Full Charge Collection Research Articles

Investigation of proton radiation damage effects on the n-Fz DSSSD for the Phase I Upgrade of new Si Tracker at the R3B experiment

Radiation hard Double Sided Silicon Strip Detectors are used at the Silicon Tracker for the detection of two-dimensional position andenergy measurement of the incident protons in the R3B experiment at FAIR. Double Sided Silicon Strip Detectors were fabricated by Micron Semiconductor Ltd., U.K. and the first set of experimental measurements havebeenperformed on the non-irradiated detectors in order to understand the macroscopic performance of the detectors for the tracker. This study is extended to the performance of the irradiated detectors in the proton radiation environmentusing proton radiation damage model. The detectors were irradiated with 23 MeV protons up to an expected fluence of 8 × 1014 neq cm-2, which is one order higher than expected fluence at an initial phase0 of the experiment. The performance characteristics of the detectors on the full depletion voltage, leakage current, and charge collection efficiency were extrapolated using SRH and CCE modelling, which is usually implemented in device TCAD. The results on the detectors were compared with the available experimental data on the detectors. A very good comparison between experimental data and calculated resulthave been recorded for non-irradiated and irradiated detectors. The agenda is to propose a proton radiation hard Double Sided Silicon Strip Detector design on the basis of the present study for the phase 1 upgrade of the experiment.

Characteristics of thin p-MCz Si Microstrip Detector Irradiated upto a mixed fluence of 1017neq./cm2for the FCC

Silicon microstrip detectors can be used for the precise particle tracking in the inner tracking region of the detector used in the future high luminosity collider experiment. In the future experiments, hadron collider provides higher luminosities on the strip detector, and therefore, a detector requires very high radiation hardness. Within CERNRD50collaboration, MCz Si is identified as a prime radiation hard material for the fabrication of the p-Si microstrip detector. In this paper, we have used the experimentally verified four level deep-trap mixed irradiation model for p-MCz Si to investigate the effect of heavy irradiations up to a mixed fluence of 1017n eq./cm2 on the full depletion voltage, leakage current, and charge collection efficiency using SRH and CCE modelling.The changes in the characteristics were evaluated, and effect of the traps on the macroscopic performance of the detectors and possible improvement in the design and semiconductor technology of the p-Mcz silicon microstrip detector.

Effect of low-temperature rapid annealing on structural and electrical properties of electroless platinum contacts on CdZnTe detectors

In this work, platinum (Pt) electrodes were deposited on CdZnTe wafers by electroless H2PtCl4 solution and subsequently annealed at different temperature from 323 K to 473 K. Focused ion beam (FIB) imaging, transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), current-voltage (I–V) analysis and energy spectra under 241Am irradiation were adopted to investigate the effect of low-temperature rapid annealing on interface structure, electrical and carrier transport properties of Pt/CdZnTe samples. Single-crystal PtTe layer with [100] orientation and thickness of 20 nm was found in the interface between electroless Pt and CdZnTe wafer. The leakage current of the Pt/CdZnTe detectors at 200 V decreased from 212 nA cm−2 to 101 nA cm−2 after low-temperature rapid annealing, due to a decrease of voltage drop across the PtTe interface layer. The energy spectra and carrier transport performance of Pt/CdZnTe detectors suggested that the optimal annealing temperature was 423 K. The energy spectra of Pt/CdZnTe detector under 241Am showed that the FWHM was improved from 23.3% to 14.4%, while the full charge collection and mobility lifetime product of electrons increasing from 611 to 625 and 3.17 × 10−3 to 3.76 × 10−3 cm2 V−1 s−1, respectively.

