Cobalt-doped zinc sulfide quantum dot thin films for next-generation electronic devices: Synthesis, characterization, and switching properties

Abstract

In this communication we comprehensively study the synthesis and characterization of Cobalt-doped ZnS quantum dots with controlled size and composition as a possible candidate for Resistive random access memory (RRAM). The pristine ZnS QDs and ZnS QDs with 10 % and 15 % cobalt doped are synthesized using sol- gel process. The basic characterization XRD and TEM confirms the formation of the material, and their particle size is found to be between 4.14 nm to 5.93 nm. The band gap of the particles is found out using UV–Visible Spectroscopy. Further, Polyvinyl alcohol (PVA) polymer composite solutions are prepared using synthesized QDs. Further, their thin films are deposited through spin coating technique and their corresponding devices ITO/PVA/Ag, ITO/Co (10 %)-ZnS QDs: PVA/Ag and ITO/Co (15 %)-ZnS QDs: PVA/Ag are fabricated. The current–voltage (I-V) measurements revealed the existence of resistive switching in all devices. Regardless of the direction of the voltage sweep, the device will exhibit write-once-read-many (WORM) memory behavior as a result of the incorporation of Co-ZnS QDs into the PVA matrix. A noticeable and enhanced resistive switching behavior in the devices was the outcome of the increased cobalt doping. The ITO/Co (15 %)-ZnS QDs: PVA/Ag device displayed an ON/OFF ratio of one order with a good data retention of 2000 s and endurance of about 2000 cycles. Ultimately, the I-V fitting demonstrates that the WORM memory in the devices is caused by the space charge area that forms at the interface between the electrode and the active material.