Intraband magnetospectroscopy of singly and doubly charged $n$-type self-assembled quantum dots

The influence of quantum dot occupancy and incident light polarization on the carrier-lattice interactions in electron-doped $\mathrm{InAs}$ quantum dots grown on $\mathrm{GaAs}$ has been investigated up to $28\mathrm{T}$ by far-infrared magnetotransmission spectroscopy. An enhancement of the electron-phonon coupling with increased electron population from one to two electrons per dot is observed, in close agreement with the predicted $\sqrt{2}$ increase due to the antisymmetrization of the electron wave function in the two-electron quantum dot system. This contrasts with two-dimensional systems in which the polaron coupling strength is reduced with increasing electron density due to the screening effect of multiple carriers on the electron-phonon interaction. A clear change of the polarization dependence for transitions from the ground to the first excited state from linear to circular has been observed as the Zeeman splitting becomes larger than the zero-field excited state splitting energy.

Figure 1

Unpolarized normal incidence transmission through sample I for various magnetic fields. The zero-field splitting is clearly visible, as are the anticrossings characteristic of a polaronic system near to 15 and $25\mathrm{T}$.

Figure 2

Variation of the conduction band $\mid \mathrm{electron},\mathrm{phonon}⟩$ basis states with magnetic field. The electron component is labeled in accordance with atomic orbitals; the phonon component is given as a whole number of LO phonons. The splitting at zero field arises from the anisotropy of the wave functions. Open circles show experimental results for sample I; solid lines show the fit; dashed lines show the basis states described in Eqs. (1, 2) used to generate the fit.

Figure 3

Variation of the normal incidence absorption peaks with applied magnetic field in the Faraday geometry. Solid (dotted) lines represent the fit to sample I (II). The dashed line attempts to fit to sample II using the parameters from sample I, but with a lower-energy zero-field value. The lower (upper) part of the figure corresponds to transitions from the electron ground state $s$ to the polaron states involving the $p_{-}$ $\left(p_{+}\right)$ electron excited state.

Figure 4

Variation of the linearly polarized absorption spectra with magnetic field, for sample I. The inset shows variation of the degree of linear polarization for the $\mid s⟩\to \mid p_{+},0⟩$ transition ($+$ symbols) in the energy range 57–$70\mathrm{meV}$ with the fit obtained from the model (solid line).