Irradiated Si Research Articles

Presence of reactive impurities in Ar+ ion beam plays a key role for Si ripple formation

We report the decisive role of reactive ion impurities in the low energy Ar+ ion beam on surface nanopattern formation. The effects of co-deposited impurities on pattern formation during ion bombardment have already been reported, but the effect of beam impurities is something new which has not been considered earlier. The possible source of experimental variance in the low energy (few keV to 10’s of KeV) Ar+ ion beam induced nano ripple formation has been identified by irradiating Si surface at an oblique angle incidence with the pure and impure Ar+ ion beam of energy 3–10 keV. No well-defined patterns are observed for the mass selected pure Ar+ ion bombardment, whereas well defined periodic ripple pattern is formed by the same experimental condition with the impure mass unanalyzed Ar+ ion irradiation. The contaminants in the mass unanalyzed beam specifically reactive nitrogen, oxygen, and carbon play the main role of pattern formation by introducing chemical instability on the Si surface. The surface morphologies of the irradiated Si surfaces are examined by Atomic Force Microscopy (AFM), whereas the surface contamination and corresponding chemical compound formation are investigated by X-ray photoelectron spectroscopy (XPS).

Microscopic Examination of the Silicon Surface Subjected to High-Dose Silver Implantation

Low-energy (E = 30 keV) Ag+ ions have been implanted into single-crystalline Si wafers (c-Si) with an implantation dose varying from 1.25 × 1015 to 1.5 × 1017 ions cm–2 and an ion beam current density varying from 2 to 15 μA/cm2. The surface morphology of implanted wafers has been examined using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy, and their structure has been studied by means of reflection high-energy electron diffraction and elemental microanalysis. It has been shown that for minimal irradiation doses used in experiments, the surface layer of c-Si experiences amorphization. It has been found that when the implantation dose is in excess of the threshold value (~3.1 × 1015 ions cm–2), Ag nanoparticles uniformly distributed over the Si surface arise in the irradiated Si layer. At a dose exceeding 1017 ions cm–2, a porous Si structure is observed. In this case, the Ag nanoparticle size distribution becomes bimodal with coarse particles localized at the walls of Si pores.

Микроскопия поверхности кремния, имплантированного ионами серебра высокими дозами

AbstractLow-energy ( E = 30 keV) Ag^+ ions have been implanted into single-crystalline Si wafers (c-Si) with an implantation dose varying from 1.25 × 10^15 to 1.5 × 10^17 ions cm^–2 and an ion beam current density varying from 2 to 15 μA/cm^2. The surface morphology of implanted wafers has been examined using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy, and their structure has been studied by means of reflection high-energy electron diffraction and elemental microanalysis. It has been shown that for minimal irradiation doses used in experiments, the surface layer of c-Si experiences amorphization. It has been found that when the implantation dose is in excess of the threshold value (~3.1 × 10^15 ions cm^–2), Ag nanoparticles uniformly distributed over the Si surface arise in the irradiated Si layer. At a dose exceeding 10^17 ions cm^–2, a porous Si structure is observed. In this case, the Ag nanoparticle size distribution becomes bimodal with coarse particles localized at the walls of Si pores.

Extraction and Analysis of Gamma Irradiated Si BJT SPICE Model

The Simulation Program with Integrated Circuit Emphasis (SPICE) model parameters of pre and post-irradiated silicon bipolar junction transistor (Si BJT) were extracted with the use of Altium Designer (AD)/SPICE model wizard. The percentage changes (Δ%) between forward and reverse-bias parameters of existing BJT (ZETEX BCW72) SPICE model were estimated and also the degradation Δ% between the experimental data of pre and post-irradiated Si BJT were calculated. Then the new measured results by comparison were imported into AD/SPICE model wizard to extracts forward-bias parameters. The extracted forward-bias parameters were used to generate reverse-bias parameters through Δ%. The final extracted Si BJT SPICE model parameters were implemented in SPICE simulator to obtained forward and reverse Gummel plots. As expected, base current (IB) increases, the collector current (IC) increases slightly at low bias base-emitter voltage, leading to current gain degradation due to positive charge trapped in the oxide and interface of the BJT device. In addition, the results of the IB in the forward Gummel flows in parallel with base-emitter junction, while the IB in the reverse Gummel flows across the base-collector junction down to the back side collector contact through the collector region. Finally, the compared results of Si BJT forward Gummel simulation and experimental data showed good agreement.

