Semiconductor Device Materials

This unit is working on the development of novel semiconductor materials for high-frequency and power electronics. The research also focuses on developing spectroscopic techniques for studying electronic and transport properties of materials from bulk to nanoscale.

III-Nitrides for applications in the next generation of wireless communication, sensing, and power infrastructures. The research focuses on optimization of epitaxial design and properties of GaN and AlGaN device structures on SiC, GaN and AlN substrates by hot-wall MOVPE. The activity covers growth of the device structures with the main aim to minimize defect densities (dislocations and background impurities), and the design of the epi-stack targeting different functionalities, e.g. power amplification, noise, and flicker-noise, switch losses, device design, etc.

Terahertz ellipsometry and optical Hall effect. We have developed unique THz ellipsometry and magneto-ellipsometry (optical Hall effect) instrumentation at the Terahertz Materials Analysis Center. These novel techniques makes it possible to explore electronic, transport and magnetic properties and phenomena in e.g, semiconductors, nanomaterials, organic materials, which cannot be assessed by other means. Current research efforts include application of THz to FIR ellipsometry to study 2DEG in transistor and quantum structures, 2D materials, conductive polymers, proteins and biomaterials.

Ultra-wide bandgap semiconductors. Main focus is put on β-Ga2O3 for applications in high-power electronic devices with substantial efficiency gain in e.g., generation and transmission of electric power, electrification of vehicles and motor drivers. Current research efforts include development of MOVPE of β-Ga2O3 and profound understanding of phonon, free charge carrier and electronic properties in relation to microstructure of thin films and device heterstructures.

2D materials. Current research activities include using THz ellipsometry to study, understand and optimize the transport, electronic and structural properties of e.g., epitaxial graphene grown on SiC, MAXens, and BN.



Anders Gustafsson, Axel Persson, Per O A Persson, Vanya Darakchieva, Zhaoxia Bi, Lars Samuelson (2024) Cathodoluminescence investigations of dark-line defects in platelet-based InGaN nano-LED structures Nanotechnology, Vol. 35, Article 255703 Continue to DOI
Daniela Gogova-Petrova, Dat Tran, Vallery Stanishev, Valdas Jokubavicius, L. Vines, M. Schubert, Rositsa Yakimova, Plamen Paskov, Vanya Darakchieva (2024) High crystalline quality homoepitaxial Si-doped β-Ga2O3(010) layers with reduced structural anisotropy grown by hot-wall MOCVD Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, Vol. 42, Article 022708 Continue to DOI
Nerijus Armakavicius, Sean Robert Knight, Philipp Kuhne, Vallery Stanishev, Dat Tran, Steffen Richter, Alexis Papamichail, Megan Stokey, Preston Sorensen, Ufuk Kilic, Mathias Schubert, Plamen Paskov, Vanya Darakchieva (2024) Electron effective mass in GaN revisited: New insights from terahertz and mid-infrared optical Hall effect APL Materials, Vol. 12, Article 021114 Continue to DOI
Sean Robert Knight, Steffen Richter, Alexis Papamichail, Megan Stokey, Rafal Korlacki, Vallery Stanishev, Philipp Kuhne, Mathias Schubert, Vanya Darakchieva (2024) Terahertz permittivity parameters of monoclinic single crystal lutetium oxyorthosilicate Applied Physics Letters, Vol. 124, Article 032101 Continue to DOI
Chaoyang Kuang, Shangzhi Chen, Min Luo, Qilun Zhang, Xiao Sun, Shaobo Han, Qingqing Wang, Vallery Stanishev, Vanya Darakchieva, Reverant Crispin, Mats Fahlman, Dan Zhao, Qiye Wen, Magnus Jonsson (2024) Switchable Broadband Terahertz Absorbers Based on Conducting Polymer-Cellulose Aerogels Advanced Science, Vol. 11, Article 2305898 Continue to DOI


