Irradiated Silicon Research Articles

Copper-rich complexes in irradiated silicon

Only copper-related deep-level centers are produced by room-temperature MeV-electron irradiation in silicon doped with a high concentration of mobile interstitial copper atoms. In oxygen-lean FZ-Si, the well-known CuPL centers of four copper atoms show up in the DLTS, Laplace-DLTS, and photoluminescence measurements. In oxygen-rich Cz-Si, two new centers appear due to the irradiation at the expense of the CuPL defect. Reaction kinetics analysis correlates the new defects with oxygen, copper, and the irradiation-induced vacancy. The new defects are annealed at temperatures of 150–250 °C and, after passing through two more new configurations, are transformed into CuPL. The strong similarities to CuPL suggest that all four new defects are CuPL-like complexes of four copper atoms perturbed by a nearby oxygen.

Testbeam results of irradiated SiGe BiCMOS monolithic silicon pixel detector without internal gain layer

Samples of the monolithic silicon pixel ASIC prototype produced in 2022 within the framework of the Horizon 2020 MONOLITH ERC Advanced project were irradiated with 70 MeV protons up to a fluence of 1 × 1016 neq/cm2, and then tested using a beam of 120 GeV/c pions. The ASIC contains a matrix of 100 μm pitch hexagonal pixels, read out by low noise and very fast frontend electronics produced in a 130 nm SiGe BiCMOS technology process. The dependence on the proton fluence of the efficiency and the time resolution of this prototype was measured with the frontend electronics operated at a power density between 0.13 and 0.9 W/cm2. The testbeam data show that the detection efficiency of 99.96% measured at sensor bias voltage of 200 V before irradiation becomes 96.2% after a fluence of 1 × 1016 neq/cm2. An increase of the sensor bias voltage to 300 V provides an efficiency to 99.7% at that proton fluence. The timing resolution of 20 ps measured before irradiation rises for a proton fluence of 1 × 1016 neq/cm2 to 53 and 45 ps at HV = 200 and 300 V, respectively.

Characterisation of highly irradiated 3D trench silicon pixel sensors for 4D tracking with 10 ps timing accuracy

3D trench silicon pixel sensors, recently developed by the TimeSPOT collaboration, have shown excellent performance in terms of spatial resolution, timing precision and detection efficiency. The combination of these three features make them one of the best candidate for inner tracking detectors operating in high luminosity hadron colliders experiments. This article presents systematic characterisations of these devices made with minimum ionising particles on irradiated sensors with neutrons up to 2.5 ⋅ 1016 1 MeV neq cm−2. The results show that 3D trench pixels have extremely high resistance to radiation. The measured time resolution and the detection efficiency of irradiated sensors match those of non-irradiated ones if a slightly higher bias voltage, few tens of Volts, is applied to the pixels. As of today, 3D trench pixels are the only sensors capable of achieving 10 ps time resolution after being irradiated at extremely high fluences, extending by far the capabilities of future tracking systems of HEP experiments operating under extreme conditions.

Identification of paramagnetic centers in irradiated Sn-doped silicon dioxide by first-principles.

We present a first-principles investigation of Sn paramagnetic centers in Sn-doped vitreous silica based on calculations of the electron paramagnetic resonance (EPR) parameters. The present investigation provides evidence of an extended analogy between the family of Ge paramagnetic centers in Ge-doped silica and the family of Sn paramagnetic centers in Sn-doped silica for SnO2concentrations below phase separation. We infer, also keeping into account the larger spin-orbit coupling of Sn atoms with respect to Ge atoms, that a peculiar and highly distorted three-fold coordinated Sn center (i.e. the Sn forward-oriented configuration) should give rise to an orthorhombic EPR signal of which we suggest a fingerprint in the EPR spectra recorded by Chiodiniet al(2001Phys. Rev.B64073102). Given its structural analogy with theEα'and Ge(2) centers, we here name it as the 'Sn(2) center'. Moreover, we show that the single trapped electron at a SnO4tetrahedron constitutes a paramagnetic center responsible for the orthorhombic EPR signal reported in Chiodiniet al(1998Phys. Rev.B589615), confuting the early assignment to a distorted variant of the Sn-E' center. We hence relabel the latter orthorhombic EPR signal as the 'Sn(1) center' due to its analogy to the Ge(1) center in Ge-doped silica.