Interaction Rates of Group-III and Group-V Impurities with Intrinsic Point Defects in Irradiated Si and Ge

A comparative study of interactions of shallow impurities with primary defects in oxygen- and carbon-lean moderately doped Si and Ge subjected to irradiation with 0.9 MeV electrons, 60Co gamma-rays, and 15 MeV protons at room temperature is presented and discussed. For the quantitative characterization of such interactions, changes in the total concentration of the original shallow group-V donor or group-III acceptor impurities in the irradiated materials are determined by Hall effect measurements over a wide temperature range. Losses of the shallow donor or acceptor states in the irradiated Si and Ge are indicative of their removal rates that can be used for estimation of production rates of primary defects interacting with the dopants. Some important factors affecting the interactions between primary defects and shallow impurities in Si and Ge are highlighted.

Laser writing of nanostructured silicon arrays for the SERS detection of biomolecules with inhibited oxidation.

The present work reports the processing of laser irradiated Si arrays (LISi) and underlines their surface enhanced Raman scattering (SERS) functionality. A nanostructured Si/SiOx surface forms providing additional fluidic and photoprotective properties. Because of their optical and surface characteristics, the arrays exhibit a SERS analytical enhancing factor of 500, without any noble metals such as gold or silver. Micro-Raman maps allowed studying LISi properties, identifying maximum amplification in nanostructured areas characterized by the presence of 7 nm Si nanocrystals. These structures are confined by a SiOx layer as illustrated by XPS valence band measurements. The highly hydrophilic LISi areas allow a pre-concentration of target molecules prior to SERS analysis. A relevant application of LISi was found in the detection of apomorphine (APO), a drug used for the treatment of Parkinson's disease. In contrast with what is obtained by using gold SERS substrates, LISi allows the detection of APO with no sign of oxidation. This invites for the use of the Si/SiOx SERS detection in future systems for the personalized delivery of APO.

Study on top sulfur hyperdoping layer covering microstructured Si by fs-laser irradiation

We studied the infrared absorption of a top sulfur hyperdoping layer covering an fs-laser irradiated microstructured Si substrate. To clarify the hyperdoping concentration distributions, and to find out how the top hyperdoping layer affects infrared absorption from 1200 to 2000 nm, a continuous etching treatment was utilized. Then we interpreted the thermal stabilization of both infrared absorption and sulfur hyperdoping concentration. The fundamental cause for infrared-absorption degradation under thermal annealing was explained. Furthermore, we discussed in detail how the interaction between the top hyperdoping layer and surface microstructure contributed to the high infrared absorption by a series of theoretical simulations using a finite-difference time-domain method. A strong localization of an incident electromagnetic wave was observed around the top sulfur hyperdoping layer covering microstructured Si, which played a critical role in improving infrared absorption. The results in this paper are especially beneficial to the subsequent fabrication of photoelectric devices and infrared response improvement.

Vaporlike phase of amorphous SiO2 is not a prerequisite for the core/shell ion tracks or ion shaping

When a swift heavy ion (SHI) penetrates amorphous $\mathrm{Si}{\mathrm{O}}_{2}$, a core/shell (C/S) ion track is formed, which consists of a lower-density core and a higher-density shell. According to the conventional inelastic thermal spike (iTS) model represented by a pair of coupled heat equations, the C/S tracks are believed to form via ``vaporization'' and melting of the $\mathrm{Si}{\mathrm{O}}_{2}$ induced by SHI (V-M model). However, the model does not describe what the vaporization in confined ion-track geometry with a condensed matter density is. Here we reexamine this hypothesis. While the total and core radii of the C/S tracks determined by small angle x-ray scattering are in good agreement with the vaporization and melting radii calculated from the conventional iTS model under high electronic stopping power $({S}_{e})$ irradiations (g10 keV/nm), the deviations between them are evident at low-${S}_{e}$ irradiation (3--5 keV/nm). Even though the iTS calculations exclude the vaporization of $\mathrm{Si}{\mathrm{O}}_{2}$ at the low ${S}_{e}$, both the formation of the C/S tracks and the ion shaping of nanoparticles (NPs) are experimentally confirmed, indicating the inconsistency with the V-M model. Molecular dynamics (MD) simulations based on the two-temperature model, which is an atomic-level modeling extension of the conventional iTS, clarified that the ``vaporlike'' phase exists at ${S}_{e}\ensuremath{\sim}5$ keV/nm or higher as a nonequilibrium phase where atoms have higher kinetic energies than the vaporization energy, but are confined at a nearly condensed matter density. Simultaneously, the simulations indicate that the vaporization is not induced under 50-MeV Si irradiation $({S}_{e}\ensuremath{\sim}3$ keV/nm), but the C/S tracks and the ion shaping of nanoparticles are nevertheless induced. Even though the final density variations in the C/S tracks are very small at the low stopping power values (both in the simulations and experiments), the MD simulations show that the ion shaping can be explained by flow of liquid metal from the NP into the transient low-density phase of the track core during the first \ensuremath{\sim}10 ps after the ion impact. The ion shaping correlates with the recovery process of the silica matrix after emitting a pressure wave. Thus, the vaporization is not a prerequisite for the C/S tracks and the ion shaping.

