Electrical Control of Hole Spin Relaxation in Charge Tunable $\mathrm{InAs}/\mathrm{GaAs}$ Quantum Dots

We report on optical orientation of singly charged excitons (trions) in charge-tunable self-assembled $\mathrm{InAs}/\mathrm{GaAs}$ quantum dots. When the charge varies from 0 to $-2$, the trion photoluminescence of a single quantum dot shows up and under quasiresonant excitation gets progressively polarized from zero to $\sim 100\%$. This behavior is interpreted as the electric control of the trion thermalization process, which subsequently acts on the hole-spin relaxation driven in nanosecond time scale by the anisotropic electron-hole exchange. This is supported by the excitation spectroscopy and time-resolved measurements of a quantum dot ensemble.

Figure 1

C-V characteristic of sample B. Inset: conduction band diagram in the vicinity of the QD layer. Bottom: schematic diagram of the charging of a single QD, in darkness ($N_{\mathrm{hole}}=0$) and in the presence of a photocreated hole ($N_{\mathrm{hole}}=1$) as a function of the bias.

Figure 2

(a) Polarization-resolved PL spectra of a single QD under ${\sigma }^{+}$ excitation at 1.32 eV. (b) Polarization of 4 trion lines as a function of the excitation energy. Error bars correspond to the deviation between two successive measurements.

Figure 3

Sketch of the charged exciton thermalization dynamics in a QD for $N=1$ (a) or $N=2$ (b) electrons before the quasiresonant ${\sigma }^{+}$ excitation. The gray-shaded areas represent the WL 2D-continuum of the QDs. In panel (a), the dotted and dashed arrows illustrate two possible paths for the photoelectron.

Figure 4

(a) Excitation spectra of sample B PL detected at 1.3 eV. The GaAs LO- and TO-phonon features (dashed lines) were identified at $-1\mathrm{V}$ by Raman diffusion in ${\sigma }^{+}{\sigma }^{-}$ configuration. (b) PL and polarization at 1.265 eV under excitation at 1.34 eV against gate voltage.

Figure 5

Polarization- and time-resolved PL intensity at 1.27 eV (solid lines) in ${\sigma }^{+}{\sigma }^{+}$ (black) and ${\sigma }^{+}{\sigma }^{-}$ (gray) configurations, and circular polarization (dots) with a multiexponential fit (dashed line) of sample B under excitation at 1.34 eV.