Electron Irradiation-induced Defects Research Articles

Evaluation of 10 MeV electron irradiation-induced defects in graphene oxide and multi-walled carbon nanotube using a multi-analytical approach

Structural defects in electron-irradiated graphene oxide (GO), and multi-walled carbon nanotubes (MWCNT) were investigated by Raman. All the samples were irradiated with a 10 MeV electron-beam to 200 kGy. XRD, FTIR, FESEM, HRTEM, XPS and Raman spectroscopy analyses were carried out. To estimate the magnitude of induced defects in the samples, the ID/IG parameter was considered in various absorbed doses. The XPS analysis exhibited a 2.5%, and 3.2% increase in the carbon to oxygen ratio for MWCNT, and GO at 50, and 100 kGy, respectively. Results of Raman spectroscopy to determine D, and G bands at characteristic wavelengths showed a good agreement with the literature data. Also, for GO, the long-term stability of the irradiation-induced defects was investigated after four months, which revealed that maybe crosslinking of the carbon atoms at high-doses greater than 100 kGy could freeze the induced defects over time.

Electron irradiation-induced defects for reliability improvement in monolayer MoS2-based conductive-point memory devices

Monolayer molybdenum disulfide has been previously discovered to exhibit non-volatile resistive switching behavior in a vertical metal-insulator-metal structure, featuring ultra-thin sub-nanometer active layer thickness. However, the reliability of these nascent 2D-based memory devices was not previously investigated for practical applications. Here, we employ an electron irradiation treatment on monolayer MoS2 film to modify the defect properties. Raman, photoluminescence, and X-ray photoelectron spectroscopy measurements have been performed to confirm the increasing amount of sulfur vacancies introduced by the e-beam irradiation process. The statistical electrical studies reveal the reliability can be improved by up to 1.5× for yield and 11× for average DC cycling endurance in the devices with a moderate radiation dose compared to unirradiated devices. Based on our previously proposed virtual conductive-point model with the metal ion substitution into sulfur vacancy, Monte Carlo simulations have been performed to illustrate the irradiation effect on device reliability, elucidating a clustering failure mechanism. This work provides an approach by electron irradiation to enhance the reliability of 2D memory devices and inspires further research in defect engineering to precisely control the switching properties for a wide range of applications from memory computing to radio-frequency switches.

M-Center in Neutron-Irradiated 4H-SiC

We report on the metastable defects introduced in the n-type 4H-SiC material by epithermal and fast neutron irradiation. The epithermal and fast neutron irradiation defects in 4H-SiC are much less explored compared to electron or proton irradiation-induced defects. In addition to the carbon vacancy (Vc), silicon vacancy (Vsi) and carbon antisite-carbon vacancy (CAV) complex, the neutron irradiation has introduced four deep-level defects, all arising from the metastable defect, the M-center. The metastable deep-level defects were investigated by deep level transient spectroscopy (DLTS), high-resolution Laplace DLTS (L-DLTS) and isothermal DLTS. The existence of the fourth deep-level defect, M4, recently observed in ion-implanted 4H-SiC, has been additionally confirmed in neutron-irradiated samples. The isothermal DLTS technique has been proven as a useful tool for studying the metastable defects.

Impact of Proton and Electron Irradiation-Induced Defects on the Dark Current of GaAs Solar Cells

The same amount of non-ionizing energy is deposited in GaAs solar cells through 1 MeV proton and electron radiation at specific fluence values. The defects created are detected and characterized via temperature-dependent dark I–V analysis, and the energy levels are correlated to trap states observed via admittance spectroscopy. A remarkable difference is observed between the defect energy levels introduced in the proton and electron cases: in the former, the recombination centers lie around the mid-gap position, while in the latter they are spread over a wider energy range in the band-gap. This induces a profound difference in the degradation of the recombination current in the space-charge region. On the other hand, the degradation of the diffusion current in the neutral regions is found to be determined by the recombination velocities at the back and front hetero-interfaces of the solar cell. They depend only on the displacement damage dose and are independent of the particle type.

