Symmetries and the Polarized Optical Spectra of Exciton Complexes in Quantum Dots

A systematic and simple theoretical approach is proposed to analyze true degeneracies and polarized decay patterns of exciton complexes in semiconductor quantum dots. The results provide reliable spectral signatures for efficient symmetry characterization, and predict original features for low $C_{2v}$ and high $C_{3v}$ symmetries. Excellent agreement with single quantum dot spectroscopy of real pyramidal $\mathrm{InGaAs}/\mathrm{AlGaAs}$ quantum dots grown along [111] is demonstrated. The high sensitivity of biexciton quantum states to exact high symmetry can be turned into an efficient uninvasive postgrowth selection procedure for quantum entanglement applications.

Figure 1

Predicted polarized radiative decay paths of $2X_{11}$. Solid and dotted lines represent allowed transitions with $\sigma$ and $z$ polarization, respectively, ($\sigma \equiv x/y/{\sigma }_{\pm }$).

Figure 2

Polarization resolved PL spectra of QDT (a) and (b) and QDS (c)–(e), normalized to the intensity of $X_{\overline{1}0}$. Grey solid lines are peak fits, with the individual peaks shown below in solid (dotted) black lines for transitions allowed (forbidden) under $D_{3h}$, for the measured polarization direction. [The fit yields vanishing intensity of ${\nu }_5$ in (a).]