Exciton Polarization, Fine-Structure Splitting, and the Asymmetry of Quantum Dots under Uniaxial Stress

Abstract

We derive a general relation between the fine-structure splitting (FSS) and the exciton polarization angle of self-assembled quantum dots under uniaxial stress. We show that the FSS lower bound under external stress can be predicted by the exciton polarization angle and FSS under zero stress. The critical stress can also be determined by monitoring the change in exciton polarization angle. We confirm the theory by performing atomistic pseudopotential calculations for the InAs/GaAs quantum dots. The work provides deep insight into the dot asymmetry and their optical properties and a useful guide in selecting quantum dots with the smallest FSS, which are crucial in entangled photon source applications.

Polarization properties of excitonic qubits in single self-assembled quantum dots

“…We believe that the correlation between emission energy and size of the dot can not be predicted in a straightforward manner especially when studying a large statistical ensemble of individual dots. Therefore it is difficult to establish general trends for the exciton fine structure versus the dots size unless an external field, like an electric field, 27 or stress applied to the structure, 17,28 is used to tune the fine structure splitting.…”

Statistical properties of exciton fine structure splitting and polarization angles in quantum dot ensembles

“…Now it is quite clear that the FSS arises from the intrinsic nonequivalence along [110] and [110] directions in zinc-blende crystals, which reduce the symmetry of the underlying lattice from T d to C 2v for pure circular lens-shaped QDs, and the other nonuniform effects such as local strain, shape irregularities, alloys and interface effects [10,11], which further reduce the symmetry to C 1 for alloyed QDs [12]. A single external field, such as electric field [13][14][15][16][17][18], magnetic field [2,19], or anisotropic stress [12,[20][21][22][23][24], is insufficient to eliminate the FSS because the lower bound of FSS is generally much larger than the homogeneous broadening of the emission line (∼ 1 µeV). To eliminate the FSS, two non-equivalent fields have to be combined [8,9].…”

“…To this end, the recently developed phenomenological model in Ref. [12] is well fitted to this problem. From the symmetry viewpoint, the Hamiltonian for a single QD can be written as H = H 2v + V 1 , where H 2v contains the kinetic energy and the potential with the crystal C 2v symmetry, and V 1 is the perturbation potential with C 1 symmetry.…”

“…We define two eigenvectors of H 2v as |3 = |Γ 2 + iΓ 4 and |4 = |Γ 2 − iΓ 4 , which are exactly along either [110] or [110] direction (ensured by the C 2v symmetry) and also real simultaneously (ensured by the time-reversal symmetry). An effective 2 × 2 Hamiltonian can be constructed from these two bright states [12],…”

Influence of the atomic-scale structure on the exciton fine-structure splitting in InGaAs and GaAs quantum dots in a vertical electric field

“…A number of surprising puzzles surround the tuning of the FSS by a vertical electric field. First, it is predicted theoretically 18 , and confirmed experimentally 10,13 and theoretically 19 , that for QDs made of random alloys (with symmetry lower than C 2v ) the two bright components of the excitons undergo an anticrossing as a function of fields applied along the {100} or {110} directions 18 . Second, since it has been established that the FSS is related to the atomistic inplane asymmetry between the [110] and [110] crystallographic directions, it would appear that such an intrinsic quantity would not lend itself to tuning via vertical field.…”