Chemical Sensing

Chemical sensing devices on diamond and III-Nitrides

This project is focused on the electrochemical characterization of diamond and III-Nitride based semiconductors (GaN, InN, AlN) and their heterostructures, and on the fabrication and optimization of Ion-Sensitive FETs (ISFETs) based on these materials.

Diamond is chemically very inert and therefore can be used for chemical sensing in harsh environments beyond the limit of other semiconductor materials. Fig. 1 shows the transfer characteristics of an ISFET structure on single crystal diamond with p-type boron delta-doped channel. The pH sensitivity of the device in strong acidic and alkaline electrolytes is due to carbon-oxygen functional groups at the surface of the ISFET channel. Recently this concept has been successfully transferred to large-area nanocrystalline diamond. The current research includes the optimization of the device structure and study of the surface termination characteristics for stable and selective sensing.

The electrochemical methods such as low-frequency impedance spectroscopy can be also used to analyze the electronic characteristics of semiconductor surfaces in electrolytes. In particular, these methods can be applied to study the oxidation mechanisms of the Nitride-based heterostructures and to evaluate the energy band diagrams of the surface after the oxidation. Fig. 2 shows an example of the electrochemical impedance spectroscopy measurements (Bode plot) of AlInN/GaN heterostructure prior to anodic oxidation process. The characteristics of the oxidised surface can be very useful to create new bio-chemical sensor devices, and also to improve the surface passivation technology of III-Nitride based HEMT devices.