Avalanche Capability of 650-V Normally-off GaN/SiC Cascode Power Device

A 650-V/84-mΩ normally-off GaN/SiC cascode power device has been developed using a high-voltage (HV) D-mode SiC JFET and a low-voltage (LV) E-mode GaN HEMT. The single-pulse avalanche capability of the GaN-HEMT/SiC-JFET cascode device is investigated using an unclamped inductive switching (UIS) testing setup. A Zener diode in parallel with the LV GaN HEMT is used to eliminate the voltage spikes at the drain terminal of LV GaN HEMT during the switching transients and is found to significantly affect the maximum single-pulse avalanche energy (E
_AS
). The voltage rating of Zener diode (V
_z
) determines how the UIS energy is consumed by the high-voltage (HV) GaN/SiC cascode power device during the avalanche breakdown process. With a higher V
_z
of 30V, the UIS energy is fully released by the SiC JFET's gate-to-drain (D
_GD
) junction diode in avalanche mode, and the maximum E
_AS
is up to 162.3mJ. With a lower V
_z
of 15V, the channel of SiC JFET can be activated at the beginning of the avalanche process of D
_GD
and undertakes part of UIS energy, facilitating a larger E
_AS
up to 342.7mJ.