Ion Beam Induced Charge Measurements Research Articles

Effects of Defects to the Performance of CdTe Pad Detectors in IBIC Measurements

We studied the impact of boundary walls and inclusions to the charge collection efficiency (CCE) of cadmium telluride (CdTe) pad detectors. By using ion beam-induced charge (IBIC) analysis, we were able to locate and classify various defects. We used 2-MeV protons that have a penetration depth of about 40 $\mu \text{m}$ in bulk CdTe. The detectors we measured had a surface area of 1 cm $\times \,\, 1$ cm and a thickness of 1 mm. They were passivated either by using aluminum nitride (AlN) or by aluminum oxide (Al2O3) and had a mesh of titanium tungsten Schottky contacts on both anode and cathode sides. In this paper, we show the results of our measurements and analyze the potential impact of the found defects on the performance of CdTe detectors with Geant4 simulations.

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.

Study on the effects of indentation-induced dislocations on the detector performance of CdZnTe crystals

The effects of indentation-induced dislocations on spectroscopic performances of CdZnTe detectors and on the deep-level defects of CdZnTe crystals are studied. The mobility-lifetime product (μτ) for electrons of the as-grown sample is determined to be 1.2 × 10−3 cm2/V by the γ-ray energy spectral measurement. However, the value reduced to 4.5 × 10−4 cm2/V after the dislocation is artificially increased by indentation. Meanwhile, the energy resolution is deteriorated from 7.45% to 28.15%. The ion beam induced charge (IBIC) measurements showed quite low carrier collection efficiency of electrons in the dislocation enriched areas. Moreover, the carrier recombination rate at dislocations was reduced with the increase in applied voltage. The thermally stimulated current measurements showed that the concentration of dislocation related defect levels observed at 0.107 eV and 0.159 eV increased almost twice after indentation. These defect levels could probably result in the carrier loss during the γ-ray energy spectrum and IBIC measurements.

Investigation of the Charge Collection Efficiency of CdMnTe Radiation Detectors

This paper presents the growth, fabrication and characterization of indium-doped cadmium manganese telluride (CdMnTe) crystals grown by the vertical Bridgman technique. The 10 × 10 × 1.9 mm3 samples have been fabricated, and the charge collection properties of the CdMnTe detectors have been measured. Alpha-particle spectroscopy measurements have yielded an average charge collection efficiency approaching 100%. Ion beam induced charge (IBIC) measurements have been performed by raster scanning focused 5.5 MeV 4He beams onto the detectors. Spatially resolved charge collection efficiency maps have been produced for a range of detector bias voltages. Inhomogeneities in the charge transport of the CdMnTe crystals have been associated with chains of Te inclusions within the detector bulk, and the reduction in charge collection efficiency in their locality has been quantified. It has been shown that the role of Te inclusions in degrading charge collection is reduced with increasing values of bias voltage. IBIC measurements for a range of low biases have highlighted the evolution of the charge collection uniformity across the detectors.

IBIC analysis of CdTe/CdS solar cells

This paper reports on the investigation of the electronic properties of a thin film CdS/CdTe solar cell with the Ion Beam Induced Charge (IBIC) technique. The device under test is a thin film (total thickness around 10 μm) multilayer heterojunction solar cell, displaying an efficiency of 14% under AM1.5 illumination conditions. The IBIC measurements were carried out using focused 3.150 MeV He ions raster scanned onto the surface of the back electrode. The charge collection efficiency (CCE) maps show inhomogeneous response of the cell to be attributed to the polycrystalline nature of the CdTe bulk material. Finally, the evolution of the IBIC signal versus the ion fluence was studied in order to evaluate the radiation hardness of the CdS/CdTe solar cells in a view of their use in solar modules for space applications.

Modeling of deep buried structures in high-power devices based on proton beam induced charge microscopy

In this paper the possible application of ion beam induced charge (IBIC)-microscopy for the analysis of the electrical field distributions within the depletion regions of high-power devices is discussed. The application of a reverse bias voltage allows one to obtain information about the field distribution within the device under working conditions from IBIC measurements. Such data are useful in the design process of high-power devices because excessive fields within protection elements (e.g. field ring structures) can be avoided. Charge collection spectra taken under reverse voltages of more than 1 kV are discussed. The results have been compared with simulations of the IBIC-processes using the code MEDICI.

On the use of pulsed microbeam in IBIC

In order to expand the application possibilities of ion beam induced charge (IBIC) technique to a wider range of semiconductor materials and devices, three novel modes of measurements have been developed. The fast beam deflector was used to produce ns pulses of single ions and the trigger signal provides a time scale for time resolved IBIC measurements. Longer pulses (>100 ns) containing tens or hundreds of ions were used to enhance IBIC signals in materials with poor charge transport properties. Continuous beam current (10 pA to 1 nA) of 3 MeV protons was used to measure ion beam induced voltage (IBIV) in thin amorphous silicon films. In these samples it was possible to correlate the charge collection properties with elemental distribution measured simultaneously with PIXE. Radiation damage was shown to be negligible for doses below 10 7 protons μm −2.

Ion microbeam analysis of CVD diamond

Abstract In order to investigate the homogeneity of the transport properties in diamond, IBIC (ion beam induced charge) technique has been widely used, in consideration of the very high electrical resistivity of undoped CVD diamond. However, even if detailed maps of the combined electron-hole drift or collection length have been obtained, some effects occurring during measurements, mainly due to space-charge produced by trapped charge, probably contribute to mask reality. These effects could be responsible for electrical polarisation, by means of which the collection efficiency may decay with time, or even for the dependence of the results on the pulse counting rate. The strong polarisation observed in some samples is an indication of poor electronic properties. Good samples do not polarise at all, but in all cases display collection efficiency maps which depend both on the type of radiation used, on its energy and on total dose delivered to them. In general, but not always, the collection efficiency improves both in average value and in homogeneity through the sample: this could be an indication that the sample is not totally depleted by the applied bias because of space charge. There are also indications that the material quality improves from the substrate side to the growth side, and that drift length for electrons is longer than for holes, at least in some samples. These and other observations and conclusions gathered during years of IBIC measurements will be presented and discussed, in order to illuminate this still relatively unknown material, CVD diamond.

The influence of ion induced damage on lateral charge collection and IBIC image contrast

High resolution, calibrated ion beam induced charge (IBIC) measurements from integrated circuit test structures have demonstrated that the measured charge collection in a device can exhibit significant change after only a few hundred ions/μm 2 exposure, which may easily be exceeded in the initial targeting of a structure. For the purposes of determining a circuit's upset immunity or undamaged charge collection characteristics, such behaviour must be accounted for in evaluating IBIC measurements. This paper examines the influence of low level, ion induced damage on the magnitude of the measured lateral charge collection and also its resulting impact on IBIC image contrast. The lateral charge collection process is first characterised by calculating the amount of charge which diffuses to a collecting junction as a function of carrier diffusion length and the distance between the ion strike and junction edge. The effect of accumulated ion induced damage on lateral charge collection is then incorporated as a decrease in the resultant diffusion length. Calibrated IBIC measurements from the drain of a test FET structure are then explained using this predicted behaviour.