Studying atomic scale ordering in semiconductors
Tom Verstijnen defended his PhD thesis at the Department of Applied Physics and Science 果冻传媒 on April 2.
In the modern world most people take for granted that they can always carry a computer around with them in the form of a smartphone or laptop. This has been made possible by advancements in chip technology and the semiconductor materials that they are based upon. Components like transistors 鈥� the building blocks of our computers 鈥� are getting smaller and smaller. Therefore, we need more enhanced control over these transistors, particularly as their sizes approaches the atomic scale. Techniques to study semiconductor materials at this scale are needed. For his PhD thesis, Tom Verstijnen used Scanning Tunneling Microscopy (X-STM) and Density Functional theory (DFT) together to study semiconductor materials.
X-STM is an advanced microscopy technique capable of imaging individual atoms in materials, while DFT is a simulation method that can describe the very same materials.
These two techniques can be combined to successfully describe material properties like the position of individual atoms in the material, local electronic properties, and relaxation behavior of the material around impurities.
III-V semiconductors
The type of semiconductor materials that studied are iso-electronically doped III-V semiconductors. These are III-V semiconductors where individual atoms in the material are replaced by another type of atom.
This doping influences the characteristics of the material and if this is done in a controlled way, it allows for the accurate tuning of materials to have the characteristics suitable for specific applications.
The way these dopants are distributed throughout the material is of vital importance as a homogeneous distribution of dopants behaves very differently from a non-homogeneous one.
This local ordering of dopants was the focus of Verstijnen鈥檚 research, and he used both experiments and simulations for this purpose.
Key findings
Verstijnen discovered that iso-electronic dopants the way they form pairs with their fellow dopants is similar for this type of material, regardless of what the type of dopant is. This means that the way the material is built up decides which pairs form rather than the dopant itself.
This insight can help the growers of these materials greatly as well as the engineers who are tasked with designing the next generation of chips.
Title of PhD thesis: . Supervisors: Paul Koenraad and Michael Flatt茅.