Abstract
For the first time, Gallium Nitride(GaN)-based Gunn diodes with side-contact and fieldplate technologies were fabricated and measured with reliable characteristics. A high negative differential resistance (NDR) region was characterised for the GaN Gunn effect using side-contact technology. The I-V measurement of the THz diode showed the ohmic and the Gunn effect region with high forward current of 0.65 A and high current drop of approximately 100 mA for a small ring diode width wd of 1.5µm with 600 nm effective diode height hd at a small threshold voltage of 8.5 V. This THz diode worked stable due to good passivation as protection from electro-migration and ionisation between the electrodes as well as a better heat sink to the GaN substrate and large side-contacts. The diodes can provide for this thickness a fundamental frequency in the range of 0.3 - 0.4 THz with reliable characteristics.
Highlights
Based on the successful use of the Gunn effect in Gallium Arsenide (GaAs) to generate high-frequency signals, several materials were already tested for their suitability for the same purpose [1]
For improving the standard GaN Gunn diode according to the negative differential resistance (NDR) stability and the heat conduction, side-contact and field-plate technologies were used (Figure 2)
New GaN Gunn diodes with a good heat sink to the conductive GaN substrate and side-contact were fabricated
Summary
Based on the successful use of the Gunn effect in Gallium Arsenide (GaAs) to generate high-frequency signals, several materials were already tested for their suitability for the same purpose [1]. Attention was drawn to the potential of so-called nitride materials for operation at much higher frequencies (up to 1 THz) and powers (up to 10 mW) Reasons for this include the achievable high saturation velocity for electrons (for GaN > 2 times higher than in GaAs), much higher electric threshold field strength for the so-called ‘‘electron transfer effect’’ (for GaN > 50 times higher than in GaAs) and the large energy band gap for higher breakdown voltage [1], [2]. Simulation for GaN-Gunn diodes [2], [3], as well as several fabrication methods and initial current-voltage characteristics were performed [2], [4] All of these results were based on Gunn diodes on sapphire substrates. Three benefits were obtained here: good passivation of the active mesa, good heat sink as well as stable diodes with smaller diode height and higher potential THz frequencies
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