Transport gap vis-a-vis electrical bistability of alloyed Zn_xCd_1-xS (x = 0 to 1) quantum dots

Abstract

We study a correlation between electrical bistability and transport gap of II-VI semiconducting quantum dots. We first grow alloyed Zn_xCd_1-xS (x = 0 to 1) quantum dots for different values of x, functionalize them with suitable (anionic) stabilizers, and form their monolayer on an electrode surface via electrostatic assembly. We characterize the monolayers of the quantum dots by scanning tunneling microscopy. Current-voltage characteristics of the monolayers evidence electrical bistability and memory phenomena that depend on composition or Zn-content of the quantum dots. The dependence is due to the fact that an addition of Zn in Zn_xCd_1-xS introduces trap-states, which assist the process of electrical bistability and play a major role in the conduction process of high-conducting states of quantum dots. Transport gap, which depends on the composition of the quantum dots, also responds to the electrical bistability; for all the quantum dots, the gap decreases during the transition from a low- to a high-conducting state. We here correlate the transport gap of Zn_xCd_1-x (x = 0 to 1) and its change upon conductance-switching with the electrical bistability of quantum dots.