Modeling of neutron radiation-induced defects in silicon particle detectors

Radiation damage of the silicon detectors in future hadron colliders poses a major challenge for its reliable operation. It is crucial to investigate the neutron-induced radiation damage owing to its large flux in the calorimeters and the trackers. Measurement results on irradiated detectors are complemented by modeling for getting a deep insight into the device behavior. This work presents the development of neutron-induced radiation damage model in silicon detectors using TCAD simulation. A wide spectrum of measurement results available on neutron-irradiated silicon detectors, viz. full depletion voltage, leakage current, charge collection, and effective trapping times, helps in constraining the model parameters, resulting in a robust model for neutron damage. Modeling has been performed within the phase-space of the measurements, i.e. for different initial bulk resistivities, active thicknesses and for both polarities up to the fluence values of 9 × 1014 1 MeV neq cm−2 (where, 1 MeV neq refers to the equivalent fluence for monoenergetic neutrons of energy 1 MeV) and for two measurement temperatures, 253 and 263 K. The results obtained from the devised neutron damage model show a good agreement with the measurement results.

Near full light absorption and full charge collection in 1-micron thick quantum dot photodetector using intercalated graphene monolayer electrodes.

Quantum dots (QDs) offer several advantages in optoelectronics such as easy solution processing, strong light absorption and size tunable direct bandgap. However, their major limitation is their poor film mobility and short diffusion length (<250 nm). This has restricted the thickness of QD film to ∼200-300 nm due to the restriction that the diffusion length imposes on film thickness in order to keep efficient charge collection. Such thin films result in a significant decrease in quantum efficiency for λ > 700 nm in QDs photodetector and photovoltaic devices, causing a reduced photoresponsivity and a poor absorption towards the near-infrared part of the sunlight spectrum. Herein, we demonstrate 1 μm thick QDs photodetectors with intercalated graphene charge collectors that avoid the significant drop of quantum efficiency towards λ > 700 nm observed in most QD optoelectronic devices. The 1 μm thick intercalated QD films ensure strong light absorption while keeping efficient charge extraction with a quantum efficiency of 90%-70% from λ = 600 nm to 950 nm using intercalated graphene layers as charge collectors with interspacing distance of 100 nm. We demonstrate that the effect of graphene on light absorption is minimal. We achieve a time-modulation response of <1 s. We demonstrate that this technology can be implemented on flexible PET substrates, showing 70% of the original performance after 1000 times bending test. This system provides a novel approach towards high-performance photodetection and high conversion photovoltaic efficiency with quantum dots and on flexible substrates.

Charge and energy deposition in thick silicon depletion layers by environmental ionizing radiation and terrestrial cosmic rays

This paper reports about the results of a long-term experiment intended to measure the energy and the charge deposited by environmental ionizing radiation in thick silicon depletion layers, which are representative of the situation encountered in some high-voltage semiconductors. These measurements have been carried out to provide quantitative and statistically consistent data to support the design of robust and reliable power devices as well as the related TCAD simulations. Special attention is paid to the charge deposition immediately before the onset of charge multiplication. The proposed experimental setup uses a calibrated, almost abrupt PiN junction detector with a 100 μm thick depletion layer, where the maximum electric filed is kept below 12 kV/cm to avoid local charge multiplication while achieving full charge collection. The dedicated spectrometry chain is capable of measuring charge deposition in the 1 to 1000 fC range to detect interactions due to terrestrial cosmic neutrons, terrestrial cosmic muons and environmental gamma radiation. The experiment has been performed in Central Europe starting from August 2017 for a duration of six months, under none, moderate, and high shielding conditions, and it has been designed to resolve fluxes above 0.00023 cm−2 h−1 with 90% confidence level.

A process modification for CMOS monolithic active pixel sensors for enhanced depletion, timing performance and radiation tolerance

