Boosting the Electric Field at Metal-Semiconductor Junctions for Better Current Flow through Transistors

KU Researchers Publish Study that Shows Presence of Nanoparticles on Graphene Helps make Silicon Produce a Larger Current at the Nanoscale

An important fundamental discovery has been made by a team of researchers at Khalifa University that may help enhance current flow between semiconductors and metals at the nanoscale. The team found that silver nanoparticles layered on an ultrathin sheet of graphene, creates an enhanced localized electric field that produces a larger current between the semiconductor and the metal.

The work has a significant fundamental research focus but with clear potential application. A paper describing the research was accepted into the IEEE Nanotechnology Council’s 14th Nanotechnology Materials & Devices Conference (NMDC), to be held in Sweden from 27-30 October.

“Our research explores the use of nanoparticles and graphene to overcome the interface limitations that occur at the point where semiconductors and metals intersect,” said UAE National and PhD student Badreyya Al Shehhi, who was the paper’s lead author. Electron flow at the point where semiconductor and metal meet is limited by electrical barriers known as Schottky barriers, which impede current flow and limit current density. Al Shehhi’s work aims to reduce the current limitation at the metal-semiconductor junction with the nanoparticles layered on graphene.

“The nanoparticles have an important effect on the current transport and electrical field enhancement, which can be further enhanced by decreasing the probing tip size of the atomic force microscope (AFM),” the paper reports. The researchers used atomic force microscopy – a type of high resolution scanning probe microscope – to fine tune the size, type, and placement of the nanoparticles on the graphene layer.

“This fine tuning in turn enables the development of customized nano-Schottky barrier properties for a range of different applications,” Al Shehhi said. The team found that a combination of noble metal nanoparticles on graphene enhanced the optical and current transport properties of the underlying graphene.

The researchers were able to simulate the behavior of the current flow at the nanoscale, enabling them to study the transport of charge carriers from nanoparticles to graphene to the silicon substrate; a vital piece of fundamental research that has not been done before.

“To study and characterize these nano-devices require advanced material and electrical characterization techniques like AFM, Raman and advanced microscopy,” Al Shehhi explained. The research was carried out using KU’s Clean Room Fabrication Facility, followed by device characterization and measurements.

“This particular research is not based on just one or a few tools. It requires a sequence of steps through different sophisticated tools to fabricate the target devices. This requires expertise to operate the equipment and develop a sense for process ‘recipes’ or sequence of steps needed to fabricate the target devices. Additionally, the supplies needed are expensive or require special handling. Thus sustained supply chain and logistics are critical for continuous success,” Dr. Irfan Saadat, Professor of Electrical Engineering and Computer Science at KU.

Al Shehhi and Dr. Saadat were joined by Dr. Ammar Nayfeh, Associate Professor Electrical Engineering and Computer Science, and Dr. Ayman Rezk, Dr. Yawar Abbas and Dr. Moh’d Rezeq, all from the KU Physics Department.

The work is a result of synergistic integration of the research expertise of Dr. Saadat’s group for cleanroom device fabrication, Dr. Nayfeh’s group for nanoparticles dispersion, and Dr. Rezeq’s group for AFM nano-probing and characterization.

The research establishes KU’s ability to leverage advanced microscopy tools and fabrication devices to “see” what is happening at each processing step. Being able to observe new phenomena at the nanoscale with sophisticated tools is a critical skill in the area of nanoscale materials and systems. This know-how will help advance understanding of the quantum physics underlying such phenomena, and can be useful for manipulating materials and processes at the nanoscale, which has a myriad of applications in key sectors from electronics and medicine, to oil and gas.

“This kind of fundamental research enables and strengthens the advanced indigenous infrastructure of knowledge and sciences, which in turn provides a platform where cross pollination can occur to tackle issues across different fields and provide innovative solutions not realized before,” Dr. Saadat shared.

Erica Solomon
Senior Editor
15 October 2019