First current-collapse-free vertical GaN power device
Researchers from Zhejiang University (ZJU) have reported a vertical GaN-on-GaN power rectifier free from dynamic ON-resistance (RON) degradation, even at only 200ns after switching from high OFF-state bias up to 500V, outperforming the state-of-the-art lateral GaN-on-Si devices. The results were reported in IEEE Transactions on Power Electronics.
They claim that this is the first time that a current-collapse-free performance has been experimentally verified in a vertical GaN power device, by using a custom-designed double pulse test (DPT) circuit with minimised delay of 200ns and the capability for precise extraction of dynamic RON.
Conventional lateral GaN-on-Si devices have been confronted with the challenge of dynamic RON degradation arising from: (i) surface trapping that could easily degrade the 2DEG conductivity at a short distance from the III-nitride surface, and (ii) buffer trapping in the carbon-doped semi-insulating buffer stack where the deep-level traps could generate negative space charges and partially deplete the 2DEG.
By comparison, the vertical GaN-on-GaN device, featuring a vertical current flow and high-quality homo-epitaxial GaN drift layer with well controlled background/compensation doping, can fundamentally overcome the grand challenge of dynamic RON degradation, say the researchers.
The dynamic RON has been systematically and quantitatively evaluated using the DPT with a clamping circuit under different switching conditions, including: (1) OFF-state bias up to 500V, (2) OFF-state time within 10-6s ~102s, (3) high temperature up to 150degC, and (4) different load current levels.
The clamping circuit enables precise measurement of the low ON-state voltage after switching from high-voltage OFF-state, and the ultrashort delay of 200 ns in the custom-designed high-speed DPT can minimise possible trap recovery during measurement, leading to an accurate and precise extraction of dynamic RON. Under all the test conditions, the vertical GaN-on-GaN rectifier developed by ZJU is free from dynamic ON-resistance degradation at only 200 ns after switching from OFF-state, outperforming the state-of-the-art commercial lateral GaN-on-Si devices and showing great potential for high-frequency applications.
Figure 2 above shows time-resolved dynamic RON/static RON of (a) vertical GaN-on-GaN SBD developed by ZJU, (b) commercial lateral GaN-on-Si device A and (c) commercial lateral GaN-on-Si Device B with OFF-state time (tOFF) of 100 μs and OFF-state bias (VOFF) varying from 50 to 500 V.
Figure 3 above shows dynamic RON of the three types of GaN devices extracted at only 200 ns after switching from: (a) varying VOFF up to 500 V, (b) tOFF_Stress of 10-6~102 s and (c) high temperature up to 150 degC.
'Current-Collapse-Free and Fast Reverse Recovery Performance in Vertical GaN-on-GaN Schottky Barrier Diode' by Shaowen Han, Shu Yang, Rui Li et al; IEEE Transactions on Power Electronics
