News Article

Researchers Grow High-performance InAs/GaAs Quantum Dot Laser On Silicon

Lasing operation up to 111degC with output power over 100mW at room temperature

Researchers from University College London (UCL) in the UK, and University of Arkansas in the US have grown a high-performance InAs/GaAs quantum dot laser directly on a silicon substrate. Their work was published last month in the journal Electronics Letters.

Growing III-V semiconductors on silicon substrates is tricky due to the formation of high-density threading dislocations. These dislocations, resulting from the lattice mismatch and thermal expansion coefficient between III-V compounds and silicon, propagate into the active media and degrade the laser performance. Therefore, for direct growth of III-V on silicon substrates, dislocation filter layers between silicon and III-V active element play a crucial role.

A few years ago, the UCL team was first to show the operation of an electrically pumped InAs/GaAs quantum-dot laser epitaxially grown on a silicon substrate. This was achieved using InGaAs/GaAs strained layer superlattices as dislocation filter layers to reduce the density of the threading dislocations. The team has since been optimising this buffer layer and this latest work shows that a higher performance can be achieved using InAlAs/GaAs.

The InAs/GaAs QD laser structure was grown on silicon substrates by molecular beam epitaxy. The schematic layer structure is shown above.

The epitaxy layer starts with a 1µm-thick n-type GaAs buffer layer, followed by InAlAs/GaAs DFLs, above this is a 1.5µm-thick n-type AlGaAs lower cladding layer and a 30nm-thick undoped AlGaAs guiding layer, followed by the undoped active region. Above the active region, a second 30nm-thick undoped AlGaAs guiding layer, a 1.5µm-thick p-type AlGaAs up cladding layer, and finally a 300nm-thick highly p-doped GaAs contact layer were deposited.

The active region consists of five-layer InAs/InGaAs dot-in-a-well (DWELL) structure,consisting of three monolayers of InAs grown on 2nm of In0.15Ga0.85As and capped by 6nm of In0.15Ga0.85As. The InAs/InGaAs DWELLs were separated by 45nm GaAs spacer layer. The InAs/InGaAs DWELLs were separated by 45nm GaAs spacer layer. For the growth of InAlAs/GaAs DFLs, first three repeats of five-periods of a 10nm In0.15Al0.85As/10nm GaAs superlattice were grown, with each layers of DFLs were each separated by a 400nm GaAs barrier, followed by a 50 periods of GaAs (5nm)/AlGaAs (5nm) superlattice, above this is grown another two repeats of five-periods of a 10nm In0.15Al0.85As/10nm GaAs superlattice.

By taking this approach, the researchers demonstrated the highest lasing temperature for InAs/GaAs QDs lasers directly grown on silicon substrates. (A laser designed for silicon photonics needs to work at a high temperature as modern silicon electronic chips often work at 65degC). The team reported that the device exhibits lasing at 1.26µm with a threshold current density of 200A/cm2 along with single facet output power exceeding 100mW at room temperature. Significantly, lasing operation for heatsink temperature up to 111degC has been achieved.

'1.3µm InAs/GaAs quantum-dot laser monolithically grown on Si substrates operating over 100degC' by SM Chen et al appeared in Electronics Letters, Volume 50, Issue 20, 25 September 2014.  DOI: 10.1049/el.2014.2414

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