Irradiated Si Research Articles

Differences in coupling between nuclear and electronic energy losses in UO2 with irradiation temperature: An in situ TEM study

To investigate the coupling between nuclear and electronic energy losses in UO2, we irradiated thin foils with 0.39 MeV Xe and/or 6 MeV Si ions at 93 K using single or simultaneous dual beam ion irradiations. The evolution of perfect dislocation loops was characterized by in situ transmission electron microscopy (TEM). Additional ex situ TEM characterizations at room temperature revealed for the first time in UO2 the presence of faulted Frank loops too small to be measured during in situ experiments and conventional bright field kinematical imaging conditions.For the single Xe irradiation, which favor dominant ballistic energy losses, we observed a continuous nucleation of small perfect dislocation loops, which increase in size for our last fluences by growing through mainly coalescence effect. Both the single Si and dual Xe & Si irradiations showed a coupling between nuclear and electronic energy losses, resulting in a significant loop density increase and a tangled line network formation, respectively. These phenomena occur at lower dpa levels, compared to the single Xe irradiation, likely resulting from the thermal spike effect of Si ions. The present results were compared to our previous work at 293 K to investigate the role of irradiation temperature on the energy losses coupling. For the Xe irradiation, the density increases and the loops are smaller at 93 K compared to 293 K, resulting from the uranium interstitials mobility being prevented or allowed. For the Si irradiation, the dislocation evolution kinetics are similar at both temperatures. The electronic excitations effect seems greater than the irradiation temperature effect in this temperature range. For the Xe & Si irradiation, the loop kinetics change resulting in a tangled line network formation is faster and thus the loop transformation into lines occurs at lower dpa levels at 93 K compared to 293 K. It appears that the irradiation temperature affecting the mobility of some small point defects reduces the electronic excitation effect in this case.

Emission of ions and electrons correlated with soft and hard x-rays evolution from thermal plasma

This paper presents a correlation between time evolution of ions and electrons with soft and hard x-rays emitted from argon plasma. The plasma setup comprises of two copper electrodes connected with a dc power supply. Faraday cups were used to monitor time evolution of ions, to extract their energy, temperature, and flux. Double Langmuir probe was employed to determine electron temperature, energy, and density. To explore time-resolved emission of soft x-rays, PIN photodiodes filtered with 24 μm aluminum, 90 μm Mylar, 80 μm copper, and 10 μm silver have been used. To evaluate temporal evolution of hard x-rays, a scintillator–photomultiplier system was utilized. The plasma was generated using argon gas at atmospheric pressure 760 Torr and constant flow rate 5 L/min at 7, 9, and 11 kV. The flux, energy, and temperature of Ar ions increase with the increase in the operating potential. Soft x-ray signals last much longer (3000 ns) than those of electrons' and ions' signals (300 ns). The plasma operated at 11 kV permits highest emission of ions, electrons, and x-rays. The ions, electrons, and hard and soft x-ray irradiation on silicon wafer exhibited the presence of damaged trails. Ion irradiation showed the presence of latent damaged trails. Electron irradiation caused more damage to the Si surface compared to ion irradiation due to higher flux and density. Soft x-rays had a lesser effect as compared to Si exposed to hard x-rays due to higher energy of the hard x-rays. In the case of hard x-rays irradiated Si, erupted volcano-like structure is formed.

Effects of gamma-ray irradiation on material and electrical properties of AlN gate dielectric on 4H-SiC

