Reduction of exciton-phonon interaction due to stronger confinement in single quantum dots

We study optical emission from single CdTe quantum dots embedded in ${\mathrm{Zn}}_{1-x}{\mathrm{Mg}}_x\mathrm{Te}$ barriers. A progressive and simultaneous reduction of (i) exciton-acoustic phonon coupling and (ii) anti-Stokes scattering with acoustic and optical phonons with increasing $\mathrm{Mg}$ concentration in the barrier material is observed. A model is presented for quantitative analysis of exciton-phonon interactions in the presence of strong phonon sidebands, with a data processing method that extracts the phonon sideband contribution from the single quantum dot spectra.

Figure 1

$\text{PL}$ spectra of a single $\mathrm{CdTe}∕\mathrm{ZnTe}$ (a) and a single $\mathrm{CdTe}∕{\mathrm{Zn}}_{0.7}{\mathrm{Mg}}_{0.3}\mathrm{Te}$ (b) $\text{QD}$ as a function of temperature.

Figure 2

(a) Continuous spectra $C\left(h\nu \right)$ at $45\mathrm{K}$, calculated by convoluting the discrete spectral shape function (inset) with the zero-phonon line (dotted curve). For the zero-phonon line we choose the one corresponding to the $\mathrm{CdTe}∕{\mathrm{Zn}}_{0.7}{\mathrm{Mg}}_{0.3}\mathrm{Te}$ $\text{QD}$ in Fig. 2b, whose calculation is detailed in the text. A fit of the center part of $C\left(h\nu \right)$ is also shown (dashed curve). (b) Measured $\text{PL}$ line from the dot shown in Fig. 1b at $45\mathrm{K}$, together with a fit of the center part (dashed curve) and the calculated zero-phonon line according to our model (dotted curve).

Figure 3

$\text{FWHM}$ of the individual $\text{PL}$ lines shown in Fig. 1 as a function of temperature. The full curve is a fit of the experimental points by means of Eq. (4). The dashed curve describes the $\text{FWHM}$ of the zero-phonon line contribution calculated according to our present model.

Figure 4

Relative variation of integrated intensity of the acoustic phonon sidebands for the $\text{PL}$ lines shown in Fig. 1 as function of temperature. The straight lines are a guide to the eye.