news digest ♦ LEDs
LED manufacturers do not need to grow an n-type GaN buffer layer and this reduces the time required for growth by about half compared with conventional methods.
Hitachi Cable says its GaN-templates are also suitable for high-output LEDs which require large currents because they allow both low resistance and high crystal formation.
The firm has developed single-crystal free-standing GaN substrates used for blue-violet lasers and developed unique HVPE-growth technology and machines for mass-production of GaN substrates.
Based on this technology, Hitachi Cable developed new high-efficiency production technology and machines for mass-production of high-quality GaN-templates.
The main characteristics of the GaN-template are as follows.
High crystal quality and high surface quality based on growth technology established in the development of free-standing GaN substrates
Low resistance n-type GaN buffer which is suitable for high-output wafers and bonding-type LEDs
Templates on flat-surface sapphire substrates and various types of PSS are available
Wafers with 2 to 6 inches in diameters are available, with an 8-inch version now planned for developmen). Photos of the substrates currently avalable are shown below.
ZnO technology could revolutionise LEDs and UV lasers
To make lasers and LEDs both n-type and p-type materials are used. Researchers have claimed that shedding excess energy at the p-n junction is what produces light in both these types of devices
Scientists from North Carolina State University say they have solved a long-standing materials science problem.
They claim that it is possible to create new semiconductor devices using zinc oxide (ZnO).
The development could pave the way for efficient ultraviolet (UV) lasers and LED devices for use in sensors and drinking water treatment, as well as new ferromagnetic devices.
“The challenge of using ZnO to make these devices has stumped researchers for a long time, and we’ve developed a solution that uses some very common elements: nitrogen, hydrogen and oxygen,” says Lew Reynolds, co-author of a paper describing the research and a teaching associate professor of materials science and engineering at NC State.
“We’ve shown that it can be done, and how it can be done and that opens the door to a suite of new UV laser and LED technologies,” continues Judith Reynolds, a research scientist at NC State and lead author of the paper.
To make laser and LED technologies, you need both “n-type” materials and “p-type” materials. N-type materials contain an abundance of free electrons. P-type materials have “holes” that attract those free electrons.
But the holes in the p-type materials have a lower energy state, which means that electrons release their excess energy in the form of light as they travel from the n-type material to the p-type material.
With this new GaN-template added to the lineup of GaN substrates and GaN epiwafers that it has been selling, Hitachi Cable aims to strengthen and expand its GaN product group and offer compound semiconductor products which respond to the various needs of clients.
The shedding of excess energy at the p-n junction is what produces light in lasers and LED devices.
Scientists have been interested in using ZnO to create these devices because ZnO produces UV light, and because it can be used to make devices with relatively fewer unwanted defects than other UV emitters. This means the resulting lasers or LEDs would be more energy efficient.
However, in the past, researchers have found it hard to consistently produce stable p-type materials out of ZnO.
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www.compoundsemiconductor.net June 2013
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