Shell Thickness-Dependent Tunable Threshold Voltage Single Quantum Dot Rectification Diode

Abstract

Ambient atmosphere single colloidal quantum dot (QD) rectifying diode with tunable threshold voltage has been fabricated by using a type-II heterojunction core/shell structure with a device geometry ITO/ZnO/QDs. Specifically, in our work we have used ZnTe/CdS core/shell QDs in which hole wave function strongly confined to the core, whereas the lowest-lying conduction band state resides in the shell. Current-voltage (I-V) characterization of this device has been done using an ambient atmosphere scanning tunneling microscope. The scanning tunneling spectra (STS) shows high rectification with a ratio of 103. The rectification is found to arise because of the bias-dependent band alignment of ZnO/QDs heterojunction and the effect of shell of each QD that presents a barrier for hole tunneling into the substrate. This barrier is overcome by the externally applied bias. This mechanism is distinct from the rectification observed in conventional p-n junction diodes. In particular, we find that even for QDs with optical band gaps of ∼1 eV, the threshold voltage may be tuned from 1 to 3 V by regulating shell thickness. © 2018 American Chemical Society.