Power electronic devices

Multi-channel GaN heterostructures

With the electrification of our society, electricity is the fastest growing form of end-use energy. Power electronics, which rely on power semiconductor devices — transistors and diodes — are responsible for controlling and converting electrical power in the most adapted form for transmission, distribution, and end-user consumption. An essential parameter for enhancing efficiency and reducing cost in power conversion is the R_ON·Area product while maintaining a high breakdown voltage. However, R_ON is intrinsically determined by the electric conductivity of the 2DEG channel, given by the product of its carrier density (N_s) and electron mobility (μ).

To drastically reduce R_ON in power devices, our group has demonstrated the new concept of multi-channel devices for future efficient power conversion. Common GaN power electronics rely on a single 2DEG channel to conduct electricity. We proposed to vertically stack multiple-channel structures to significantly increase N_s without affecting μ. We developed this concept entirely — from the epitaxial growth of the multiple channels to the conception and demonstration of the final power transistor, resulting in state-of-the-art performance. The multi-channel structure led to a significant reduction in sheet resistance compared to single-channel devices, up to nearly 10-fold, reaching ultra-low values down to 36 Ω/sq.

Multi-channel power devices

We proposed vertically stacking multiple AlGaN/GaN channels to dramatically increase the sheet carrier density N_s without degrading mobility. The multi-channel structure reduces sheet resistance by up to 10× compared to single-channel devices, reaching ultra-low values down to 52 Ω/sq. Combined with our 3D tri-gate architecture, these devices achieve an ultra-low R_ON,sp of 0.46 mΩ·cm², enhancement-mode operation, breakdown voltages up to 1300 V, and record figures of merit of 4.6 GW/cm² (d-mode) and 3.8 GW/cm² (e-mode) — significantly outperforming all conventional single-channel devices.

Enhancement-mode multi-channel GaN transistors

A key challenge in multi-channel devices is achieving enhancement-mode operation: the large carrier density inherent to stacked 2DEG channels makes it significantly harder to reach sufficiently positive threshold voltages. To address this, our group demonstrated e-mode multi-channel GaN transistors based on conformally deposited p-type LiNiO and SiO₂/NiO over tri-gates, forming a multi-channel junction gate structure. As a result, e-mode operation was achieved with 3× larger tri-gate fins compared to SiO₂ alone, with V_th of 0.7 V (at 1 μA/mm), negligible threshold voltage hysteresis, together with a small R_ON of 2.8 mΩ·cm² and V_BR of 2.7 kV.

Slanted tri-gate field plates

We proposed the novel concept of slanted tri-gates, designed to work as field plates and enhance the breakdown voltage in GaN power devices. Our slanted tri-gate relies on a simple lateral design, by slanting the tri-gate sidewalls, which is obtained with a single lithographic step. This structure led to a 25-fold increase in breakdown voltage. Our multi-channel power devices exhibited an ultra-low R_ON of 0.46 mΩ·cm², enhancement-mode operation, breakdown voltages as high as 1300 V, and a record figure-of-merit (4.6 GW/cm² for d-mode devices and 3.8 GW/cm² for e-mode devices), considerably surpassing single-channel devices.