invention of the blue LEDinvention

The path to the blue LED took several decades. The main difficulty: obtaining a semiconductor with a bandgap of about 3.4 eV (corresponding to blue light) and doping it p-type (adding impurities to create hole conductivity). Shuji Nakamura at the Japanese company Nichia first created high-quality GaN films on a sapphire substrate and developed a thermal annealing method to activate magnesium acceptors, obtaining p-GaN. In 1993, he demonstrated a bright blue LED, and later — the first blue laser.

For a long time, scientists could make red and green LEDs, but blue remained elusive — a material with a wide bandgap was needed that could efficiently emit blue light and operate long-term. In the 1990s, Shuji Nakamura, using gallium nitride (GaN), managed to grow a crystal of the required quality and build a bright blue LED based on it. This completed the RGB triad (red, green, blue), allowing colors to be mixed to produce white light.

The invention of the blue LED is based on the physics of wide-bandgap group III-nitride semiconductors (GaN, InGaN). Under forward bias of a p-n junction, electrons recombine with holes, emitting photons with energy close to the bandgap E_g. For blue emission with λ ~ 450 nm, E_g ≈ 2.76 eV is required, but due to quantum size effects in InGaN quantum wells, layers with varying indium concentration are actually used, allowing wavelength tuning. Key challenges: obtaining monocrystalline GaN without defects, p-type doping (long unsuccessful), and creating high-quality electrical contacts.