Irradiation effects in semiconductor

Samples of crystalline silicon, porous silicon, gallium arsenide and silicon diodes were exposed to 50–80 MeV silicon and oxygen ions in the fluence range of the order of 10¹³ to 10¹⁴ ions/cm². The irradiated samples were characterized to obtain information on the relative concentration and depth distribution of the induced defects. For comparison a few silicon diodes and crystalline silicon samples were also exposed to 6 MeV electrons. The main techniques used for the analysis of silicon samples were low angle X-ray diffraction, photo-luminescence spectroscopy and lifetime of minority carriers, whereas diodes were characterized on the basis of switching parameters. It is observed that a large number of defects are produced in the surface region of each of the irradiated semiconductor sample though the energy deposited in the surface region through electronic loss is three orders of magnitude greater than that of nuclear collisions.     

The response of a CsI(Tl) scintillator with photodiode readout to light particles and heavy ions

The response of a small (1 cm³) CsI(Tl) crystal coupled to a silicon photodiode to light particles and heavy ions has been investigated using proton, alpha and oxygen beams in the energy range 10–25 MeV/n.Pulse-height resolution of 1.2 and 2.9% [fwhm] have been measured for 98 MeV ⁴He and 278 MeV ¹⁶O. The use of CsI(Tl)-photodiode assembly in nuclear physics experiments with intermediate energy heavy-ions beams is envisaged     

Precision measurement of target position during irradiation

We have developed a technique to measure the position of thin target foils (≤ 10 μm/cm²) during irradiation with an accuracy of ∼ 7 μm. The experiment makes use of a kinematic coincidence technique, recording the scattered as well as the recoil particles in a precisely known geometrical setup. For 3 μm/cm² carbon foils bombarded by 4 MeV ¹²C²⁺ ions, target foil movements of about 4 μm/h were observed.     

High-resolution short range ion detectors based on 4H-SiC films

The energy resolution of SiC detectors has been studied in application to the spectrometry of α particles with 5.1–5.5 MeV energies. The Schottky barrier structure of the detector was based on a CVD-grown epitaxial n-4H-SiC film with a thickness of 26 μm and an uncompensated donor concentration of (1–2)×10¹⁵ cm^?3. An energy resolution of 0.5% achieved for the first time with SiC detectors allows fine structure of the α particle spectrum to be revealed. The average energy of the electron-hole pair formation in 4H-SiC is estimated at 7.71 eV.     

Development of integrated ΔE-E silicon detector telescope using silicon planar technology

An integrated ΔE-E silicon detector telescope using silicon planar technology has been developed. The technology developed is based on standard integrated circuit technology and involves double sided wafer processing. The ΔE and E detectors have been realized in a PIN configuration with a common buried N⁺ layer. Detectors with ΔE thicknesses of 10, 15 and 25 μm, and E detector with thickness of 300 μm have been fabricated and tested with alpha particles using ²³⁸Pu-²³⁹Pu dual alpha source. The performance of the detector with ΔE detector of thickness 10 μm and E detector of thickness 300 μm has been studied for identification of charged particles using 12 MeV ⁷Li⁺ ion beam on carbon target. The results of these tests demonstrate that the integrated detector telescope clearly separates the charged particles, such as alpha particles, protons and ⁷Li. Due to good energy resolution of the E detector, discrete alpha groups corresponding to well known states of ¹⁵N populated during the reaction could be clearly identified.     

Determination of the flouride concentration profile in tooth enamel using a nuclear resonance technique

The ¹⁹F (p,αγ) ¹⁶O reaction has been used to measure the concentration profile of fluorine in tooth enamel. By observing the characteristic 6.13 MeV gamma ray with a high resolution Ge(Li) detector, the fluorine concentration was measured to a depth of 2.1 μm in teeth treated with K₂ZrF₆, NaF and acidulated fluorophosphate. The differential depth resolution was better than 0.1 μm at the surface of the teeth. Additional information on the average elemental concentration within the first 2 μm was obtained by observing the characteristic X-ray produced by 1.8 MeV protons. The exploratory data developed in this study have indicated that the highest uptake of fluoride was achieved through the application of K₂ZrF₆.     

