Role of Carbon on the electrical, optical and structural properties of GaN

• Applicant: Professor Dr.-Ing. Thomas Mikolajick
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Synthesis and Properties of Functional Materials
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 348524434

Intense interest and research over the past 3 years in gallium nitride (GaN) doped with carbon points at the fact that carbon will not act as a practical acceptor in GaN. Independent experiments concluded on a deep acceptor state ~ 0.7 – 1 eV above the valence band and with this, room temperature p-type conductivity of carbon-doped GaN seems illusive. Our recent research on C-doped GaN grown by molecular beam epitaxy (MBE) supports these aspects, as we could not identify the acceptor character spectroscopically or electrically, as e.g. possible for the case of GaN doped with magnesium. The exact microscopic character of the deep defect formed by C in GaN remains of big interest, since it presents a possibility to compensate residual n-type conductivity. MBE-grown ultra-pure GaN represents a perfect reference system, as it allows for the comparison between this reference and material with intentionally introduced impurities. Our recent results point at the formation of structural defects during the growth of carbon-doped GaN. This aspect will be further investigated by referring spectroscopic photoluminescence signatures in the energy range between 3.0 and 3.4 eV to the carbon doping level. Further it was realized that carbon is not exclusively related to the appearance of a yellow luminescence band around 2.2 eV, which will be studied in further detail by co-doping carbon-containing material. A last pillar of the proposed work are investigations to link carbon concentrations in AlGaN/GaN HEMT layer stacks with their electrical properties and operation modes.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Stefan Schmult