‘Shedding light’ on the role of undesired impurities in gallium nitride

The semiconductor industry and a lot of electronics dominate silicon today. In transistors, computer chips, and solar cells, silicon has been a standard component for decades. But all this may change soon, with gallium nitride (GaN) emerging as a powerful, superior, alternative.

Not very well known, GaN semiconductors have been in the electronics market since the 1990s and are often used in power electronic devices due to their relatively large bandgap compared to silicon – an aspect that is considered to be high-voltage and High temperature makes it a better candidate for applications. . In addition, current travels faster through GaN, which ensures lower switching losses during switching applications.

Not everything about Gaen is perfect, though. Although impurities are generally desirable in semiconductors, unwanted impurities can often reduce their performance. In GaN, impurities such as carbon atoms often cause poor switching performance due to being trapped in the ‘deepest level’ of the charge carrier, thought to arise from the energy level created by impurity defects in GaN crystal layers and the presence of carbon impurities. A nitrogen site.

A curious experimental manifestation of deeper levels is the presence of a long-lived yellow luminescence in the photolumination spectrum of GaN, along with a longer charge carrier recombination time, as well as time-resolved photoluminescence (TR-PL) and microwave photocondensity. Characterization is reported by characterization techniques such as caries (μ-PCD). However, the mechanism underlying this longevity is unclear.

In a recent study published in the Journal of Applied Physics from Japan, looking at how TR-PL and μ-PCD signals with temperature detected a deep level effect on yellow luminesicin decay time and carrier recombination.

“Only by understanding the effects of impurities in GaN power semiconductor devices, we can push for the development of impurity control technologies in GaN crystal growth,” says Prof. Mashi Kato from Nagoya Institute of Technology, Japan, who studied Led.

The scientists prepared two samples of Gaen layers grown on Gaene substrate, one from silicon and the other from iron. Unintentional doping of carbon impurities occurred during the silicon doping process.

For the TR-PL measurements, the team recorded signals up to 350 ° C for temperatures, while up to 250 ° C due to system limitations for μ-PCD. They used a 1 nanosecond-long UV laser pulse to excite the samples and measured the reflection of microwaves from the samples for μ-PCD.

The TR-PL signals from both samples showed a slow (decay) component with a decay time of 0.2–0.4 milliseconds. Additionally, the use of a long-pass filter with a cut-off at 461 nm confirmed that yellow light was included. In both samples, and for both TR-PL and μ-PCD measurements, the decay time fell above 200 ° C, consistent with previous reports.

To explain these findings, scientists resorted to numerical calculations, which showed that deeper levels are essentially trapped in “holes” (the absence of electrons) that eventually recombine with free electrons, but not electrons.

It took a long time to do so due to the extremely low probability. Occupied a deeper level. However, at higher temperatures, the holes managed to escape the trap and recombine with electrons through a more rapid recombination channel, explaining the degradation of decay times.

“To minimize the effects of the slow decay component, we must either maintain a low carbon concentration or adopt device structures with injection of suppression holes,” says Prof. Keto.

With this information, it is probably only a short time ago that scientists know how to avoid these pitfalls. But with the rise in power of GaN, will it just be better electronics?

Pro. Kato thinks otherwise. “GaN enables less power loss in electronic devices and therefore saves energy. I think it can go a long way in mitigating greenhouse effects and climate change,” he concludes optimistically. These conclusions on impurities may be such that lead us to a clean, green future!

Leave a Reply

Your email address will not be published. Required fields are marked *