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
The authors acknowledge financial support from the Engineering and Physical Sciences Research Council (EPSRC) through EP/H011366/1, EP/H011862/1, EP/H012532/1 and EP/H012966/1.
- planar Gunn diodes, terahertz, impact ionisation, composite anode contact, anode design