Conductivity Modulation in Vertical GaN PiN Diode
Zhejiang University team reveals dependence of the forward transient behaviours in vertical GaN PiN diode on time, current and temperature
Researchers from Zhejiang University (ZJU) in China have identified the experimental evidence for conductivity modulation in the direct-bandgap GaN vertical PiN diode.
For the first time, the dependence of the forward transient behaviors in vertical GaN PiN diode on time, current and temperature are comprehensively investigated, providing profound evidence for photon-enhanced conductivity modulation in transient/dynamic level. It is fundamentally important to answer the question whether the direct-bandgap GaN bipolar devices have the conductivity modulation capability and are suitable for high-power applications. Thanks to the conductivity modulation, the vertical GaN PiN diode can also deliver negative dynamic RON performance.
In contrast with the PiN diodes based on indirect-bandgap semiconductors (e.g. Si and SiC) with relatively long minority carrier lifetime, the direct-bandgap GaN vertical PiN diode enables radiative recombination of electron/hole pairs in conduction mode and exhibits an ultrashort minority carrier lifetime of ~10-8s. Whether the direct-bandgap GaN bipolar devices have the conductivity modulation capability is fundamentally important for high-power applications, but the evidence for which was lacking for a long time.
The forward transient behaviours have been characterised by using pulse-mode and time-resolved measurements as well as board-level switching tests. The conductivity modulation and its dependence on conduction time (tON), conduction current (ION) and temperature have been identified in the vertical GaN PiN diode. Thanks to the limited trapping effects and photon-enhanced conductivity modulation, the vertical GaN-on-GaN PiN diode can also deliver superior dynamic RON performance, showing great potential for high-power and high-efficiency power conversion.
The figures above show time-resolved forward voltage shift of the vertical GaN PiN diode (a) at various applied ION at 25degC, (b) at 50 mA at elevated temperature. (c) Time-resolved normalized dynamic RON of the vertical GaN PiN diode after switching from VOFF of 300 V and 400 V to varying ION of 1~4 A. (d) Dynamic RON at tON of 500 ns and 3000 ns as a function of ION and VOFF.
‘Conductivity Modulation in Vertical GaN PiN Diode: Evidence and Impact’ by Shaowen Han et al; IEEE Electron Device Letters, vol. 42, no. 3, Mar. 2021.