Diamond SGFETs

For applications in biosensors and the field of bioelectronics, diamond has a number of advantageous properties such as chemical and electrochemical stability, well-controlled surface functionalization, and biocompatibility. Through termination of the surface with hydrogen, undoped diamond becomes surface conductive (Fig. 1a). [The hydrogenation leads to an upward bending of the valence band above the Fermi level, thereby generating a two-dimensional hole gas (2DHG) beneath the surface. ] This surface conductivity can be controlled e.g. by operating the device in electrolyte and applying a voltage across the diamond/electrolyte interface, creating a solution-gated field effect transistor (SGFET).
This basic device concept can be used as pH and ion sensitive sensor, functionalized with enzymes for enhanced selectivity (ENFET) and employed to detect the electrical signals of cells. 
Beyond the advancement of the diamond SGFETs in biosensing and bioelectronics, we are interested in understanding the physics behind such devices, and in particular the effect of the electrolyte on the electronic transport and on the accumulation of charge carriers in the diamond.

To this end, we investigate the electronic transport with Hall-effect measurements in electrolyte to reveal its limitations due to impurities in the diamond lattice, its dependence on the crystal orientation and the influence of ions close to the surface. We support the experimentally acquired data by simulating the charge distribution at the diamond/electrolyte interface with nextnano.

People on the project:

Markus Dankerl, Moritz Hauf, Lucas Hess, Magalí Ros

Selected publications:

• Diamond Transistor Array for Extracellular Recording From Electrogenic Cells
  M. Dankerl, S. Eick, B. Hofmann, M. Hauf, S. Ingedbrandt, A. Offenhäusser, M. Stutzmann, and J.A. Garrido
  Advanced Functional Materials 19, 1–9 (2010)
  Online Reference
• Low-frequency noise in diamond solution-gated field effect transistors
  M.V. Hauf, L.H. Hess, J. Howgate, M. Dankerl, M. Stutzmann, and J.A. Garrido
  Applied Physics Letters 97, 093504 (2010)
  Online Reference
• The surface conductivity at the Diamond/Aqueous electrolyte interface
  J.A. Garrido, A. Hartl, M. Dankerl, A. Reitinger, M. Eickhoff, A. Helwig, G. Muller, and M. Stutzmann
  Journal of the American Chemical Society 130, 12 4177-4181 (2008)
  Online Reference
• Resolving the controversy on the pH sensitivity of diamond surfaces
  M. Dankerl, A. Reitinger, M. Stutzmann, and J.A. Garrido
  Physica Status Solidi - Rapid Research Letters 2, 31-33 (2008)
  Online Reference

Cooperations:

Element Six Ltd., UK

P. Bergonzo, CEA, France

Funding:

Diamond to Retina Artificial Microinterface Structures (DREAMS, FP6-NMP-2006–676033345),
Nanosystems Initiative Munich (NIM),
Graduate School for Complex Interfaces (CompInt)
BACATEC