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.

     

Signal,recombination effects and noise in amorphous silicon detectors

Some properties of hydrogenated amorphous silicon diodes are described. Back biased diodes of the Schottky, p-i-n type, in thicknesses ranging from 5–15 μm, have been tested with 6 MeV alpha particles and with 1 and 2 MeV protons. Large signal saturation, due to electron-hole recombination, occurs for high LET particles. Diodes have been exposed to fast neutron fluences up to 10¹³ cm⁻² and shown to have better radiation resistance than similarly exposed crystalline silicon detectors. From our measurements we extrapolate that minimum ionizing particles can be detected with stacked layers 100–120 μm thick, with adequate signal/noise levels.     

GaN optical degradation during high energy Sn<Superscript>5+</Superscript> ion irradiation

GaN(0001) epilayers grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD) have been irradiated with 75 MeV Sn⁵⁺ ions at the fluences of 10¹¹, 10¹², and 10¹³ ions/cm². Structural and optical studies reveal that GaN epilayer withstands 75 MeV Sn⁵⁺ ion irradiations up to 10¹¹ ions/cm² ion fluences. High resolution X-ray diffraction results showed that the FWHM corresponding to (0002) plane increased from 227 to 279 arc-seconds after Sn-ions irradiation. Red shift was observed in the yellow luminescence (YL) emission by photoluminescence (PL), corresponds to the concentration of ion fluences. Donor-bound exciton (DBE) and free exciton (FE^A, FE^B and FE^C) emissions were observed for as-grown and irradiated GaN samples up to 10¹² ions/cm² at 2K PL measurements. Free excitons are dominated by low-temperature PL measurements for as-grown and irradiated GaN samples at 10¹¹ and 10¹² ion fluences. Atomic force microscopy images show the RMS roughness increases with increasing Sn-ion fluences by removing as-grown GaN surface defects.     

Ion beam studies of multi-quantum wells of III-nitrides

III-Nitrides have attracted much attention due to their versatile and wide range of applications, such as blue/UV light emitting diodes. Strained layer super lattices offer extra degree of freedom to alter the band gap of lattice-mismatched heterostructures. Swift heavy ion irradiation is a post-growth technique to alter the band gap of semiconductors, spatially. In the present study, strained AlGaN/GaN multi-quantum wells (MQWs) were grown on sapphire with insertion of AlN and GaN as buffer layers between substrate and epilayers. Such grown AlGaN/GaN MQWs, AlGaN/GaN heterostructures and GaN layers were irradiated with 200 MeV Au and 150 MeV Ag ions at a fluence of 5 × 10¹¹ ions/cm² and 5 × 10¹² ions/cm² respectively. As-grown and irradiated samples have been characterized by high resolution XRD, photoluminescence and RBS/channelling. Measured strain values show that strain increases upon irradiation and the luminescence properties are enhanced. RBS/channelling confirms the increase in strain values upon irradiation. In this paper we describe the effects of swift heavy ion irradiation on structural and optical properties.     

Mixing induced by swift heavy ion irradiation at Fe/Si interface

The present work deals with the mixing of metal and silicon by swift heavy ions in high-energy range. Threshold value for the defect creation in metal Fe calculated was found to be ∼ 40 keV/nm. A thin film of Fe (10 nm) was deposited on Si (100) at a pressure of 4 × 10⁻⁸ Torr and was irradiated with 95 MeV Au ions. Irradiation was done at RT, to a dose of 10¹³ ions/cm² and 1 pna current. The electronic energy loss was found to be 29.23 keV/nm for 95 MeV Au ions in Fe using TRIM calculation. Compositional analysis of samples was done by Rutherford backscattering spectroscopy. Reflectivity studies were carried out on the pre-annealed and post-annealed samples to study irradiation effects. Grazing incidence X-ray diffraction was done to study the interface. It was observed that ion beam mixing reactions at RT lead to mixing as a result of high electronic excitations.     

