Tunneling current through self-assembled InAs quantum dots embedded in symmetric and asymmetric AlGaAs

In order to study tunnelling current through individual self assembled quantum dots, we have fabricated tunnel diodes with a small number of self-assembled Ins quantum dots embedded in symmetric and asymmetric AlGaAs barriers. In the current-voltage characteristics of the symmetric barrier diode, we have observed current peaks due to resonant tunneling through zero-dimensional states in the individual quantum dots for both voltage polarities. In contrast, we have found that the behavior of the asymmetric barrier diodes depends on the voltage polarity. For the voltage polarity such that the electrons enter the quantum dots through the thick barrier and leave through the thin one, the zero-dimensional resonant tunneling current peaks are observed as in the symmetric barrier case. On the other hand, in the opposite voltage polarity, such that collector barrier is less transparent, current step structures are observed. The step structures are attributed to Coulomb staircase due to enhanced electron accumulation in the quantum dots. Assuming a double tunnel capacitor model, the size of the conducting channel deduced from the step-width of the staircase is in agreement with the lateral size of one quantum dot obtained by atomic force microscope measurements. (C) 1998 Elsevier Science Ltd. All rights reserved.