Tuning resonant transmission through geometrical configurations of impurity clusters

Abstract

Resonant tunneling features through impurity clusters embedded in an insulating matrix have been examined through the inter-play between the size of the clusters and the inter-cluster distance. Constructive interference phenomena were tuned through a systematic study of different geometrical configurations, thereby controlling confinement in quasi-bound states. Gaussian trap potentials have been used to simulate the imperfect barrier-well interface associated with disordered materials. Strongly localized states can be formed successfully despite weak disorder as illustrated by breaking the symmetry in the horizontal configuration. To this end, triangular cluster configurations were investigated under a variety of conditions including various shapes and orientations. The effects of disorder created effectively by the arbitary configurations destroy the Fano resonance, which is previlent in conductance spectra and consequently reduce the peak to valley ratio of the resonant peak in current vs. voltage curves. However the formation of two quasi-bound states is demonstrated, suggesting possible applications for disordered naturally grown systems of impurity clusters. This work addresses the controlled lifetime of quasi-bound states and can inform the design of fast switching devices based on high band gap materials by the astute incorporation of impurity clusters with specific geometrical configurations.

Understanding resonant tunnel transport in non-identical and non-aligned clusters as applied to disordered carbon systems

“…15, however currently extend their original work on two impurity channels to 'N' impurities. 23 According to the model, the Hamiltonian at the tunnel junction (nano-electrodes) is expressed by…”

“…In our previous work on equilateral triangles, we showed only one broad DOS peak appearing from three weakly coupled clusters. 23 By decomposing this peak, we saw an increase of FWHM with the decrease of coupling (C) or scaling parameters described as the ratio of the inter-cluster distance (X 1,2 in nm) and the diameter of the clusters (D in nm) [see Fig. 1(a), inset].…”

“…In symmetric triangular configurations, FWHM of both peaks was found to increase with X/D or coupling strength, i.e., with D as expected. 23 For vertical and horizontal configurations, the FWHM of antibonding peak increases with D, i.e., inter-cluster coupling which means the disorder increases and the lifetime of electron decreases with the band energy gap [Figs. 4(b) and 4(c)]; whereas the bonding peak behaves in opposite manner since it signifies the decrease of disorder with band gap.…”

“…20 In our previous report, we found that for a triangular structure formed by three QDs of similar size and inter-cluster distance, negative differential resistance (NDR) was very difficult to observe. 23 Here, we show that the NDR signature of current steps and NDR can be produced by using unequal distances between the QDs of different sizes and artificially controlling the coupling between the dots, which can explain the switching behavior in carbon structures observed experimentally. 13 Both intensity and the width of the peaks can be varied over a wide energy range in a systematic manner by controlling the size of the clusters as well as their separation for triangular configuration in Subsection III A; for vertical and horizontal configurations in Subsection III B; and for aligned configurations in Subsection III C which can be imagined as a combination of horizontal and vertical configurations.…”

“…[18][19][20] Earlier, the quantum conductance features for two-impurity centres were described as a combination of two states; one a long lifetime (narrow peak) and the other of a short lifetime (broad peak), 17,18 which has been extended in various fields of application, recently in spintronics and high frequency devices 21 and to understand the electronic properties of graphene QDs. 22 This energy difference between two unequal clusters can be manipulated by a third cluster, which was studied extensively for three dots of finite and equal size in a symmetric configuration and also by breaking the symmetry of the configurations, 23 however further study is needed to improve understanding of quantum transport. In reality, incorporation of impurities in semiconductors can introduce a finite distribution of clusters in size and distance depending on the diffusion of the dopants at different energies.…”