Joy, A; (2017) Simulations of the physics and electronics in 2D semiconductor pixel detectors. Doctoral thesis , UCL (University College London).

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Abstract

In this thesis, simulations have been developed of entire 2D Semiconductor pixel detectors, including the physics and electronic responses. The most important concept of this is the separation of simulation into three distinct physical regimes, which should each be simulated in a different manner. The first stage is a particle level simulation of X-Ray photons and their secondary particles interacting with the detector, and recording where interactions depositing energy in the sensitive layer occur. This uses Geant4, as the energy range in use lies just within Geant4’s minimum energy bound. The second stage is a charge cloud simulation of the interaction energy conversion to electron hole pairs, and then the movement of these electrons or holes in the sensitive layer towards the collection area or pixels. This uses an analytic solution to the problem of a charge cloud moving and interacting with itself within a semiconductor, this work is based upon the earlier HORUS simulation and more detailed lattice simulations by R. F. Fowler, et al. The third stage is an electronics level simulation of how the collected charge is manipulated by the detector into a digital read out signal. This is done with a collection of functions representing the response of electronic components to a signal, that can be used in turn to represent the electronic response to an electrical signal. Work was also conducted to develop a model of simulating the charge plasma effects expected to be seen in European XFEL detectors at high charge densities, however a lack of suitable data to test or tune the model renders this a theoretical exercise. Simulations using the software have been compared to data taken with real detectors to test the accuracy of the simulation, with a focus on the charge cloud simulation. The software has been written to be adaptable so that it can simulate all three main detectors at European XFEL, this adaptability then means that it can in principle be used for any other pixel detector.

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