This article investigates the radiation effects on as-deposited and annealed AlN films on 4H-SiC substrates under gamma-rays. The AlN films are prepared using plasma-enhanced-atomic-layer-deposition on an n-type 4H-SiC substrate. The AlN/4H-SiC MIS structure is subjected to gamma-ray irradiation with total doses of 0, 300, and 600 krad(Si). Physical, chemical, and electrical methods were employed to study the variations in surface morphology, charge transport, and interfacial trapping characteristics induced by irradiation. After 300 krad(Si) irradiation, the as-deposited and annealed samples exhibit their highest root mean square values of 0.917 nm and 1.190 nm, respectively, which is attributed to N vacancy defects induced by irradiation. Under irradiation, the flatband voltage (V fb) of the as-deposited sample shifts from 2.24 to 0.78 V, while the annealed sample shifts from 1.18 to 2.16 V. X-ray photoelectron spectrum analysis reveals the decomposition of O-related defects in the as-deposited AlN and the formation of Al(NO x ) y compounds in the annealed sample. Furthermore, the space-charge-limits-conduction (SCLC) in the as-deposited sample is enhanced after radiation, while the barrier height of the annealed sample decreases from 1.12 to 0.84 eV, accompanied by the occurrence of the SCLC. The physical mechanism of the degradation of electrical performance in irradiated devices is the introduction of defects like N vacancies and O-related defects like Al(NO x ) y . These findings provide valuable insights for SiC power devices in space applications.

Investigating the impact of physical vapour deposition of palladium on electron-irradiated silicon substrates

This study reports on the effect of resistive physical vapour deposition of Pd Schottky contacts on the defects observed in an irradiated n-type Si substrate. Deep-level transient spectroscopy (DLTS) was used in order to investigate the possible defects in Schottky diodes on the n-type Si. In this study the defects present where the diode was deposited first and then irradiated (“post irradiated”) were compared to those present where the substrate was irradiated first, and the Pd deposited after irradiation (“pre-irradiated”). In the post-irradiated material, the familiar radiation-induced defects were observed. However, in the pre-irradiated material, fourteen new defects were observed, with DLTS signatures differing from those of the defects in the post-irradiated diodes. The newly identified defects seemed to be specifically caused by the deposition of Pd contacts after irradiation of the substrate, as these defects were not observed when other metals such as Au, Ni, Al and Ag were deposited after irradiation. In this paper, we will refer to the observed effect that Pd deposition replaced the familiar radiation-induced defects in Si with the new set of defects as the “Pd effect”. Careful experiments ruled out annealing due to inadvertent heating of the sample during deposition as a possible cause. Care was taken to avoid all sources of contamination: The effect was observed for different sources of Pd and crucibles. This effect was inhibited by the presence of a thin intermediate layer of Pd or Au deposited before irradiation. We therefore conclude that the effect is only observed when Pd is deposited directly onto the irradiated Si surface. Out of the fourteen newly observed defects, four defects, with activation energy of 182, 220, 360 and 607 meV, had DLTS signatures corresponding to those of defects previously observed in Pd-containing Si. For the rest of the defects, no defects with similar DLTS signatures were found in literature. We therefore believe that the defects observed are produced by defect enhanced diffusion of Pd. Overall, the study enhances our understanding of defect behaviour in silicon-based devices, particularly under irradiation and metal deposition conditions, and reveals the unique properties and effects of Pd.

Investigating ripple pattern formation and damage profiles in Si and Ge induced by 100 keV Ar+ ion beam: a comparative study.

Desired modifications of surfaces at the nanoscale may be achieved using energetic ion beams. In the present work, a complete study of self-assembled ripple pattern fabrication on Si and Ge by 100 keV Ar+ ion beam bombardment is discussed. The irradiation was performed in the ion fluence range of ≈3 × 1017 to 9 × 1017 ions/cm2 and at an incident angle of θ ≈ 60° with respect to the surface normal. The investigation focuses on topographical studies of pattern formation using atomic force microscopy, and induced damage profiles inside Si and Ge by Rutherford backscattering spectrometry and transmission electron microscopy. The ripple wavelength was found to scale with ion fluence, and energetic ions created more defects inside Si as compared to that of Ge. Although earlier reports suggested that Ge is resistant to structural changes upon Ar+ ion irradiation, in the present case, a ripple pattern is observed on both Si and Ge. The irradiated Si and Ge targets clearly show visible damage peaks between channel numbers (1000-1100) for Si and (1500-1600) for Ge. The clustering of defects leads to a subsequent increase of the damage peak in irradiated samples (for an ion fluence of ≈9 × 1017 ions/cm2) compared to that in unirradiated samples.

