Electron Spin Resonance (ESR) is an established method for the investigation of the paramagnetic states in semiconductors.
In amorphous and microcrystalline silicon applied in thin film solar cells the electronic states created by the structural defects are of particular interest. The research with ESR is focused on:
- The identification of the nature, location and microscopic environment of a defect, its energy position in the density of states and number of such states per unit volume;
- The influence of these defects as trapping and recombination centers on the electronic and optical properties of the material.
In ESR experiments the interaction of external magnetic field with the magnetic moment of electrons is utilized. The interaction leads to the splitting of the electronic energy states known in optics as a Zeeman Effect. Interaction of the electronic magnetic moment with internal magnetic fields e.g. induced by nuclei with magnetic moment might lead to further effects such as a hyperfine splitting of an electronic energy state.
The electronic transitions between these states are detected by measuring the absorption of electro-magnetic radiation in the microwave range (e.g. 9-10 GHz, the so-called X-Band)
- Two ESR spectrometers are currently available at IEF-5 Photovoltaik:
- An X-Band spectrometer for cw- (continuous wave) and pulse-ESR operation (Bruker ELEXSYS E500). The maximum magnetic field is limited to 1 Tesla. The range of temperatures available for measurements is 4.2 K – 300 K. In cw-mode the temperature range can be extended above 300K with use of a high temperature resonator. For the optical excitation used to detect light-induced ESR (LESR) or for the optically detected magnetic resonance (ODMR) the complete range of laser facilities of the Photoluminescence lab is available by means of an optical fiber cable.
An X-Band spectrometer for cw- operation (Bruker ESP300E).