The Science and History of Blue LED Development

Shuji Nakamura revolutionized lighting by inventing blue LEDs, overcoming significant material challenges through innovative techniques.

### The Fascinating Journey of Blue LEDs: From Theory to Commercial Success
* 💡 LEDs are made of two separate semiconductor layers - **n-type and p-type** - with a **depletion region** in between.
* 💡 When a voltage is applied, electrons flow from the n-type to the p-type, creating **light as they recombine with electron holes**.
* 💡 Blue LEDs were historically challenging to create due to the **high energy required for the blue photon emission**.
* 💡 Shuji Nakamura, working for Nichia Corporation, overcame these challenges by **perfecting the growth of gallium nitride crystals**.
* 💡 Nakamura's breakthrough came in 1992, when he successfully created the **first commercial blue LED**.
* 💡 To increase brightness and shift the color to a more desirable blue, Nakamura introduced **aluminum gallium nitride and indium gallium nitride layers**.
* 💡 By 1994, Nichia was manufacturing a **million blue LEDs per month**, revolutionizing the display and lighting industries.
* 💡 This achievement was a **significant milestone**, as it enabled the development of white LEDs and **transformed various technologies**.

⚡The LED that was thought impossible - Tingyi L

UWCS - University of Warwick Computing Society

Blue LEDs are made from two layers of semiconductor material: n-type with extra electrons and p-type with electron holes.

The junction between these layers creates a depletion region, allowing electrons to flow in one direction when a voltage is applied.

The movement of electrons from the conduction band to the valence band generates light, with the energy from the electron transition producing photons.

Blue LEDs were not developed until 1992, long after red and green LEDs, due to the high photon energy required for blue light.

Gallium nitride and zinc selenide were the two materials researched for blue light production, with gallium nitride ultimately being favored.

The growth of gallium nitride crystals was problematic, with a high number of imperfections, leading to lower efficiency and inconsistent blue light emission.

Nakamura used silicon doping to add extra electrons for n-type GaN, and innovated MOCVD by flowing two materials as gases, resulting in perfect crystal growth.

The GaN buffer layer contributed to the crystals' perfection, while Nakamura's unique method of cooking the material in an oven at 600° for 24 hours effectively broke hydrogen bonds and released excess hydrogen.

This approach was pivotal in overcoming inefficiencies and played a significant role in the popularity of blue LEDs.

Louis showcased a blue-violet light from a unique GaN layer structure, but its alpha power of 42 microwatts was too low for commercial viability.

The design faced issues with electron flow at the MP Junction, hindering the release of blue light.

To increase brightness and shift the color to a more vivid blue, Nakamura used Aluminium Gallium Nitride (AlGaN) as a hill material, effectively blocking electron flow and creating a larger band gap.

The structure of the blue LED is complex, with aluminum gallium nitride and indium gallium nitride layers, resulting in a brilliant blue glow.

Unveiled in 1992, the blue LED's production quickly ramped up, quadrupling the manufacturer's income and making white LEDs possible.

The technology has since become a staple for various applications, including lighting and display screens.