Study of bulk damage of high dose gamma irradiated p-type silicon diodes with various resistivities

The bulk damage of p-type silicon detectors caused by high doses of gamma irradiation has been studied. The study was carried out on three types of n+-in-p silicon diodes with comparable geometries but different initial resistivities. This allowed to determine how different initial parameters of studied samples influence radiation-induced changes in the measured characteristics. The diodes were irradiated by a Cobalt-60 gamma source to total ionizing doses ranging from 0.50 up to 8.28 MGy, and annealed for 80 minutes at 60 °C. The Geant4 toolkit for simulation of the passage of particles through matter was used to simulate the deposited energy homogeneity, to verify the equal distribution of total deposited energies through all the layers of irradiated samples, and to calculate the secondary electron spectra in the irradiation box. The main goal of the study was to characterize the gamma-radiation induced displacement damage by measuring current-voltage characteristics (IV), and the evolution of the full depletion voltage (V FD) with the total ionizing dose, by measuring capacitance-voltage characteristics (CV). It has been observed that the bulk leakage current increases linearly with total ionizing dose, and the damage coefficient depends on the initial resistivity of the silicon diode. The effective doping concentration and therefore V FD significantly decreases with increasing total ionizing dose, before starting to increase again at a specific dose. We assume that this decrease is caused by the effect of acceptor removal. Another noteworthy observation of this study is that the IV and CV measurements of the gamma irradiated diodes do not reveal any annealing effect.

Carrier-induced formation of electrically active boron-interstitial clusters in irradiated boron-doped silicon

Excess minority carriers create boron-related recombination centers that degrade the efficiency of the non-particle-irradiated silicon solar cells. However, the carrier-induced reactions among the radiation-induced defects are poorly understood for devices exposed to particle radiation. This study investigates the structure, electronic properties, formation and annihilation mechanisms, and diffusion dynamics of the carrier-induced defects in particle-irradiated boron-doped silicon using density-functional modeling and junction spectroscopy. By revisiting the ground-state structures of the boron-di-interstitial clusters (BI2), we find that the calculated acceptor and donor levels of such defects agree well quantitatively with the carrier-induced deep-level transient spectroscopy (DLTS) hole emission signatures at 0.43 and 0.53 eV above the valence band edge (Ev), respectively. We also find that the formation of BI2 is thermally activated by an energy of 0.50 eV, which we explain theoretically by the reduction of the migration barrier of mono-interstitials to 0.53 eV in the presence of excess minority carriers. Moreover, we discover that the BI2 are potentially mobile with a migration barrier of 1.18 eV, contrary to the present understanding.

Impact of MeV-Ag ions irradiation of silicon substrate on structural and optical properties of porous silicon

Porous silicon (PSi) was formed by an electrochemical etching of crystalline silicon substrates irradiated with silver (Ag) ion beam with energy of 1.25 MeV. Micro-Raman scattering results reveal that the irradiation process induces amorphization in the silicon substrate. Scanning electron microscopy, energy dispersive X-ray spectroscopy and micro-Raman scattering results show that the irradiation process induces important morphological and structural modifications in the PSi layer. The irradiation process leads to a considerable enhancement in the etching rate, a significant increase in the O/Si ratio and a reduction in the average size of the silicon nano-crystallites (nc-Si) from ∼7.76 nm to ∼2.26 nm in the skeleton of the PSi layer. These changes resulted in an important modification of photoluminescence (PL) properties of the PSi layer. Additional PL peak associated with the ‘F-band’ of the PSi was de-convoluted in the PL spectrum of the PSi layer formed on the irradiated silicon substrate.

Formation of corrugated nano-fuzz tungsten thin film on silicon via helium plasma irradiation

Tungsten thin films were deposited onto silicon substrates using sputtering techniques, and helium plasma irradiation was performed in a linear plasma device. Observations of the surface and cross-sectional morphology revealed the presence of a corrugated fiberform nanostructure, referred to as corrugated nano-fuzz, on the irradiated silicon samples. This structure has a distinct pattern of ridges and valleys with nanofibers on the surface. In addition to its unique morphology, the corrugated nano-fuzz demonstrates remarkable optical absorptivity, as revealed by optical absorptivity measurements, even after being exposed to helium plasma even for a short duration. The utilization of silicon-substrate thin film holds the potential to not only accelerate the processing for nanostructure growth but also yield uniformly corrugated structures and high optical absorptivity. These findings offer valuable insights for advancing the development of efficient fabrication methods within the field of nanotechnology.