For the upgrade of its Inner Tracking System, the ALICE experiment plans to install a new tracker fully constructed with monolithic active pixel sensors implemented in a standard 180 nm CMOS imaging sensor process, with a deep pwell allowing full CMOS within the pixel. Reverse substrate bias increases the tolerance to non-ionizing energy loss (NIEL) well beyond 10131MeVneq∕cm2, but does not allow full depletion of the sensitive layer and hence full charge collection by drift, mandatory for more extreme radiation tolerance. This paper describes a process modification to fully deplete the epitaxial layer even with a small charge collection electrode. It uses a low dose blanket deep high energy n-type implant in the pixel array and does not require significant circuit or layout changes so that the same design can be fabricated both in the standard and modified process. When exposed to a 55Fe source at a reverse substrate bias of −6 V, pixels implemented in the standard and the modified process in a low and high dose variant for the deep n-type implant respectively yield a signal of about 115 mV, 110 mV and 90 mV at the output of a follower circuit. Signal rise times heavily affected by the speed of this circuit are 27.8+∕−5 ns, 23.2+∕−4.2 ns, and 22.2+∕−3.7 ns rms, respectively. In a different setup, the single pixel signal from a 90Sr source only degrades by less than 20% for the modified process after a 10151MeVneq∕cm2 irradiation, while the signal rise time only degrades by about 16+∕−2 ns to 19+∕−2.8 ns rms. From sensors implemented in the standard process no useful signal could be extracted after the same exposure. These first results indicate the process modification maintains low sensor capacitance, improves timing performance and increases NIEL tolerance by at least an order of magnitude.

Thick CVD diamond films grown on high-quality type IIa HPHT diamond substrates from New Diamond Technology

The suitability of type IIa diamonds prepared by High Pressure High Temperature (HPHT) in cubic presses at New Diamond Technology was assessed as substrates for the growth of thick detector-grade quality Chemically Vapour Deposited (CVD) diamond films. The substrates were found to possess a moderate dislocation density of about 103cm−2 and a reduced amount of residual impurities as compared to standard type Ib crystals. Using these diamonds as seeds for homoepitaxial growth, CVD films with improved structural characteristics were obtained although extended defects could not be completely prevented from forming and propagating. Their performance as detectors for β radiation was however improved leading to almost full charge collection which shows significant improvement as compared to CVD films grown under the same conditions on standard Ib HPHT diamonds. The availability of this new material source opens the way to the fabrication of higher quality CVD material for electronics applications.

Study of cubic and hexagonal cell geometries of a 3D diamond detector with a proton micro-beam

A detector from single crystal synthetic diamond with conducting wires has been prepared with an improved femto-second laser process. The detector was characterised with a 4.5MeV proton micro-beam (Ruđer Bos̆ković Institute, Zagreb). The charge collection efficiency and the transient current response have been investigated with high spatial resolution. A hexagonal and square cell geometry is investigated. Both cell geometries show full charge collection at 40V bias voltage, and little charge sharing between neighbouring cells. The experimental data is compared to a simulation and qualitative agreement is observed.

Prototyping and performance study of a single crystal diamond detector for operation at high temperatures

Prototype single crystal diamond detectors with different types of metallization and post metallization treatment were fabricated for the applications requiring fast neutron measurements in the Indian Test Blanket Module (TBM) at the International Thermonuclear Experimental Reactor (ITER) Experiment. The detectors were characterized by leakage current measurements to ascertain that the leakage currents are low and breakdown voltages are higher than the voltage required for full charge collection. The detector response to charged particles was evaluated using a 238+239 Pu dual energy alpha source. The detectors showed an energy resolution of about 2% at 5.5MeV. In order to study their suitability for the operation at higher temperatures, leakage current variation and alpha response were studied up to 300°C. At 300°C, peaks corresponding to 5.156MeV and 5.499MeV alphas could be separated and there was no significant degradation of energy resolution. Finally, the detector response to fast neutrons was evaluated using a Deuterium-Tritium (D-T) neutron generator. The observed spectrum showed peaks corresponding to various channels of n-C interactions with a clear isolated peak corresponding to ~8.5MeV alphas. The detectors also showed high sensitivity of 3.4×10−2cps/n/(cm2s)–4.5×10−2cps/n/(cm2s) and excellent linearity of response in terms of count rate at different neutron flux in the observed range of 3.2×105n/(cm2s) to 2.0×106n/(cm2s).