Photoelectrochemical Proton-Coupled Electron Transfer of TiO2 Thin Films on Silicon.

TiO2 thin films are often used as protective layers on semiconductors for applications in photovoltaics, molecule-semiconductor hybrid photoelectrodes, and more. Experiments reported here show that TiO2 thin films on silicon are electrochemically and photoelectrochemically reduced in buffered acetonitrile at potentials relevant to photoelectrocatalysis of CO2 reduction, N2 reduction, and H2 evolution. On both n-type Si and irradiated p-type Si, TiO2 reduction is proton-coupled with a 1e-:1H+ stoichiometry, as demonstrated by the Nernstian dependence of the Ti4+/3+ E1/2 on the buffer pKa. Experiments were conducted with and without illumination, and a photovoltage of ∼0.6 V was observed across 20 orders of magnitude in proton activity. The 4 nm films are almost stoichiometrically reduced under mild conditions. The reduced films catalytically transfer protons and electrons to hydrogen atom acceptors, based on cyclic voltammogram, bulk electrolysis, and other mechanistic evidence. TiO2/Si thus has the potential to photoelectrochemically generate high-energy H atom carriers. Characterization of the TiO2 films after reduction reveals restructuring with the formation of islands, rendering TiO2 films as a potentially poor choice as protecting films or catalyst supports under reducing and protic conditions. Overall, this work demonstrates that atomic layer deposition TiO2 films on silicon photoelectrodes undergo both chemical and morphological changes upon application of potentials only modestly negative of RHE in these media. While the results should serve as a cautionary tale for researchers aiming to immobilize molecular monolayers on "protective" metal oxides, the robust proton-coupled electron transfer reactivity of the films introduces opportunities for the photoelectrochemical generation of reactive charge-carrying mediators.

TCAD Simulation of X-ray irradiated Si microstrip detector : Impact on full depletion voltage and leakage current

In the intense x-ray radiation environment at synchrotron sources, it is reported that the performance of the silicon pixel detectors degrades with an increasing x-ray dose up to 10 MGy. To study the impact of x-ray irradiation effects in the n-Fz Si microstrip detector, the microscopic radiation damage parameters of x-ray radiation were extracted from the current–voltage, and capacitance-voltage experiments on test Si microstrip detector. The damage parameters are implemented in Synopsys TCAD. In this paper, we have irradiated the test structure up to 10 MGy, and the results on full depletion voltage, and leakage current are compared with the TCAD simulation results. A very good agreement in between experimental and simulation results is observed in the leakage current for the non-irradiated, and 1 MGy irradiated detectors, where for high doses up to 10 MGy, experimental leakage current was fifty times higher than the simulated leakage current at full depletion voltage. The full depletion voltage in 0 MGy detector is also well matched with the simulation result, and further, it shows the full depletion voltage performance of x-ray irradiated detector. Finally, the new detector design specifications and process parameters are proposed for the optimum performance of the radiation hard p+n Si pixel detector equipped with guard rigs at cut edge for the next generation photon science applications.

TCAD simulation of the mixed irradiated n-MCz Si detector: Impact on space charges, electric field distribution

In the mixed irradiations at HL-LHC, n- MCz Si as a detector material is reported as a prime applicant. To study the non-homogeneous distribution of space charges and electric field distribution in mixed irradiated p+n MCz silicon pad detectors, four-level numerical modeling of mixed irradiation induced deep traps using microscopic parameters obtained from experimental measurements were implemented in Synopsys T-CAD. These advanced damage model parameters were sufficiently tuned to reproduce the experimental data’s on the full depletion voltage and leakage current at 293K. In this paper, the influence of effective introduction rate of shallower donor deep trap E30 K has been determined using SRH theory calculations for experimental effective doping concentration f and the behavior of space charges and electric field distribution in the presence of deep traps are thoroughly investigated.

