Manipulation of the spontaneous emission dynamics of quantum dots in two-dimensional photonic crystals

We demonstrate the ability to control the spontaneous emission dynamics of self-assembled quantum dots via the local density of optical modes in two-dimensional (2D) photonic crystals. We show that an incomplete 2D photonic band gap is sufficient to significantly lengthen the spontaneous emission lifetime $(>2\times )$ over a wide bandwidth $(\Delta \lambda ⩾40\mathrm{nm})$. For dots that are both spectrally and spatially coupled to strongly localized $[V_{\mathit{\text{modes}}}\sim 1.5{(\lambda ∕n)}^3]$, high $Q\sim 2700$ optical modes, we have directly measured a strong Purcell-enhanced shortening of the emission lifetime $⩾5.6\times$, limited only by our temporal resolution. Analysis of the spectral dependence of the recombination dynamics shows a maximum lifetime shortening of $19\pm 4$. From the directly measured enhancement and suppression we show that the single-mode coupling efficiency for quantum dots in such structures is at least $\beta =92\%$ and is estimated to be as large as $\sim 97\%$.

Figure 1

(a) PL spectra recorded from a series of $H1$ PC cavities as a function of the ratio of hole radius $r$ to periodicity $a$. [inset of (a)] The SEM images show typical cavities. The ensemble PL is shown for comparison. (b) Measured $Q$ factors for the cavity modes of $>40$ cavities as a function of $r∕a$. (c) Calculations of the TE-polarized three-dimensional (3D) band structure with $a=300\mathrm{nm}$ showing the localized dipolelike modes $M1$ and $M2$ inside the photonic band gap and the experimental data. [inset of (b)] Calculated electric-field profile of the cavity modes.

Figure 2

(a) PL spectrum of the selected cavity. (b) Comparison of decay transients recorded from QDs detuned from the cavity modes $({\lambda }_{\mathit{det}1}=1037\mathrm{nm})$ either (i) within the unpatterned GaAs membrane (${\tau }_0$—open circles) or (ii) from the PC (${\tau }_1$—filled circles). The dashed line is the instrument response function (IRF) of our setup. (c) Decay transients recorded from the PC $H1$ cavity both in resonance with $M2$ at ${\lambda }_{\mathit{det}2}=1031.5\mathrm{nm}$ (filled squares) and detuned at ${\lambda }_{\mathit{det}1}=1037\mathrm{nm}$ (filled circles).

Figure 3

Spectral dependence of the decay lifetimes for dots within the PC (filled squares) and within the unpatterned membrane (open circles). The dotted line represents a guide to the eye showing the stronger suppression of the spontaneous emission for wavelengths closer to ${\lambda }_{\mathit{mid}}^{\mathit{TE}}$. (inset) Fit of Eq. (1) to the spectral dependence of the decay lifetime.