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We investigate resonant tunneling through two coupled self-assembled quantum dots. The strong confinement and the high crystalline quality provided by the self-assembled dots, in combination with the tunneling coupling between the dots, create a system that may be thought of as an artificial molecule. We are able to isolate one single artificial molecule and detailed investigations of the electrical properties are performed. Peak-to-valley ratios above 1000 and full width half maximum of a few millivolts are measured at 4 K. By changing the temperature we also observe Coulomb blockade effects in a different way. [ABSTRACT FROM AUTHOR]

Resonant tunneling through a single layer of self-assembled quantum dots (QDs) is compared to tunneling through two layers of vertically aligned (stacked) dots. The difference can be viewed as going from a two-dimensional emitter to a zero-dimensional emitter. The temperature dependence of current peaks originating in tunneling through individual QDs and individual stacks is used to clarify this point. In addition, we show that the statistical size distribution of self-assembled quantum dots causing the inhomogeneous broadening in luminescence experiments can be analyzed in a resonant tunneling experiment. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Resonant tunneling was observed through single InAs quantum dot (QD) stacks embedded in InP barriers with peak-to-valley ratios as high as 85 at 7 K. Negative differential resistance in the current-voltage [I(V)] characteristics was obtained up to a point above the temperature of liquid nitrogen. These features were observed in measurements on low-density QD stacks, in which a macroscopic ohmic contact covered less than 150 QD stacks. Due to the design of the structure, the upper QD in the stack has the function of a zero-dimensional emitter. Electrons easily fill the upper dot, whereas tunneling through the entire structure is only allowed when two states in the dots align energetically, resulting in sharp resonant tunneling peaks with high peak-to-valley ratios. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]