External-field effects on the optical spectra of self-assembled InP quantum dots

The effects of external electric and magnetic fields on InP self-assembled quantum dots (QDs) were investigated by means of single dot spectroscopy. By systematically changing a bias applied to the sample, successive energy shifts of the photoluminescence (PL) peaks from excitons and biexcitons due to the quantum confined Stark effect were clearly observed. The quadratic Stark coefficient was evaluated to be of the order of 10-31 Fcm2. The energy separation of the PL peaks arising from the excitons and biexcitons changed with the applied electric field, reflecting a slight difference of the Stark coefficient between the exciton and biexciton states. The existence of permanent dipole moments was also revealed in both the exciton and biexciton states. The spatial separations between the electrons and holes along the growth direction in a QD were estimated to be 7 Å for the exciton state, and 8 Å for the biexciton state. Further, the diamagnetic shift and the Zeeman splitting of the exciton states were clearly observed in a magnetic field. It was found that the diamagnetic coefficient gradually decreases on decreasing the QD size. A simple qualitative model can explain that this result is due to competition between quantum confinement and magnetic confinement