Conference Agenda

This presentation will discuss recent advancements and emerging

technologies based on III-Nitride semiconductors that aim to address

some of the challenges in power electronics. We will highlight the

significant improvements in device performance achieved through the use

of multi-channel structures, resulting in figures of merit that far exceed

current standards. To address the challenge of managing high heat fluxes

in compact devices, we will explore recent advancements in the thermal

management of GaN devices. This includes the co-design of microfluidics

and electronics within the same semiconductor substrate, a technology

that offers significantly greater cooling capabilities than currently available

and enables denser integration of GaN devices on a single chip. These

emerging technologies present exciting opportunities for the future

development of III-nitride electronic devices.

In this work, we present the electrical performance of quasi-vertical Schottky barrier diodes (SBDs) featuring a 500 nm n-GaN layer grown on a silicon carbide (SiC) substrate. The effect of rapid thermal annealing (RTA) on the Schottky contact was examined by comparing two annealing temperatures. The fabricated diodes demonstrate a low specific ON-resistance (RON,sp) of 1.23 mΩ·cm², a high forward current density of 543 A/cm², and a breakdown voltage of 78 V/μm, highlighting the potential of GaN-on-SiC SBDs for high-power and high-frequency applications.

Power switching devices are the key drivers for innovation in energy systems, ranging from the power utility grid, wind and solar power generation, and EVs, but also IT, servers and AI data centers.

4H-SiC MOSFETs have already become the preferred switches for EV drives and chargers, with commercial devices being available with blocking voltages of 1200V, 900V and 600V. More recently, Infineon announced a 400V 4H-SiC MOSFET, aimed at providing an alternate device to GaN HEMTs and silicon superjunction (SJ) MOSFETs for lower voltage applications. The latter two have typically been considered preferable at lower voltage because of their higher channel mobility and lower substrate cost. However, 8” 4H-SiC substrates are now available with ever lower cost per wafer and 4H-SiC trench MOSFETs with submicron channel length have led to lower channel resistance. This warrants a closer look.

This presentation provides a detailed analysis of the switching behavior of 4H-SIC MOSFETs as well as 3C-SiC MOSFETs. The analysis shows that the specific on-resistance can be as low as 1.1 mOhm-cm^2 and 0.25 mOHm-cm^2 respectively for quarter-micron gate-length 400V trench MOSFETs, where the difference is attributed to the higher channel mobility and lower substrate resistivity of the 3C-SiC MOSFET.

The low specific on-resistance combined with the higher thermal conductivity of SIC substrates enables operation at 400 A/cm^2 and 600 A/cm^2 for the 4H-SiC and 3C-SiC MOSFETs respectively. This enables smaller area devices with lower capacitance. Switching times shorter than 1.4ns and 0.46ns have been obtained with a switching energy less than 2.08uJ and 0.69 uJ for 10A, 400V, 4H-SiC and 3C-SiC MOSFETs respectively.

Detailed graphs showing the device performance as a function of key design parameters, including channel length, substrate thickness, junction temperature and operating frequency will be presented.

Finally, the performance of the SiC MOSFETs will be compared with that of equivalent GaN HEMTs and silicon SJ MOSFETs, highlighting advantages and trade-offs of each technology.

We report the successful development of Schottky barrier diodes (SBDs) that exhibit both a high breakdown voltage and the ability to withstand extreme temperatures. By utilizing a GaN epitaxial structure on sapphire substrate with a 5 µm thick drift layer and depositing a molybdenum-GaN Schottky contact annealed at 700 °C for 60 seconds. We have fabricated functional SBDs that deliver excellent performances including an ideality factor of 1.33, a breakdown voltage of 363 V and a very low on-resistance of 1.8 mΩ.cm².

Vertical GaN Nanowire (NW) Field Emitters (FE) are promising candidates for next generation devices. GaN NWs were grown selectively on SiO2 masked GaN/Al2O3 substrates for FE applications. Arrays of ~4 mm2 each with varied NW diameters and pitches were fabricated on a single GaN-based sample. A custom-made vacuum test system with an integrated micromanipulator High-Voltage setup was used for device characterization. The devices exhibited the expected Fowler-Nordheim (FN) tunneling behavior. Increased pitch from 1 μm to 3 μm, for given diameter of 100 nm, leads in lower current, possibly due to the decreased number of GaN NWs. Moreover, an increased diameter from 300 to 400 nm for given pitch of 5 μm, leads in higher current due to a larger emitting surface.

Surface-trap effects play a crucial role in understanding the operating principle of two-terminal devices based on AlGaN/GaN nanochannels. The trapping and de-trapping of carriers at the boundary surfaces are particularly significant, not only due to their influence on the current levels within the nanochannels but also because of their impact on the saturation of the current-voltage (I-V) curve. In this study, Monte Carlo simulations, incorporating traps through two different models, are done to replicate the experimental behaviour of the I-V curve and to identify the surface charge location under forward and reverse bias.