Spectacular oscillations in the dark and photocurrent in thiol-capped CdS quantum dots embedded in PMMA matrix

Abstract

In this work, experimental results of low-frequency, time-dependent current oscillations (under both dark and photoexcitation) in the sample cells of thiol-capped CdS quantum dots (QDs) embedded in poly(methyl methacrylate) (PMMA) matrix have been presented. Dark and photocurrent oscillatory behaviours have been studied under diverse conditions, such as sample cell temperature, applied bias voltage across the electrodes and concentration of thiol-capped CdS QDs. Oscillation amplitude gradually increases with applied bias voltage at a particular temperature and also with increasing sample cell temperature. The period of oscillation (i.e., frequency) can be tuned over a wide range either by changing the sample temperature, applied bias voltage, or varying concentration of thiol-capped CdS QDs. Existing theories of current oscillations in semiconductors have failed to explain the observed low-frequency current oscillations in these semiconductors. Such current oscillations are possibly associated with the formation of some kind of charge density waves in the PMMA films embedded with thiol-capped CdS QDs.