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(a) A single InAs quantum dot deterministically nucleated on an InP pyramidal mesa. (b) After InAs dot nucleation, the dot is capped with InP resulting in a pyramidal nanostructure with a single quantum dot embedded near the apex of the nano-pyramid. (c) The inset shows an exploded view of the InP pyramid on the InP substrate with the silicon dioxide CSL directly above.
(a) PL measurement of exciton s-shell emission of as-grown dot. (b)After the application of 54.6 nm CSL, emission redshifts 16.47 meV (c) followed by a RTA duration of 1 min blueshifting the emission 32.53 meV. The s-shell emission points, (c) and (d), are calculated by solving the Navier and Schrodinger equations using the finite-element method described in the theoretical section of the paper.
The relative emission energy of a single quantum dot that has gone through multiple CSL and RTA steps. The initial dot emission at 878.8 meV has a 51.2 nm thick CSL. (a) RTA for 30 s duration blueshifts emission 12.19 meV. (b) Removal of the CSL further blueshifts emission by 9.26 meV. (c) Application of second 53.4 nm thick CSL redshifts emission by 11.85 meV. (d) Second RTA for a 1 min duration blueshifts emission by 38.84 nm. A total blueshift of 48.45 meV was achieved through multiple process steps of the same single InAs without the integrity of the linewidth being compromised.
The effect of CSL and RTA on sp-shell spacing on dot-pyramid nanostructure whose s-shell emission was shown in Figure 1 . All the s-shell emissions were aligned with the as-grown emission in order to study the relative sp-shell spacing differences. (a) p-Shell emission of as-grown dot with sp-shell spacing of 35.5 meV. (b) Spacing increases to 38.3 meV with the application of application 54.6 nm CSL. (c) Spacing decreases to 32.8 meV following the 1-min RTA. Points (d)–(f) are finite-element simulation results of the p-shell emission that consider the effects of the CSL strain and intermixing on the electron-hole shell states. The simulation results follow the experimental results very closely. The inset is a close-up plot of the p-related emissions near the s-shell emission. We see that they follow thesame spacing trend as the p-shells, that is, they shift out for the CSL and then shift in after the subsequent intermixing step.
Images (a) and (c) present the displacement contour of the InP pyramid and InAs dot, respectively, under a 50 nm thick CSL with images (b) and (c) showing how the strain looks through an exaggerated shape deformation plot. The center inset shows where the embedded dot is relative to the pyramid apex. The legends show the amount of shape displacement under the tensile strain caused by the 50 nm CSL.
Elastic strain in the growth and in-plane directions across the SiO2 CSL, InP pyramid, and embedded InAs dot. The solid red curve is the elastic strain in the z-direction, growth direction, the dotted green curve is the elastic strain in the y-direction and the dashed blue curve is the elastic strain in the x-direction. The three shaded areas indicate the three different regions. Two of the directions in theCSL, the z- and x-directions, experience tensile strain while the y-direction experiences compressive strain. In the pyramid and dot regions, however, all the directions experience tensile strain indicating the complicated nature of strain in non-planar geometries and the need for finite-element analysis. The inset shows the regions where the scan of strain values is taken. The difference in magnitude between the tensile strain in the growth direction and the in-plane direction is a direct result of the stress-sensitive location of the dot.
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