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QD Lasers Grown on Silicon Show Record Performance

SANTA BARBARA, Calif., and BETHLEHEM, Pa., Feb. 25, 2014 — Direct growth of III-V lasers on silicon (Si) with quantum dot (QD) active regions is a competitive alternative to wafer bonding lasers grown on native substrates, a new study shows.

The 1.3-µm wavelength indium arsenide (InAs) QD lasers were developed by researchers at the University of California, Santa Barbara, and IQE Inc., and have demonstrated record performance.

The structures were grown on germanium-on-silicon (Ge-on-Si) substrates using molecular beam epitaxy (MBE). These 150-mm-diameter (100) silicon substrates, miscut 6° degrees in the [111] direction, were prepared with chemical vapor deposition of 500-nm germanium.

A 1130 × 10-µm device with silicon nitride facet coatings and undoped barriers showed a maximum power output of 176 mW, which the researchers said is “the highest reported for telecom lasers on silicon.” Devices with p-doped barriers in the active region had similar characteristics. An 1155 × 4-µm device with polished facets had a threshold current of 21 mA and maximum output power of almost 54 mW at 20 °C.

Such epitaxial approaches not only provide a lower barrier to entry for silicon photonics devices through potential large-scale growth, the researchers said, but also take advantage of the benefits inherent to QD-based optoelectronics and yield performance characteristics that typically are difficult to achieve in quantum well devices.

The initial MBE included a thermal anneal to create bi-atomic step arrays for nucleation of epitaxial gallium arsenide (GaAs). This enabled the growth of mirrorlike layers with reasonable dislocation densities. The substrate was then separated into smaller virtual GaAs substrates before the laser material was grown.

Until now, such demonstrations have used wafer bonding techniques to combine III-V and silicon technologies. Direct growth of III-V materials is challenging and requires careful process control to achieve low defect densities. The III-V QD lasers have proved to be less sensitive to nonradiative defects.

The research was published in Applied Physics Letters. (doi: 10.1063/1.4863223)

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