Photocurrent is generated using optical energy in the form of a monochromatic light beam. The concept of photoconductivity can be described by dividing the process in three major parts: the optical absorption of light creating the free charge carriers; the electrical transport of these carriers that contribute to the overall current; the capture of the photo-generated excess carriers, leading to trapping or recombination. All photocurrent-based techniques have in common that they are highly sensitive spectroscopic techniques that allow the detection of small concentrations of dopants, defects or charge-transfer complexes in a material. The “quasi-steady-state photocurrent technique” (PC), which can be considered the basic type of photocurrent technique, measures the photo-excited current in function of the incident photon energy, allowing the investigation of the electronic structure of for example dopant atoms. At IMO-IMOMEC multiple dedicated set-ups are available, including PC, constant photocurrent method (CPM), and Fourier-transform photocurrent spectroscopy (FTPS). The use of different excitation sources enables the investigation of organic and inorganic materials in an energy range spanning IR, visible and UV light, while cryostats provide means to control the surrounding temperature between 77 and 500 K.
This techniques is based on a double beam UV-Vis spectrometer that is employed for the characterisation of thin films, usually supported by a transparent substrate material. By measuring the transmittance and reflectance spectra the film's thickness, index of refraction and absorption coefficient are estimated.