SEMICONDUCTOR lasers have finally gone green, plugging a gaping hole in the spectrum and paving the way for full-colour projectors for cellphones.
Costly solid-state green lasers already exist, but the new green semiconductor laser can be used with existing red and blue semiconductor lasers to provide cheap full-colour output on a tiny scale.
鈥淕reen semiconductor lasers combined with red and blue give full-colour output on a tiny scale鈥�
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The colour emitted by the laser depends on its chemistry. A gallium indium nitride active layer over a gallium nitride substrate makes for a blue laser, and adding more indium to the active layer should turn the blue light green 鈥� but in practice the extra indium atoms, which are larger than gallium atoms, stress the crystal structure at the interface, introducing cracks that render the laser useless.
Now two companies 鈥� in Regensburg, Germany, and in Goleta, California 鈥� have overcome the problem. The firms won鈥檛 reveal precise details, but Soraa says their technique involves cutting the gallium nitride substrate along a crystal face characterised by a structure that more closely matches the gallium indium nitride, lowering the risk of cracks developing.
Soraa鈥檚 lasers convert about 2 per cent of input electricity into green light. 鈥淥ur feeling is that you need 8 per cent efficiency for commercial success,鈥� says vice-president Paul Rudy. Soraa is aiming for 10 per cent within a year, he says.
