30 Septembre – Thesis defense - Oriane Baussens
10 h Room Chrome - MINATEC (Grenoble)
New perovskite material for medical radiography.
Using semiconductor materials instead of the scintillators currently used in medical radiography would allow increasing both the X-ray sensitivity and the spatial resolution of imagers. However, to date, no semiconductor material is compatible with the specifications of large area (40cm×40cm) medical radiography.
Halide perovskites are a class of semiconductors exhibiting remarkable optoelectronic and photovoltaic properties. The objective of this work is to assess the viability of halide perovskites for medical radiography. Cr/MAPbBr3/Cr type devices are used as a study model to meet this objective.
The first part of the study focuses on the measurement of the interest parameters for X-ray detection. Three observations can be drawn from this study. Firstly, the sensitivity under X-ray irradiation measured is twice that of the scintillators usually used but does not reach its theoretical maximum value. Secondly, the dark current is at least two orders of magnitude too high. Thirdly, the noise limits the counting performances of the devices.
The second part of the study focuses on understanding the physical origin of the limits observed on the detection parameters. Four conclusions can be made from this study. First, the growth conditions and crystals’ quality cannot be correlated to the detection performances. Second, the sensitivity depends on both the electrons’ and holes’ transport properties and the electric field distribution within the devices. Third, the dynamics of the dark current are linked to the ionic migrations in the devices. Fourth, the noise measured on the devices for the frequencies of interest of gamma spectroscopy (10kHz-20MHz) reveal that, below 200kHz, the 1/f noise of the devices dominates.