Electronic structure of a semiconductor device visualised for first time

Electronic devices fundamentally function based on the behaviour of electrons within the materials in question which is, in turn, dictated by the electronic structures. The current flowing through the material influences this behaviour which can also vary depending on the voltage applied. This is because the current is the flow of charge, which are the electrons. Voltage makes a difference because it is, in essence, the force that is felt by the charge carriers as they move around the circuit.

Changes in the electronic structure directly affect the efficiency of the microelectronic circuits. Despite this understanding, the key missing link was that there was no method of being able to directly view the changes in the electronic structure brought about by changes in the current and voltage, which was limiting our understanding of how these processes work.

There was no method of being able to directly view the changes in the electronic structure brought about by changes in the current and voltage

After a collaboration between the University of Warwick and the University of Washington, researchers were, for the first time, able to visualise the electronic structure of a semiconductor in a microelectronic device. Microelectronic devices are atomically thin and are often called two-dimensional materials.

The technique used in the research is angle-resolved photoemission spectroscopy (ARPES), whereby a beam of ultraviolet or x-ray light is focussed in a localised area on the atoms and the electrons within are excited and subsequently knocked out. Scientists measure the energy and direction of travel of the electrons that are removed and are therefore able to measure the energy and momentum of the material being studied using the laws of conservation of energy and momentum.

After a collaboration between the University of Warwick and the University of Washington, researchers were, for the first time, able to visualise the electronic structure of a semiconductor in a microelectronic device

Using the data obtained, scientists can construct visual representations of the electronic structures of the materials and this gives us a lot of information. The information can be compared with theoretical predictions based on electronic structure calculations performed in this research by the co-author, Dr Nicholas Hine. This would tell us something about how well electronic structure can be computationally predicted. The understanding of the electronic structure can further guide engineers about the optimum use of the materials in electronics.

Firstly, graphene was used to test the material followed by the two-dimensional transition metal dichalcogenide (TMD) semiconductors. In this way, this research has opened the pathways to develop finely-tuned high performance and efficient electronic devices that will find use in the field of photovoltaics, mobile devices, and quantum computers, among other fields.

The understanding of the electronic structure can further guide engineers about the optimum use of the materials in electronics

When it comes to studying the electronic structure of semiconductors, and other solid-state materials in general, one of the fundamental parameters that need to be understood are the band gaps of the materials. From the Department of Physics at the University of Warwick, Dr Neil Wilson commented that the band gap is the most important parameter affecting the behaviour of materials, “from what wavelength of light they emit, to how they switch current in a transistor.”

This research was published in Nature and Dr David Cobden remarked: “We can directly measure the electronic spectrum in detail and see how it changes in real-time. This changes the game.”