Polarization-resolved fine-structure splitting of zero-dimensional In${}_x$Ga${}_{1-x}$N excitons

The fine-structure splitting of quantum confined In${}_x$Ga${}_{1-x}$N excitons is investigated using polarization-sensitive photoluminescence spectroscopy. The majority of the studied emission lines exhibits mutually orthogonal fine-structure components split by 100–340 μeV, as measured from the cleaved edge of the sample. The exciton and the biexciton reveal identical magnitudes but reversed sign of the energy splitting.

Figure 1

Schematic decay diagrams for excitons of (a) type 1 and (b) type 2 for symmetric $C_{3v}$ and asymmetric $C_s$ QDs. The gray (black) lines indicate $x$-polarized ($y$-polarized) transitions, and dashed lines indicate the $z$-polarized transitions.

Figure 2

(a) The μPL spectra of a single In${}_x$Ga${}_{1-x}$N QD-like potential excited with laser powers as indicated, measured for the light emitted in the growth direction. The baselines are successively shifted vertically for clarity. (b) The integrated intensities of X ($I_{\mathrm{X}}$) and XX ($I_{\mathrm{XX}}$) plotted as a function of excitation powers. The inset shows the polar plots of the linear polarization dependence of peaks X and XX together with fitted lines on the form αsin${}^2$ θ $+$ βcos${}^2$ θ, where α and β are constants and θ is the polarization angle.

Figure 3

The μPL spectra of In${}_x$Ga${}_{1-x}$N QD-like potentials excited with laser powers as indicated, measured for the light emitted in the $[10\overline{1}0]$ direction. The baselines are successively shifted vertically for clarity. The inset shows a schematic and orientation of the sample.

Figure 4

Polarization-resolved μPL spectra of the In${}_x$Ga${}_{1-x}$N QD-like potentials recorded for linear polarization vectors along $[0001]$ and $[1\overline{2}10]$. The inset shows polar plots of the linear polarized emission of peaks X and XX together with the fitted lines, as in Fig. 2(b).

Figure 5

The expanded view of the polarization-resolved spectra of peaks X and XX. All spectra are normalized, and the baseline of peak XX is shifted vertically for clarity. The insets show the fine-structure splitting of 14 emission lines plotted as a function of their energies (left) and the schematic of the cascade decay of XX and X (right).