Emission Channeling Lattice Location Studies in Semiconductors using Highly Pixellated Timepix Detectors

The implantation of dopant impurities in semiconductor crystals and the understanding of their lattice site location behaviour in the manufacturing process is essential for the control of their electrical, magnetic and optical properties. The development and improvement of the detection systems used in lattice location experimental techniques with charged particles, specifically Rutherford Backscattering Spectrometry with Channeling (RBS/C) and Emission Channeling (EC), has been seen as a fundamental step in the enhancement of the quantitative capacities of these techniques. In this thesis, a highly pixelated timepix-quad detector developed by the Medipix collaboration based at CERN was studied with the aim of testing its performances, envisaging a replacement detector for the previously used pad detector. The new detector was mounted in a custom-built vacuum chamber and annexed to the existing EC experimental setup. The timepix detector causes a large increase in details of measured channeling patterns due to its array of 512 × 512 pixels with 55 × 55 μm² area each, much finer than the one of the pad detector composed of 22 × 22 pixels with 1.3 × 1.3 mm² area. The impact of the new detector on the lattice location results was studied regarding the reduction of the statistical uncertainties and the dispersion of results between axes measured, together with the practical aspects of its use. This purpose required the development of a new fitting software, PyFDD, that can use a chi-square or a maximum likelihood parameter optimization and has proven essential for fitting patterns with a low number of counts per pixel, and for accurately calculating the resulting uncertainties. Additionally, the background of beta and gamma radiation was also investigated as a source of uncertainty. The new analysis software allowed the comparison of the new timepix with the pad detector in the measurement of the isotopes 43K, 24Na, and 27Mg implanted into gallium nitride, GaN. These tests have shown that the results from both detectors agree in the obtained relative lattice site fraction. However, some differences were observed in the absolute fractions which are mostly thought to be caused by the lack of accuracy of the gamma background on EC measurements.