Indium gallium nitride

Indium gallium nitride, written InGaN, is gallium nitride in which some of the gallium atoms are swapped for indium. It isn't a fixed compound but an alloy: the share of indium can be anything from zero up, and that share sets the color of light it gives off.

It's grown in the same reactor as the gallium nitride beneath it, continuing its crystal. Alongside the gallium and ammonia gases, an indium compound, trimethylindium, is added, so indium atoms slip into the crystal in place of some gallium. Indium atoms are larger and loosely held, so these layers are grown cooler, around 700 to 800 °C, or the indium won't stay in. They're extremely thin, about 2 to 3 nanometers, roughly ten atomic layers, and are stacked several times with gallium nitride between them. These are the quantum wells.

In a blue LED chip, electrons and holes are trapped in these wells and combine, giving off light. More indium narrows the band gap and shifts the color toward green. Blue LEDs replace around 15% of the gallium. Green ones need more, which strains the crystal, one reason green LEDs are less efficient than blue.