arXiv subjects
Publications and source records attributed to C. Da'Via.
The motivation for investigating the use of GaAs as a material for detecting particles in experiments for High Energy Physics (HEP) arose from its perceived resistance to radiation damage. This is a vital requirement for detector materials that are to be used in experiments at future accelerators where the radiation environments would exclude all but the most radiation resistant of detector types.
The present understanding of the charge collection in GaAs detectors with respect to the materials used and its processing are discussed. The radiation induced degradation of the charge collection efficiency and the leakage current of the detectors are summarised. The status of strip and pixel detectors for the ATLAS experiment are reported along with the latest results from GaAs X-ray detectors for non-high energy physics applications.
Semi-insulating, undoped, Liquid Encapsulated Czochralski (SI-U LEC) GaAs detectors have been irradiated with 1MeV neutrons, 24GeV/c protons, and 300MeV/c pions. The maximum fluences used were 6, 3, and 1.8~10$^{14}$ particles/cm$^{2}$ respectively. For all three types of irradiation the charge collection efficiencies (cce) of the detector are reduced due to the reduction in the electron and hole mean free paths. Pion and proton irradiations produce a greater reduction in cce than neutron irradiation with the pions having the greatest effect. The effect of annealing the detectors at room temperature, at 200$^{o}$C and at 450$^{o}$C with a flash lamp have been shown to reduce the leakage current and increase the cce of the irradiated detectors. The flash-lamp anneal produced the greatest increase in the cce from 26% to 70% by increasing the mean free path of the electrons. Two indium-doped samples were irradiated with 24GeV/c protons and demonstrated no improvement over SI U GaAs with respect to post-irradiation cce.
GaAs Schottky diode detectors have been fabricated upon Low Pressure Vapour Phase Epitaxial GaAs. The devices were characterised before and after a $1.25 \times 10^{14}$~cm$^{-2}$ 24GeV/c proton fluence. The as fabricated Ti-GaAs barrier height was measured, via two electrical methods, to be $0.81\pm0.005$ and $0.85\pm0.01$~eV and a space charge density of $2.8 \pm 0.2 \times 10^{14}$~cm$^{-3}$ was determined. The current was greater than that expected for an ideal barrier with the excess attributed to generation current from the bulk. The charge collection efficiency, determined from front alpha illumination and 60 keV gamma irradiation, was inexcess of 95% at 50V reverse bias. After irradiation the reverse current, measured for a bias of 200V at 20$^{o}$~C, increased from 90~nA to 1500~nA due to radiation induced generation centres. Deep levels were showed to be present using capacitance techniques. The charge collection of the device determined from front alpha illumination fell to $32\pm5$% at a reverse bias of 200V.