Single-electron tunneling through individual InAs quantum dots within a saddle point potential

InAs quantum dots were embedded in a two-dimensional electron gas of a modu lation doped heterostructure. a constriction was lithographically defined t o allow electron transport through at maximum three quantum dots. Sharp res onances appear at the onset of the conductance which are attributed to elec tron tunneling through the first excited state of a single dot within the c onstriction. A Coulomb blockade energy of approximate to 12 meV was estimat ed for this energy level which is in good agreement with capacitance data m easured on a dot ensemble. When the source bias is varied Coulomb blocked r egimes can be observed which are typical for single electron devices.