Scientists at Japan’s National Institute of Advanced Industrial Science and Technology claim to have developed a new highly efficient ultraviolet light emitting semiconductor. The key is have they made it long lasting and stable ? If they have then the benefits of zinc over gallium LEDs would be realized. The benefits would be lower costs and higher efficiency.
The new technology relies on a zinc oxide compound combined with minute quantities of magnesium oxide. This is claimed to offer several advantages over existing materials used for similar devices.
A breakthrough in the fundamental technology behind devices like LEDs and lasers could lead to advances in a wide range of products, including optical disks, light sources and flat-panel displays.
Name Abbreviation Wavelength range in nanometres
Near NUV 400 nm – 200 nm
UVA, long wave, or black light 400 nm – 320 nm
UVB or medium wave 320 nm – 280 nm
UVC, short wave, or germicidal Below 280 nm
Far or vacuum FUV, VUV 200 nm – 10 nm
Extreme or deep EUV, XUV 31 nm – 1 nm
The main hurdle to making zinc oxide devices has been getting stable, reliable p-type material—material with an excess of holes, or electron deficiencies. Making an LED or laser diode requires a junction between p-type and n-type material. But when some of the zinc oxide is engineered to act as p-type material, it tends to revert to its natural n-type state after a few months, which would cause a device to fail. In contrast, blue LEDs made from gallium nitride have expected lifetimes of 100 000 hours, or over 10 years.
Henry White, a professor of physics at the University of Missouri and a cofounder of MOXtronics, says that the new LEDs have the potential to reach wavelengths as low as 200 nm, which is deep in the UV region. He expects the devices’ efficiencies and output power to compete with those of today’s white LEDs, made of gallium nitride, in two to three years. The company is also in the process of making UV laser diodes, he says
Zinc oxide has a very good shot at meeting the difficult demands of the solid-state white light market, which analysts predict will dominate over incandescent and fluorescent bulbs by 2025, saving US $150 billion a year in power in the United States alone.
Both Zhang and Look single out the imperative need for a convenient way of making p-type material that lasts for more than two years.