Electron irradiation-induced defects and photoelectric properties of Te-doped GaSb

Electron irradiation causes atomic displacement damage and produces point defects in semiconductor materials. The formation and variation of defects determine the optical properties of semiconductors during the irradiation process. In this paper, Te-doped GaSb was irradiated by 1 MeV electrons, with fluence of 1 × 1015 electrons cm−2, and its optical properties investigated by temperature-dependent photoluminescence (PL) before and after irradiation. After irradiation, the peak position had a blue-shift and intensity was significantly enhanced. The carrier concentration increased from 4.14 × 1017 to 7.82 × 1017 cm−3 but mobility decreased from 2690 to 1780 cm2 V−1 s−1. These phenomena could be explained by the complex mechanism of defect decomposition, that is, the VGaGaSbTeSb defect decomposed into two independent VGaGaSb and TeSb defects. To verify this mechanism, undoped GaSb was irradiated under the same conditions and PL results indicated that electron irradiation had little effect on optical properties of undoped GaSb.

Electron-irradiation induced defects in Yb2Ti2.05O7

We present a scanning transmission electron microscopy (STEM) analysis of electron irradiation-induced defects in Yb2Ti2O7, which form in material with a deliberate Ti excess. No defects were observed to form in stoichiometric or Yb-rich material. The defects in the Ti rich materials are regions of lower density, roughly 1.5 nm in thickness, lying along {111} or {110} planes. A minority of defects also contain extrinsic partial dislocation loops. We use geometric phase analysis of atomically-resolved annular-dark field STEM images combined with dislocation tensor analysis in a new program BurgersVectors to show that the Burgers vector of the partial dislocations are of 1/4〈110〉 type. Atomically-resolved energy-dispersive X-ray analysis shows that, although some cation disorder is observed in the affected region, the material does not fully transition to a defect fluorite structure. It is proposed that these phenomena, and their absence in stoichiometric and Yb-rich material, can be explained by the presence of negatively-charged Yb vacancies that are only present in material with a Ti excess. The injection of oxygen Frenkel pairs under energetic electron irradiation provides oxygen interstitials that can neutralize positively charged Ti atoms on the Yb sites, while the mobile oxygen vacancies combine with Yb vacancies and condense to form the observed low-density regions.

Charge puddles in a completely compensated topological insulator

Compensation of intrinsic charges is widely used to reduce the bulk conductivity of 3D topological insulators (TIs). Here we use low temperature electron irradiation-induced defects paired with in situ electrical transport measurements to fine-tune the degree of compensation in Bi2Te3. The coexistence of electrons and holes at the point of optimal compensation can only be explained by bulk carriers forming charge puddles. These need to be considered to understand the electric transport in compensated TI samples, irrespective of the method of compensation.

Photoluminescence Analysis of Injection-Enhanced Annealing of Electron Irradiation-Induced Defects in GaAs Middle Cells for Triple-Junction Solar Cells**Supported by the National Natural Science Foundation of China under Grant Nos 10675023, 11075018 and 11375028, and the Specialized Research Fund for the Doctoral Program of Higher Education under Grant No 20120003110011.

Photoluminescence measurements are carried out to investigate the injection-enhanced annealing behavior of electron radiation-induced defects in a GaAs middle cell for GaInP/GaAs/Ge triple-junction solar cells which are irradiated by 1.8MeV with a fluence of 1 × 1015 cm−2. Minority-carrier injection under forward bias is observed to enhance the defect annealing in the GaAs middle cell, and the removal rate of the defect is determined with photoluminescence radiative efficiency recovery. Furthermore, the injection-enhanced defect removal rates obey a simple Arrhenius law. Therefore, the annealing activation energy is acquired and is equal to 0.58 eV. Finally, in comparison of the annealing activation energies, the E5 defect is identified as a primary non-radiative recombination center.

Electron irradiation-induced defects in Mo-diluted FeCrNi austenitic alloy during void swelling incubation

The microstructural features and the effect of Mo addition in FeCrNi austenitic alloy during incubation period were investigated using positron annihilation technique and micro- Vickers Hardness. The electron irradiation, which could induce vacancy defects in material, was performed at room temperature up to the dose of 1.7×10-4 and 5×10-4 dpa, respectively. The defect concentration was estimated about 10-4–10-7 though the standard trapping model. The added Mo atoms could trap vacancies to form Mo-vacancy complexes, which may restrain the migration and growth of vacancy defects during electron irradiation. In addition, the microstructural evolution during electron radiation resulted in hardening, while the added Mo might improve the hardening property of the alloy.

