Vertical Gallium Nitride PowerDevices: Fabrication and Characterisation - Hentschel, Rico

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Résumé :
Efficient power conversion is essential to face the continuously increasing energy consumption of our society. GaN based vertical power field effect transistors provide excellent performance figures for power-conversion switches, due to their capability of handling high voltages and current densities with very low area consumption. This work focuses on a vertical trench gate metal oxide semiconductor field effect transistor (MOSFET) with conceptional advantages in a device fabrication preceded GaN epitaxy and enhancement mode characteristics. The functional layer stack comprises from the bottom an n+/n--drift/p-body/n+-source GaN layer sequence. Special attention is paid to the Mg doping of the p-GaN body layer, which is a complex topic by itself. Hydrogen passivation of magnesium plays an essential role, since only the active (hydrogen-free) Mg concentration determines the threshold voltage of the MOSFET and the blocking capability of the body diode. Fabrication specific challenges of the concept are related to the complex integration, formation of ohmic contacts to the functional layers, the specific implementation and processing scheme of the gate trench module and the lateral edge termination. The maximum electric field, which was achieved in the pn- junction of the body diode of the MOSFET is estimated to be around 2.1 MV/cm. From double-sweep transfer measurements with relatively small hysteresis, steep subthreshold slope and a threshold voltage of 3 - 4 V a reasonably good Al2O3/GaN interface quality is indicated. In the conductive state a channel mobility of around 80 - 100 cm?/Vs is estimated. This value is comparable to device with additional overgrowth of the channel. Further enhancement of the OFF-state and ON-state characteristics is expected for optimization of the device termination and the high-k/GaN interface of the vertical trench gate, respectively. From the obtained results and dependencies key figures of an area efficient and competitive device design with thick drift layer is extrapolated. Finally, an outlook is given and advancement possibilities as well as technological limits are discussed.

Biographie:
Date of birth November 17th 1988 Place of birth Rochlitz, Germany Nationality German ACADEMIC CAREER Scientist/PhD student April. 2014 -July 2020 NaMLab gGmbH/TU Dresden: Research on GaN/AlGaN based lateral and vertical devices Master studies (M.Sc.) Oct. 2011 - Feb. 2014 Electronic- and sensormaterials, TU-Bergakademie FreibergMaster thesis Influence of device geometry, buffer doping conditions and terminal potentials on the dynamic RDSon and breakdown voltage of GaN power HEMTs with Infineon Technologies Austria AG Project work 2013 & & Der Einsatz von Beschleunigungssensoren zur Lageerfassung am Beispiel eines Formula Student Fahrzeugs und Entwicklung eines Versuchsaufbaus zur Aufnahme von Beschleunigungs- und Sto?vorg?ngen Bachelor studies (B.Sc.) Oct. 2008 -- Sep. 2011 Electronic- and sensormaterials, TU-Bergakademie Freiberg, Germany Bachelor thesis: Entwicklung von Anschlusskontaktierungen f?r OLED in Beleuchtungsanwendungen with Novaled AG Research work 2011 Komposite aus feinporigen anorganischen Materialien und organischen Farbstoffmolek?len f?r Anwendungen in der Photonik und Sensorik