Exciton dephasing in self-assembled $\mathrm{CdSe}$ quantum dots

We report experimental studies of exciton dephasing in self-assembled $\mathrm{CdSe}$ quantum dots using techniques based on spectral hole burning. The hole-burning response reveals directly in the spectral domain the zero-phonon-line (ZPL) as well as contributions from acoustic and LO-phonon assisted transitions. The observed strong coupling to acoustic phonons is in good agreement with theoretical expectation. The measured decoherence rate associated with the ZPL is as small as $3.5\mu \mathrm{eV}$, comparable to that in self-assembled $\mathrm{InGaAs}$ quantum dots.

Figure 1

SHB spectrum at $T=10\mathrm{K}(\Omega =10\mathrm{kHz},I_{\text{pump}}=2I_{\text{probe}}=2\mathrm{W}∕{\mathrm{cm}}^2)$. The inset on the right shows the PL spectrum for excitation in the wetting layer; the dotted line indicates the pump energy used in the SHB. The inset on the left shows an expanded scan of the ZPL and acoustic phonon pedestal $\Omega =3\mathrm{MHz}$.

Figure 2

Modulation frequency dependence of the ZPL linewidth at $T=10\mathrm{K}(I_{\text{pump}}=10I_{\text{probe}}=4\mathrm{W}∕{\mathrm{cm}}^2)$. The inset shows high-resolution scans of the ZPL demonstrating a narrowing of the ZPL.

Figure 3

(a) Temperature dependence of the ZPL $(\Omega =3\mathrm{MHz}\text{and}{I}_{\text{pump}}=10I_{\text{probe}}=4\mathrm{W}∕{\mathrm{cm}}^2)$; (b) dephasing rate as obtained from (a). The dotted line is a guide to the eye. The inset shows the pump intensity dependence.

Figure 4

Calculated linear absorption spectrum for a $\mathrm{CdSe}$ QD at $12\mathrm{K}(L_z=1.1\mathrm{nm})$ with deformation potential coupling constants $D_e=11\mathrm{eV}$ and $D_h=8.9\mathrm{eV}$ (Ref. 16).