Degradation of KNN-Based Lead-Free Piezoelectric Material Under Gamma Irradiation

(Na0.5K0.5)NbO3-(Bi0.5Li0.5)TiO3-BaZrO3 lead-free piezoelectric ceramics are irradiated to 50 Mrad(Si) by Co-60 gamma rays. The degradation behaviors of piezoelectric and ferroelectric characteristics are investigated. Most characteristics degrade fast during the first 10-Mrad(Si) irradiation and then degrade slowly. The 30% degradation of material performance at about 15 Mrad(Si) has been observed, which is much worse than that of lead zirconate titanate [Pb(Zr52Ti48)O3, PZT] ceramics. The (K, Na)NbO3-based ceramics have much more complex microstructures and interfaces than PZT ceramics, leading to the existence of much more defects and neutral traps. During irradiation, more ionized carriers are trapped. Stronger built-in electric field is established by inducing faster degradation of the material performance. The saturation of trapped charges at the domain wall might be the cause of the slowly degradation curve. Therefore, to successfully replace the lead-based piezoelectric material and improve the radiation tolerance in extreme radiation environment, the appropriate material compositions and corresponding fabrication process need to be considered.

The CiCs(SiI)n Defect in Silicon from a Density Functional Theory Perspective.

Carbon constitutes a significant defect in silicon (Si) as it can interact with intrinsic point defects and affect the operation of devices. In heavily irradiated Si containing carbon the initially produced carbon interstitial–carbon substitutional (CiCs) defect can associate with self-interstitials (SiI’s) to form, in the course of irradiation, the CiCs(SiI) defect and further form larger complexes namely, CiCs(SiI)n defects, by the sequential trapping of self-interstitials defects. In the present study, we use density functional theory to clarify the structure and energetics of the CiCs(SiI)n defects. We report that the lowest energy CiCs(SiI) and CiCs(SiI)2 defects are strongly bound with −2.77 and −5.30 eV, respectively.

Spectroscopic and morphological investigation of laser ablated silicon at various laser fluences

The effect of laser fluence by using laser-induced breakdown spectroscopy on the ablation mechanisms of Si (100) has been investigated. For this purpose a Q-switched Nd-YAG laser with the wavelength of 1064 nm, pulse duration of 10 ns was employed. For the very first time by using linearly polarized Nd:YAG laser, the effect of fluence and optical emission spectroscopy has been carried out for various laser fluences ranging from 1.4 × 102 to 11.3 × 102 J/cm2 under the ambient environment of He, Ne and Ar at a constant pressure of 200 torr. Boltzmann plot and Stark broadening method were used to determine the influence of laser fluences on plasma parameters such as electron temperature and number density. Our experimental results suggest that the laser fluence in different ambient environment play a significant role for plasma evolution, ambient gas causes a confinement effect that generation, recombination, and expansion of plasma and consequently affect the excitation temperature as well as electron density of plasma. The morphological analysis of laser irradiated Si was performed by Scanning Electron Microscope (SEM). Various kinds of structures e.g. Laser Induced Periodic Surface Structures (LIPSS) or ripples, droplets and craters have been generated and their density and size are found to be dependent upon the laser fluence and ambient environment. A quantitative analysis of crater depth measured from SEM images showed strong correlation between laser fluence and the growth of micro/nano structures on modified Si surface.

