# Prof. Dr. Peter Deák

| Materials science of electronic devices Calculation of the electronic, optical and chemical properties of point defects and surfaces Developing methods for accurate electronic structure calculation of defects. |

Publications | Google Scholar |

| Textbook: Essential Quantum Mechanics for Electrical Engineers |

Course | Introduction to the physics of semiconductors and their defects |

## Research

The research interest lies in solving practically relevant problems of materials science by using atomistic quantum mechanical simulations in close cooperation with experiments. The four decades of my research carrier included one spent with applied research for industrial companies, while the rest encompassed electronic structure calculations on point defects and surfaces of semiconductors/insulators, as well as method development for that. I am primarily interested in how local changes on the atomic scale influence the functional properties in micro/optoelectronic and photovoltaic/catalytic materials. I have in-depths experience with diamond-, silicon‑, SiC-, and Ga-based systems, as well as with TiO_{2}. Presently I am working on the following projects.

## Methods to correct for the errors of local and semi-local exchange functionals in DFT

In exact DFT, the total energy ought to be a piecewise linear function of the fractional occupation numbers. The standard implementations (LDA, GGA) fail to provide that and, thereby, underestimate the band gap of semiconductors and the localization of their defect states, causing substantial errors. **We have shown** that the HSE hybrid functional can be tuned to restore this property, and the results are highly accurate. However, the optimal parameters are materials specific, the ones determined for the bulk are less accurate on the surface, and HSE calculations are expensive. Presently we are working to remedy these problems by developing a **transferable exchange functional**, taking the local variation of electronic screening into account, and we have already developed a strategy for a **low-cost alternative** which can be used both in the bulk and on the surface.

## Methods in DFT to correct for the errors to treat charged defects in supercell models

Defects are mostly calculated in a supercell using DFT. In case of charged defects, a compensating jellium must be applied to avoid the divergence of the Coulomb-energy, but that causes spurious interactions between the repeated cells. We have developed a computer code (**SLABCC**) which calculates the necessary correction of the total energy and can be applied to both 3D and 2D systems. Now we are working on a self-consistent potential correction (**SCPC**), which automatically corrects one-electron energies and wave-functions as well.

## Localized defect states in the bulk, on the surface, and in 2D semiconducting materials

We apply the methods described above to defect-related problems in semiconductors, used actively or under development these days, in opto- and power-electronics (Si_{x}Ge_{1-x}, **GaN, Ga2O3, GaSe, hBN**), in photovoltaics (**CuGaxIn1‑xS2‑ySey**) and in photocatalysis (**TiO2**, TiO_{2-x}N_{x}). Our work is aimed at identifying the point defects in the bulk which influence device behavior, clarify chemical reaction mechanisms on the surface, help band-gap engineering, and investigate low-dimensional effects.