ELEGAN · Advanced characterisation of ELEctronic properties of GAllium Nitride based devices

Advanced characterisation of ELEctronic properties of GAllium Nitride based devices

GaN-based high-electron mobility transistors (HEMTs) are excellent candidates for high power and high frequency applications, primary because of the very high sheet carrier concentration induced by polarization effects as a two-dimensional electron gas in the HEMT channel. Moreover, AlGaN/GaN as well as InAlN/GaN heterostructures have shown great potential for applications in harsh environment due to its high thermal and chemical stability. However, GaN materials, despite their extraordinary properties are still at R&D stage, mainly for reasons linked to a need of better understanding of electrical effects in those materials. One of the main identified bottlenecks relates to the dispersive phenomena observed, which limit substantially the device performances. ELEGAN was addressing directly the design relative new components e.g. normally-off AlGaN/GaN high electron mobility transistors HEMT, power bar transistors, transistors for high frequency applications as well as understanding of the trapping effects in these components. The project was divided into two parts. The first part was mainly about transistors for power application. This part included standard normally-on as well as normally-off transistors. This whole period was done along the ENIAC project entitled Nanoelectronics for an Energy Efficient Electrical Car (E3Car). The objectives of the project were to build a solid nanoelectronics technology base, to establish reference designs and platforms for electrical vehicles and to develop efficient semiconductor components for the first industrial generation of electrical vehicles. We prepared first normally-off transistors in our laboratory with significant reduction of leakage current. In addition our power bar transistors reached the biggest drain current never demonstrated in our laboratory ( 30 A) with very significant reduction of leakage current In this period, the researcher was trained on all equipment, which is needed for processing and characterization of the transistors. The second part of the project was more focused on problems which are caused by traps in GaN devices. For this study we used devices which were designed for high frequency applications. In these devices, the influence of traps is bigger in comparison with transistors for power application, and reduction of the trapping effect is crucial. We prepared transistors with various SiN passivations. Dedicated Metal/Insulator/Metal (MIM) structures were also prepared. The SiN films were prepared in various laboratories working closely with III-VLab. Consequently, by comparing the different films we found out that the properties of transistors are strongly impacted and induce different drain current, gate leakage and threshold voltage.

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