20 Feb 2003
A team of scientists in China reports that it has obtained enhanced blue light emission from porous silicon.
Chinese scientists claim to have found a way to obtain enhanced blue light emission from porous silicon. The result may aid the development of LEDs and displays that can be easily integrated with electronic chips. (Applied Physics Letters 82 1018)
Although conventional silicon is the material of choice for making electronic circuits, it does not emit light. As a result, engineers wishing to make optoelectronic devices are forced to use other semiconductors such as gallium arsenide or gallium nitride which are awkward to integrate with silicon circuitry.
Scientists have known for sometime that etching silicon, to create many tiny pores, enables it to emit red, green and blue light. To date, the problem has been improving the efficiency and stability of the light emission from this so-called porous silicon.
Qianwang Chen and his colleagues from the University of Science and Technology of China in Hefei, now claim to have made samples of porous silicon that emit blue light that is "stable, strong and visible to the naked eye even after exposure in an ambient atmosphere for a year."
Their samples were made by etching single-crystal silicon wafers in aqueous hydrogen fluoride to give the surface a series of microscopic pillars measuring 8 nm in diameter and 270 nm tall. Pulsed laser deposition was then used to fill the gaps between the pillars with a ferroelectric material (PZT).
When pumped with ultraviolet light at 256 nm the structures emitted blue light at 435 nm that was "visible to the naked eye".
"We are now planning to measure and increase and the quantum efficiency and lifetime of the blue emission," commented Chen. "A quantum efficiency of more than 1% is enough for display applications"
Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.