4H-SiC Schottky diode radiation hardness assessment by IBIC microscopy

We report findings on the Ion Beam Induced Charge (IBIC) characterization of a 4H-SiC Schottky barrier diode (SBD), in terms of the modification of the Charge Collection Efficiency (CCE) distribution induced by 20 MeV C ions irradiations with fluences ranging from 20 to 200 ions/um2. The lateral IBIC microscopy with 4 MeV protons over the SBD cross section, carried out on the pristine diode evidenced the widening of the depletion layer extension as function of the applied bias and allowed the measurement of the minority carrier diffusion lengths. After the irradiation with C ions, lateral IBIC showed a significant modification of the CCE distribution, with a progressive shrinkage of the depletion layer as the fluence of the damaging C ions increases. A simple electrostatic model ruled out that the shrinkage is due to the implanted charge and ascribed the perturbation of the electrostatic landscape to radiation-induced defects with positive charge state

Modification of the electrical and optical Properties of Single Crystal Diamond with Focused MeV Ion Beams

AbstractIn 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

Deep level defects in 4H-SiC introduced by ion implantation: the role of single ion regime

We characterized intrinsic deep level defects created in ion collision cascades which wereproduced by patterned implantation of single accelerated 2.0 MeV He and 600 keV H ions into n-type 4H-SiC epitaxial layers using a fast-scanning reduced-rate ion microbeam. The initial deep level transient spectroscopy measurement performed on as-grown material in the temperature range 150–700 K revealed the presence of only two electron traps, Z1/2 (0.64 eV) and EH6/7 (1.84 eV) assigned to the two different charge state transitions of the isolated carbon vacancy, VC (=/0) and (0/+). C–V measurements of as-implanted samples revealed the increasing free carrier removal with larger ion fluence values, in particular at depth corresponding to a vicinity of the end of an ion range. The first DLTS measurement of as-implanted samples revealed formation of additional deep level defects labelled as ET1 (0.35 eV), ET2 (0.65 eV) and EH3 (1.06 eV) which were clearly distinguished from the presence of isolated carbon vacancies (Z1/2 and EH6/7 defects) in increased concentrations after implantations either by He or H ions. Repeated C–V measurements showed that a partial net free-carrier recovery occurred in as-implanted samples upon the low-temperature annealing following the first DLTS measurement. The second DLTS measurement revealed the almost complete removal of ET2 defect and the partial removal of EH3 defect, while the concentrations of Z1/2 and EH6/7 defects increased, due to the low temperature annealing up to 700 K accomplished during the first temperature scan. We concluded that the ET2 and EH3 defects: (i) act as majority carrier removal traps, (ii) exhibit a low thermal stability and (iii) can be related to the simple point-like defects introduced by light ion implantation, namely interstitials and/or complex of interstitials and vacancies in both carbon and silicon sub-lattices

Depth Profile Analysis of Deep Level Defects in 4H-SiC Introduced by Radiation

Deep level defects created by implantation of light-helium and medium heavy carbon ions in the single ion regime and neutron irradiation in n-type 4H-SiC are characterized by the DLTS technique. Two deep levels with energies 0.4 eV (EH1) and 0.7 eV (EH3) below the conduction band minimum are created in either ion implanted and neutron irradiated material beside carbon vacancies(Z1/2). In our study, we analyze components of EH1 and EH3 deep levels based on their concentration depth profiles, in addition to (-3/-2) and (-2/-) transition levels of silicon vacancy. A higher EH3 deep level concentration compared to the EH1 deep level concentration and a slight shift of the EH3 concentration depth profile to larger depths indicate that an additional deep level contributes to the DLTS signal of the EH3 deep level, most probably the defect complex involving interstitials.We report on the introduction of metastable M-center by light/medium heavy ion implantation andneutron irradiation, previously reported in cases of proton and electron irradiation. Contribution ofM-center to the EH1 concentration profile is presented

