A deep knowledge of the fundamental physics phenomena involved in Silicon Detectors is mandatory for their optimal use in dedicated applications. In the present manuscript, this concept is represented for the particular case of two types of Silicon Detectors: (1) the Silicon Photomultipliers (SiPM) and their applications in medical imaging and (2) the Planar Pixel Sensors (PPS) and their application for the upgrade of the ATLAS inner detector at high-luminosity LHC. My personal work on SiPM detectors started around 10 years ago. Therefore, the first part (A) of my HDR will firstly relate the physical principle of the Geiger-Mode Avalanche Photodiodes (GM-APD), representing the elementary cell of a SiPM detector. Then, the concept of the SiPM detector is introduced and its main physical characteristics are reviewed. The experimental set-ups developed for the measurement of these detectors as well as the SiPM characteristics from main producers are presented. Since the temperature dependence of SiPM parameters represents a particular drawback in different applications, my dedicated work on this subject is also presented showing that this dependence can become negligible if the operating conditions are well controlled. The SiPM detectors present important electrical, optical and mechanical advantages allowing for flexible design in applications where large detection area is required. Therefore, they are very "appetizing" devices for medical imaging applications and my work on using SiPM arrays in two medical applications is also presented: high resolution small animal PET scan and hand-held radiation detector for assisting the surgeon in locating and removing the solid tumors. In parallel with the SiPM activity, in the last years I was involved in the design and characterization of new PPS detectors for the upgrade of the ATLAS inner detector at high luminosity LHC. Therefore, the second part (B) of my HDR details the experimental methods like Secondary Ion Mass Spectrometry (SIMS) and Spreading Resistance Profiling (SRP) used for the doping profiles measurements of PPS detectors. The importance of these measurements for the fabrication process control and the calibration of the Technology-Computed Aided Design simulations (TCAD) are shown. Simulations results predicting the behavior of new planar pixel sensors with improved geometrical and radiation hardness characteristics for the upgrade of the ATLAS inner detector at high-luminosity LHC are also presented.
