Zeljko Pastuovic

Deterioration of Electrical and Spectroscopic Properties of a Detector Grade Silicon Photodiode Exposed to Short Range Proton, Lithium and Oxygen Ion Irradiation

The electrical properties and spectral response of a Hamamatsu S5821 silicon PIN photodiode were investigated in-situ during and after irradiation by 430 keV H⁺, 2.15 MeV Li²⁺, 4 MeV O³⁺ and 6.5 MeV O⁴⁺ ion beams focused to a sub-micrometer beam size. Ion species and their respective energies were selected to approximately have the same end range of 5 mum within the depletion region of the unbiased photodiode. Particle irradiation fluences (Phi) of 10⁸ to 10¹² cm^-2 were selected, such that displacement damage dose (D_d) values within the material had a similar range of 10¹⁰ to 10 ³ MeV/g for the selected particles. Under these conditions, it has been observed that protons produce the largest increase in device capacitance. At 100 V an increase in the generation current from 2.3 nA/cm² for a unirradiated sample to 1.7 muA/cm², 2.4 muA/cm², and 3 muA/cm² for samples irradiated by protons, lithium, and oxygen ions, respectively, was determined for a displacement damage dose of 3.9 times 10¹¹ MeV/g. The ion beam-induced charge (IBIC) technique was used to investigate the charge collection efficiency (CCE) of the irradiated photodiodes. The irradiation-induced changes of the CCE for both protons and oxygen were compared with respect to the non-ionizing energy loss (NIEL), which is a good measure of displacement damage introduced into a material by ionizing particles. The measured reduction of the pulse height with increasing displacement damage dose was fitted to a radiation damage function. The calculated equivalent damage factors, <i>K</i> _ed, for the proton probe on proton damaged silicon (3.6 plusmn0.4) times 10^-15 g/MeV, the proton probe on oxygen damaged silicon (3.90 plusmn0.07) times 10^-15 g/MeV , and the oxygen probe on oxygen damaged silicon (3.65 plusmn0.03) times 10^-14 g/MeV have been obtained.

Time-resolved ion beam-induced charge collection measurement of minority carrier lifetime in semiconductor power devices by using Gunn's theorem

Abstract Ion microbeam techniques like ion beam-induced charge collection (IBICC) are very powerful methods in order to investigate and to map the transport properties in different technologically important semiconductors and in particular in materials proposed for nuclear detection. Time-resolved ion beam-induced charge collection (TRIBICC) represents a further improvement with respect to more traditional IBICC, since it can supply not only the charge collection efficiency (and through it data on mobility and trapping time of carriers in drift regions) but also the time behaviours of the charge collection. For long collection times, this means to gather information, also about diffusion lengths and lifetimes of carriers in the diffusion regions, which are always present in undepleted electronic devices, in particular power devices, and which are of paramount importance as inputs for simulation codes. By TRIBICC, in fact, some difficulties could be avoided in analysis of data collected in cases when lifetimes and shaping times of electronic chain are similar, and the sensitivity of the method is worse. In order to suitably analyse TRIBICC data, a theoretical model should be available: in general, Ramos theorem is used, but its validity in cases when space charge is present is questionable. A more general and powerful method is presented in this work by using Gunns theorem and a particular formulation of the generation function in order to solve the adjoint of the continuity equation in the time-dependent case. An application of this method to a commercial power device is presented and discussed.

Accelerator-Based Nuclear Techniques for Processing and Characterization of Oxide Semiconductors for Solar Energy Conversion

Accelerator-based nuclear techniques are an important tool for the modification and characterization of surfaces in general, down to a depth of around one micrometer. For oxide semiconductors used in solar energy conversion, the surface plays a critical role in facilitating the use of solar photon energy to obtain hydrogen via spontaneous water oxidation. For such a process, the required surface properties are complex and include specific chemical composition, as well as the defect composition, and both of these characteristics may be augmented using accelerator-based nuclear techniques. The targeted modification of surfaces makes use of ion implantation for changing the chemical composition, and ion irradiation for changing the defect structure. The defect formation is a very complex process, and in this work we placed more emphasis on this aspect. We attempted to present the defect formation under the irradiation of ion beams at the two extremes: formation of extensive and large-scale cluster defects; and formation of small-scale point defects. In addition, we review the main characterization techniques based on ion beams, with examples from work carried out on semiconductors and oxide semiconductors.

Modification of the electrical and optical properties of single crystal diamond with focused MeV ion beams

In this paper an overview is given on recent results obtained in the framework of an Italian/Croatian collaboration aimed to explore the potential of techniques based on focused MeV ion beams to locally modify the structural, electrical and optical features of diamond. Experiments were carried out using light (H, He, C) ion beams with energies of the order of MeV, focused to micrometer-size spot and raster scanned onto the surface of monocrystalline (IIa or Ib) diamond samples. Different energies, ion species and fluences were used, in conjunction with variable thickness masks and post annealing processes, to define three-dimensional structures in diamond, whose electrical/optical/structural properties have been suitably characterized. Finite element numerical methods have been employed in the modeling of the material modification and in device design.