Effect of calcium on primary silicon particle size in hypereutectic Al–Si alloys

Abstract

Modification of hypereutectic Al-Sialloy, B390 alloy for the refinement of primary silicon particles, and its effects on tensile and impact properties were examined. Calcium was found to have an effect on the size of primary silicon particles. Primary silicon particle size was refined as calcium content decreased. Control of calcium content by the addition of Ti₂Cl₆ to the melt resulted in successful refinement of primary silicon particles. The minimum size of primary silicon particles was 20.3 μmwitha residual calcium content of 16 ppm. The microstructure was composed of very fine 20.3 μm primary silicon particles, compared to 24.5 μm primary silicon particles obtained using the AlCuP method, previously reported as the most effective method. Refinement of primary silicon particles led to an improvement in the mechanical properties of the alloy, especially elongation.     

Silicon nitride films prepared by reactive plasma sputtering

Silicon nitride films were prepared by reactive plasma sputtering in nitrogen at a pressure of 2×10^-4 Torr. The residual gas in the reactor during film sputtering was analysed. The chemical composition of the films was determined from infrared absorption spectra in the wavelength region 2.0–15.0 μm and by the elastic scattering of ³He particles.The best quality silicon nitride films were obtained in pure nitrogen at the minimum residual gas pressures. An absorption minimum at 11.0 μm in the infrared spectra, corresponding to the Si-N chemical bond in the Si₃N₄ molecule, was observed in our films, indicating that their composition was close to stoichiometric.With a residual hydrogen pressure above 10% or a residual oxygen pressure above 2% the generation of new chemical bonds Si-H, N-H and Si-O respectively was observed in the silicon nitride films.     

A study of the effect of electron and proton irradiation on 4H-SiC device structures

The changes of the current–voltage characteristics and the uncompensated donor-impurity concentration (N _d –N _a ) in the base electrode of Schottky diodes and JBS diodes based on 4H-SiC have been studied upon their irradiation with 0.9-MeV electrons and 15-MeV protons. The carrier-removal rate was 0.07–0.15 cm^–1 under electron irradiation and 50–70 cm^–1 under proton irradiation. It was shown that the current–voltage characteristics of the devices under study remain rectifying at electron irradiation doses of up to ~1017 cm^–2. It was demonstrated that the radiation hardness of the SiC-based devices under study substantially exceeds that of silicon p–i–n diodes with similar breakdown voltages.

     

Dopant concentration dependence of the response of SiC Schottky diodes to light ions

The responses of Silicon Carbide (SiC) Schottky diodes of different dopant concentration to ¹²C ions at 14.2, 28.1 and 37.6 MeV incident energies are compared. The relation between the applied reverse bias and the thickness of the depleted epitaxial region is studied for different dopant concentrations. The experimental data show that SiC diodes with lower dopant concentration need lower reverse bias to be depleted. Moreover it has been observed that the energy resolution, measured as a function of the applied reverse bias and of the ions incident energies, does not depend on the dopant concentration. The radiation damage, produced by irradiating SiC diodes of different dopant concentration with ¹⁶O ions at 35.2 MeV, was evaluated by measuring the degradation of both the signal pulse-height and the energy resolution as a function of the ¹⁶O fluence. Diodes having a factor 20 lower dopant concentration exhibit a radiation hardness reduced by 60%. No inversion in the signal at the breakdown fluence was observed for ¹⁶O ions stopped inside the diode epitaxial region.     

Surface texturing of silicon by dynamic recoil mixing

A technique known as dynamic recoil mixing is used in which a film of constant mass of gold can be maintained on a silicon substrate whilst it is being bombarded by energetic ions. The technique is used to produce surface texturing of silicon. Scanning electron microscopy and Rutherford backscattering techniques have been used to study the development of surface texture as a function of 10 keV Ar⁺ ion fluence. The results show the regrowth of silicon crystallites into the gold film as the Ar⁺ ion fluence increases until at high doses of 1 × 10¹⁷ ions cm^-2 the silicon crystallites coalesce and overlap the initial layer burying some of the gold beneath them. IR transmission of the silicon textured surface shows an increase of 4% for an ion fluence of (1–6) × 10¹⁶ ions cm^-2 in the wavelenght range 2.5–3 μm.     

