Spectroscopic access to single-hole energies in InAs/GaAs quantum dots

We present a purely spectroscopic way to determine single-particle energy level splittings in individual InAs/GaAs QDs. The method is based on a combination of μ-photoluminescence spectroscopy (μPL) with resonant excitation and μ-photoluminescence excitation spectroscopy (μPLE) of charged QDs. The approach allows elimination of all contributions from few-particle interactions such that true single-particle energy level distances are determined. For the present InAs/GaAs QDs, showing ground-state recombination energies between 1.23 to 1.27 eV, the splitting between the hole ground state (h₀) and first excited state (h₁) is Δ(h₀h₁)=(27.1±1.8) meV. The splitting between the first and second excited hole states is Δ(h₁h₂)=(10.8±0.3) meV. These values are in good agreement with results from eight-band k·p calculations on lens-shaped InAs/GaAs QDs. Theoretical investigations identify unambiguously the heavy-hole-light-hole coupling as the decisive parameter leading to a nonzero h₁-h₂ splitting.