Yoshihiko Muramoto | Nitride Semiconductors Co., Ltd.: How can you boost microLED brightness by 70% without increasing power? The answer lies in nano-structuring the chip surface with a photonic crystal.

Why did the Nobel Prize for blue LEDs highlight a fundamental flaw in GaN, and how can gallium droplets fix it for high-efficiency UV microLEDs?

A core problem in growing Gallium Nitride (GaN) on a sapphire substrate is the high density of crystal defects, known as threading dislocations. These dislocations act as non-radiative recombination centers, which kill the efficiency of an LED. The Nobel Prize-winning breakthrough for blue LEDs was the discovery that incorporating indium into the active region (InGaN) creates "indium composition fluctuations." These fluctuations form localized potential wells that trap charge carriers, allowing them to recombine radiatively before they can find a dislocation, thus enabling bright emission despite the high defect density.

This solution, however, creates a new problem for UV LEDs. To achieve shorter UV wavelengths, the indium content must be reduced and aluminum must be added (AlGaN), which eliminates the protective indium fluctuation effect. This makes the underlying dislocations a major efficiency killer once again. Furthermore, the traditional GaN buffer layer, used to manage the lattice mismatch between GaN and sapphire, is highly absorptive at UV wavelengths, trapping the very light the device is designed to emit.

Nitride Semiconductors presents a three-pronged materials science solution to create high-efficiency UV wafers. First, they use proprietary technology involving gallium droplets during growth to create a carrier-localizing effect that mimics the benefit of indium fluctuations. Second, they employ advanced epitaxial techniques to directly reduce the physical density of threading dislocations. Finally, they engineer the buffer layer to be transparent to UV light, solving the fundamental materials and optical challenges that prevent conventional GaN platforms from producing efficient UV microLEDs.

In this short video, you can learn:
* The role of indium composition fluctuation in overcoming dislocation defects in blue GaN LEDs.
* Why conventional GaN growth techniques fail for high-efficiency UV LEDs.
* A proprietary three-part strategy using gallium droplets and buffer layer engineering to create high-performance UV epi-wafers.
📋 **Clip Abstract** The speaker explains the fundamental material science challenges in growing high-quality GaN for UV LEDs, a problem not solved by the Nobel Prize-winning techniques for blue LEDs. He introduces Nitride Semiconductors' proprietary use of gallium droplets and buffer layer engineering to overcome these issues.
🔗 Link in comments 👇

Can you make efficient red microLEDs from GaN? This data shows the brutal reality of the "green gap" and why UV LEDs are far more stable.

The speaker presents a direct, data-driven comparison of red, green, blue, and UV microLEDs, all fabricated from the same InGaN material system. A key metric for mass transfer and display uniformity is wavelength consistency. The data shows that while red is acceptable (8.5nm variation), the green (21nm) and blue (17nm) are significantly worse. In stark contrast, the UV microLED is exceptionally uniform, with only a 3.9nm variation across the wafer, making it a far more manufacturable and consistent starting point for a display.

The fundamental challenge for native GaN-based red LEDs is the extremely high indium composition required, which severely degrades material quality and efficiency. The speaker reveals their InGaN red required a 45.6% indium composition, resulting in an external quantum efficiency (EQE) of only 2-3%. The efficiency collapses as the wavelength increases from blue and UV (both over 22% EQE) to green (~17%) and finally to red, clearly quantifying the infamous "green-red gap" in the InGaN material system.

For a high-quality display, color must remain stable as brightness changes. The speaker's data reveals a critical flaw in visible InGaN LEDs: a significant 8nm wavelength shift for the red LED as drive current increases. The blue and green LEDs also shift by 2nm. However, the UV microLED exhibits virtually zero wavelength shift with current, proving it is an exceptionally stable pump source, ensuring consistent color coordinates for a color-converted display regardless of the brightness level.

In this short video, you can learn:
* Comparative data on wavelength uniformity for InGaN-based R, G, B, and UV microLEDs.
* How external quantum efficiency (EQE) collapses for red InGaN LEDs due to high indium content.
* The superior color stability (zero wavelength shift) of UV microLEDs compared to visible InGaN LEDs under changing drive currents.
📋 **Clip Abstract** This clip presents compelling experimental data comparing InGaN-based microLEDs across the R, G, B, and UV spectrum. It quantifies the severe efficiency drop-off and color instability in red InGaN LEDs, making a strong, data-driven case for the UV-plus-phosphor approach.
🔗 Link in comments 👇