Enhanced shot noise in tunneling through coupled self‐assembled InAs quantum dots

Abstract

We present measurements of the shot noise of vertically coupled self-assembled InAs quantum dots (QDs) and find a surprising enhancement with a distinct double-peak structure. 1By applying an external bias voltage we observe pronounced peaks in the dc current -voltage characteristics that correspond to electron transport through a stack of vertically coupled QDs. At these peaks we find enhanced shot noise in contrast to suppressed shot noise at a single layer of QDs. To characterize the measured shot noise S the so-called Fano factor α is introduced. At both sides of the current peak the Fano factor α rises to values up to 1.4, whereas the noise is reduced on top of the peak ( 1 α < ). We discuss qualitative agreement with a theoretical model which predict such a super-Poissonian shot noise.Shot noise is a frequency independent fluctuation of current and has its origin in the discreteness of the charge carrying the current [1]. Its average noise power S is proportional to the average current I, 2 S eI = . Investigations of the shot noise properties on tunneling barrier devices have shown that measuring shot noise grants access to further information than the DC current provides [2][3][4][5].In this paper we will discuss the shot noise properties of transport through vertically coupled zerodimensional systems, so-called quantum dots (QDs).The active part of our sample consists of a GaAs-AlAs heterostructure with embedded InAs quantum dots in vertical direction. The GaAs electrodes consist of a 15 nm undoped spacer layer followed by a GaAs buffer with graded doping ( Fig. 1. Due to the remaining strain the QDs in the second layer are vertically aligned to the dots in the first layer [7]. The dots in the first layer are slightly smaller than the corresponding QDs in the second layer which leads to a higher ground state energy. The QDs are 10 to 15 nm in lateral dimension and about 3 to 4 nm high. Below the etched diode structure of 40 m 40 ¥ m about one million QDs are randomly placed. For similar samples with a single layer of QDs it has been shown that only a small fraction of the selfassembled QDs participates in the electronic transport [8].The transport measurements were carried out in a 4He bath cryostat allowing temperatures down to 1.4 K. By applying an external bias voltage SD V we drive a current through the device which was amplified by a low-noise current amplifier. The setup was tested by measuring the thermal noise of film resis-

Temperature-dependent broadening of coherent current peaks in InAs double quantum dots

“…1b. However, as visible in the transmission electron microscope image 19 , the quantum dots penetrate into the barriers, therefore reducing the effective barrier thickness, resulting in an asymmetric coupling to the leads. Similar devices show typical quantum-dot (QD) diameters of 10 nm ≲ d ≲ 20 nm with heights of 2 nm ≲ h ≲ 4 nm.…”

Spectral broadening and electron–photon coupling in III–V infrared detectors of low dimensional quantum confined system

“…Measurements of the shot noise of vertically coupled self-assembled InAs quantum dots (QDs) reveals a surprising enhancement with a distinct double-peak structure. By applying an external bias voltage, Barthold et al [7] observed pronounced peaks in the dc currentvoltage characteristics. At these peaks they found enhanced shot noise in contrast to suppressed shot noise at a single layer of QDs.…”

Current and shot noise measurements in a carbon nanotube-based spin diode (invited)

“…Shot noise measurements can provide an additional window into the dynamics of a system 20 . Noise measurements are useful for examining the correlation of tunneling events in a system, and have been studied for double-barrier tunnel junctions [21][22][23] . Here we extend upon previous results by considering the current noise of a CNT-based spin diode.A schematic of our device is given in Figure 1 (a).…”