Structural,optical, and electrical characteristics of 70 Mev Si<Superscript>5+</Superscript> ion irradiation-induced nanoclusters of gallium nitride

We report the formation of nanoclusters on the surface of gallium nitride (GaN) epilayers due to irradiation with 70 MeV Si ions with the fluences of 1 × 10¹² ions/cm² at the liquid nitrogen temperature (77 K). GaN epilayers were grown using a metal organic chemical vapor deposition system. Omega scan rocking curves of (002) and (101) plane reflection shows irradiation-induced broadening. Atomic force microscopy imagery revealed the formation of nanoclusters on the surface of the irradiated samples. X-ray photoelectron spectroscopy confirms that the surface features are composed of GaN. The effects of ion-beam-produced lattice defects on the surface, electrical, and optical properties of GaN were studied and possible mechanisms responsible for the formation of nanoclusters during irradiation have been discussed.     

Defect formation in silicon implanted with ∼1 MeV/nucleon ions

Defect formation processes in silicon implanted with ∼1 MeV/nucleon boron, oxygen, and argon ions have been studied using microhardness and Hall effect measurements. The results indicate that ion implantation increases the surface strength of silicon single crystals owing to the formation of electrically inactive interstitials through the diffusion of self-interstitials from the implantation-damaged layer to the silicon surface. The radiation-induced surface hardening depends significantly on the nature of the ion, its energy, and the implant dose. In the case of low-Z (boron) ion implantation, the effect had a maximum at an implant dose of ∼5 × 10¹⁴ cm⁻², whereas that for O⁺ and Ar⁺ ions showed no saturation even at the highest dose reached, 1 × 10¹⁶ cm⁻². When the ion energy was increased to ∼3 MeV/nucleon (210-MeV Kr⁺ ion implantation), we observed an opposite effect, surface strength loss, due to the predominant generation of vacancy-type defects.     

Modifications induced by silicon and nickel ion beams in the electrical conductivity of zinc nanowires

This paper presents the modification in electrical conductivity of Zn nanowires under swift heavy ions irradiation at different fluences. The polycrystalline Zn nanowires were synthesized within polymeric templates, using electrochemical deposition technique and were irradiated with 80 MeV Si⁷⁺ and 110 MeV Ni⁸⁺ ion beams with fluence varying from 1 × 10¹² to 3 × 10¹³ ions/cm². I–V characteristics of exposed nanowires revealed a decrease in electrical conductivity with increase in ion fluence which was found to be independent of applied potential difference. But in the case of high fluence of Ni ion beam (3 × 10¹³ ions/cm²), electrical conductivity was found to increase with potential difference. The analysis found a significant contribution from grain boundaries scattering of conduction electrons and defects produced by ion beam during irradiation on flow of charge carriers in nanowires.     

12C5+ radiation effects in SR-86 track recording polymer

The samples of SR-86 polymer were irradiated with¹²C⁵⁺ ions of energy 5·0 MeV/u using fluences of 10¹¹−10¹⁴ ions/cm² at NSC Pelletron in a high vacuum scattering chamber. The optical studies show an increase in absorption of UV or IR in the shorter wavelength region (250–500 nm). The study also reveals that the increase in radiation dose extends the optical absorption region to longer wavelengths. It is observed that the bulk etch rate of this polymer is enhanced after heavy ion irradiation.     

Structural and electrical properties of swift heavy ion beam irradiated Fe/Si interface

The present work deals with the mixing of iron and silicon by swift heavy ions in high-energy range. The thin film was deposited on a n-Si (111) substrate at 10⁻⁶ torr and at room temperature. Irradiations were undertaken at room temperature using 120 MeV Au⁺⁹ ions at the Fe/Si interface to investigate ion beam mixing at various doses: 5 × 10¹² and 5 × 10¹³ ions/cm². Formation of different phases of iron silicide has been investigated by X-ray diffraction (XRD) technique, which shows enhancement of intermixing and silicide formation as a result of irradiation. I-V measurements for both pristine and irradiated samples have been carried out at room temperature, series resistance and barrier heights for both as deposited and irradiated samples were extracted. The barrier height was found to vary from 0·73–0·54 eV. The series resistance varied from 102·04–38·61 kΩ.     

