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With electroluminescence microcopy towards more reliable AlGaN/GaN transistors

: Baeumler, M.; Dammann, M.; Wespel, M.; George, R.; Konstanzer, H.; Maroldt, S.; Polyakov, V.M.; Müller, S.; Bronner, W.; Brueckner, P.; Benkhelifa, F.; Waltereit, P.; Quay, R.; Mikulla, M.; Wagner, J.; Ambacher, O.; Graff, A.; Altmann, F.; Simon-Najasek, M.; Lorenzini, M.; Fagerlind, M.; Wel, P. van der; Roedle, T.


Razeghi, M. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Optical Sensing, Imaging, and Photon Counting: Nanostructured Devices and Applications : 11-13 August 2015; San Diego, California, United States
Bellingham, WA: SPIE, 2015 (Proceedings of SPIE 9555)
ISBN: 9781628417210
Paper 95550Y, 14 pp.
Conference "Optical Sensing, Imaging, and Photon Counting - Nanostructured Devices and Applications" <2015, San Diego/Calif.>
Conference Paper
Fraunhofer IAF ()
Fraunhofer IWM ()
electroluminescence microscopy; AlGaN/GaN HEMT; failure analysis; reliability; degradation mechanism; transmission electron microscopy; drain-current step stress; high temperature reverse bias stress

Long-term stability and reliability of AlGaN/GaN high electron mobility transistors (HEMT) can be validated by various stress tests which allow studying the physical mechanisms responsible for degradation. As the electroluminescence (EL) intensity is related to the kinetic energy and density of the channel electrons accelerated in the electric field, both local current and electric field changes can result in an increase or decrease of the EL intensity. The electric field distribution in source drain direction peaks at the drain side edge of the gate foot and the field plates. It is strongly dependent on the gate design and the passivation /semiconductor interface trap density. Although the spatial resolution of the electroluminescence microscopy (ELM) set-up is limited to a few microns, the technique allows to monitor submicron changes in the device geometry and hence to identify elevated electric field peaks being responsible for the acceleration of the degradation process. ELM also benefits from the fact that submicron imperfections at the Schottky interface of the gate electrode result in strong local current variations. It has been used to selectively identify suitable positions for further failure analysis of focused ion beam prepared cross sections by scanning and transmission electron microscopy. Process induced imperfections as voids at the Schottky interface after stress have been localized.