Wide Band Gap Compound Semiconductor Detectors for X-ray Spectroscopy in Harsh Environments
thesisposted on 27.04.2012, 12:19 by Anna Megan Barnett
Novel photon counting Al0.8Ga0.2As, GaAs and SiC X-ray photodiodes were investigated through experiments and Monte Carlo computer simulations for their suitability as spectroscopic soft (≤ 25 keV) X-ray detectors in high temperature (up to 90 °C) environments. Photon counting Al0.8Ga0.2As and GaAs non-avalanche p+-i-n+ mesa X-ray photodiodes were shown to operate at temperatures as high as 90 °C. The temperature dependences of their spectral resolutions (FWHM at 5.9 keV) are reported. Analyses of the noise sources contributing to the devices’ measured performances are presented which suggest that efforts to improve the spectral resolutions would be well targeted at reducing the noise contributions from the packaging of the detectors. For the GaAs diodes, the X-ray characterisation of the devices was extended to higher energies (25 keV). Internal detector X-ray fluorescence was demonstrated and Monte Carlo computer simulations were compared with the experimental results. Prior to the research presented in this thesis, the only Al0.8Ga0.2As photon counting X-ray avalanche photodiodes reported in the literature (Lees et al., 2008, Nucl. Instr. and Meth. A, Vol. 594, pp. 202-205) had shown anomalies in the obtained spectra. Through new experimental measurements and computer simulations, the anomaly is explained. A new method was developed which uses the phenomenon to extract measurements of the electron and hole ionisation coefficients of Al0.8Ga0.2As at a typical operating field and the first report of their temperature dependence is made. Measurements characterising the X-ray spectroscopic performance of Semi-Transparent SiC Schottky Diodes over an energy range ~6 keV to 25 keV at temperatures up to 80 °C are presented and discussed, along with relative efficiency measurements and data showing the temperature dependence of the leakage current in such devices. The research presented in this thesis shows that Al0.8Ga0.2As, GaAs and SiC X-ray detectors are promising devices for high temperature soft X-ray spectroscopy.