Structural and Optical Characterization of Bilayer QD Heterostructures

Efforts are being made to obtain efficient quantum dot heterostructures which possess excellent uniformity in size distribution as well as capable to extend the emission wavelength to technologically useful telecommunication wavelengths, specifically 1.3 and 1.55 μm. In InAs/GaAs single-layer quantum dot (SQD) structure, higher InAs monolayer coverage for the QDs gives rise to larger dots emitting at longer wavelengths but results in inhomogeneous dot-size distribution. The bilayer quantum dots (BQDs) can be used as an alternative to SQDs, which can emit at longer wavelengths (1.229 μm at 8 K) with significantly narrow linewidth (~16.7 meV) owing vertical ordering and electronic coupling between the two layers of dots separated by a thin (7–9 nm) spacer layer. Morphological and optical properties of bilayer InAs/GaAs quantum dot heterostructure are investigated. As compared to the similar single-layer quantum dot (SQD) structure, the bilayer quantum dot (BQD) structure showed a more uniform spatial distribution and increased size homogeneity of the dots. It also exhibited longer wavelength photoluminescence (PL) emission at room temperature, with the peak at a wavelength (1.34 μm) in the infrared communication window. In an interesting study, the emission linewidth of our BQD sample is found to be insensitive towards post-growth treatments due to the strain interaction between the layers of dots.