Chinese Team Develops Kilovolt GaN Diode
Vertical unipolar GaN power rectifier has figure of merit of 825 MW/cm2 and 8-order ON/OFF current ratio at −600V,
Researchers from Zhejiang University (ZJU) in China have developed a 1 kV/1.2 mΩ·cm2 vertical GaN-on-GaN Schottky barrier diode (SBD) featuring a high Baliga’s figure-of-merit of 825 MW/cm2 and 8-order ON/OFF current ratio at −600 V, which is one of the best among the reported vertical unipolar GaN power rectifiers.
To overcome the challenge of electric field crowding-induced leakage at the junction edge and premature breakdown, the ZJU team has developed a e planar nitridation-based termination (NT) technique, which can effectively suppress the reverse leakage by over 104 and boost the breakdown voltage up to 1 kV.
Furthermore, researchers revealed the mechanism of leakage suppression by NT by using ultraviolet photoemission spectroscopy (UPS) characterisation and TCAD simulations.
It is experimentally verified that the NT structure yields an enlarged barrier height and/or effective barrier thickness at the junction edge, and consequently, electron transport via thermionic field emission or tunnelling can be suppressed, leading to significantly suppressed edge leakage.
This is believed to be the first report revealing the physical mechanism of termination technology that is well suited for high-voltage vertical GaN power devices.
The 1 kV/1.2 mΩ·cm2 vertical GaN SBD exhibits a high current swing of ~1013, large forward current density over kA/cm2, and nearly ideal Schottky contact with a low ideality factor of 1.01‒1.04, showing great potential for high-power and high-frequency applications.
The figures above show (a) Current-voltage (I-V) characteristics of the NT-SBD in semi-log scale at 25degC. Inset: Comparison of the I-V characteristics and ideality factor η between the unterminated-SBD and NT-SBD. (b) Forward I-V characteristics of the NT-SBD in linear scale and extracted differential RON,sp of the NT-SBD. (c) Reverse I-V characteristics of the unterminated-SBD and NT-SBD.
'High-voltage and high-ION/IOFF vertical GaN-on-GaN Schottky barrier diode with nitridation-based termination' by Shaowen Han et al; IEEE Electron Device Letter, vol. 39, no. 4, pp. 572-575, Apr. 2018.