Analysis of Bulk and Surface Radiation Damage in n+ in p SFz Si Micro Strip Detectors for the Future High Luminosity Collider Experiments: TCAD Simulation and Measurements

Within the framework of CERN RD50 collaboration, several radiation damage models for n/p-SFz, n-MCz Si have been explored for the better understanding of the experimental results in radiation damage analysis of the irradiated Si detectors. In the present paper, the important review on the microscopic radiation damage model for the p-type SFz Si detector combining the surface and radiation damage effects that can be used to simulate radiation damages effects in the heavily irradiated detectors for the good comparison of the experimental data and simulation result. The surface radiation damage models were extracted from the experimental measurements on the p-MOS capacitor and Gate-Controlled Diodes irradiated by Gamma or X-ray radiations in the range of 10 to 500 Mrad (Si). Whereas, the bulk damage model microscopic parameter was extracted from the experimental (TSC, DLTS) measurements on the n in p-SFz Si microstrip detector. The radiation damage (surface and bulk) models can be fed into the commercial Synopsys TCAD device simulator program for the designing and optimization of the detector, which can be used in the very harsh radiation environment of the HL-LHC, or FCC experiment. The objective of this analysis was to verify the experimental results using the new microscopic radiation damage models on the p-SFz Si for the radiation damage analysis of p- SFz Si detectors irradiated by proton, neutron or mixed at very high fluences. The results were verified by comparison of the experimental data with TCAD simulation.

Focus on the Avalanche Breakdown Characteristic of Si- and InP-Based APDs Irradiated by Fast Neutrons.

The Si- and InP-based APDs as the most important weak light semiconductor photodetectors to have achieved commercial success and are widely used in irradiation environments. Investigating the influencing mechanism of neutron irradiation on the above two types of APDs is of scientific and practical importance. In this paper, the dark current and gain characteristics of Si- and InP-based APDs around breakdown voltage were analyzed in detail before and after irradiation. The increase of dark current and the decrease of gain were observed for both the neutron irradiated Si- and InP-based APDs. Generation centers induced by neutrons are responsible for the increased dark current. The decrease of gain can be attributed to the increase of multiplied dark current and the change of electric field distribution in APD. The Si-based APD exhibits soft breakdown with the breakdown voltage reduced by ~8 V under the neutron fluence of 1.0 × 1012 cm-2, while the soft breakdown occurs along with a small change of breakdown voltage of ~1.5 V under the neutron fluence of 1.0 × 1013 cm-2 for InP-based APD. The difference in the change of breakdown voltage probably occurs because the Si-based APD uses p-doped Si as the multiplication layer, in which the neutron induced carrier removing effect cannot be ignored to keep the electric field distribution away from the optimal state. Therefore, using an intrinsic multiplication layer in APD is helpful to improve the neutron radiation resistance. The findings here are not only useful for the radiation hardened design of APD, but also deepen the understanding of irradiation mechanism.

The Effects of Total Ionizing Dose on the SEU Cross-Section of SOI SRAMs

The total ionizing dose (TID) effects on single-event upset (SEU) hardness are investigated for two silicon-on-insulator (SOI) static random access memories (SRAMs) with different layout structures in this paper. The contrary changing trends of TID on SEU sensitivity for 6T and 7T SOI SRAMs are observed in our experiment. After 800 krad(Si) irradiation, the SEU cross-sections of 6T SRAMs increases by 15%, while 7T SRAMs decreases by 60%. Experimental results show that the SEU cross-sections are not only affected by TID irradiation, but also strongly correlate with the layout structure of the memory cells. Theoretical analysis shows that the decrease of SEU cross-section of 7T SRAM is caused by a raised OFF-state equivalent resistance of the delay transistor N5 after TID exposure, which is because the radiation-induced charges are trapped in the shallow trench, and isolation oxide (STI) and buried oxide (BOX) enhance the carrier scattering rate of delay transistor N5.

