From bicycle lamps to aircraft landing lights, flashlights to Christmas displays, light-emitting diodes or “LEDs” are everywhere. And that’s no surprise.
Not only are LEDs much more energy efficient than traditional lightbulbs, but they produce almost no heat and can have a lifespan of 25,000 hours compared to the 1,000 hours of incandescent lights.
So, how are LEDs made? And how are LED lights manufactured in quantities?
How do LED Lights Work?
To understand how to manufacture LED lights, it’s important to know how they work.
Electricity is the movement of the part of atoms known as electrons. When electrons get excited, they move. And when they move, they generate light. This is called electroluminescence and it’s the basis of how an LED works.
So, how does one excite an electron? Give it somewhere to go, and a very clear route to get there.
How are LEDs Made? Exciting Electrons
There are two aspects to the number of electrons in an atom’s outer shell: The number it has and the number it wants. These don’t always match. If it has too many, the “spare” electrons are free to move. If it has too few, it will try to fill the gaps. As for the electrons, they are negatively charged, the gaps are positive and the two attract. In other words, they’ll always head for the gaps.
For example, silicon atoms want eight electrons, but only have four. So, they share with each other. If one silicon atom has four others arranged around it, each one will share one of its electrons with it and it will share one right back. Each electron does double duty and every atom gets the eight electrons they need. It’s a delicate balance based on each atom being able to share and borrow the exact right amount of electrons. This is not exciting. The electrons remain still. At this point, the silicon is an insulator.
So how do you get those electrons excited? And how does that work as part of answering “How are LED lights manufactured?”
How are LED Light Bulbs Made? Doping Semiconductors
To get electrons moving, there needs to be either a lack or abundance of electrons in the atoms present. So some of the silicon atoms are swapped out. In terms of “how are LED lights manufactured”, this is done in two opposite ways. On one side, some atoms will be replaced by others that have too many electrons (N-Type), like Phosphorus. So on that side there are free electrons looking for somewhere to go. On the other side some will be replaced by atoms with too few electrons (P-Type), like aluminium. They want electrons. This is called doping.
How to manufacture LED lights is to join the N-type and P-type sections together to form a diode. Diodes are the one-way system of electrical circuits. They only allow electrons to move in one direction. As soon as a current is applied, it’s like a game of electrical musical chairs. The excess phosphorus electrons will rush over to the aluminium side to fill those spaces. And that movement makes light.
How are LED lights made in different colours?
Note that in the above explanation, silicon is used because it is a semiconductor. While some atoms are stuck being either a conductor or an insulator, it can switch between the two with a little encouragement.
In terms of “how are LEDs made”, the semiconductors used are gallium, arsenic and phosphor. As for “how are LED lights made in different colours”, different combinations of semiconductors will make different coloured LEDs. For example, mixing gallium arsenide phosphide, aluminium gallium indium phosphide and gallium phosphide can make red, orange or yellow light, while gallium phosphide, gallium nitride and indium gallium nitride makes green.
But how are LED lights manufactured in practice?
How are LEDs made? Starting with the Semiconductor Wafer
To answer ‘how are LED lights manufactured’, the N-type and P-type sides are created as wafer-thin layers of semiconductor materials which are chemically doped.
The process guiding how LED light bulbs are made begins with growing the semiconductor wafer. This involves making a solution of semiconductors, usually some combination of gallium, arsenic and phosphor.
The materials are placed in a crucible chamber where they are exposed to high levels of both heat and pressure, causing them to liquify. This molten liquid is mixed to ensure a uniform solution. Still being mixed, a pencil sized silicon rod is dipped into this solution and slowly retracted at a rate of around 1.5 millimetres per minute. The liquid cools onto the rod, crystallising into a long cylindrical shape. This is then carefully sliced into 10mm wide wafers and polished until smooth. This is all part of making the uniform atom structure the semiconductor needs to equally share electrons.
How are LED Lights Manufactured? Chemical Doping
After the wafer is cleaned, it’s time for doping. This is done through a process called Liquid Phase Epitaxy (LPE) in which the wafer is immersed in a doped chemical alloy (often gallium arsenide phosphide) as more layers of semiconductor (epitaxy) are applied to it.
How to Manufacture LED Lights: Adding Metal
Metal contacts are added to the wafer according to a computer-generated design, which is transferred to the wafer via a process similar to photolithography. A light-sensitive compound is applied to the wafer, which is then placed under a photoresist. When the wafer is then exposed to light, the resist acts like a stencil, only allowing light through in certain places to recreate the design. The metal is evaporated and sticks only to the light-exposed parts of the wafer. The metal and wafer are bonded in a furnace for several hours.
Mounting and packaging
The wafer is cut into very small chips or “dies” which are placed on a “package”. This is essentially the apparatus to match its application. One common mode of packaging is coating the back of the die with metal and placing it on a lead surface. This is attached to two metal prongs and connected by a gold wire. To create the dome around this, the die is then placed in a mould and covered in epoxy or liquid plastic. Removed from the mould, it is then cured. And it’s ready.
So that’s the answer to the question “how are LEDs made?” Hopefully it’s been illuminating.