experiment and theory that the effective mass of silicon greatly decreases itself when the electrons of the metal film and the electrons of the silicon interface interact at the interface. This happens when a metal layer that is very thin as 0.3 nanometers, only a single layer of metal atoms, becomes connected with silicon.

Professor Yeom’s study displays that the electronic band of a monolayer lead film drives a hole band of the Si inversion layer formed at the interface with the film to have a nearly linear dispersion with an effective mass about 20 times lighter than bulk Si and comparable to graphene, which was found using angle-resolved photoemission. The reduction in mass can be accounted for by a repulsive interaction between neighboring bands of the metal film and Si substrate.

Their recent discovery is a breakthrough in the sense that the electron’s effective mass is lighter than any other semiconductor materials, and that it utilizes silicon, an element that facilitates the easy commercialization of the device. Hence, this discovery is expected to greatly increase the possibilities of application to silicon-based thinfilm devices, and also to a number of semiconductor varieties.

The study was accomplished by Professor Yeom’s team in joint research with Professor Myung Ho Kang, Dr. Keun Su Kim and Mr. Sung Chul Jung in support from the Ministry of Education, Science and Technology and the Korea Science and Engineering Foundation. The discovery was published in the June 18th edition of the Physical Review Letters and will be applied for international patents.