III-nitride semiconductors, particularly indium gallium nitride (InGaN) and aluminum gallium nitride (AlGaN), have become the cornerstone of high-efficiency light-emitting diodes (LEDs) for modern lighting applications. Their unique material properties enable the emission of light across the visible spectrum, from ultraviolet to green and red wavelengths, making them indispensable for solid-state lighting, displays, and optoelectronic devices. The success of these materials lies in their direct bandgap, high electron mobility, and robustness under high-power operation. However, achieving high efficiency in III-nitride LEDs involves overcoming significant challenges related to lattice mismatch, polarization effects, and efficiency droop. Recent advancements in metalorganic chemical vapor deposition (MOCVD) and the development of nanostructured active regions have pushed the boundaries of LED performance.

One of the primary advantages of InGaN-based LEDs is their ability to tune the emission wavelength by adjusting the indium composition. For blue and green LEDs, InGaN quantum wells (QWs) serve as the active region, where the indium content determines the bandgap energy. Higher indium incorporation shifts the emission toward longer wavelengths, but this comes with trade-offs. The lattice mismatch between InGaN and GaN introduces strain, leading to defects such as dislocations that act as non-radiative recombination centers. These defects reduce internal quantum efficiency (IQE) by providing pathways for carriers to recombine without emitting photons. To mitigate this, strain-compensating layers and advanced buffer layer designs have been developed to minimize dislocation densities. For example, growing InGaN QWs on relaxed templates or using superlattices can reduce strain-induced defects, improving luminescence efficiency.

Polarization effects in III-nitride materials further complicate LED design. Nitride semiconductors exhibit strong spontaneous and piezoelectric polarization due to their wurtzite crystal structure. In conventional c-plane LEDs, polarization-induced electric fields separate electrons and holes in the quantum wells, reducing their overlap and leading to a phenomenon known as the quantum-confined Stark effect (QCSE). This effect lowers radiative recombination rates and shifts emission wavelengths. To address this, researchers have explored alternative crystal orientations, such as non-polar (m-plane or a-plane) and semi-polar orientations, where polarization fields are reduced or eliminated. Non-polar GaN substrates have shown promise in enhancing electron-hole overlap, leading to higher efficiency LEDs, particularly in the green spectral range where efficiency traditionally drops.

Efficiency droop is another critical challenge in high-power III-nitride LEDs. Droop refers to the decline in external quantum efficiency (EQE) as the injection current density increases. Several mechanisms contribute to droop, including Auger recombination, carrier leakage, and insufficient hole injection. Auger recombination, a non-radiative process where an electron-hole pair recombines and transfers energy to a third carrier, becomes significant at high carrier densities. Mitigating droop requires optimizing the active region design to reduce Auger coefficients and improve carrier confinement. Techniques such as using thicker quantum wells, incorporating electron-blocking layers, and engineering the band structure to enhance hole injection have been explored. Additionally, nanostructured active regions, such as quantum dots or nanowires, offer improved carrier confinement and reduced Auger rates due to their discrete density of states.

Advancements in MOCVD growth techniques have played a pivotal role in improving the performance of III-nitride LEDs. Precise control over gas-phase reactions, temperature gradients, and precursor flows enables the growth of high-quality InGaN and AlGaN layers with minimal defects. In situ monitoring tools, such as reflectance anisotropy spectroscopy and laser interferometry, allow real-time adjustments to growth parameters, ensuring uniformity and reproducibility. The development of pulsed MOCVD, where precursors are introduced in alternating pulses, has improved indium incorporation in InGaN QWs by reducing parasitic gas-phase reactions. This technique enables higher indium content without phase separation, extending the emission range of InGaN LEDs into the green and yellow regions.

Nanostructured active regions represent a breakthrough in LED technology. By replacing conventional quantum wells with quantum dots or nanowires, researchers have achieved superior carrier confinement and reduced efficiency droop. Quantum dots, with their atom-like discrete energy levels, suppress Auger recombination and enhance radiative rates. Nanowire LEDs, grown vertically on substrates, offer additional advantages such as reduced dislocation densities due to strain relaxation at the nanowire sidewalls. These structures also enable efficient light extraction by minimizing total internal reflection. Core-shell nanowire designs, where the active region surrounds the nanowire core, further enhance light emission by increasing the active volume and improving current spreading.

The integration of AlGaN in the electron-blocking layer (EBL) and p-type regions has also contributed to LED performance improvements. AlGaN EBLs prevent electron leakage from the active region, ensuring that more carriers participate in radiative recombination. However, the high aluminum content in AlGaN can impede hole injection due to the large valence band offset. Graded AlGaN layers and polarization-induced doping strategies have been employed to enhance hole transport while maintaining effective electron confinement. Additionally, magnesium doping in p-type GaN remains a challenge due to its high activation energy. Advanced doping techniques, including delta doping and surface activation treatments, have improved hole concentrations and reduced resistive losses in p-type layers.

In summary, III-nitride semiconductors have revolutionized high-efficiency LED technology, enabling energy-efficient lighting solutions with superior performance. Overcoming challenges such as lattice mismatch, polarization effects, and efficiency droop has required innovative approaches in epitaxial growth and device design. The adoption of MOCVD advancements and nanostructured active regions has pushed the limits of LED efficiency, particularly in the green spectral range where traditional devices struggle. Continued research into material engineering, carrier dynamics, and light extraction mechanisms will further enhance the capabilities of III-nitride LEDs, solidifying their role in next-generation lighting and display technologies.