http://hdl.handle.net/1983/1800 Thu, 13 Jun 2013 10:54:07 GMT 2013-06-13T10:54:07Z http://hdl.handle.net/1983/1825 Optical investigation of degradation mechanisms in AlGaN/GaN high electron mobility transistors: generation of non-radiative recombination centers Hodges, CJ; Killat, N; Kaun, SW; Wong, MH; Gao, F; Palacios, T; Mishra, UK; Speck, JS; Wolverson, D; Kuball, M Degradation mechanisms in AlGaN/GaN high electron mobility transistors (HEMTs) have been studied under pinch-off conditions. Sites of localized emission of electroluminescence (EL) in the form of hotspots, known to be related to gate leakage currents, are shown to be the result of the generation of non-radiative recombination centers in the AlGaN device layer during device stress. EL from the hotspot site contains both hot-carrier emission from the acceleration of charge carriers in the device channel, and defect-related transitions. Gate leakage through the generated centers is the most likely mechanism for the observation of EL hotspots. Tue, 13 Mar 2012 00:00:00 GMT http://hdl.handle.net/1983/1825 2012-03-13T00:00:00Z http://hdl.handle.net/1983/1803 Reduction of impact ionisation in GaAs-based planar Gunn diodes by anode contact design Montes Bajo, M; Dunn, G; Stephen, A; Khalid, Ata; Li, C; Cumming, D; Oxley, CH; Hopper, RH; Kuball, M Impact ionisation in GaAs-based planar Gunn diodes is studied through electroluminescence analysis with the aim of reducing its magnitude by means of contact design and shaping and thus enhance device performance and reliability. Designs in which the diode ohmic anode has an overhanging Schottky extension (composite anode contact) are shown to result in a significantly reduced amount of impact ionisation compared to a simple ohmic contact design. The electroluminescence results are consistent with Monte Carlo simulations which show a reduced impact ionisation in composite anode contact devices due to a reduced electron density beneath the anode Schottky extension that, on the one hand, weakens the Gunn domain electric field and softens its variations near the anode edge, and, on the other hand, reduces the number of electrons capable of generating holes by impact ionisation. A comparison between standard and composite anode contact approaches in terms of RF operation of the devices is made showing oscillations up to 109 GHz with an output power of -5 dBm in devices featuring the composite anode contact and no oscillations from all-ohmic contact devices. The findings reported in this work may be useful not only for the design and fabrication of planar Gunn diodes, but also for other devices such as HEMTs where impact ionisation can result in reliability limitations. This article is a version that has been revised by the author to incorporate review suggestions, and which has been accepted by IEEE for publication in the journal, IEEE Transactions on Electron Devices Wed, 23 Nov 2011 00:00:00 GMT http://hdl.handle.net/1983/1803 2011-11-23T00:00:00Z