TCAD simulation of radiation hard n-MCz and n-Fz Si microstrip detector for the HL-LHC

A radiation hard Si detector is used in the new CMS tracker detector at HL-LHC. It has been observed that n-MCz and n-Fz Si as a material can be used for the Si micro strip detector. The detector design for this material should be simulated and optimized to get high CCE. In order to understand the charge collection behavior of the n-MCz/n-FzSi detector, it is required to simulate and compare the radiation damage effects in the mixed irradiated n-MCz Si and proton irradiated n-Fz Si micro strip detector equipped with metal overhang and multiple guard rings. In this paper, we have done analysis and optimization of the radiation hard n-MCz Si/n-Fz Si strip detector design for the HL-LHC experiment in order to get high CCE.

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.

Operating Characteristics of Gamma Irradiated Si BJT

Operating Characteristics of Gamma Irradiated Si BJT

To define nonradiative defects in semiconductors: An accurate DLTS simulation based on first-principle

Deep level transient spectroscopy (DLTS) is a crucial technique to characterize the defects in semiconductor devices. Within the framework of the state-of-the-art density functional theory (DFT), the simulation for experimental DLTS spectra is realized successfully with high accuracy and intrinsic physics in this work, of which the reliability is confirmed by nonlocal hybrid functional. The electron–phonon coupling is included to describe the thermal-activated behavior of the hot carrier nonradiative capture reflected by DLTS signal. In the case study, the divacancy in silicon is employed for the flow of DLTS calculation as a benchmark, of which the results are verified by our 40 MeV Si irradiation experiments on the NPN and PNP bipolar junction transistors and previous reports. The problem we can address is the identification of defect characterized in DLTS experiments. The realization of DLTS simulation would have a profound significance for understanding the underlying physics in experimental observations and be a powerful leverage to define defect nature in semiconductors.

Investigation of mixed irradiation effects in p-MCz thin silicon microstrip detector for the HL-LHC experiments

A lot of R&D work is carried out in the CERN RD 50 collaboration to find out the best material for the Si detectors that can be used in the harsh radiation environment of HL-LHC, n and p-MCz Si was identified as one of the prime candidates as a material for strip detector that can be chosen for the phase 2 upgrade plan of the new Compact Muon Solenoid Tracker detector in 2026. In this work, four level deep-trap mixed irradiation model for p-MCz Si is proposed by the comparison of experimental data on the full depletion voltage and leakage current to the Shockley Read Hall recombination statistics results on the mixed irradiated p-MCz Si PAD detector. The effective introduction rate (η eff) of shallower donor deep trap E30K is extracted using SRH theory calculations for experimental N eff and that can show the behavior of space charges and electric field distribution in the p-MCz Si strip detector and compared its value with the η eff of shallower donor deep trap E30K in the nMCz Si microstrip detector. Prediction uncertainty in the p-MCz Si radiation damage mixed irradiation model is considered in the full depletion voltage and leakage current. A very good agreement is observed in the experimental and SRH results. This radiation damage model is also used to extrapolate the value of the full depletion voltage at different mixed (proton + neutron) higher irradiation fluences for the thin p-MCz Si microstrip detector.

Structural analysis of high-energy implanted Ni atoms into Si(100) by X-ray absorption fine structure spectroscopy

Ni silicide synthesis by Ni ion beam irradiation into Si attracts attention due to its advantages including the ability of formation of local structures, the controllability of ion beams, the formability of silicide without heat treatment and the high reproducibility of the resulting specimen. In this work, we investigate the local atomic structure of Si implanted with 3.0 MeV Ni+ ions. Analysis of Ni K-edge fluorescent-yield extended X-ray absorption fine structure reveals that Ni atoms have mixed structure of metallic-like face-centered cubic Ni and NiSi2 phases at the initial stage of the irradiation and the formation of NiSi2 promotes significantly with the ion fluence above 1015 ions⋅cm−2. With consideration of the agreement between the ion fluence threshold for the structural transition and the critical Si-amorphization fluence (7.1 × 1014 ions⋅cm−2), it is concluded that the amorphization of Si plays an important role in the synthesis of the NiSi2 phase in Ni+-irradiated Si.