3D Simulation and Modeling of Ultra-fast 3D Silicon Detectors

3D detectors with very small electrode spacing can provide ultra-fast detection due to their extremely small charge collection time. Since the detector full depletion voltage and charge collection time are independent to the detector thickness, ultra-fast 3D detectors can be made relatively thick (or not too thin, ~200 μm) to ensure a large signal. The results of the 3D simulations and modeling of 3D silicon detectors with very small electrode spacing and relatively large thickness will be shown in this paper. The column spacing LP is in the range of 5 μm to 10 μm. At a bias voltage of only a few volts, the electric field in the detector can be large enough to ensure the carrier saturation drift velocity in most volume of the detector, and the detector charge collection time there can be as short as 10’s of ps. In this paper, we will analysis the simulated electrical characteristics of this detector structure through systematic 3D simulations using the Silvaco’s TCAD tool. Profiles of detector electric potential and electric field will be presented. We will investigate the region of low electric field (the “slow region”) in the detector. We will also exam whether the detector reach the breakdown condition at operation voltages suggested in this work.

Diamond Particle Detectors for High Energy Physics

Diamond devices have now become ubiquitous in the LHC experiments, finding applications in beam background monitoring and luminosity measuring systems. This sensor material is now maturing to the point that the large pads in existing diamond detectors are being replaced by highly granular tracking devices, in both pixel and strip configurations, for detector systems that will be used in Run II at the LHC and beyond. The RD42 collaboration has continued to seek out additional diamond manufacturers and quantify the limits of the radiation tolerance of this material. The ATLAS experiment has recently installed, and is now commissioning a fully-fledged pixel tracking detector system based on diamond sensors. Finally, RD42 has recently demonstrated the viability of 3D biased diamond sensors that can be operated at very low voltages with full charge collection. These proceedings describe all of these advances.

Study of a 3D diamond detector with photon and proton micro-beams

To form a 3D diamond detector electrodes were produced in diamond by a femtosecond laser-induced phase transition of diamond to graphite. The process parameters were varied to study the influence on electrode resistivity and induced stress. A technique for a relative measurement of stress induced in 3D diamond detectors is described. The detector was characterised with a 15keV photon micro-beam (Diamond Light Source, Oxford) and a 4MeV proton micro-beam (Ruđer Bošković Institute, Zagreb). The detector shows characteristics consistent with full charge collection. Spatially resolved transient current measurements were obtained with protons for the first time, and the results were compared to simulations of the detector.

A 3D diamond detector for particle tracking

In the present study, results towards the development of a 3D diamond sensor are presented. Conductive channels are produced inside the sensor bulk using a femtosecond laser. This electrode geometry allows full charge collection even for low quality diamond sensors. Results from testbeam show that charge is collected by these electrodes. In order to understand the channel growth parameters, with the goal of producing low resistivity channels, the conductive channels produced with a different laser setup are evaluated by Raman spectroscopy.

3D cylindrical silicon microdosimeters: fabrication, simulation and charge collection study

This paper reports on the fabrication, simulation, and charge collection characteristics of a new generation of cylindrical silicon microdosimeters fabricated on SOI wafers. The devices consist of an array of p+ electrodes surrounded by trench n+ electrodes creating well defined, cylindrical sensitive volumes. A first batch of microsensors with 5.4 μm active thickness has been successfully fabricated. The devices are fully functional with good diode behavior and a depletion voltage of only 3 V. Their charge collection characteristics have been investigated using the IBIC technique with protons and alpha particles. The IBIC maps show a 100% yield of active cells in a microdosimeter array and full charge collection efficiency in the active area of the unit microsensors. These devices constitute an step forward in the current status of microdosimeters based on silicon technologies.

ALPIDE, the Monolithic Active Pixel Sensor for the ALICE ITS upgrade

A new 10m2 inner tracking system based on seven concentric layers of Monolithic Active Pixel Sensors will be installed in the ALICE experiment during the second long shutdown of LHC in 2019–2020. The monolithic pixel sensors will be fabricated in the 180nm CMOS Imaging Sensor process of TowerJazz. The ALPIDE design takes full advantage of a particular process feature, the deep p-well, which allows for full CMOS circuitry within the pixel matrix, while at the same time retaining the full charge collection efficiency. Together with the small feature size and the availability of six metal layers, this allowed a continuously active low-power front-end to be placed into each pixel and an in-matrix sparsification circuit to be used that sends only the addresses of hit pixels to the periphery. This approach led to a power consumption of less than 40mWcm−2, a spatial resolution of around 5μm, a peaking time of around 2μs, while being radiation hard to some 10131MeVneq/cm2, fulfilling or exceeding the ALICE requirements.Over the last years of R & D, several prototype circuits have been used to verify radiation hardness, and to optimize pixel geometry and in-pixel front-end circuitry. The positive results led to a submission of full-scale (3cm×1.5cm) sensor prototypes in 2014. They are being characterized in a comprehensive campaign that also involves several irradiation and beam tests. A summary of the results obtained and prospects towards the final sensor to instrument the ALICE Inner Tracking System are given.

