Shell structures in self-assembled InAs quantum dots probed by lateral electron tunneling structures

We have investigated electron filling in single InAs quantum dots (QDs) using a lateral electron transport structure, i.e., nanolithographically defined metallic leads with nanogaps. Elliptic InAs QDs with a diameter of $∼60∕80nm$ exhibited clear shell filling up to 12 electrons before the gate leakage became significant. Shell-dependent charging energies and level quantization energies for the $s$⁠, $p$⁠, and $d$ states were determined from the addition energy spectra. Furthermore, it was found that the charging energies and the tunneling conductances strongly depend on the shell, reflecting that the electron wave functions for higher shells are more extended in space.