Capacitance and tunneling spectroscopy of InAs quantum dots

A Schottky diode type sample (Au/i-GaAs/InAs/i-GaAs/n(+)-GaAs) with InAs quantum dots (QDs) embedded in the intrinsic GaAs region between the Schottky contact and the n-doped GaAs-back contact was used to investigate the electron transport into and through InAs QDs. According to a simple leverage law the QD ground state resonance shifts to higher gate voltages when the thickness of the tunneling barrier t(2) between the QDs and the Schottky contact is reduced from t(2)=90 nm to t(2)=10 nm. Additionally, the transition from a pure capacitive to a predominant conductive signal of the QD ground state is observed. The gate voltage offset between the charging and the tunneling signal of the s-shell is explained by QDs of different size dominating the ohmic and the capacitive I-V traces, respectively. This interpretation is confirmed by different Coulomb blockade energies as well as different confinement energies of the QD ground state determined from both types of signal. (C) 2004 American Institute of Physics.