This paper reports on vertical GaN Schottky barrier diodes (SBDs) fabricated on a free-standing GaN substrate with different sizes of Schottky electrode. The fabricated SBDs with 3 × 3 mm2 Schottky electrodes exhibited both a forward current of 50 A and a blocking voltage of 790 V. To our knowledge, the characteristics of operation with a simultaneous high forward current and high blocking voltage are reported for the first time for vertical GaN SBDs on free-standing GaN substrates. The dependence of these characteristics on the Schottky electrode size is also reported in detail.

In this paper, we report on a vertical GaN trench MOS barrier Schottky (TMBS) rectifier for attaining low leakage current at high temperature and high reverse voltage. At 200 °C, a high blocking voltage of 750 V was achieved at a leakage current of 1 mA/cm2. To the best of our knowledge, this blocking voltage is the highest ever reported for GaN Schottky rectifiers operating at such a high temperature. Furthermore, the fabricated TMBS rectifier operated at large forward currents up to 10 A. These results verify that the developed vertical GaN TMBS rectifiers have great potential as high-power and high-temperature devices.

We have fabricated and investigated AlGaN/GaN heterojunction field‐effect transistors (HFETs) with thick AlN surface passivation films. The HFETs exhibit increased drain currents and the transconductances with suppression of the self‐heating‐induced negative differential conductance at high applied voltages. Since the effects are more prominent for thicker AlN films, we conclude that the AlN films cause not only surface passivation, but also self‐heating reduction. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We have carried out delay time analysis for the high-frequency characteristics of AlGaN/GaN heterojunction field-effect transistors (HFETs) on sapphire substrates, focusing on a comparison between the effects of AlN and SiN surface passivation. HFETs with AlN passivation, in comparison with those with SiN passivation, exhibit high current gain cut-off frequencies f T with good flatness, in accordance with high intrinsic transconductance due to the self-heating reduction effect of AlN. From the delay time analysis, we find that the effective saturation electron velocity for AlN and SiN passivation is similar, while the electron mobility under the gate for AlN passivation is higher. This implies that the higher f T is mainly due to the higher electron mobility under the gate owing to the self-heating reduction by AlN passivation. This is consistent with the fact that the saturation velocity has a weak temperature dependence, while the mobility has a strong dependence.

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