Comparative measurements of highly irradiated n-in-p and p-in-n 3D silicon strip detectors

Silicon detectors in 3D technology are a candidate for applications in environments requiring an extreme radiation hardness, as in the innermost layers of the detectors at the proposed High-Luminosity LHC. In 3D detectors, the electrodes are made of columns etched into the silicon perpendicular to the surface. This leads to higher electric fields, a smaller depletion voltage and a reduced trapping probability of the charge carriers compared to standard planar detectors. In this article, the signal and the noise of irradiated n-in-p and p-in-n 3D silicon strip detectors are compared. The devices under test have been irradiated up to a fluence of 2×10¹⁶ 1 MeV neutron equivalent particles per square centimetre (n_eq/cm²), which corresponds to the fluence expected for the inner pixel detector layers at the High-Luminosity LHC. A relative charge collection efficiency of approximately 70% was obtained even after the highest irradiation fluence with both detector types. The influence of different temperatures on the signal and the noise is investigated and results of annealing measurements are reported.     

Flow‐Through Microbial Capture by Antibody‐Coated Microsieves

A new flow‐through method for rapid capture and detection of microorganisms is developed using optically‐flat microengineered membranes. Selective and efficient capture of Salmonella is demonstrated with antibodies coated on membranes (microsieves) having a pore size much larger than the microorganism itself. The silicon‐nitride membranes are first photochemically coated with 1,2‐epoxy‐9‐decene yielding stable Si–C and N–C linkages. The resultant epoxide‐terminated microsieves are subsequently biofunctionalized with anti‐Salmonella antibodies. The capture efficiency of antibody‐coated microsieves with different pore sizes (2.0–5.0 μm) is studied with Salmonella enterica enterica serotype Typhimurium suspensions (10⁷ cfu mL^–1). The antibody‐coated microsieves capture 52% (2 μm microsieves), 30% (3.5 μm microsieves), and 12% (5 μm microsieves) of Salmonella from the suspension. The influence of flow rate (0.8–16 μL min^–1 mm^–2) on the capture efficiency of antibody‐coated 3.5 μm microsieves is investigated. The capture efficiency increases from ≈30% to ≈70% when the flow‐rate decreases from 16 to 0.8 μL min^–1 mm^–2. Antibody‐coated 3.5 μm microsieves can capture Salmonella rapidly and directly from fresh milk suspension (capture 35% at concentration of 80 cfu mL^–1). The use of antibody‐coated microsieves as microbial selective capture devices is thus shown to be highly promising for the direct capture of microorganisms.     

Alloyed inversion layer solar cells with n-Si substrates and TiOx antireflection coatings

Minority carrier inversion layer solar cells on n-type single-crystal silicon substrates have been fabricated. The photovoltaic structure used consists of a p⁺ −n alloyed aluminium grid pattern with a layer of chemically vapour-deposited titanium oxide as the antireflection coating. The titanium oxide layer contains negative charges (of the order of 10¹² cm⁻²) which can induce positive charges (holes) on the silicon surface and so cause inversion of the n-type substrate. A back surface field is obtained by heavily doping the back surface of the substrate with phosphorous which also provides the ohmic contact.An air mass 1 active area efficiency of 15.7% (13.6% total area efficiency) has been achieved with a 133 μm grid spacing on a 10–20 Ω cm polished single-crystal material. Similar efficiencies have also been obtained from rough-surface cells (i.e. with unpolished silicon surfaces).     

Hot-pressing behaviour of silicon carbide powders with additions of aluminium oxide

The hot-pressing behaviour of different silicon carbide powders (average particle sizes ranging from ～ 0.5 to 9 μm) with aluminium oxide additions ranging from 0.01 to 0.15 volume fractions was investigated. Using powders with an average particle size < 3 μm, densities ≥ 99% theoretical could be achieved at 1950° C (1 h) with 28 MN m^?2 for volume fractions of AI₂O₃ \(\bar > \) 0.02. A liquid phase forms at high temperatures which dissolves the silicon carbide particles to promote densification by a solution-reprecipitation mechanism.     