ТАЛШЫҚТЫ-ОПТИКАЛЫҚ БАЙЛАНЫС ЖОЛДАРЫ НЕГІЗІНДЕ ЭНЕРГИЯ ТАРАТУ ЖҮЙЕСІНІҢ ЗЕРТХАНАЛЫҚ ҮЛГІСІН ӘЗІРЛЕУ ЖӘНЕ ЗЕРТТЕУ

In this article, a laboratory sample of an energy transmission system over a fiber-optic communication line is being developed and investigated, which makes it possible to provide power to autonomous ultra-low-power electronic devices located at a considerable distance from energy sources. The system being developed will make it possible to abandon the use of copper conductors and batteries for autonomous stationary devices, which is associated with certain difficulties from the point of view of technical implementation. The result of this study is a developed laboratory sample that allows measuring the values of current and voltage in the branch of the photodetector. The method of an equivalent generator was used, as well as the well-known laws of a circuit with two dedicated nodes for an active two- pole. When analyzing the literature, scientific achievements and discoveries in the field of research, a proprietary research concept was formulated that differs from foreign analogues. During the experiment, the photodetector was in idle, short-circuit mode and was connected to a high-resistance load. Based on experimental data, volt-ampere characteristics (VAC) were constructed using a radiation source (laser) with a power of 10 and 30 MW. The technical parameters and characteristics of the radiation source and the irradiated silicon crystal are given. The output electrical power is determined using the laws of electrical engineering, including Ohm's law. To process the results obtained, quadratic interpolation of the function, the results of the root-mean-square approximation were used, and regression analysis was also performed. Absolute and relative errors were calculated. The student's coefficient was determined with a confidence interval of 0.95. According to the results of the study, the efficiency of a laboratory sample of an energy transmission system over a fiber-optic communication line was determined.

Power supply via fiber-optical conductor for sensors of mine working monitoring system

The article describes a system of power transmission via fiber-optic cable, which allows the supply of power to sensors and other electronic devices of ultra-low power located in places of mining workings, for which the mandatory requirement is fire safety. The developed system will allow to replace the application of copper conductors. The result of this research is the developed laboratory bench that allows measuring the current and voltage parameters in the photodetector branch. The equivalent generator method has been used, as well as the known circuit laws with two dedicated nodes for an active two-terminal network. When analyzing the literature, the existing scientific achievements, and discoveries in the field of research, an own concept of research has been formed that is different from foreign analogs. During the experiment, the studies have been performed when the photodetector was in the short circuit, idle mode, and connected to a high-resistance load. Based on the results obtained, current-voltage characteristics (CVC) and histograms have been built using a radiation source (laser) with a power of 10 and 30 mW. The parameters and technical characteristics of the irradiated silicon crystal and the radiation source have been given. The obtained electrical power has been determined using the known laws of electrical engineering, including the Ohm law. To process the experimental data, there has been used quadratic interpolation of the function, the results of the root-mean-square approximation, and there has been carried out the regression analysis. Absolute and relative errors have been calculated. The Student coefficient has been determined with a confidence interval of 0.95. Based on the results of the study, the efficiency of the power transmission system has been determined

Neutron irradiation and electrical characterisation of the first 8” silicon pad sensor prototypes for the CMS calorimeter endcap upgrade

As part of its HL-LHC upgrade program, the CMS collaboration is replacing its existing endcap calorimeters with a high-granularity calorimeter (CE). The new calorimeter is a sampling calorimeter with unprecedented transverse and longitudinal readout for both electromagnetic and hadronic compartments. Due to its compactness, intrinsic time resolution, and radiation hardness, silicon has been chosen as active material for the regions exposed to higher radiation levels. The silicon sensors are fabricated as 20 cm (8”) wide hexagonal wafers and are segmented into several hundred pads which are read out individually. As part of the sensor qualification strategy, 8” sensor irradiation with neutrons has been conducted at the Rhode Island Nuclear Science Center (RINSC) and followed by their electrical characterisation in 2020-21. The completion of this important milestone in the CE's R&D program is documented in this paper and it provides detailed account of the associated infrastructure and procedures. The results on the electrical properties of the irradiated CE silicon sensors are presented.

