Spatial regularity of InAs-GaAs quantum dots: quantifying the dependence of lateral ordering on growth rate

Abstract

The lateral ordering of arrays of self-assembled InAs-GaAs quantum dots (QDs) has been quantified as a function of growth rate, using the Hopkins-Skellam index (HSI). Coherent QD arrays have a spatial distribution which is neither random nor ordered, but intermediate. The lateral ordering improves as the growth rate is increased and can be explained by more spatially regular nucleation as the QD density increases. By contrast, large and irregular 3D islands are distributed randomly on the surface. This is consistent with a random selection of the mature QDs relaxing by dislocation nucleation at a later stage in the growth, independently of each QD’s surroundings. In addition we explore the statistical variability of the HSI as a function of the number N of spatial points analysed, and we recommend N > 103 to reliably distinguish random from ordered arrays.

III–V compounds as single photon emitters

“…A GaAs cap on top of the dots is used to enable bright emission and can also produce a redshift in the QD emission energy. Note a sacrificial AlGaAs layer fabricated above the GaAs buffer and below the dots is necessary for the production of an air bridge in the following cavity fabrication processes [61]. Various growth schemes have been adopted with different epilayer thickness or cap-layers such as InGaAs caps, in order to optimize the optical performance of the QDs [47].…”

“…This build-up strain becomes energetically favourable for the adatoms to form 3D-like structures beyond a certain critical thickness. InAs/GaAs QDs are obtained by strain-driven nucleation in the Stranski-Krastanov (S-K) growth mode [60] . In these low energy interface structures, the strain energy increases with the thickness of the epilayers.…”

High-temperature continuous-wave operation of 1310 nm InAs/GaAs quantum dot lasers

“…While these do improve the dot density to (4-5)×10 10 cm −2 , introduction of single large QDs is also seen and this degrades the QD uniformity. [16,17] In order to enhance the QD quality further, suppression of the introduction of single large QDs needs to be achieved. Various methods, such as increasing the surface adatom mobility, [16] introducing a strain reducing layer (SRL) [18] and optimizing the growth rate, [19,20] have been investigated for improving QD size uniformity.…”

Molecular beam epitaxial growth of high quality InAs/GaAs quantum dots for 1.3- μ m quantum dot lasers*

“…[22,23] For further enhancement of the QD quality, this introduction of singular large QDs needs to be suppressed. Various methods such as increasing the surface adatom mobility, [26] introducing a strain reducing layer (SRL), [27] and optimizing the growth rate [14,16,28,29] have been investigated for improving the QD size uniformity. By introducing the strain reducing layer, the linewidth was reduced to 21 meV while the density only achieved 1.0 × 10 10 cm −2 .…”