Electroluminescence analysis of injection-enhanced annealing of electron irradiation-induced defects in GaInP top cells for triple-junction solar cells

Direct injection-enhanced annealing of defects in a GaInP top cell for GaInP/GaAs/Ge triple-junction solar cells irradiated with 1.8MeV electrons with a fluence of 1×1015 cm−2 has been observed and analyzed using electroluminescence (EL) spectra. Minority-carrier injection under forward bias conditions is observed to enhance defect annealing in the GaInP top cell, and recovery of the EL intensity of the GaInP top cell was observed even at room temperature. Moreover, the injection-enhanced defect annealing rates obey a simple Arrhenius law; therefore, the annealing activation energy was determined and is equal to 0.51eV. Lastly, the H2 defect has been identified as the primary non-radiative recombination center based on a comparison of the annealing activation energies.

Photoluminescence analysis of electron irradiation-induced defects in GaAs/Ge space solar cells

Photoluminescence measurements were carried out to investigate the degradation for GaAs/Ge space solar cells which were irradiated with 1.0, 1.8, and 11.5MeV electrons with fluences up to 3×1015cm−2. The product of the defect introduction rate and the minority carrier capture cross section by electron irradiation-induced defects was determined with photoluminescence radiative efficiency related to the non-radiative recombination lifetime. Then the cross section was acquired according to the relation between the defect introduction rate and the non-ionizing energy loss. Furthermore, the non-radiative recombination could be identified among all the detected defects by comparing the cross section of the minority carrier capture.

Atomistic observation of electron irradiation-induced defects in CeO2

ABSTRACTWe have investigated the atomistic structure of radiation-induced defects in CeO2 formed under 200 keV electron irradiation. Dislocation loops on {111} habit planes are observed, and they grow accompanying strong strain-field. Atomic resolution scanning transmission electron microscopy (STEM) observations with high angle annular dark-field (HAADF) and annular bright-field (ABF) imaging techniques showed that no additional Ce layers are inserted at the position of the dislocation loop, and that strong distortion and expansion is induced around the dislocation loops. These results are discussed that dislocation loops formed under electron irradiation are non-stoichiometric defects consist of oxygen interstitials.

Influence of irradiation-induced disorder on the Peierls transition in TTF–TCNQ microdomains

The combined influence of electron irradiation-induced defects, substrate-induced strain and finite size effects on the electronic transport properties of individual micron-sized thin film growth domains of the organic charge transfer compound tetrathiafulvalene– tetracyanoquinodimethane (TTF–TCNQ) have been studied. The TTF–TCNQ domains have been isolated and electrically contacted by focused ion beam etching and focused ion and electron-beam-induced deposition, respectively. This allowed us to measure the temperature-dependent resistivity and the current–voltage characteristics of individual domains. The dependence of the resistivity on temperature follows a variable-range hopping behaviour which shows a crossover of the exponents as the Peierls transition is approached. The low temperature behaviour is analysed within the segmented rod model of Fogler, Teber and Shklovskii which was developed for charge-ordered quasi one-dimensional electron crystals (Fogler et al 2004 Phys. Rev. B 69 035413). The effect of substrate-induced biaxial strain on the Peierls transition temperature is discussed with regard to its interplay with the defect-induced changes.

Study of Compensation Defects and Electron Irradiation-Induced Defects in Undoped SI-InP by Positron Lifetime Spectroscopy

Positron annihilation lifetime (PAL) spectroscopy，photo-induced current transient spectroscopy (PICTS) and thermally stimulated current (TSC) have been employed to study the formation of compensation defects and their evolvement under iron phosphide (IP) ambience or pure phosphide (PP) ambience. In the formation of IP SI-InP, the diffusion of Fe atoms suppresses the formation of some open-volume defects. As to PP SI-InP, VInH4 complexes dissociate into acceptor vacancies VInHn(n-3)(n=0,1,2,3), which compensate residual donor type defects and make the sample semi-insulating. Electron irradiation-induced deep level defects have been studied by TSC in PP and IP SI-InP, respectively. In contrast to a high concentration of irradiation-induced defects in as-grown and PP annealed InP, IP SI-InP has a very low concentration of defects.

A study of the dependence of electron-induced defects on the doping impurity density in n-type germanium by deep-level transient spectroscopy (DLTS)

We have measured the electrical characteristics of electron irradiation-induced defects in n-type (1 1 0), (1 1 1) and (1 0 0) germanium doped with antimony (Sb) by deep-level transient spectroscopy (DLTS) and Laplace-DLTS. The following electron traps at 0.04, 0.15, 0.20, 0.21, 0.23, 0.31 and 0.38 eV below the conduction band were observed and two hole traps at 0.09 and 0.30 eV above the valence band were recorded in the low doping (10 14 cm −3) samples. In the higher doping (10 15 cm −3) samples, similar electron traps were observed but the electron trap at 0.04 eV below the conduction band and hole trap at 0.09 eV above the valence band was not observed. The electron trap at 0.38 eV is identified as the (V–Sb) −−/− center and the hole trap at 0.30 eV assigned the (V–Sb) 0/− appeared in almost equal concentrations in the higher-doped samples but in the lowest-doped samples the hole trap (V–Sb) 0/− was more dominant. We have also presented the annealing behavior of these electron-induced defects.

