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14 February 2011.
Researchers at the University of California Berkeley (UCB) have developed a new type of hybrid silicon laser based on nanopillars of gallium arsenide deposited directly on a silicon wafer.  Connie Chang-Hasnain and her team claim this is the first time that gallium arsenide has been grown on silicon using a process that’s compatible with standard CMOS manufacturing.
The ability to integrate lasers and electronics holds great promise for high-speed optical interconnects and high-performance computing chips.  On-chip lasers are expected to provide a low-cost, low-power way to move data from chip to chip.  However, silicon doesn’t emit light.
One way to sidestep this problem is to combine silicon with a material that does emit light, such as gallium arsenide. Unfortunately, silicon and gallium arsenide have different crystal lattice structures, which makes it tricky to grow one material directly on the other.  Intel and University of California Santa Barbara have pursued an alternative approach, using wafer bonding to join the two materials together, but this approach is relatively expensive and is incompatible with CMOS processing methods.
The UCB work, reported in the journal Nature Photonics, is an important step towards hybrid silicon lasers because it demonstrates that it’s possible to grow hexagonal nanopillars of gallium arsenide directly on top of silicon with good crystal quality (defects in the crystal would prevent light emission).  But there’s plenty of work still to do; the researchers also need to add electrical contacts to power the laser, and integrate the lasers with optical waveguides to couple light onto the silicon chip.
By Pauline Rigby.