We fabricated and characterized black polycrystalline diamond field effect transistors. By implementing a C-H bonded channel with a wide gate-drain length up to 20 μm, a breakdown voltage of 1.8 kV was achieved, which is the highest value reported for a diamond field effect transistor (FET) to date. Several of our devices achieved a breakdown voltage/wide gate-drain length ratio > 100 V/μm. This is comparable to the performance of lateral SiC and GaN FETs. We investigated the effects of voltage stress up to 2.0 kV, and showed that the maximum current density fell to 26% of its initial value of 2.42 mA/mm before the device eventually broke down at 1.1 kV.
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