Investigations on surface morphology and bandgap engineering of single crystal boron-doped silicon irradiated by a nanosecond laser.

We irradiate the single crystal boron-doped silicon (Si) at various laser fluences with 100 laser shots in ambient air at room temperature using an Nd:YAG laser and investigate its surface morphology and optical properties. The optical microscopy gives evidence of the formation of a crater and reveals that the heat-affected zone and melted area are increased with increase in laser fluence from 1.1 to 15.4 J/cm2. The micrographs obtained by scanning electron microscopy (SEM) show that the micro- and nano-structures such as microcracks, bubbles, nucleation sites, clusters, redeposited layered material, nanoparticles, and alike water droplet structures are formed on a laser-exposed Si surface. The optical profilometry of the irradiated Si further confirms the ablation and redeposition of the material and shows that the depth of the crater is increased from 12.1 to 15.2μm with increase in fluence from 1.1 to 15.4 J/cm2. Raman spectroscopy of the samples shows that the irradiation generates anneal effects due to higher temperature, which increases the crystallinity of the Si. The ellipsometric analysis shows that the irradiation of Si with increasing laser fluence changes its optical constants (refractive index and extinction coefficient), which further influence its optical properties, e.g.,reflectivity, absorptivity, and energy bandgap. The absorptivity of laser irradiated Si tends to increase with increasing laser fluence, and the energy bandgap is decreased accordingly due to increase in structural disorders. Our study shows that the controlled laser irradiation can tune the energy bandgap of exposed Si, and it makes the Si materials useful for the fabrication of optoelectronic devices such as solar cells, photovoltaic cells, and LEDs.

Read Static Noise Margin Decrease of 65-nm 6-T SRAM Cell Induced by Total Ionizing Dose

Read static noise margin (SNM) decrease of 65-nm 6-T cell induced by total ionizing dose (TID) was observed in this paper. The static random access memory (SRAM) cell test structure allowing precise measurement of read SNM was specifically designed and irradiated by gamma ray. Experimental results show that read SNM of 65-nm 6-T cell is sensitive to TID irradiation. The largest decrease of read SNM is 48 mV after 1000 krad(Si) irradiation, which is 36% of the value before TID irradiation. Being dependent on the measurement of radiation responses of cell transistors and simulation results, we conclude that the read SNM decrease is due to a threshold voltage shift induced by TID. Because narrow width transistors are employed in SRAM cells, threshold voltage of cell transistors will be shifted by charges trapped in shallow trench isolation, known as “Radiation-Induced Narrow Channel Effect.”

Interaction rates of group-III and group-V impurities with intrinsic point defects in irradiated Si and Ge -=SUP=-*-=/SUP=-

Interaction rates of group-III and group-V impurities with intrinsic point defects in irradiated Si and Ge -=SUP=-*-=/SUP=-

The COV defect in neutron irradiated silicon: An infrared spectroscopy study

We report infrared (IR) spectroscopy studies on defects in carbon containing neutron irradiated Czochralski grown silicon (Cz-Si). Prior to irradiation the material was subjected to high temperature treatments (HT) at 1000°C. Two weak bands at 842 and 852cm−1 were mainly investigated. It was found that their intensity depends on the oxygen and carbon content of Si. Additionally, the bands exhibit an annealing behavior similar to that of the 3942cm−1 optical band of the carbon-oxygen-vacancy (COV) complex, previously reported in electron irradiated Si. Semi-empirical calculations of the local vibration mode (LVM) frequencies of a proposed structure of the COV complex are in very good agreement with our experimental data. These findings led us to assign the pair of bands at 842 and 852cm−1 to the COV defect.

