Section Semiconductors

Section Semiconductors


As one of the world leading research teams in semiconductor bulk single crystals, we are focusing on cutting-edge topics for key enabling technologies such as quantum computing, power electronics, silicon photonics, besides persistently working on the growth of conventional semiconductors of group IV and III-Vs. We are also increasing our capabilities by developing 8-inch dia Float Zone system for silicon (Si), and by utilizing our KristMAG® technology in Vertical Gradient Freeze (VGF) and Czochralski (Cz) techniques. We are providing crystals with custom properties to academic institutions for collaborations or as a service and further working closely with our industrial partners for production efficiency.  

Research activities

On the success of 28Si kilogram prototype project, we are positioning as a valuable contributor to the international joint research projects like ultra-high pure germanium for neutrinoless double-beta decay detection, Si-Fibers and Si-mirrors to Einstein telescope for gravitational waves detection. We produce isotopically enriched and ultrahigh purity, high crystalline perfection Si single crystals by Float Zone method and its related crucible-free growth processes. We also devote the process development and optimization of VGF and Cz growth technology for III-Vs and Si respectively, especially using non-stationary magnetic fields to control the undesirable impurities and defects. We prepare Germanium single crystals with high doping level as well.

Head of section
PD Dr. habil. R. Radhakrishnan Sumathi

PD Dr. habil. R. Radhakrishnan Sumathi

Ph. +49 30 6392 3127



Silicon single crystals with ultrahigh purity and crystalline perfection are crucial for demanding applications in power electronics, photonics or basic research. The Float-Zone (FZ) method is particularly suitable for the growth of such crystals. We aim to provide FZ know-how, growth processes and custom-made crystals needed for enabling technologies in trends as e-mobility, smart and renewable energy or for the emerging field of quantum computing.

Our activities include the further development of FZ and related crucible-free growth processes (Pedestal, Silicon Granular Crucible method). For our partners in science and industry, we provide dislocation-free crystals with very high resistivity (>10kΩcm) and purity or targeted doping, e.g. with B, P, Bi, Ga, Al, Sb, Au, N. Our FZ furnaces allow the growth of crystals with a diameter of a few mm up to 200 mm. A special focus lies on the growth of isotopically enriched 28Silicon crystals.

Dr.-Ing. Robert Menzel

Dr.-Ing. Robert Menzel

Ph. +49 30 6392 3071


The Czochralski (Cz) group specializes in the growth of group-IV semiconductor crystals, silicon (Si), germanium (Ge) and their related alloys for a wide range of applications in electronics, photonics, plasmonics, thermoelectrics and efficient x-ray and γ-ray monochromators. As a member of the grand international GERDA/LEGEND collaboration, we are also striving to produce ultra-high purity Ge single crystals to be used as radiation detectors in astrophysics studies, in the quest for fundamental understanding of the universe. The focus lies in developing and establishing the whole value-chain process technology under one roof. 

  • Single crystal growth of ultra-high-purity Ge (n < 1011 cm-3), including the reduction of natural GeO2, isotopically enriched 76GeO2 to Ge and zone-refining of Ge up to 12N
  • Growth optimization of heavily-doped (n > 1018 cm-3) Ge crystals using novel gas-phase doping technique, for THz Plasmonics applications
  • Si, Ge crystals specifically doped with exotic dopants like Magnesium or Bismuth for their carrier dynamic studies with Free-Electron-Lasers
  • SiGe mosaic crystals and gradient crystals for synchrotron beam line optics; GeSn and SiGeSn crystals for photonics applications

R. Radhakrishnan Sumathi, Alexander Gybin, Kevin-P. Gradwohl, Pradeep C. Palleti, Mike Pietsch, Klaus Irmscher, Natasha Dropka, Uta Juda
Development of Large-Diameter and Very High Purity Ge Crystal Growth Technology for Devices
Crystal Research and Technology, Vol. 58 (2023) p. 2200286
DOI: 10.1002/crat.202200286

Aravind Subramanian,  Nikolay Abrosimov, Alexander Gybin, Christo Guguschev, Uta Juda,  Andreas Fiedler, Florian Bärwolf, Ioan Costina, Albert Kwasniewski, Andrea Dittmar, R. Radhakrishnan Sumathi
Investigation of Doping Processes to Achieve Highly Doped Czochralski Germanium Ingots
Journal of Electronic Materials, Vol. 52 (2023) p.5178.
DOI: 10.1007/s11664-023-10534-3

R. Radhakrishnan Sumathi, Nikolay Abrosimov, Kevin-P. Gradwohl, Matthias Czupalla, Jörg Fischer
Growth of heavily-doped Germanium single crystals for mid-Infrared Applications
Journal of Crystal Growth 535 (2020) 125490
DOI: 10.1016/j.jcrysgro.2020.125490

PD Dr. habil. R. Radhakrishnan Sumathi

PD Dr. habil. R. Radhakrishnan Sumathi

Ph. +49 30 6392 3127


Gallium Arsenide (GaAs) is beside Silicon (Si) the most commonly industrially used semiconductor material and is the one main focus of the group’s work.  Research activities are centered on the improvement and optimization of the  Vertical Gradient Freeze ( VGF) process with simultaneous application of magnetic fields, for example to improve process efficiency.  A critical factor thereby is the precise and predictable control of fluid flow.  A further central point of research is the VGF growth of III-V single crystals with specific characteristics for applications in basic research as well as special industrial applications such as detectors.

  • Vertical Gradient Freeze (VGF) growth of III-V single crystals (ø = 4“) using KristMAG® heater-magnet-modules (HMM)
  • Growth and characterization of III-V single crystals with custom specifications for research and industry
  • VGF growth process development and optimization
  • Realization of feasibility studies related to applications of KristMAG®  technology
  • Study of doping and impurity incorporation into crystals under the influence of external fields such as magnetic and ultrasonic fields

Christiane Frank-Rotsch, Natasha Dropka, Alexander Glacki, Uta Juda
VGF growth of GaAs utilizing heater-magnet module
Journal of Crystal Growth
DOI: 10.1016/j.jcrysgro.2013.12.063

Christiane Frank-Rotsch, Natasha Dropka, Peter Rotsch
III Arsenide
In Woodhead Publishing Series in Electronic and Optical Materials, Single Crystals of Electronic Materials,
Woodhead Publishing
DOI: 10.1016/B978-0-08-102096-8.00006-9

Christiane Frank‐Rotsch, Natasha Dropka, Frank‐Michael Kießling, Peter Rudolph
Semiconductor Crystal Growth under the Influence of Magnetic Fields
Crystal Research and Technology
DOI: 10.1002/crat.201900115

Dr. Christiane Frank-Rotsch

Dr. Christiane Frank-Rotsch

Ph. +49 30 6392 3031