Dislocation tolerance in InAs quantum dots determined by operating temperature

The demand for fast data has generated significant interest in photonic integrated circuits (PICs) on silicon (Si) for a host of applications, from quantum computing to optical communications. But for PICs to reach their full potential, better on-chip light sources are needed.

Integrating lasers made from direct-bandgap semiconductor thin films on Si has been seen as a promising solution. Unfortunately, crystal defects known as dislocations generated through the epitaxial process limit performance in traditional devices.

To address this problem, several groups have studied the epitaxial growth of quantum dots (QDs) made from indium arsenide (InAs) on Si chips. They found that the defect tolerance level is significantly higher than that of traditional quantum wells, but commercialization needs even greater tolerance.

There are hundreds of dislocations per laser device. To account for the tolerance, research has suggested that the atom-like electronic structure of QDs isolates carriers from the dislocations, which eliminates negative consequences of the defects.

Selvidge et al. found, instead, that tolerance is dependent on the device’s operating temperature. The carriers in QDs can easily migrate to dislocations at room temperature using the wetting layer, a thin quantum-well-like structure that forms naturally during the self-assembly of QDs.

Only at cold temperatures (200 K and below) do the carriers become trapped within the deeper states of the QD. Unable to thermalize to the wetting layer now, the carriers are prevented from migrating to nearby dislocation trap sites, thus enabling defect tolerance.

“Our results suggest that InAs QD designs are not as effective in localizing carriers at room temperature and above as anticipated, so we must figure out how to eliminate the misfit dislocations themselves,” co-author Kunal Mukherjee said.

Source: “Non-radiative recombination at dislocations in InAs quantum dots grown on silicon,” by Jennifer Selvidge, Justin Norman, Michael E. Salmon, Eamonn T. Hughes, John E. Bowers, Robert Herrick, and Kunal Mukherjee, Applied Physics Letters (2019). The article can be accessed at https://doi.org/10.1063/1.5113517 .