A Breakthrough Silicon Carbide Design Substantially Upgrades Electric Cars and Trains

Electric vehicles have reached a threshold in performance.

And a team of scientists has made significant progress in exploring ways of substantially enhancing the design of silicon carbide power devices that are slated for use in electric vehicles, trains, and many other vehicles, according to a recent study published in the journal Physical Status Solidi (b).

When these roll out into the market, it could substantially increase the range, performance, and energy efficiency of all-electric vehicles.

Improving the performance, size, and energy consumption of electric vehicles

Silicon carbide (SiC) unipolar semiconductors have seen widespread commercial use, but to operate them, we face a Catch-22 between specific on-resistance, or a breakdown voltage, and specific resistance of the drift layer. So the researchers looked to something called a super junction structure, which denotes the arrangement of the "n and p layers" inside trenches in the drift layer, which allows for the bipolar operation in such devices. And this opens a loophole to surpass the unipolar limit.

And in the recent study, researchers based in Japan explored the depth distribution defects found in SiC bipolar diodes created from Aluminum doping (Al doping). Al doping involves either epitaxial or ion implantation, the former of which requires a layer-by-layer deposition of semiconductor materials onto a substrate material. Ion implantation, on the other hand, requires that you bombard the layers of the semiconductor material with charged high-energy particles. But ion implantation can create defects embedded deep in the semiconductor layers, potentially leading to negative effects on conductivity modulation, which can disrupt performance.

And in researching how and when this happens, the researchers are exploring the "engineering space" for solutions that will substantially improve EV performance. "Our findings will help with the optimum design of SiC power devices, which will soon be employed in electric vehicles, trains, etc.," said Associate Professor Masashi Kato of Nagoya Institute of Technology, Japan, who led the recent study, in a press release shared with IE via email. "These results will ultimately help improve the performance, as well as the size and energy consumption of traction systems in vehicles and trains." To further explore the depth distribution of defects, the research team created two SiC PiN diodes using Al-doped p-layers.

The low power consumption of SiC power devices will become crucial for future vehicles

One of the diodes was made via epitaxial growth, and the other via ion implantation. Afterward, they evaluated the distribution of defects in both diodes with the help of conventional "deep level transient spectroscopy" (DLTS), which enabled them to investigate their properties with cathodoluminescence (CL). And the research team found that p-type layer deposition via epitaxial growth left no additional damage in the adjacent n-type layers. While this was promising, the same epitaxially-grown diode also exhibited a minor instability that caused deep-level defects to form. Additionally, the specific on-resistance of this diode was low because of the effects of conductivity modulation, surmounting one of the two main obstacles described above.

On the other side of the experimental spectrum, the researchers discovered that Al doping in the diode created via ion implantation succeeded in reaching a high specific on-resistance without altering the conductivity modulation. The researchers also noticed that the defects in the semiconductor device penetrated to at least 20 micro-meters (µm) from the area of implantation. "Our study shows that the ion implantation in SiC bipolar devices need[s] to be processed at least 20 µm away from the active regions," said Kato in the release shared with IE. It's specifically the low power consumption found in SiC power devices that will become crucial for future vehicles as the effects of climate change exacerbate everything going wrong in the world, thanks in large part to the fossil fuel industry. But by advancing semiconductor technology at unprecedented speeds, we might lessen the collateral on humanity and other species on Earth, and make a more sustainable future a reality far sooner than present estimates expect.