Charge state control in single InAs/GaAs quantum dots by external electric and magnetic fields

Abstract

We report a photoluminescence (PL) spectroscopy study of charge state control in single selfassembled InAs/GaAs quantum dots by applying electric and/or magnetic fields at 4.2 K. Neutral and charged exciton complexes were observed under applied bias voltages from -0.5 V to 0.5 V by controlling the carrier tunneling. The highly negatively charged exciton emission becomes stronger with increasing pumping power, arising from the fact that electrons have a smaller effective mass than holes and are more easily captured by the quantum dots. The integrated PL intensity of negatively charged excitons is affected significantly by a magnetic field applied along the sample growth axis. This observation is explained by a reduction in the electron drift velocity caused by an applied magnetic field, which increases the probability of non-resonantly excited electrons being trapped by localized potentials at the wetting layer interface, and results in fewer electrons distributed in the quantum dots. The hole drift velocity is also affected by the magnetic field, but it is much weaker.

Observation of coupling between zero- and two-dimensional semiconductor systems based on anomalous diamagnetic effects

“…Figure 3 shows PL spectra as a function of magnetic field with different applied bias voltages at pumping power of 7.11 μW and 11.85 μW. At 7.11 μW, only X 0 , X − , and X 2− can be identified in splitting and a diamagnetic shift as a function of magnetic field, as reported earlier [14]. Two branches of X 2− with singlet and triplet final states show opposite diamagnetic shifts.…”

“…The second peak of X 2− at the low-energy side is due to the exchange-split final states, singlet and triplet states [27]. The main PL peaks are negatively charged, which is due to the built-in electric field in the Schottky diode and the different injection rates for electrons and holes with non-resonant pumping [14]. The details of peak assignation as a function of the external bias are shown in Fig.…”

“…The binding energy between X − and X 2− is only approximately 370 μeV, which is considerably lower than that between X + and X 0 or between X − and X 0 . The third electron in X 2− occupies the p-shell and has less wavefunction overlap with the electrons and holes in the s-shell, resulting in a smaller Coulomb interaction [14]. Because of the larger injection rate for electrons than that for holes in non-resonant pumping, the exciton states are more negatively charged with increasing pumping power.…”

“…Strong excitation power and positive bias voltages are required to observe the extra PL peaks, which are also the criteria for achieving highly negatively charged exciton states in our structure [14]. With increasing excitation power, optically generated electrons prefer to occupy the ground state (s-shell) and the first excited state (p-shell) of the conduction band of the QD, followed by the continuum state in the wetting layer.…”

Light absorption of cylindrical quantum dot with Morse potential in the presence of parallel electrical and magnetic fields

“…External electric and magnetic fields causing quantization are alternative control tools for the energy spectrum of charge carriers inside QD [12,[18][19][20][21][22]. Strong external fields, at certain values of their intensities, may have the same, or even stronger size quantization effect than quantum dot shape Remind that the magnetic field affects the electron or hole motion only in transversal direction, in difference to the electrical field.…”