Bistable Boron-Related Defect Associated with the Acceptor Removal Process in Irradiated p-Type Silicon—Electronic Properties of Configurational Transformations

The acceptor removal process is the most detrimental effect encountered in irradiated boron-doped silicon. This process is caused by a radiation-induced boron-containing donor (BCD) defect with bistable properties that are reflected in the electrical measurements performed in usual ambient laboratory conditions. In this work, the electronic properties of the BCD defect in its two different configurations (A and B) and the kinetics behind transformations are determined from the variations in the capacitance-voltage characteristics in the 243–308 K temperature range. The changes in the depletion voltage are consistent with the variations in the BCD defect concentration in the A configuration, as measured with the thermally stimulated current technique. The A→B transformation takes place in non-equilibrium conditions when free carriers in excess are injected into the device. B→A reverse transformation occurs when the non-equilibrium free carriers are removed. Energy barriers of 0.36 eV and 0.94 eV are determined for the A→B and B→A configurational transformations, respectively. The determined transformation rates indicate that the defect conversions are accompanied by electron capture for the A→B conversion and by electron emission for the B→A transformation. A configuration coordinate diagram of the BCD defect transformations is proposed.

Increase of the surface recombination velocity at high bias voltage in silicon irradiated by neutrons to extremely high fluences

The upgrading of ionizing radiation detectors is an actual problem especially related to the high energy physics and space research experiments. The simplest way to restore the signal of the irradiation degraded detector is the increase of the detector bias voltage. This method is widely used worldwide, including high energy physics experiments in ATLAS and CMS. This work presents an effect, which was caused by increased bias voltage in detectors irradiated to extreme high neutron fluence at low temperature. The effect could be related to the increase of surface recombination velocity.The intrinsic photoconductivity spectra were exploited in order to investigate the properties of highly irradiated silicon as this effect depends on parameters that are important in radiation detectors. Two characteristic effects were observed in such highly irradiated samples: the increase of photoconductivity quantum yield and the enhancement of surface recombination at higher bias voltages. The increase of the quantum yield was analyzed in Ref. [1]. The increase of the surface recombination with bias electric field was analyzed in this work as an extension of the performed investigation in the same samples as in Ref. [1]. The investigated silicon samples were irradiated by neutrons to wide range fluence up to 1017 n/cm2.The origin of this effect was analyzed and related to the radiation clusters, which decrease the free carrier lifetime.

Improvement in the aged silicon solar cells parameters by thermal annealing

In this paper, to simulate and accelerate the effects of aging, solar cells were exposed to the different doses of co60 gamma radiation. The current–voltage (I–V) characteristics of mono-crystalline solar cells under AM1.5 illumination condition were studied before and after the gamma irradiation. Experimental results showed that the solar cell parameters such as open circuit voltage (Voc), short circuit current (Isc) and efficiency (η) decrease with the increase of the gamma radiation doses. The effect of subsequent thermal annealing on solar cells degraded by gamma irradiation is investigated. A significant improvement in the electric parameters of by low doses gamma irradiated silicon solar cells is observed after the thermal annealing.

Thermophysical study of neutron irradiated silicon nitride nanoparticles

Silicon nitride (Si3N[Formula: see text] nanoparticles were irradiated with neutrons at different energy fluxes. Differential thermal analysis of non-irradiated and neutron irradiated samples was performed in the temperature range of 300–1400 K. Based on the obtained experimental results, relevant thermophysical parameters were calculated and discussed in detail. All analyses were comparatively discussed for non-irradiated and neutron irradiated nano-Si3N4 particles. On the basis of endotherms observed in DTA spectra, entropy and enthalpy in Si3N4 are interpreted in detail. Compared with the non-irradiated sample, slightly negative values of enthalpy indicate the formed [Formula: see text]P isotope due to neutron irradiation. In the mentioned temperature range, the values of the free Gibbs energy were calculated for all samples, and it was determined that it is varied around zero up to 600 K. Moreover, the effect of neutron transmutations on heat transfer in Si3N4 nanoparticles has been studied.

10 ps timing with highly irradiated 3D trench silicon pixel sensors

In this paper the results of a beam test characterization campaign of 3D trench silicon pixel sensors are presented. A time resolution in the order of 10 ps was measured both for non-irradiated and irradiated sensors up to a fluence of 2.5 × 1016 1 MeV neq cm−2. This feature and a detection efficiency close to 99% make this sensors one of the best candidates for 4D tracking detectors in High-Energy-Physics experiments.

