Panasonic grows power LEDs on GaN substrates
Panasonic is to introduce white LEDs based on blue chips grown on GaN substrates, eliminating many of the problems associated with LED growth on sapphire.
|Panasonic power LEDs|
Most GaN-based LEDs are manufactured using wafers of either sapphire or silicon carbide (SiC) as the starting substrate. GaN-based material is deposited onto these wafers to form the LED layer structure.
The company says that the use of GaN substrates, which have very high thermal and electrical conductivity, substantially improves LED performance in the high current area.
At an emission wavelength of 460 nm, Panasonic's new blue GaN-based chips on GaN substrates have a total radiative flux of 355 mW at a forward current of 350 mA, with an external quantum efficiency of 38%.
Panasonic intends to introduce three product types to meet the diverse needs of power and size. These are a 3 W lighting LED (LNJ090W3GRA), claimed to be the industry's smallest; a reflector type LED (LNJ0H0V8KRA) best suited for flash applications; and a point light source (LNJ0Y0F9KRA) for use in ultra-compact lights.
Panasonic has developed a proprietary white LED manufacturing technology based on flip-chip bonding, which eliminates wire bonds for high reliability. The blue LED chip is covered with a uniform fluorescent layer resulting in a very compact white high-power LED with little color variation.
Panasonic says that it will start sample shipments in early March, with a sample price of 500 yen/unit (approx $4.30).
New growth substrate
The ideal substrate for the growth of a GaN-based LED layer structure is GaN itself, since there will no mismatch in lattice constant or thermal expansion coefficient, and this should reduce defects in the LED layers.
The substrate and the light-emitting layers will also have the same refractive index, which significantly reduces optical losses at the interface. Panasonic says that its new structure has a "light delivery efficiency over 1.5 times that of the company's conventional sapphire-based LED element."
Another problem with sapphire-grown LEDs is poor heat dissipation properties, which tend to result in saturation of output at high currents. Panasonic says that the GaN substrate provides good high-current characteristics and enables the industry's highest-level output for a blue power LED.
One of the biggest drawbacks with GaN substrates is lack of availability of high-quality material in reasonable wafer sizes. Most GaN-based LED production employs 2-inch, and sometimes 3-inch, wafer diameters. Panasonic did not specify the size or type of GaN substrates used.