Three-dimensional graphite electrodes in CVD single crystal diamond detectors: Charge collection dependence on impinging β-particles geometry

The charge collection performance of a three-dimensional diamond-graphite detector is reported. Buried graphite pillars with high aspect ratio were formed inside a single crystal synthetic diamond slab by using a femtosecond IR laser with 200kHz of repetition rate. Grouped in two series and connected by graphite strips on the surface, eight independent 3D electrodes were used to collect the charge carriers generated by energy deposited in the detector by 90Sr,Y β-particles. Different impinging configurations were used to test charge collection and signal dependence on voltage. Reversing the bias polarity the pulse height distribution does not changes and the charge collection saturation of any group of connected pillars was observed around ±80V (0.53V/μm). The average charge collected by one pillars row is Qav=1.60±0.02fC, with electrons impinging orthogonally the rows, in such a way demonstrating full charge collection.

Characterization of the charge‐carrier transport properties of IIa‐Tech SC diamond for radiation detection applications

Single crystal (SC) diamond has since years demonstrated its interest for the fabrication of radiation detectors, especially where the material properties are providing superior interests with respect to the detection application. Among the industrial suppliers able to provide on a commercial basis high‐grade single crystal diamond, IIa‐Tech has recently appeared in the market as a new player. The aim of this paper is to assess the quality of one SC sample when characterized under α‐particles for the measurement of its carrier transport properties. We observed that full charge collection could be observed at biases as low as 0.11 V/μm with no space charge build‐up (conventionally typical bias values used are closer to 1 V/μm). Velocity reached values of 38 μm/ns and 53 μm/ns for electrons and holes, respectively (values probed at 0.33 V/μm). Similarly, the α detection spectrum displays a sharp line demonstrating the good uniformity of the material over its surface. By combining the measurements with more conventional optical observations such as birefringence and cathodoluminescence spectroscopy, it comes that the material demonstrates its ability to be used as a detector, with properties that can compare with the highest grade materials today available on the market.

Radiation damage on the LHCb-VELO

The LHCb Vertex Locator (VELO) is designed to reconstruct charged particle trajectories and vertices produced at the LHCb interaction region. This is a silicon strip detector system operating at the closest distance from the interaction region among all the currently installed detectors at the CERN LHC. The geometry of the sensors implies that every detector region is exposed to a different dose of radiation depending mainly on the radial distance from the beam line. In the first 2 years of operation they have been exposed to a range of fluences up to a maximum value of about 4.5×1013 1MeVneutron equivalent (neq)cm−2. At the end of 2012 a maximum of about 1.5×1014neq has been reached; data analysis is ongoing. Sensor currents, full depletion voltage and charge collection efficiencies have been studied at various fluences. Observation of type inversion of the n-type silicon sensors has been made (about after 10–15×1012neq). The n-type bulk sensors have been compared with the only p-type bulk detectors installed in the LHC. A reduction in the charge collection efficiency due to charge losses to a second metal layer (used for routing the signal to the readout electronics in LHCb-VELO sensors) has been measured. Possible solutions to this undesirable effect are planned to be studied in the framework of the LHCb-VELO upgrade.

Simulation and characterization of a dual-type 3-dimensional silicon detector

A three-dimensional (3D) silicon detector is an alternative semiconductor detector for high radiation environments. The 3D detector has several advantages such as radiation hardness so it can be used for a longer period of time in a high radiation environment without replacement. A dual-type 3D silicon detector is simulated, and the full depletion voltage, capacitance, response time and charge collection efficiency are measured.