Defect characterization studies on irradiated boron-doped silicon pad diodes and Low Gain Avalanche Detectors

High-energy physics detectors with internal charge multiplication, like Low Gain Avalanche Detectors (LGADs), that will be used for fast timing in the High Luminosity LHC experiments, have to exhibit a significant radiation tolerance. In this context, the impact of radiation on the highly boron-doped gain layer is of particular interest, since due to the so-called Acceptor Removal Effect (ARE) a radiation-induced deactivation of active boron dopants takes place, that is causing a progressive loss in the gain with increasing irradiation level. In this paper we present defect-spectroscopy measurements (Deep-Level Transient Spectroscopy and Thermally Stimulated Current technique) on neutron, proton and electron irradiated p-type silicon pad diodes of different resistivity as well as LGADs neutron irradiated at fluences up to 1×1015 neq/cm2. We show that compared to silicon pad diodes the determination of LGAD defect introduction rates is less straightforward as they are strongly influenced by the impact of the gain layer. The measured gain layer capacitance has a strong frequency and temperature dependence which makes DLTS measurements challenging to perform with results difficult to interpret. With the TSC technique the defects formed in the LGADs are nicely observed and can be compared to the defects formed in the silicon pad diodes. However, the exact assignment of defects to the gain layer or bulk region remains challenging and the charge amplification effect of the LGADs impacts the exact determination of defect concentrations. We also demonstrate that, depending on the TSC measurement conditions, defect induced internal electric fields are built up in the irradiated LGADs which impact the signal current.

Analysis of activation energy and conductivity in 1 MeV neutron irradiated silicon diodes

In a highly 1 MeV neutron-irradiated silicon (Si) diode, an ohmic current-voltage (I-V) behaviour is observed, with the ohmic region increasing with radiation fluence. Reverse current (minority carrier density) increasing more drastically than forward current (majority carrier density) explains the conductivity-type inversion of material-based devices from n-to p-type after irradiation. The reverse current activation energy decreases from 0.86 eV for unirradiated Si diodes to 0.54 eV for the highest irradiated diodes, confirming the material conductivity-type inversion. The activation energy is independent of the radiation fluence just below the Si intrinsic Fermi energy, showing that when the defects near the centre of the Si band gap dominate the conduction mechanism, diode properties are independent of incident radiation. Despite its detrimental effects, radiation can improve the stability of diode properties. The stability of the properties is important for the fabrication of sensors for current and future high-energy physics experiments. The improved stability is because of radiation-induced defect levels close to the centre of the band gap that behave as generation-recombination (g-r) centres in Si.

Investigation of Energy Levels of Small Vacancy Clusters in Proton Irradiated Silicon by Laplace Photoinduced Transient Spectroscopy

Laplace photoinduced transient spectroscopy has been applied to determine the electronic properties and concentrations of deep traps in high purity n-type silicon irradiated with high fluences of 23-MeV protons. From the temperature dependence of thermal emission rates of excess charge carriers obtained by the analysis of the photocurrent relaxation waveforms measured at temperatures of 30–320 K, eight deep traps with activation energies ranging from 255 to 559 meV have been resolved. The dependence of these trap’s concentrations on the proton fluence are demonstrated for the fluence values ranging from 1 × 1014 to 5 × 1015 neq/cm2. In comparison to the previously reported results of theoretical and experimental studies on the electronic properties of small vacancy clusters in irradiated silicon, we tentatively attribute four detected traps with activation energies of 255, 367, 405, and 512 meV to the energy levels related to the 2−/− charge state changes of divacancy (V2), trivacancy (V3), tetravacancy (V4), and pentavacancy (V5), respectively. Simultaneously, we propose the attribution of four deep traps with higher activation energies of 415, 456, 526, and 559 meV to the energy levels related to the −/0 charge state changes of these small vacancy clusters, respectively.

One-step femtosecond laser-induced monocrystalline silicon structure towards enhanced nano-hardness

• The atomic structure of silicon irradiated by femtosecond laser was characterized. • The laser irradiated silicon region consists of a dislocation layer. • The existence of the dislocation layer enhances the nano-hardness of silicon. In this work, a one-step fs laser-induced monocrystalline silicon (Si) structure was fabricated to improve the nano-hardness properties. According to the atomic structure, three layers were found in the irradiated Si structure, namely, the amorphous Si (a-Si) layer, dislocation layer, and Si crystal layer. The a-Si layer on the surface layer was attributed to the re-solidification of melting Si material, while the dislocation layer between the a-Si and Si crystal layers contained numerous dislocations and lattice distortions, which positively affected the nano-hardness of the irradiated Si structure. The Si crystal layer was not affected by laser irradiation and maintained the initial atomic structure. This work provides a new perspective on the phase transition and microstructure study of fs laser-induced structures.