Theoretical study of optical excitation in quantum dots by circularly polarized light

We study theoretically electron states in quantum dots and their excitations by circularly polarized light. First, we calculate the hole states in a quantum dot modeled by three-dimensional harmonic confinement potential. In the bulk direct-gap semiconductors, the k·p perturbation method around F point adequately yields heavy-hole, light-hole and split-off bands. We adopt the effective-mass approximation based on the k-p perturbation method and obtain quantized energy levels for holes in the quantum dot. The ground levels are two-fold degenerate and mainly consist of |j, m> = |3/2, ±3/2> components. It should be mentioned that a small amount of |3/2, ±1/2> components are coherently mixed in the states. Second, we examine an electron-hole excitation by the irradiation of circularly polarized light σ̄. The main component of the exciton is |3/2, -3/2> hole|1/2, -1/2>electron. The electron state |1/2, 1/2>electron is also excited owing to the mixture between |3/2, ±3/2> and |3/2, ±1/2> components in the hole states, which should lead to an inaccuracy in the manipulation of electron spins. The Overhauser field created by nuclear spins plays a role when it is larger than an external magnetic field. It randomizes the direction of electron spins excited by the circularly polarized light a- in an ensemble of self-assembled quantum dots.