When a beam of 275 nm UV-C light penetrates a microbial cell, its energy precisely targets the pyrimidine bases in the DNA molecules, like an invisible blade slicing through the chain of genetic material — this is the ultimate secret behind UV-C LED disinfection. But from the moment the switch is flipped to the moment this “light blade” is produced, a precise collaboration unfolds in the microscopic world. So how exactly does this dazzling transformation occur? Let’s zoom in and take a closer look at the fascinating journey from current injection to germicidal light emission.
I. Semiconductor Chip: The Origin of UV-C Light
At the heart of a UV-C LED lies a semiconductor chip made of aluminum gallium nitride (AlGaN), typically only a few square millimeters in size. Its crystal structure forms the foundation for energy conversion. Unlike conventional visible light LEDs, UV-C wavelengths (200–280 nm) require a much wider bandgap (3.4–6.2 eV). AlGaN achieves this by precisely adjusting the aluminum content — when the aluminum ratio exceeds 50%, the bandgap becomes wide enough to emit germicidal light in the 260–280 nm range.
The chip has a “sandwich” structure: an n-type layer (electron supply zone), a multiple quantum well (MQW) active layer (light emission zone), and a p-type layer (hole supply zone). These thin layers are grown atom-by-atom using metal-organic chemical vapor deposition (MOCVD), with each layer just a few nanometers thick, ensuring atomic-level crystal quality.
II. Current Injection: Electron-Hole Recombination
Once the electrodes are powered on, an external voltage drives free electrons from the n-type layer into the active region, while holes (positively charged carriers) from the p-type layer move in the opposite direction, disrupting the semiconductor’s equilibrium. This delicate interaction must overcome energy losses caused by material resistance — one reason why LEDs generate heat during operation.
In the MQW structure, electrons and holes recombine at peak efficiency. These quantum wells — formed by alternating layers of GaN and AlGaN — act like finely tuned “reaction chambers.” Electrons drop from the high-energy conduction band to the low-energy valence band, combining with holes and releasing their energy in the form of photons. This is the electroluminescence process.
The amount of energy released determines the photon’s wavelength. For UV-C applications, the high energy corresponds to shorter wavelengths — a 275 nm photon carries just enough energy to break covalent bonds in microbial DNA. In comparison, visible light LEDs have smaller bandgaps — blue LEDs, for instance, have a bandgap around 2.6 eV and emit at ~475 nm.
III. Light Extraction: Breaking Through the Chip Barrier
Not all photons generated through recombination escape the chip. AlGaN’s high refractive index often causes light to reflect internally — like a beam trapped within glass. Early UV-C LEDs had light extraction efficiencies below 20%, with most energy “trapped” inside the device.
Engineers have overcome this with three key technologies:
Surface nanostructures (e.g., nanopillars, roughening) alter reflection angles to release trapped light.
Transparent conductive layers like Indium Tin Oxide (ITO) replace opaque metal electrodes, minimizing light blockage.
Flip-chip designs emit light from the sapphire substrate side, avoiding electrode shadowing.
These advancements have raised commercial UV-C LED light extraction efficiency to over 30%.
IV. Germicidal Action: Precise Microbial Destruction
Only when UV-C light successfully reaches its target does the germicidal process truly begin. UV-C photons between 260–280 nm match the absorption peak of thymine and cytosine in DNA. Once absorbed, adjacent pyrimidine molecules form dimers — effectively tying a knot in the DNA strand.
This structural damage is irreversible. The microorganism loses its ability to replicate, rendering it inactive. Studies show that a 275 nm UV-C dose of 30 mJ/cm² can achieve 99.99% inactivation of E. coli, while more resistant spores (e.g., Bacillus subtilis) require doses above 100 mJ/cm².
Compared to traditional mercury lamps, UV-C LEDs offer precise wavelength control (e.g., 275 nm ± 5 nm), avoiding the more harmful 200–230 nm range and concentrating energy within the most efficient germicidal band — 260–270 nm. This enables targeted and effective disinfection.
V. Energy Losses: The Ongoing Challenge of Efficiency
Throughout the conversion chain from electrical power to germicidal effect, energy losses are unavoidable:
Electrode contact resistance: ~5–10%
Non-radiative recombination losses: ~30–40% (where recombination releases heat instead of light)
Light extraction losses: ~50–60%
This means current commercial UV-C LEDs typically have wall-plug efficiencies of only 10%–15%, much lower than visible light LEDs, which exceed 50%.
Key breakthroughs to improve efficiency lie in optimizing MQW design — adjusting well width and aluminum composition to reduce non-radiative processes like Auger recombination — and adopting patterned sapphire substrates (PSS) to reduce defect density. As of 2023, industry leaders have achieved lab-scale efficiencies of up to 20%, indicating that more electrical energy can be converted into germicidal light in the future.
Conclusion: Microscopic Journey with Macroscopic Impact
From current injection to DNA disruption, the UV-C LED mechanism is a perfect fusion of quantum physics and molecular biology. Each germicidal photon undergoes a complex journey involving carrier transport, quantum recombination, and light extraction. Understanding this process not only helps optimize technical parameters — such as adjusting drive currents (typically 20–350 mA) to balance output and chip longevity — but also clarifies the path forward.
As AlGaN crystal defect densities drop from 10⁸/cm² to 10⁶/cm² and light extraction efficiency surpasses 40%, UV-C LEDs are poised to unleash massive potential across medical sterilization, water purification, and food preservation. Through precise control at the microscopic level, we can better safeguard public health and safety on a global scale.