Surface conduction behaviour of 100 Mev Si ion irradiated kapton-H polyimide

The surface conduction behaviour of kapton-H polyimide irradiated with 100 MeV Si⁺ ion (Fluences 2.3 × 10¹¹, 2.3 × 10¹² and 1.3 × 10¹³ ions/cm²) has been investigated in the temperature range 21 to 150°C. The current-voltage (I-V) characteristics in the low field region i.e., below 10 kV/cm show ohmic behaviour whereas non-linearity occurs in the high field region. The non-linear region is temperature dependent. The nature of I-V characteristics of pristine kapton-H samples doesnt differ much from the irradiated samples suggesting that the surface charge conduction mechanisms are not much affected due to irradiation. The ionic jump distance estimations (3–18 Å) supports to ionic conduction process below 110°C. The Poole-Frenkel and Schottky coefficient estimations show that Poole-Frenkel and Schottky conduction mechanisms are operative at moderate and low temperatures, respectively. The observed change in surface resistivity () in the irradiated samples has been associated to the increase in delocalized -electrons and cross-linking.     

Visualization of the ion projected range region in GaAs irradiated with argon ions

Cleavages of GaAs samples irradiated with 2.1, 4.6, and 8.4 MeV Ar⁺ ions were studied by scanning electron microscopy (SEM). SEM visualization of the ion projected range region was used to determine the range of Ar⁺ projectiles in the semiconductor target.     

Characterization of electron irradiated GaN n-p diode

Electron-beam irradiated GaN n⁺-p diodes were characterized by deep level transient spectroscopy (DLTS) and optical responsivity measurements. The GaN n⁺-p diode structures were grown by metal organic chemical vapor deposition technique, and the electron irradiation was done by the energies of 1 MeV and 2 MeV with dose of 1 × 10¹⁶ cm^− 2. In DLTS measurement, the defect states of E_c − 0.36 eV and E_c − 0.44 eV in the electron irradiated diodes appeared newly. The optical responsivity of GaN n⁺-p diode was characterized in ultra-violet region, and then the maximum optical responsivity at 350 nm was decreased after electron-beam irradiation.     

Mössbauer studies of iron doped poly(methyl methacrylate) before and after ion beam modification

High-energy MeV ions from accelerators are known to produce drastic modifications in polymers. The typical effects include chain scissions, crosslinks, molecular emission and double bond formation. Poly(methyl methacrylate) was doped with Fe(III) and irradiated with 95 MeV O⁷⁺ ions.⁵⁷Fe-Mössbauer studies were done on the doped samples before and after irradiation. Before irradiation, no Mössbauer absorption was observed. The irradiated samples showed a good Mössbauer absorption, which seems to indicate that there is a significant interaction between the metal ion and the polymer matrix. Two possibilities exist at these doses (～ 22 × 10¹² ions/cm): Fe(III) ions may be bridging the various polymer segments through crosslinking or amorphization of the sample leading to Fe-C bonding. Studies of FTIR, conductivity and glass transition temperatures on these samples support these observations.     

Radiation hardness of cryogenic silicon detectors

We shall review test results which show that silicon detectors can withstand at 130 K temperature a fluence of 2×10¹⁵ cm^–2 of 1 MeV neutrons, which is about 10 times higher than the fluence tolerated by the best detectors operated close to room temperature. The tests were carried out on simple pad devices and on microstrip detectors of different types. The devices were irradiated at room temperature using reactor neutrons, and in situ at low temperatures using high-energy protons and lead ions. No substantial difference was observed between samples irradiated at low temperature and those irradiated at room temperature, after beneficial annealing. The design of low-mass modules for low-temperature trackers is discussed briefly, together with the cooling circuits for small and large systems.     

