Search

One-dimensional modeling and simulations of the electric and weighting fields have been systematically carried out for 2D-Planar-Electrode and 3D type detectors. Poisson and Laplace equations have been solved analytically in Cartesian and cylindrical coordinates with well defined boundary conditions. It has been found that the electric field profile and full depletion voltage depend in general on the detector effective doping density (N e f f) and electrode spacing (λ C), while the weighting field depends only on the electrode spacing and relative geometry size of the collecting electrode with respect to the electrode spacing. For 2D-Planar-Electrode strip and pixel detectors, the full depletion voltage will be somewhat higher than that of 2D pad detectors, and the weighting field will be more concentrated near the collecting electrode due to the "small pixel" effect. For 3D-Trench-Electrode (cylindrical type) detectors, however, exact one-dimensional solutions have been obtained for electric and weighting fields. The results are compared to those obtained for 2D-Planar-Electrode pad detectors and conventional 3D-Column-Electrode detectors. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study is the evaluation of radiation effects in detectors based on p-type magnetic czochralski (MCz) Si that was converted to n-type by thermal donor (TD) introduction. As-processed p+-p-n+ detectors were annealed at 430°C resulting in p+-n(TD)-n+ structures. The space charge sign and the electric field distribution E(x) in MCz Si p+-n(TD)-n+ detectors irradiated by 24GeV/c protons were analyzed using the data on the current pulse response and the Double Peak (DP) electric field distribution model for heavily irradiated detectors. The approach considers an irradiated detector as a structure with three regions in which the electric field depends on the coordinate, and the induced current pulse response arises from the drift process of free carriers in the detector with variable electric field. Reconstruction of the E(x) profile from the pulse response shapes is performed employing a new method for DP electric field reconstruction. This method includes: (a) a direct extraction of charge loss due to trapping and (b) the fitting of a simulated pulse response to the “corrected” pulse by adjusting the electric field profiles in the three regions. Reconstruction of E(x) distribution showed that in the diodes irradiated by a proton fluence of (2–4)×1014 p/cm2 space charge sign inversion has occurred. This is the evidence that the influence of 24GeV/c proton radiation on MCz Si p+-n(TD)-n+ detectors is similar to that on p+-n-n+ detectors based on FZ or diffusion oxygenated n-type Si. [Copyright &y& Elsevier]

Abstract: Positive space charge build-up was observed in proton—and neutron—irradiated high-resistivity magnetic Czochralski (MCZ) n-type Si detectors after gamma radiation. Space charge sign re-inversion (SCSRI) from negative to positive was achieved at the high dose of 454Mrad in a low-fluence proton irradiated MCZ Si detector. No SCSRI has been observed yet for low-fluence neutron-irradiated MCZ Si detectors at the highest dose in this study (662Mrad), but positive space charge is building up, and SCSRI is expected at higher doses. Up to the highest dose in this study, the double junction or double peak electric field distribution is still preserved even after SCSRI. No SCSRI was observed in control FZ Si detectors. Space charge sign inversion was also observed in high-resistivity as-processed MCZ p-type Si detectors after gamma radiation. [Copyright &y& Elsevier]

Abstract: Non-uniform distribution of the electric field outlined as double peak distortion (DPD) is considered for heavily irradiated silicon strip detectors, which were developed for the CERN-ATLAS semiconductor tracker. DPD originates from the non-uniform accumulation of electrons and holes from the bulk generated current that are captured by radiation induced defects: deep acceptors and donors with mid-gap energy levels. This corresponds to the formation of the low electric field region in the detector central part that consequently will delay charge collection. The electric field distributions at different reverse biases, fluences and detector operational temperatures are calculated using a one-dimensional Poisson equation as it was done earlier for pad detectors. It has been shown that due to the electric field focusing at the strips the DPD effect is more pronounced for strip detectors as compared to that in pad detectors. The double peak electric field distribution is evinced experimentally in current pulse response shape when the charge is collected along the strip axis. [Copyright &y& Elsevier]

This study focuses on the properties of the B i O i (interstitial Boron–interstitial Oxygen) and C i O i (interstitial Carbon–interstitial Oxygen) defect complexes by 5.5 MeV electrons in low resistivity silicon. Two different types of diodes manufactured on p-type epitaxial and Czochralski silicon with a resistivity of about 10 Ω ⋅ cm were irradiated with fluence values between 1 × 1015 cm-2 and 6 × 1015 cm-2. Such diodes cannot be fully depleted and thus the accurate evaluation of defect concentrations and properties (activation energy, capture cross-section, concentration) from Thermally Stimulated Currents (TSC) experiments alone is not possible. In this study we demonstrate that by performing Thermally Stimulated Capacitance (TS-Cap) experiments in similar conditions to TSC measurements and developing theoretical models for simulating both types of B i O i signals generated in TSC and TS-Cap measurements, accurate evaluations can be performed. The changes of the position-dependent electric field, the effective space charge density N eff profile as well as the occupation of the B i O i defect during the electric field dependent electron emission, are simulated as a function of temperature. The macroscopic properties (leakage current and N eff) extracted from current–voltage and capacitance–voltage measurements at 20 °C are also presented and discussed. [ABSTRACT FROM AUTHOR]

