Light-emitting diode
A light-emitting diode is a tiny light that turns on when an electric charge is applied to the right end. It is made of semiconductor.
LEDs used for a backlight are called high-brightness LEDs, often shortened as HBLEDs.
LEDs can be used as the backlights for a liquid-crystal display.
Operating principle[edit]
Light is produced by the recombination of electrons and electron holes in a semiconductor portion of a light-emitting diode. The wavelength of the light depends on the band gap of the semiconductors used. Since these materials have a high index of refraction, design features of the gadgets such as special optical coatings and die shape are required to efficiently emit light.[1]
Construction[edit]
There is a junction of a p type semiconductor and an n type semiconductor.
Materials/substrates[edit]
There is typically an n-type material as the substrate, with p-type deposited on top.
High brightness LEDs are typically made using a sapphire substrate.[2]
The idea is to take a high brightness blue LED and layer phosphor over it. The phosphor turns the blue into white, and does so with a high color renering index (CRI).
Manufacturing[edit]
See also: XVRWiki:How to make an LED
LEDs, including high-brightness LEDs can be manufactured on wafers.
It is recommended to make LEDs using microfabrication processes. They must be made using implantation or deposition processes. MOCVD is recommended.
LED production can be done using a sapphire wafer and doing epitaxial growth on top of it.[3]
It uses epiwafers, meaning epitaxial wafers.
Gallium nitride is recommended. A GaN-on-Si process can be used.
Typically, the wafers are sapphire. The sapphire crystal can be in a number of orientations. It may be typical to have a sapphire substrate aligned to one of the crystal planes: the R plane, C plane, A plane, and M plane. C-plane sapphire substrates can be used to grow gallium nitride (GaN) for making high brightness blue LEDs.[4]
Wafer size[edit]
Machines that support up to 4 inch wafers are probably sufficient for small amounts of manufacturing.
There are various sizes of wafers that can be used, such as 2-inch, 3-inch, and 4-inch.
LEDs may be made on 200mm wafers.[5]
4-inch-wafer LED production was new in the year +2007.[6]
Singulation[edit]
LEDs can be singulated using laser scribing. One type of laser singulation is thermal laser singulation, also called laser ablation dicing or thermal ablation. It can be used to dice brittle wafers such as sapphire, LEDs, GaAs, and InP. A laser beam may have limited cut depth, so multiple beam passes of the laser may be needed depending on the wafer thickness and geometry.[7]
Sorting, also known as binning[edit]
A sorting process may happen after the manufacturing, because some of the LEDs may have slightly different color or brightness once they are made. This is called binning.[8]
Considerations[edit]
The dimensional precision required to make an LED is lower than that of making a complex logic device.
References[edit]
- ↑ Pearsall, Thomas (2010). Photonics Essentials, 2nd edition. McGraw-Hill. ISBN 978-0-07-162935-5. https://www.mheducation.com/highered/product/photonics-essentials-second-edition-pearsall/9780071629355.html.
- ↑ "HBLED Applications". https://plasma.oxinst.com/campaigns/markets/hbled-applications.
- ↑ https://www.youtube.com/watch?v=Hb4M29eQ124
- ↑ "Sapphire Substrate Wafers". https://www.pmoptics.com/sapphires_wafers.html.
- ↑ "200mm Silicon Wafers". 2018-10-01. https://www.universitywafer.com/200mm-silicon-wafers.html.
- ↑ "Cree qualifies first 4-inch LED process". https://compoundsemiconductor.net/article/84378/Cree_qualifies_first_4-inch_LED_process.
- ↑ "Error: no
|title=specified when using {{Cite web}}". https://www.photonicsmanufacturing.org/sites/default/files/documents/assembly.pdf. - ↑ Leschhorn, Gunther; Young, Richard. "LED measurements in the production line". https://www.instrumentsystems.com/fileadmin/Downloads/Articles/laserphotonics_2018-01_LED-measurements-in-the-production-line_GLE_free.pdf.