Transient photocurrent spectroscopy: Electrical detection of optical absorption for supported semiconductor nanocrystals in a simple device geometry

The optical absorption of supported cadmium sulfide nanocrystals is directly detected as an electrical signal using a method described in this letter. Cadmium sulfide nanocrystals were epitaxially deposited onto highly oriented, pyrolitic graphite surfaces using a hybrid electrochemical/chemical synthesis method. The resulting submonolayer of cadmium sulfide nanocrystals was then covered with a thin (10–100 nm) insulating Formvar layer and a semitransparent gold top electrode. We exposed this structure to monochromatic chopped light and detected the transient photocurrent phase-sensitively and without applied bias. In the resulting device spectra, the absorption edge of the cadmium sulfide nanocrystals was clearly discernible at room temperature. The device response spectrum is compared with photoluminescence spectra acquired for the quantum dots in these devices at 20 K.