Analysis of uniformity of as prepared and irradiated SI GaAs radiation detectors

Abstract

SI (semi-insulating) LEC (Liquid Encapsulated Czochralsky) GaAs (gallium arsenide) Schottky barrier detectors have been irradiated with high energy protons (24 GeV/c, fluence up to 1 6 . 4 5~1 0 '~ p/cm2). The detectors have been characterised in terms of I/V curves, charge collection efficiency (cce) for incident 5.48 MeV a-, 2 MeV proton and minimum ionizing P-particles and of cce maps by microprobe technique IBIC (Ion Beam Induced Charge).At the highest fluence a significant degradation of the electron and hole collection efficiencies and a remarkable improvement of the FWHM energy resolution have been measured with aand proton particles. Furthermore the reduction in the cce is greater than the one measured with pparticles and the energy resolution worsens with increasing the applied bias, V,, above the voltage Va necessary to extend the electric field all the way to the ohmic contact. On the contrary, in the unirradiated detectors the charge collection efficiencies with a-, pand proton particles are quite similar and the energy resolution improves with increasing V, > Vd.IBIC spectra and IBIC space maps obtained by scanning a focused (8 pm' ) 2 MeV proton microbeam on front (Schottky) and back (ohmic) contacts, support the observed electric field dependence of the energy resolution both in unirradiated and most irradiated detectors.The results obtained let us explain the effect of the electric field strength and the plasma on the collection of the charge carriers and the FWHM energy resolution.

Silicon carbide and its use as a radiation detector material

“…It is well known that some damage to the crystalline lattice (defects) induced by the radiation can act as trapping centres for the charge carriers leading to incomplete charge collection and to a worse energy resolution. Moreover the damage tends to be relatively minor for highly ionizing radiation (beta particles or x-and gamma rays) but can become quite significant with neutrons and heavy charged particles [5][6][7][8][9][10]. Primary defects generated by high-energy particle bombardment are vacancies (V), interstitials (I), Frenkel pairs (V + I) and antisites [6].…”

“…The range of these alpha particles extends less than 17 µm in SiC, so that if a totally depleted 40 µm detector is irradiated, the Bragg ionization distribution indicates that the induced charge will be due to both the charge carriers (holes and electrons). Unfortunately the presence of a thick (300 µm) substrate (figure 5) does not allow the distinction of the contributions to the total charge signal of each charge carrier (as was possible to do, for example, by irradiating the back (ohmic) contact of GaAs semi-insulating detectors [10]).…”