AlGaN-based ultraviolet (UV) light-emitting diodes (LEDs) represent a critical advancement in semiconductor optoelectronics, particularly for applications requiring short-wavelength emission. These devices leverage the tunable bandgap of aluminum gallium nitride (AlGaN) alloys, which can be adjusted by varying the aluminum composition. The bandgap of AlGaN ranges from approximately 3.4 eV (GaN) to 6.2 eV (AlN), enabling emission wavelengths from 365 nm (near-UV) to 210 nm (deep-UV). This flexibility makes AlGaN UV LEDs suitable for sterilization, water purification, and medical diagnostics, where precise UV emission is essential.

Bandgap engineering in AlGaN UV LEDs is achieved by controlling the aluminum content during epitaxial growth. Higher aluminum fractions increase the bandgap, shifting emission toward shorter wavelengths. However, this introduces challenges in material quality and device performance. Increased aluminum incorporation often leads to higher defect densities, particularly threading dislocations, which degrade internal quantum efficiency (IQE). The lattice mismatch between AlGaN and underlying substrates, such as sapphire or silicon carbide, exacerbates this issue. Strain relaxation mechanisms must be carefully managed to minimize defects and maintain crystal integrity.

Doping AlGaN for efficient carrier injection is another significant challenge. p-type doping becomes increasingly difficult at higher aluminum concentrations due to the deep activation energy of magnesium (Mg) acceptors in Al-rich AlGaN. The ionization energy of Mg increases with aluminum content, reducing hole concentration and leading to higher series resistance in p-type layers. This results in inefficient hole injection into the active region, lowering overall device efficiency. n-type doping with silicon (Si) is more straightforward but still faces limitations at high aluminum fractions due to compensating defects and reduced dopant solubility.

The active region of AlGaN UV LEDs typically consists of multiple quantum wells (MQWs) designed to confine electrons and holes for radiative recombination. The quantum-confined Stark effect (QCSE), caused by polarization fields in AlGaN heterostructures, can reduce recombination efficiency by spatially separating electrons and holes. Engineering the well and barrier thicknesses, as well as using polarization-matched structures, can mitigate QCSE and improve radiative efficiency. Additionally, the use of AlGaN with lower aluminum content in the quantum wells relative to the barriers enhances carrier confinement while maintaining the target emission wavelength.

External quantum efficiency (EQE) is a key metric for evaluating AlGaN UV LED performance. EQE is the product of internal quantum efficiency (IQE), injection efficiency, and light extraction efficiency (LEE). State-of-the-art devices in the UVC range (200–280 nm) have demonstrated EQEs between 5% and 20%, depending on wavelength and material quality. Near-UV LEDs (300–365 nm) achieve higher EQEs, often exceeding 30%, due to lower aluminum content and reduced defect densities. Improving LEE is critical, as AlGaN’s high refractive index causes significant light trapping within the device. Strategies such as patterned substrates, photonic crystals, and flip-chip designs enhance light extraction by redirecting photons toward the escape cone.

Thermal management is a major concern for AlGaN UV LEDs, as high operating temperatures degrade performance and reliability. The thermal conductivity of AlGaN decreases with higher aluminum content, exacerbating heat buildup. Elevated temperatures increase non-radiative recombination rates, reducing IQE and output power. Efficient heat dissipation is achieved through advanced packaging techniques, including thermally conductive substrates like silicon carbide or diamond, and the integration of heat sinks. Junction temperature must be carefully monitored, as even modest increases can lead to significant efficiency droop and accelerated device aging.

Applications of AlGaN UV LEDs in sterilization are particularly noteworthy. UVC radiation (200–280 nm) is highly effective at inactivating bacteria, viruses, and other pathogens by damaging their DNA and RNA. AlGaN LEDs emitting at 265 nm, near the DNA absorption peak, offer a compact, energy-efficient alternative to traditional mercury lamps. These LEDs are used in portable sterilization devices, water disinfection systems, and air purification units. Unlike mercury lamps, they do not contain toxic materials, can be instantaneously switched, and enable targeted wavelength delivery for optimal germicidal efficacy.

The efficiency of sterilization systems depends on UV dose, which is a function of irradiance and exposure time. AlGaN LEDs must deliver sufficient optical power to achieve the required dose within practical timeframes. For example, a typical water disinfection system may require a UV dose of 40 mJ/cm², necessitating LEDs with high wall-plug efficiency (WPE) to minimize energy consumption. WPE, defined as the ratio of optical output power to electrical input power, is influenced by EQE and operating voltage. Advances in device design and material quality continue to improve WPE, making AlGaN UV LEDs increasingly viable for large-scale applications.

Despite progress, challenges remain in scaling AlGaN UV LED technology for widespread adoption. Cost-effective manufacturing methods are needed to reduce epitaxial growth expenses, particularly for high-aluminum-content layers. Reliability testing under continuous operation is essential to validate lifetime performance, especially in harsh environments. Further improvements in EQE and thermal management will enhance competitiveness against conventional UV sources. Research into novel device architectures, such as tunnel junctions for improved hole injection, and alternative substrates like bulk AlN, may address current limitations.

In summary, AlGaN-based UV LEDs are a transformative technology with significant potential in sterilization and beyond. Bandgap engineering enables precise wavelength control, while ongoing efforts to overcome doping challenges and thermal limitations are critical for advancing performance. Efficiency metrics such as EQE and WPE provide benchmarks for progress, and applications in disinfection highlight their societal impact. Continued innovation in materials science and device engineering will drive the next generation of UV LED solutions.