Shell-like formation of self-organized $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dots

The photoluminescence (PL) of self-organized $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dots (QD’s) shows a decomposition into a set of eight rather narrow lines upon antimony-surfactant mediated growth. This decomposition results from a shell-like growth mode, which means a discrete variation of the QD size in monolayer steps. Based on the PL monolayer splitting, indicative of structurally and chemically well-defined upper interfaces, structural and optical properties can be correlated much more in detail than previously possible for strongly broadened QD ensembles. A comparison of the spectral positions to predictions of eight-band $\mathbf{k}\mathbf{\bullet }\mathbf{p}∕\text{configuration}$ interaction model calculations for truncated pyramidal $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ QD’s yields excellent agreement only for the shell-like QD growth mode.

Figure 1

Typical cross section high resolution transmission electron micrograph of an $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dot. Evaluation of the shape yields a truncated pyramid with a height of six monolayers.

Figure 2

Photoluminescence spectra of samples A and B recorded at $7\mathrm{K}$ at an excitation density below $5\mathrm{mW}{\mathrm{cm}}^{-2}$.

Figure 3

PL and PLE spectra (shifted vertically) of sample B recorded at $\mathrm{T}=7\mathrm{K}$ and excitation densities below $5\mathrm{mW}{\mathrm{cm}}^{-2}$. The detection energies of the PLE spectra are marked by arrows.

Figure 4

Energy separation and FWHM of emission peaks observed for sample B as a function of the height of the QD’s. The data have been obtained by a multi-Gaussian fit to the PL spectrum (see Ref. 28).

Figure 5

Contour plot of the PL intensity in dependence on the detection and excess excitation energies. The plot was generated from a series of PLE spectra and the intensity is given on a logarithmic scale.

Figure 6

Normalized PL spectra of three pieces of sample B, which are as-grown or have been annealed for $10\min$ at $700°\mathrm{C}$ and $730°\mathrm{C}$, respectively. The inset shows corresponding PLE spectra detected at $1.185\mathrm{eV}$.

Figure 7

The five steps involved in modeling the electronic and optical QD properties (see text).

Figure 8

Absorption spectra calculated in an eight-band $\mathbf{k}\bullet \mathbf{p}$ model for $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ QD’s as a function of the height. A truncated pyramidal shape with (110)-side facets and base lengths of $13.6\mathrm{nm}$ was assumed.

Figure 9

(a) Predicted (solid symbols) and observed (open symbols) energies of the ground $(n=0)$ and first excited $(n=1)$ exciton transition in truncated pyramidal $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ QD’s as a function of height. (b) The corresponding energy separation between the $n=0$ and $n=1$ transitions.