ASET and TID Characterization of a Radiation Hardened Bandgap Voltage Reference in a 28-nm Bulk CMOS Technology

Analog single-event transient (ASET) and total ionizing dose (TID) characterization of a radiation-hardened bandgap voltage reference (BGR) is investigated in a 28-nm commercial bulk CMOS technology. Different radiation hardened by design (RHBD) techniques are used for ASET mitigation in the circuit and layout, and the circuit is optimized to ensure the BGR can still work correctly even using fast nMOS and slow pMOS for TID mitigation. Heavy-ion (linear energy transfer (LET) = 76.3 MeV <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /mg) experiments show the maximum amplitude of positive (negative) ASET is just 30 mV (90 mV), and Co <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> gamma-ray experiments show the maximum output voltage reduction is just 37 mV after 1.2 Mrad(Si) irradiation, and the final output voltage reduction is just 11 mV after 48 h of annealing. All of the experiments indicate that ASET is significantly mitigated by the RHBD techniques, and the BGR has naturally good TID response due to the design margin. The investigation also indicates that the proposed BGR is a good substitute for space application due to the excellent ASET and TID tolerance capability.

Radiation-Induced Nucleation and Growth of CaSi2 Crystals, Both Directly during the Epitaxial CaF2 Growth and after the CaF2 Film Formation.

The radiation-induced phenomena of CaSi2 crystal growth were investigated, both directly during the epitaxial CaF2 growth on Si (111) and film irradiation with fast electrons on Si (111) after its formation, while maintaining the specified film thickness, substrate temperature and radiation dose. Irradiation in the process of the epitaxial CaF2 film growth leads to the formation of CaSi2 nanowhiskers with an average size of 5 µm oriented along the direction <110>. The electron irradiation of the formed film, under similar conditions, leads to the homogeneous nucleation of CaSi2 crystals and their proliferation as inclusions in the CaF2 film. It is shown that both approaches lead to the formation of CaSi2 crystals of the 3R polymorph in the irradiated region of a 10 nm thick CaF2 layer.

Enhancement of the radiation resistance of cerium-containing fluorophosphate glasses through codoping with Sb2O3 and Bi2O3

The growing demand for radiation-resistant optical glasses for space and nuclear radiation applications has attracted significant research interest. However, radiation-resistant fluorophosphate glasses have been poorly studied. In this work, we report on the tailoring and performance of radiation-resistant fluorophosphate glasses that contained cerium through codoping with Sb2O3 and Bi2O3. The physical properties, optical properties, microstructure, and defects of fluorophosphate glasses were investigated using transmittance measurements, absorption measurements, as well as Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy. The results showed that the radiation resistance of all codoped fluorophosphate glasses was better than the undoped cerium-containing fluorophosphate glasses after 10–250 krad(Si) irradiation. Especially in glasses doped with Bi2O3, the optical density increment at 385 nm was only 0.1482 after 250 krad(Si) irradiation. The CeO2 prevented the development of phosphate-related oxygen hole center (POHC) defects, whereas further codoping with Bi2O3 suppressed the formation of oxygen hole center (OHC) and POEC defects, reducing the breaking of phosphate chains caused by CeO2. Bi3+ is more likely than Sb3+ to change the valence, affecting the transition equilibrium of intrinsic defects and reducing the concentration of defects produced by irradiation. When codoping with Sb2O3 and Bi2O3, Bi2O3 does not enhance radiation resistance owing to the scission effect of Sb2O3 on the phosphate chain, which is not conducive to the radiation resistance of glasses. This indicates that the cerium-containing fluorophosphate glasses doped with Bi2O3 can effectively suppress the defects caused by irradiation and improve the radiation resistance of the glasses.