White LEDs became possible only after the most difficult primary colour—blue—was mastered. The key material is gallium nitride (GaN), a direct-band-gap semiconductor whose high-quality crystal growth and p-type doping were long considered mission impossible. Akasaki and Amano reduced crystal defects by inserting an AlN buffer layer on sapphire, whereas Nakamura invented a low-temperature GaN buffer followed by high-temperature growth. By doping GaN with magnesium and activating it through electron-beam or thermal annealing, they produced a p-type layer, and the resulting GaN p-n junction emitted intense blue light. The blue LED enabled phosphor-converted white LED lamps that deliver the same brightness as incandescent bulbs using less than one sixth of the power. Lighting accounts for roughly 15–20 percent of global electricity consumption, so LED adoption greatly cuts CO2 emissions and supports a sustainable society. Their work also opened the way for violet and blue laser diodes used in Blu-ray discs, high-resolution printers and optical communication. It is a textbook example of crystal growth, materials science and device physics coming together to solve societal challenges.

Gallium nitride (GaN) is a III-V compound semiconductor with a 3.4 eV wide band gap and a direct transition, making it highly efficient for blue-violet emission. However, no cheap lattice-matched substrate exists, so GaN grown on sapphire originally exhibited dislocation densities of about 10^9 cm^-2, severely lowering internal quantum efficiency. The Akasaki–Amano group used a two-step AlN buffer in MOVPE to suppress dislocations to roughly 10^8 cm^-2. Nakamura, meanwhile, developed a two-temperature method with a low-temperature GaN nucleation layer followed by high-temperature growth, and achieved low-resistivity n-GaN through Si doping. Mg-doped GaN is self-compensated by Mg–H complexes, but electron-beam irradiation or high-temperature annealing removes hydrogen and pushes hole concentrations into the 10^17 cm^-3 range. Employing InGaN/GaN multiple quantum wells as the active region harnesses exciton localization and yields internal quantum efficiencies of 60–80 percent. Combining a blue LED with YAG-based phosphors produces white LEDs with wall-plug efficiencies exceeding 300 lm W^-1 and lifetimes beyond 100,000 hours. Consequently, energy consumption and replacement costs in illumination have been dramatically reduced. GaN-based laser diodes at around 409 nm exploit the short wavelength for high-density optical storage, head-up displays and photonic sterilization. Materials research has expanded to AlGaN deep-UV LEDs and non- or semipolar GaN substrates, broadening the solid-state-lighting platform. The success of the blue LED revitalized interest in III-N material physics and fostered new industrial domains such as power electronics and RF devices through monolithic integration. Thus, the 2014 Nobel-winning work continues to exert groundbreaking impact on both materials science and optoelectronics.

Efficiency of GaN blue LEDs hinges on four pillars: crystal quality, p-type activation, quantum-well design and light-extraction engineering. Akasaki et al. suppressed threading dislocations by MOVPE growth of GaN on sapphire with an AlN buffer, optimizing crack formation derived from lattice and thermal mismatch. Nakamura’s low-temperature nucleation followed by high-temperature overgrowth induces a 3D-to-2D transition that anneals dislocations in situ through self-organization. Dissociation of Mg–H complexes leaves a shallow acceptor level of about 160 meV, providing sufficient holes at room temperature. Composition-graded InGaN/GaN MQWs promote elastic relaxation and dot-like indium clusters; exciton localization mitigates non-radiative recombination, yielding high IQE. Internal electric fields on polar c-planes cause quantum-confined Stark shifts, motivating research into non-polar or semipolar planes and nanowire devices. Light extraction is enhanced by sapphire backside roughening, patterned sapphire substrates and sidewall reflectors. Package-level wall-plug efficiency now exceeds 65 percent, enabling TRIAC dimming and human-centric lighting. In the deep-UV regime, high defect formation energy in AlGaN is addressed through flip-chip designs and nanocathode excitation. GaN-on-Si wafer technology allows monolithic integration of lighting chips with power HEMTs, reducing fabrication cost toward silicon lines. Device modelling using Monte-Carlo methods with non-equilibrium transport, polaron effects and phonon scattering quantifies exciton-density nonlinearity and Auger recombination as limits to high-power operation. The Akasaki–Amano–Nakamura breakthroughs have redefined III-nitride semiconductor physics and continue to drive developments such as quantum-dot lasers, µLED displays and optical LiFi communication.