Interaction of electron irradiation with nitrogen-related deep levels in InGaAsN

The authors present an investigation of 1MeV electron irradiation-induced defects in p-InGaAsN and their impact on nitrogen-related defects. A hitherto existing nitrogen-related electron trap E1 (0.20eV) shows a significant increase in concentration after 1MeV electron irradiation. In addition, 1MeV electron irradiation induced a hole trap H1 at energy of about 0.75eV above the valence band. Isothermal annealing analysis indicates that E1 is a complex defect involving an interstitial or a substitutional atom in combination with some other defect, whose concentration is enhanced by irradiation. A correlation exists between the recovery of free carrier concentration and recovery of the E1 center to preradiation concentrations, which indicates the possibility of the E1 as an acceptorlike center.

Silicon displacement threshold energy determined by electron paramagnetic resonance and positron annihilation spectroscopy in cubic and hexagonal polytypes of silicon carbide

Both for electronic and nuclear applications, it is of major interest to understand the properties of point defects into silicon carbide (SiC). Low energy electron irradiations are supposed to create primary defects into materials. SiC single crystals have been irradiated with electrons at two beam energies in order to investigate the silicon displacement threshold energy into SiC. This paper presents the characterization of the electron irradiation-induced point defects into both polytypes hexagonal (6H) and cubic (3C) SiC single crystals by using both positron annihilation spectroscopy (PAS) and electron paramagnetic resonance (EPR). The nature and the concentration of the generated point defects depend on the energy of the electron beam and the polytype. After an electron irradiation at an energy of 800keV vSi mono-vacancies and vSi–vC di-vacancies are detected in both 3C and 6H–SiC polytypes. On the contrary, the nature of point defects detected after an electron irradiation at 190keV strongly depends on the polytype. Into 6H–SiC crystals, silicon Frenkel pairs vSi–Si are detected whereas only carbon vacancy related defects are detected into 3C–SiC crystals. The difference observed in the distribution of defects detected into the two polytypes can be explained by the different values of the silicon displacement threshold energies for 3C and 6H–SiC. By comparing the calculated theoretical numbers of displaced atoms with the defects numbers measured using EPR, the silicon displacement threshold energy has been estimated to be slightly lower than 20eV in the 6H polytype and close to 25eV in the 3C polytype.

Electron irradiation-induced defects in InP pre-annealed at high temperature

Electron irradiation-induced deep level defects have been studied in InP which has undergone high-temperature annealing in phosphorus and iron phosphide ambients, respectively. In contrast to a high concentration of irradiation-induced defects in as-grown and phosphorus ambient annealed InP, InP pre-annealed in iron phosphide ambient has a very low concentration of defects. The phenomenon has been explained in terms of a faster recombination of radiation-induced defects in the annealed InP. The radiation-induced defects in the annealed InP have been compared and studied.

Electron irradiation-induced defects in ZnO studied by positron annihilation

ZnO crystals were subjected to 3 MeV electron irradiation up to a high dose of 5.5×10 18 cm −2. The production and recovery of vacancy defects were studied by positron annihilation spectroscopy. The increase of positron lifetime and Doppler broadening S parameter after irradiation indicates introduction of V Zn related defects. Most of these vacancies are annealed at temperatures below 200 °C. However, after annealing at around 400 °C, secondary defects are produced. All the vacancy defects are annealed out at around 700 °C.

Positron study of electron irradiation-induced vacancy defects in SiC

Based on positron annihilation experiments, we have proposed that in 3C-SiC isolated silicon vacancies are responsible for positron trapping after electron irradiation. We have also proposed that in hexagonal SiC one type of vacancy defects survives after annealing at 1000 °C which is attributable to carbon–vacancy–carbon–antisite complexes or silicon–vacancy–nitrogen pairs, while carbon vacancies, silicon vacancies and divacancies are excluded. In this study, from the theoretical calculations of positron lifetime and Doppler broadening of annihilation radiation, the above proposals are confirmed.