InGaN is a critical material for the development of blue LEDs. Recently, an international research team made significant progress in understanding the core mechanism that limits the indium content in InGaN films. Their findings were 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 the InGaN quantum well is typically increased. However, the latest research revealed that simply increasing the indium content through traditional methods does not lead to efficient red or green LEDs. Despite advancements in green LED and laser technology, scientists have long struggled with a 30% indium concentration limit in InGaN, without fully understanding its cause—whether it's due to environmental factors or intrinsic properties of the material.
This mystery was finally addressed in January when a collaborative team from Germany, Poland, and China uncovered the underlying mechanism behind the indium content limitation. Their study provided new insights into why the indium concentration cannot be increased beyond a certain threshold.
The researchers conducted experiments by growing a single atomic layer of indium nitride (InN) on gallium nitride (GaN). Surprisingly, the indium concentration remained stable between 25% and 30%, indicating that the limitation is not caused by external growth conditions but rather by inherent structural constraints within InN itself.
Using advanced techniques such as transmission electron microscopy (TEM) and reflection high-energy electron diffraction (RHEED), the team observed that when the indium content reached 25%, nitrogen atoms formed a regular pattern. The indium gallium monolayer exhibited a specific arrangement: alternating columns of indium and gallium atoms.
Through detailed computational analysis, the researchers concluded that this atomic ordering is influenced by surface reconstruction. Indium atoms form stronger bonds with four neighboring atoms, leading to more stable chemical interactions between indium and nitrogen. This stability allows InGaN to grow at higher temperatures, resulting in better material quality. However, this ordered structure only supports an indium concentration of up to 25%, which represents a fundamental barrier under normal growth conditions.
Dr. Tobias Schulz, a member of the research team, emphasized that the indium concentration limit prevents InGaN from emitting red and yellow-green light. He highlighted the need for innovative approaches to overcome this challenge and unlock broader color capabilities in future LED technologies.
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