Resolution tests of CsI(Tl) scintillators read out by pin diodes

Cylindrical CsI(Tl) scintillators of 38 mm diameter and 100 mm length read out with PIN diodes of 400 mm² area were tested with respect to their response to medium energy light particles (p, d, t, α). Resolutions of better than 1% were achieved for 50 MeV protons and 90 MeV α-particles. For many crystals the resolution was found to be limited to 2–3% by local crystal nonuniformities which caused variations of the light output efficiency of several percent. A bench test is described which allows the detection of inhomogeneities to better than 0.5% accuracy. The quality of particle identification obtained with ΔE-E and pulse shape discrimination techniques are investigated as a function of count rate.     

Radiation damage in silicon strip detectors

Silicon strip detectors with 5 μm spatial resolution have been used during 1982–1985 in the ACCMOR spectrometer at CERN. After a local beam flux of about 10¹⁴ minimum ionizing particles per cm² we observe a significant increase in dark current and systematic distortions in the measured coordinates which are explained in terms of a decrease in the effective donor concentration.     

Characteristics of subcooled water boiling on structured surfaces

Characteristics of the process and heat transfer of subcooled water boiling on mesostructured surfaces obtained by microarc oxidation of titanium foil with formation of a TiO₂ layer and deposition of Al₂O₃ particles from boiling nanofluid have been experimentally investigated. The experiments have been carried out in the forced flow of deaerated water in a vertical rectangular channel, 21 × 5 mm in size. The ranges of regime parameters are as follows: water mass velocity is up to 650 kg/(m2 s), subcooling is 30–75°C, pressure is ~10⁵ Pa, and heat flux rate is 0.7–5.0 MW/m². It is established that the number of active nucleation sites is (70–80) × 105 1/(m² s) at the heat flux of 1.5–2.0 MW/m². Significant subcooling of the liquid and good wettability of the structured surface provide intense deactivation and lead to random spatial distribution of the nucleation sites. The characteristic size of vapor bubbles is about 200–250 μm and the bubble lifetime is 200–500 μs. Application of the coating prepared by microarc oxidation enhances heat transfer by 20–30%. At high subcoolings of liquid, the characteristics of boiling on smooth surfaces and surfaces with the coating were fairly close.     

DLTS study of the influence of annealing on deep level defects induced in xenon ions implanted n-type 4H-SiC

In this study, nitrogen-doped 4H-SiC samples were bombarded with 167 MeV xenon ions to a fluence of 1?×?10⁸ cm^?2 at 300 K prior to the fabrication of Schottky barrier diodes. The implanted samples were annealed at approximately 900 °C for 1 h before the resistive evaporation of nickel Schottky barrier diodes. In comparing the current–voltage results of the implanted devices with as-deposited ones, generation-recombination took place in the implanted Schottky barrier diodes. Four defects (100, 120, 170, and 650 meV) were present in as-deposited Schottky barrier diodes when characterized by deep level transient spectroscopy (DLTS). In addition to the defects observed in the as-deposited samples, two additional defects with activation energies of 400 and 700 meV below the conduction band minimum were induced by Xe ions implantation. The two deep level defects present have signatures similar to defects present after irradiated by MeV electron. The two defects present after irradiation disappeared after annealing at 400 °C which indicate instability of the defects after annealing implanted samples.

     

Growth conditions and properties of evaporated semicrystalline silicon layers

Semicrystalline silicon layers 50–100 μm thick were vacuum deposited onto stainless steel and Pyrex glass substrates using an electron beam evaporation process. Because of the ultrahigh deposition rate (20–50 μm min^-1) the silicon layers had a columnar structure on substrates that had been previously coated with aluminium.The layers on stainless steel contained both grain boundaries and twin planes whereas the layers on Pyrex glass showed only twin planes. This difference in structure can be explained by considering the crystallinity of the substrates and the difference in surface temperatures during growth due to the different thermal properties of stainless steel and Pyrex glass.