InGaN is a critical material for the development of blue LEDs. Recently, an international team of researchers uncovered a key mechanism that limits the indium content in InGaN films. Their groundbreaking study was published in the journal *Physical Review Materials* in January this year.
To achieve red and green light emission in III-nitride LEDs as part of the RGB color system, the indium concentration in InGaN quantum wells is typically increased. However, the latest findings reveal that simply increasing the indium content does not lead to more efficient red or green LEDs, challenging previous assumptions about how these materials behave.
Despite advancements in green LED and laser technology, scientists have long struggled to surpass the 30% indium concentration limit in InGaN. The underlying cause remained unclear—was it due to growth conditions or fundamental material properties? This mystery was finally addressed by a research team from Germany, Poland, and China, who provided a detailed explanation of the limitation in their recent study.
The team experimented by growing a single atomic layer of indium nitride (InN) on gallium nitride (GaN). Surprisingly, the indium concentration remained stuck between 25% and 30%, indicating that the limit is not influenced by external factors but is instead inherent to the material itself.
Using advanced techniques such as transmission electron microscopy (TEM) and reflection high-energy electron diffraction (RHEED), the researchers observed that when the indium content reached 25%, nitrogen atoms were incorporated into the structure. The resulting indium gallium monolayer exhibited a regular pattern: alternating columns of indium and two columns of gallium.
Through comprehensive computational analysis, the team concluded that this atomic ordering is driven by specific surface reconstructions. Indium atoms form stronger bonds with neighboring atoms, creating a more stable configuration. This stability allows the material to grow at higher temperatures, improving its overall quality. However, this ordered arrangement only permits an indium concentration of up to 25%, which appears to be an unbreakable barrier under standard growth conditions.
Dr. Tobias Schulz, a member of the research team, emphasized that the indium content limit prevents InGaN from emitting red and yellow-green light. He stressed the need for new strategies to overcome this challenge and unlock broader color capabilities in future LED technologies.
With this discovery, scientists are now better equipped to explore alternative methods for enhancing indium incorporation in InGaN, potentially leading to breakthroughs in full-color LED displays and lighting systems.
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