Sean Robert Knight, Steffen Richter, Alexis Papamichail, Philipp Kuhne, Nerijus Armakavicius, Shiqi Guo, Axel R. Persson, Vallery Stanishev, Viktor Rindert, Per O. Å. Persson, Plamen P. Paskov, Mathias Schubert, Vanya Darakchieva (2023) Room temperature two-dimensional electron gas scattering time, effective mass, and mobility parameters in AlxGa1−xN/GaN heterostructures (0.07 ≤ x ≤ 0.42) Journal of Applied Physics, Vol. 134, Article 185701 Continue to DOI
F. K. Urban, D. Barton, Mathias Schubert (2023) Numerical ellipsometry: A method for selecting a single ß-gallium oxide monoclinic crystal orientation able to determine the complete permittivity tensor Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, Vol. 41, Article 013402 Continue to DOI
Joseph Matson, Md Nazmul Alam, Georgios Varnavides, Patrick Sohr, Sean Robert Knight, Vanya Darakchieva, Megan Stokey, Mathias Schubert, Ayman Said, Thomas Beechem, Prineha Narang, Stephanie Law, Joshua Caldwell (2023) The Role of Optical Phonon Confinement in the Infrared Dielectric Response of III-V Superlattices Advanced Materials Continue to DOI
Viktor Rindert, Steffen Richter, Sean Knight, Mathias Schubert, Vanya Darakchieva (2023) THz Spectroscopic Electron Paramagnetic Resonance of the Fe<SUP>3+</SUP> Defect in GaN 2023 48TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES, IRMMW-THZ Continue to DOI
Philipp Gribisch, Rosalia Delgado Carrascon, Vanya Darakchieva, Erik Lind (2023) Tuning of Quasi-Vertical GaN FinFETs Fabricated on SiC Substrates IEEE Transactions on Electron Devices, Vol. 70, p. 2408-2414 Continue to DOI
Alexis Papamichail, Axel Persson, Steffen Richter, Philipp Kuhne, Vallery Stanishev, Per O A Persson, R. Ferrand-Drake Del Castillo, M. Thorsell, H. Hjelmgren, Plamen Paskov, N. Rorsman, Vanya Darakchieva (2023) Tuning composition in graded AlGaN channel HEMTs toward improved linearity for low-noise radio-frequency amplifiers Applied Physics Letters, Vol. 122, Article 153501 Continue to DOI
Dat Tran (2023) Thermal conductivity of wide and ultra-wide bandgap semiconductors
Dat Tran, Ferenc Tasnadi, Agne Zukauskaite, Jens Birch, Vanya Darakchieva, Plamen Paskov (2023) Thermal conductivity of ScxAl1-xN and YxAl1-xN alloys Applied Physics Letters, Vol. 122, Article 182107 Continue to DOI
Ding-Yuan Chen, Axel Persson, Vanya Darakchieva, Per O A Persson, Jr-Tai Chen, Niklas Rorsman (2023) Structural investigation of ultra-low resistance deeply recessed sidewall ohmic contacts for AlGaN/GaN HEMTs based on Ti/Al/Ti-metallization Semiconductor Science and Technology, Vol. 38, Article 105006 Continue to DOI
Hengfang Zhang, Ingemar Persson, Jr-Tai Chen, Alexis Papamichail, Dat Tran, Per O A Persson, Plamen P. Paskov, Vanya Darakchieva (2023) Polarity Control by Inversion Domain Suppression in N-Polar III-Nitride Heterostructures Crystal Growth & Design, Vol. 23, p. 1049-1056 Continue to DOI




  • Prof. M. Schubert, University of Nebraska-Lincoln, USA
  • Prof. N. Grandjean, EPFL, Switzerland
  • Dr. S. Ruffenach, University of Montpellier, France
  • Prof. K. Kishino, Sofia University, Japan
  • Prof. W. J. Schaff, Cornell University, USA
  • Prof. Y. Nanishi, Retsumeikan University, Japan
  • Dr. T. Monteiro, University of Aveiro, Portugal
  • Prof. L.-C. Cheng, National Taiwan University, Taiwan
  • Prof. A. Yoshikawa, Chiba University, Japan
  • Prof. E. Valcheva, Sofia University, Bulgaria.
  • Prof. L. W. Tu, National Sun Yat-Sen University, Taiwan
  • Dr. H-W. Becker, Rhur University, Germany
  • Dr. K. Lorenz, ITN/IST, Portugal
  • Dr. A. Tiberj, University of Montpellier 2, France




Industrial collaborations

  • Dr. T. Tiwald, Dr. G. Hertzinger and Prof. J. Woollam, J.A. Woollam Co , USA - ellipsometry equipment and software
  • Dr. O. Kordina, SweGaN AB, Sweden - AlGaN, HEMTs
  • Dr. F. Allerstam, On Semiconductor, USA - high-frequency electronics
  • Dr. C.-Y. Chen, ABB, Sweden - high power electronics
  • Dr. M. Higashiwaki, Tamura Co., Japan - Ga2O3
  • Prof. R. Yakimova, Graphensic AB, Sweden - graphene
  • Prof. A. Usui, Furukawa Co., Ltd., Japan - bulk GaN


  • Prof. H. Zirath and Dr. N. Rorsman, Chalmers University - electronic devices
  • Prof. R. Yakimova - graphene
  • Dr. F. Tasnadi - ab initio calculations
  • Prof. J. Birch - novel nitride alloys
  • Dr. P. Persson - TEM
  • Prof. E. Janzen - HEMTs
  • Dr. A. Kakanakova - AlN and AlGaN
  • Prof. B. Monemar - PL and InN

External media

Chapter on Phonon Properties published in book Gallium Oxide

In this chapter, written by members of our team we present and discuss the complete set of infrared-active phonon modes in monoclinic-symmetry crystal modification gallium oxide. This chapter attempts to summarise the current state of knowledge about the optical phonon mode propoerties and their coupling with free charge carriers in gallium oxide with monoclinic crystal structure.

You can find the book at

April 2019 - Inside front cover in Journal of Materials Chemistry C

Our paper on the anomalous optical conductivity dispersion of electrically conducting polymers determiend by ultra-wide spectral range ellipsometry combined with a Drude-Lorentz model is selected as inside front cover in the April issue of Journal of Materials Chemistry C.

J. Mater. Chem. C, 2019,7, 4350-4362.

April 2019 - Eva Bittrich from Leibniz Institute of Polymer Research Dresden is visiting

Eva Bittrich from Leibniz Institute of Polymer Research Dresden is visiting THeMAC for a week. She is working on applying far-infrared and terahertz spectroscopic ellipsometry to study the H-bonding in thin polycristalline films of ellagic acid and other semiconducting films of small organic molecules. Eva presented a Faculty seminar on Nanostructured organic thin films for biosensing and energy harvesting. We are looking forward to this new exciting collaboration in polymer research. 



Student projects

Student project

Recently Shiqui Guo has joined our group. He will spend the next few months (spring term 2021) working on his Bachelor project on graded AlGaN HEMTs. He will work closely with Ph.D. student Alexis Papamichail and focus on the characterization of the HEMTs.