Deep level defects in single ion regime implanted 4H-SiC epitaxial layers

We present a study of deep level defects created in isolated ion cascades produced in nitrogen-low-doped 4H-SiC epitaxial layers by implantation of either accelerated H (600 keV) or He (2 MeV) ions using fast-scanning reduced-rate microbeams, in the so-called single ion regime. In the first DLTS measurement, defects labelled as ET2 (0.65 eV) and EH3 (1.06 eV) have been clearly distinguished from the presence of the dominant carbon vacancies (Z1/2 and EH6/7) in increased concentrations for irradiated samples. However, the second DLTS measurement revealed the almost complete removal of ET2 trap and the partial removal of EH3 trap, while the concentrations of Z1/2 and EH6/7 traps have further increased, due to the relatively low temperature annealing up to 700 K, accomplished during the first temperature scan of DLTS measurement. Since majority carrier concentration reduced after irradiation recovers with decreasing ET2 and EH3, those might act as majority carrier removal traps.29th International Conference on Defects in Semiconductors (ICDS2017

4H-SiC Schottky Barrier Diodes for Efficient Thermal Neutron Detection

We present the improved efficiency of 4H-SiC Schottky barrier diodes-baseddetectors equipped with the thermal neutron converters. This is achieved by optimizing the thermal neutron converter thicknesses. Simulations of the optimal thickness of thermal neutron converters have been performed using two Monte Carlo codes (Monte Carlo N–Particle Transport Code and Stopping and Range of Ions in Matter). We have used 6LiF and 10B4C for the thermal neutronconverter material. We have achieved the thermal neutron efficiency of 4.67% and 2.24% with 6LiF and 10B4C thermal neutron converters, respectively

Characterisation and evaluation of a PNP strip detector for synchrotron microbeam radiation therapy

The Quality Assurance requirements of detectors for Synchrotron Micro-beam Radiation Therapy are such that there are limited commercial systems available. The high intensity and spatial fractionation of synchrotron microbeams requires detectors be radiation hard and capable of measuring high dose gradients with high spatial resolution sensitivity. Silicon single strip detectors are a promising candidate for such applications. The PNP strip detector is an alternative design of an already proven technology and is assessed on its contextual viability. In this study, the electrical and charge collection efficiency properties of the device are characterised. In addition, a dedicated TCAD model is used to support ion beam induced charge measurements to determine the spatial resolution of the detector. Lastly, the detector was used to measure the full width half maximum and peak to valley dose ratio for microbeams with only a slight over response. With the exception of radiation hardness the PNP detector is a promising candidate for quality assurance in microbeam radiation therapy

Deep Level Defects in 4H-SiC Epitaxial Layers

We present a study of electrically active radiation-induced defects formed in 4H-SiC epitaxial layers following irradiation with fast neutrons, as well as 600 keV H+ and 2 MeV He++ ion implantations. We also look at electron emission energies and mechanisms of the carbon vacancy in 4H-SiC by means of first-principles modelling. Combining the relative stability of carbon vacancies at different sites with the relative amplitude of the observed Laplace-DLTS peaks, we were able to connect Z1 and Z2 to emissions from double negatively charged carbon vacancies located at the h- and k-sites, respectively

Double negatively charged carbon vacancy at the h- and k- sites in 4H-SiC: Combined Laplace-DLTS and DFT study

We present results from combined Laplace-Deep Level Transient Spectroscopy (Laplace-DLTS) and density functional theory studies of the carbon vacancy (VC) in n-type 4H-SiC. Using Laplace-DLTS, we were able to distinguish two previously unresolved sub-lattice-inequivalent emissions, causing the broad Z1/2 peak at 290K that is commonly observed by conventional DLTS in n-type4H-SiC. This peak has two components with activation energies for electron emission of 0.58 eV and 0.65 eV. We compared these results with the acceptor levels of VC obtained by means of hybrid density functional supercell calculations. The calculations support the assignment of the Z1/2 signalto a superposition of emission peaks from double negatively charged VC defects. Taking into account the measured and calculated energy levels, the calculated relative stability of VC in hexagonal (h) and cubic (k) lattice sites, as well as the observed relative amplitude of the Laplace-DLTS peaks, we assign Z1 and Z2 to VC(h) and VC(k), respectively. We also present the preliminaryresults of DLTS and Laplace-DLTS measurements on deep level defects (ET1 and ET2) introduced by fast neutron irradiation and He ion implantation in 4H-SiC. The origin of ET1 and ET2 is still unclear