Cambridge University (Dr Colin Humphrey) has come up with a reliable way to deposit gallium nitride on much cheaper silicon wafers, which they estimate could cut production costs to a tenth of what they are at the moment.
Because the atomic lattice structure of gallium nitride is better matched to sapphire than it is to silicon, making LEDS on silicon without distortions has proved extremely tricky. The technique used at Cambridge involves depositing additional layers of gallium nitride-based materials, one as a "compression layer" to provide greater resilience and another as an ultra-thin mask that increases the accuracy of fabrication.
A gallium nitride LED on sapphire has internal quantum efficiency of around 70%. In the past year Dr Humphrey's team has improved its silicon based ones from 25% to 45%. Even at this early stage he thinks gallium nitride-on -silicon LEDS may make commercial sense. Besides the lower cost of silicon, the process could use larger and more economical six inch (15cm) wafers and be carried out with more common fabrication equipment.
Developments like the use of cheap silicon make the case for switching to LED lighting even more compelling. About 20% of the world's electricity is used for lighting. America's Department of Energy thinks that, with LEDS, this could be cut in half by 2024 saving more than 130 new power stations in America alone.
Meanwhile Philips is planning to launch a small solar-powered LED reading light for Africa, where an estimated 500 million people live without electricity. The simplest version, which it hopes to sell for less than $15, is designed to allow children to do their homework in the evenings without a candle or smoky kerosene lamp. Either way, more affordable efficient LEDs should increase the practicality of lighting coupled to various forms of energy harvesting.
Top image: Light emitting diodes. Source: Home renovation trends.
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