Scientists from North Carolina State University (NC State) have unraveled a long-standing physics puzzle: why electronic devices sometimes fail completely under irradiation. The results are published in the journal IEEE Transactions on Nuclear Science. Understanding this mechanism could help create electronics capable of operating in extreme conditions - from nuclear power to space.
The focus was on aluminum nitride (AlN), a semiconductor with a so-called ultrawide bandgap. This means the material can withstand high electrical loads and is therefore theoretically suitable for operation in a radioactive environment. To test this, the researchers studied a phenomenon known as "single-event burnout" (SEB). This is the name for a catastrophic device failure when a single high-energy radiation particle causes irreversible damage and the device stops working. SEB occurs when high voltage is applied to a device under irradiation. Different devices withstand different voltages before this effect occurs.
"We wanted to characterize the AlN-based electronics we developed to understand how much power it can withstand before SEB," says Kristjan Quinones, lead author of the paper and a recent NC State graduate. According to him, the device design affects what voltage the semiconductor can withstand. Therefore, to compare materials, one should look not at voltage but at electric field strength. It turned out that AlN can withstand significantly higher fields than other semiconductors.
To explain the observations, the scientists analyzed their data together with existing information about SEB in other materials and, using computer modeling, built an analytical model describing the physics of the process. "Previously we knew that SEB occurs and could test how resistant a device is," says Quinones. "Now we know why."
The mechanism is as follows: under irradiation, heavy ions pass through the material and create charge carriers. Under the applied voltage, positive and negative charges separate, and a local electric field arises. When it reaches a critical magnitude, an avalanche-like growth in the number of electrons begins, leading to the release of a large amount of energy over a tiny area - essentially a micro-explosion. This is SEB.
"Understanding the physics of SEB is important because it allows us to purposefully create radiation-resistant materials and devices," explains co-author Ramon Collazo, a professor of materials science and engineering at NC State. "Previously we could not do this because we did not know exactly what happens in detail. Now we can develop design rules to protect devices from radiation and minimize damage from SEB."
The researchers tested their model against SEB data obtained for other devices and materials, and it described the observations well. "Our model explained everything we saw," notes Quinones. According to Collazo, the model could become a valuable tool for creating devices used in nuclear power, space exploration, biomedical technologies and fusion experiments.