Study of the formation of defects in optoelectronic diodes by the low-frequency noise method under illumination and at low temperature.

Abstract:
The applications of diodes using the photoelectric effect are numerous, ranging from photovoltaic technologies to photodetectors in different frequency bands. All these applications have in common that each electron-hole pair generated by a photon must not be recombined before collection, at the risk of decreasing their performance (efficiency, responsivity, etc.). It is therefore essential for these components to reduce the presence of defects that behave like recombining centers and to avoid their formation over time.
The formation of these defects is currently poorly understood, in particular due to the absence of a quantitative electrical characterization method allowing an accurate extraction of the densities of recombination centers. This absence also prevents an improvement of the technological processes limiting their presence from their manufacture.
The low frequency noise measurement method is perfectly adapted to this problem, because the fluctuations of current reflect the microscopic activity of defects in semiconductors. This method is well developed for the characterization of MOSFETs, but is not sufficiently exploited for diodes. Initial work carried out at the CROMA laboratory has demonstrated its strong potential for photovoltaic components, without achieving the objective of developing a quantitative method for extracting the of defects’ density in these devices.
One way to achieve this goal, partially explored in the literature, is the optical excitation of defects. The results obtained seem to show that it is possible, by using different wavelengths, to stimulate specific traps. Another approach, whose implementation is complex, is to measure the noise at low frequency in temperature, in order to extract the activation energies of the defects and their densities, like the Deep Level Transient Spectroscopy technique.
This thesis aims to develop a new quantitative technique that has not yet been used. It consists in coupling the low frequency noise measurement method under illumination with low temperature measurements. The optical stimulation of defects, modulated by the characteristic time variations at low temperature, will allow access to information on the defects currently inaccessible, and thus, in fine, to better understand the processes of defect formation in these components.