Development of Reliable Nitrogen-Polar GaN-based Transistors – N-Polar

High Electron Mobility Transistors (HEMTs) are most suited to high power millimeter-wave (RF) applications. Developments on silicon substrates are of interest because of CMOS techniques availability and lower cost of substrates. In this project, we aim at nitrogen (N)-polar GaN-based transistor on silicon substrates, to be later substituted with high thermal conductivity diamond or Aluminum Nitride (AlN) backside processing. In this project, we aim to produce nitrogen polarity transistors (N-Polar or N-Face) on silicon substrates, which will then be substituted for a high thermal conductivity diamond substrate or machined on the back side for deposition of an Aluminum Nitride (AlN) heat sink. N-Polar materials are not very developed in Europe, while they are the subject of growing interest in the United States and Japan using either carbon-faced SiC substrates or bulk GaN and AlN substrates with nitrogen polarity. The N-polar family demonstrates state-of-the-art performance in applications ranging from a few GHz to above 100 GHz. In this project, we develop an innovative approach on silicon substrate using an epitaxial niobium nitride (NbN) layer to control the nitrogen polarity of GaN and associated nitrides. Project partners are CRHEA for MBE HEMT growth of N-polar structures, IEMN for device processing and backside AlN processing, III-V Lab for ohmic contact regrowth and integration on diamond, and CIMAP for transmission electron microscopy (TEM) studies. Based on convincing preliminary results and several innovations, the project aims to demonstrate nitrogen polarity HEMT structures on silicon substrates and to optimize the thermal performance of the structures in order to develop a new high-performance and reliable sector of nitrogen polarity HEMT transistors in Europe. Developing high-frequency and high-power innovating devices are of interest to III-V Lab's mother companies, namely Thales, Nokia and CEA, and also to the French-German foundry United Monolithic Semiconductors (UMS).