High resolution X-ray diffraction studies on unirradiated and irradiated strontium hexaferrite crystals

High-resolution X-ray diffraction technique, employing a three-crystal monochromator?Ccollimator combination is used to study the irradiation induced defects in flux grown Sr-hexaferrite crystals irradiated with 50?MeV Li³⁺ ion beams at room temperature with a fluence value of 1 × 10¹⁴ ions/cm². The diffraction curves of the irradiated crystals suggest the possibility of creation of low angle grain boundaries and other point/clusters of defects causing amorphization in the irradiated crystals. The perfection of the irradiated and unirradiated (0001) cleaved surfaces of the crystals is studied using the bulk method of X-ray topography. The topographs supplement the findings suggestive of modifications in the crystalline quality of SrFe₁₂O₁₉ on irradiation with SHI of Li^3?+?. Etching of the (0001) cleaved surfaces in H₃PO₄ at 120°C suggests that the dissolution characteristics of the surfaces get affected on irradiation with SHI of Li^3?+?, besides supporting the findings of HRXRD and X-ray topography regarding modifications in the perfection of SrFe₁₂O₁₉ on irradiation.     

Optical study of ion-induced effects in Ge20Se80−xBix thin films

Incorporation of impurities into the semiconductors by high energy heavy ions is a non-equilibrium process, which can result in intriguing near surface or subsurface property changes depending upon the energy of the ion. Present work deals with the optical study of Ni ion irradiated Ge₂₀Se_80−xBi_x thin films samples. The thin film samples were deposited by the flash evaporation method at 10⁻⁵ Torr and were characterized by XRD, XRF, EPMA and DSC. Irradiation was done on samples with a Ni ion beam of 75 MeV energy. The optical spectra of the films were recorded and the optical band gap study was done both as a function of dose (5 × 10¹² to 10¹⁴ ions/cm²) as well as composition of the samples. The optical band gap was found to decrease with increasing Bi content as well as with increasing dose.     

Radiation damage in negative-differential resistance devices

Tunnel diodes made with silicon and gallium arsenide have been tested in both neutron- and gamma-radiation environments. Experimental data show that failure usually occurs in the range 10¹⁴–10¹⁸ n cm^–2 or 50-270 Mrad range. The primary failure mechanism for neutron-irradiated ] samples is an increase in the valley current (from 0.10 mA to 0.58 mA and from 1.5 A to 30 A for silicon and GaAs diodes, respectively). In the case of gamma-irradiated silicon samples, the valley current reaches a value of 0.48 mA, at 260.8 Mrad, although their initial values are 0.1 mA. As a result, the peak-to-valley current ratios of the irradiated devices were shown to decrease severely. Both the valley and forward peak voltage values were shown to decrease with radiation. Values of 0.18 and 0.25 V for silicon samples were measured after exposure to 5 × 10¹⁶ n cm^–2 although their initial values were 0.42 and 0.80 V, respectively. As a result, the devices' output power were shown to be affected seriously. Finally, silicon devices irradiated for 48h in the ET-RR-1 research reactor, Egypt, for up to 1.872 × 1011 n cm^–2 or to gamma doses up to 2.6 × 10⁸ rad, were greatly influenced and they lost their main feature as PN-junctions.     

Comparative studies of defect production in heavily doped silicon under fast electron irradiation at different temperatures

Production processes of electrically active defects in degenerate silicon subjected to 2.5 MeV electron irradiation at T = 4.2 K and T = 300 K have been studied. The production rates of primary and secondary defects in irradiated samples are analyzed on the basis of the known properties of radiation-produced defects in Si. It has been demonstrated that a striking difference in the production rates of electrically active defects in n- and p-Si under irradiation at cryogenic temperatures may be related to the different fate of Frenkel pairs in both materials. The production rate of primary defects in degenerate Si was found to be between 1.5 cm⁻¹ and 2 cm⁻¹.     

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.