Enhancement of thermionic emission and conversion characteristics using polarization- and band-engineered n-type AlGaN cathodes

We observed enhancement of thermionic emission (TE) and conversion (TC) characteristics by controlling spontaneous and piezo polarization and the band diagram of n-type AlGaN/GaN thermionic cathodes. The obtained TE current from N-polarity n-AlGaN films grown on an n-GaN substrate was 0.29 mA at 500 °C in a Cs gas atmosphere in the vacuum gap between the cathode and a stainless steel anode. This TE current was 5.0 times and 1.6 times higher than that from the surface of Ga-polarity n-GaN substrate and that of the Ga-polarity n-AlGaN film on the substrate, respectively.