Grown on silicon: QD-based micro-ring GaAs lasers operate from 0.6mA

September 20, 2017 // By Julien Happich
Led by professor John E. Bowers from the Optoelectronics Research Group of the University of California, an international team of researchers has not only succeeded in designing electrically-pumped quantum dot micro-ring lasers directly grown on silicon, the researchers also claim the sub-milliamp lasing threshold (0.6mA) and the device footprint are orders of magnitude smaller than those of previously reported lasers epitaxially grown on silicon.

Emitting at 1.3μm, the micro laser was tested under continuous-wave lasing at up to 100°C, making it very promising for integration into compact optical communication systems.

Their paper "1.3 μm submilliamp threshold quantum dot micro-lasers on Si" published in the Optica journal reveals a novel GaAs-on-Si heterogeneous growth strategy which confines dislocations and growth defects and allows for direct growth on silicon with no germanium buffer layer or substrate miscut. This was combined with a quantum dot (QD)-based active medium, known to effectively alleviate the negative influence of dislocations and surface recombination arising from lattice-mismatched growth and device fabrication.

Schematic of the GaAs-on-Si template.

First, the researchers etched V-grooves along the [100] direction on a (001) silicon substrate, which they filled with an array of GaAs in-plane nanowires grown directly inside the silicon V-grooves by selective-area metal-organic chemical vapor deposition.

Then further GaAs was grown including 15 periods of Al0.3Ga0.7As∕GaAs (5/5nm) superlattice for annihilating the threading dislocations. Eventually the GaAs nanowires were coalesced into a 1.5μm-thick continuous and smooth surface, on top of which a GaAs∕AlxGa1−xAs graded-index separate-confinement laser heterostructure was grown in a molecular beam epitaxy system. This included seven InAs/InGaAs quantum dot-in-a-well layers incorporated in the laser active region, with a quantum dot density approaching 6×1010 cm−2.

The paper reports that the 4.1% lattice mismatch between GaAs and silicon was mostly accommodated by the formation of a few nanometer-thick stacking faults in the V -grooved structure, enabling the fabrication of a defect-free GaAs laser with performances comparable to devices built on a native GaAs substrate.