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 $t2$ between the QDs and the Schottky contact is reduced from $t2=90 nm$ to $t2=10 nm.$ 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.