Abstract: The reverse current of irradiated Si detectors was analyzed in terms of carrier generation via defects with the energy levels in the Si bandgap. The data for detectors irradiated by 23GeV protons and 1MeV neutrons were obtained in the temperature (T) range of 200–300K. Two models of the bulk generation current were developed to allow fitting and simulation of the reverse current vs. T data. These are a model of carrier generation via a single effective energy level for the direct estimation of detector performance, and a model of two generation centers with the effective energy levels originating from radiation-induced deep levels adjacent to the midgap. The influence of the bandgap temperature dependence (E g (T)) on the parameters of the current generation centers was estimated. The first model gives the effective level energy of E v +0.65eV and a linear dependence of the effective defect concentration on fluence. The second model involves contribution from deep donors and deep acceptors positioned at E v +0.48eV and E c −0.52eV, respectively, and is adapted for simultaneous calculation of the reverse current and the electric field distribution in irradiated detectors. The results of the study show that: (a) both models fit well to the experimental data; (b) contribution of the E g (T) dependence to E t does not exceed 5%; (c) taking into consideration the bulk generation current gives the correct electric field distribution, which is a key reference for other characteristics of irradiated Si detectors; and (d) the generation lifetime is significantly larger than the carrier trapping time constant pointing to additional levels taking part in trapping of the drifting charge. [Copyright &y& Elsevier]

Abstract: The model explaining an enhanced collected charge in detectors irradiated to 1015–1016 neq/cm2 is developed. This effect was first revealed in heavily irradiated n-on-p detectors operated at high bias voltage ranging from 900 to 1700V. The model is based on the fundamental effect of carrier avalanche multiplication in the space charge region and in our case is extended with a consideration of p–n junctions with a high concentration of the deep levels. It is shown that the efficient trapping of free carriers from the bulk generation current to the deep levels of radiation induced defects leads to the stabilization of the irradiated detector operation in avalanche multiplication mode due to the reduction of the electric field at the junction. The charge collection efficiency and the detector reverse current dependences on the applied bias have been numerically simulated in this study and they well correlate to the recent experimental results of CERN RD50 collaboration. The developed model of enhanced collected charge predicts a controllable operation of heavily irradiated detectors that is promising for the detector application in the upcoming experiments in a high luminosity collider. [Copyright &y& Elsevier]

Abstract: A heavily irradiated (3×1015 1MeVneq/cm2) Current Injected Detector (CID) was tested with 225GeV muon beam at CERN H2 beam line. In the CID concept the current is limited by the space charge. The injected carriers will be trapped by the deep levels and this induces a stable electric field through the entire bulk regardless of the irradiation fluence the detector has been exposed to. The steady-state density of the trapped charge is defined by the balance between the trapping and the emission rates of charge carriers (detrapping). Thus, the amount of charge injection needed for the electric field stabilization depends on the temperature. AC-coupled 16cm2 detector was processed on high resistivity n-type magnetic Czochralski silicon, and it had 768 strips, 50μm pitch, 10μm strip width and 3.9cm strip length. The beam test was carried out using a silicon beam telescope that is based on the CMS detector readout prototype components, APV25 readout chips, and eight strip sensors made by Hamamatsu having 60μm pitch and intermediate strips. The tested CID detector was bonded to the APV25 readout, and it was operated at temperatures ranging from −40 to −53°C. The CID detector irradiated at 3×1015 1MeVneq/cm2 fluence shows about 40% relative Charge Collection Efficiency with respect to the non-irradiated reference plane sensors. [Copyright &y& Elsevier]

Abstract: Experimental results and simulations of Charge Collection Efficiency (CCE) of Current Injected Detectors (CIDs) are focused. CID is a concept where the current is limited by the space charge. The injected carriers will be trapped by the deep levels. This induces a stable electric field through the entire bulk regardless of the irradiation fluence the detector has been exposed. Our results show that the CCE of CIDs is about two times higher than of regular detectors when irradiated up to 1×1016 cm−2. The higher CCE is achieved already at −50°C temperatures. [Copyright &y& Elsevier]