Fabrication of nanoporous Si electrocathode by high-energy argon ion irradiation for improved electrocatalytic hydrogen production

Developing a cost-effective material to replace Pt catalysts for hydrogen evolution reaction (HER) holds great promising for clean energy technologies. In this work, we developed a simple way to prepare nanoporous Si by argon ion irradiation at 90 keV to fluences of 0.5, 1, 2 × 1017 ions/cm2. After post-irradiation annealing at 700 °C in vacuum (2 × 10−4 pa) for 5 h, the nanoporous Si was formed which displays largely enhanced electrocatalytic water splitting compared with the unirradiated Si. We also investigated the influence of fluence on morphology and the HER performance of the electrocathodes. It was found that 1 × 1017 Ar+ ions/cm2 irradiated Si showed the highest HER performance. The largely enhanced HER activity comes from the unique morphology which results by Ar+ ions irradiation and post-irradiation annealing. We further fabricated electrocathodes by coating Ni film on the nanoporous Si, significant improvement of the HER performance compared with Ni coated planar Si was found. Using the ion irradiation technology, we developed a new method to fabricate electrocathode with large specific surface area for largely enhanced hydrogen evolution reaction activities.

Multipulse nanosecond laser irradiation of silicon for the investigation of surface morphology and photoelectric properties

We irradiate the single crystal boron-doped silicon (Si) with different number of laser pulses at constant fluence (7.5 J cm−2) in ambient air using Nd:YAG laser and examine its surface morphology and photoelectric properties in details. The results obtained from optical micrographs reveal the increase in heat affected zone (HAZ) and melted area of laser irradiated Si with increasing number of laser pulses. The SEM micrographs evidence the formation of various surface morphologies like laser induced periodic surface structures, crater, microcracks, clusters, cavities, pores, trapped bubbles, nucleation sites, micro-bumps, redeposited material and micro- and nano-particles on the surface of irradiated Si. The surface profilometry analysis informs that the depth of crater is increased with increase in number of incident laser pulses. The spectroscopic ellipsometry reveals that the multipulse irradiation of Si changes its optical properties (refractive index and extinction coefficient). The current–voltage (I–V) characteristic curves of laser irradiated Si show that although the multipulse laser irradiation produces considerable number of surface defects and damages, the electrical properties of Si are well sustained after the multipulse irradiation. The current findings suggest that the multipulse irradiation can be an effective way to tune the optical properties of Si for the fabrication of wide range of optoelectronic devices.

Anneal induced transformations of defects in hadron irradiated Si wafers and Schottky diodes

In this research, the anneal induced transformations of radiation defects have been studied in n-type and p-type CZ and FZ Si samples, irradiated with relativistic protons (24GeV/c) and pions (300MeV/c) using particle fluences up to 3 × 1016cm−2. The temperature dependent carrier trapping lifetime (TDTL) spectroscopy method was combined with measurements of current deep level transient spectroscopy (DLTS) to trace the evolution of the prevailing radiation defects. The contactless TDTL technique has been shown to be preferential when the radiation induced trap density approaches or exceeds the dopant concentration and when it is necessary to avoid modification of a detector structure due to annealing processes at elevated temperatures. The deep level spectra were complementarily examined by using DLTS spectroscopy on Schottky diodes made of irradiated Si wafer fragments. The dominant radiation defects and their transform paths under isothermal and isochronal anneals have been revealed. A good agreement between the DLTS and TDTL spectra has been obtained.

Modifying the Morphology of Silicon Surfaces by Laser Induced Liquid Assisted Colloidal Lithography.

Single, or isolated small arrays of, spherical silica colloidal particles (with refractive index ncolloid = 1.47 and radius R = 350 nm or 1.5 μm) were placed on a silicon substrate and immersed in carbon tetrachloride (nliquid = 1.48) or toluene (nliquid = 1.52). Areas of the sample were then exposed to a single laser pulse (8 ps duration, wavelength λ = 355 nm), and the spatial intensity modulation of the near field in the vicinity of the particles revealed via the resulting patterning of the substrate surface. In this regime, ncolloid < nliquid and the near-field optical intensification is concentrated at and beyond the edge of the particle. Detailed experimental characterization of the irradiated Si surface using atomic force microscopy reveals contrasting topographies. The same optical behavior is observed with both liquids, i.e., the incident laser light diverges on interaction with the colloidal particle, but the resulting interaction with the substrate is liquid dependent. Topographic analysis indicates localized ablation and patterning of the Si substrate when using toluene, whereas the patterning induced under carbon tetrachloride is on a larger scale and extends well below the original substrate surface—hinting at a laser induced photochemical contribution to the surface patterning.

Beta-induced decrease in the content of the Si-II, Si-XII, Si-III, and α-Si silicon phases formed under an indenter

Volumes of the metastable Si-II, Si-XII, Si-III, and α-Si silicon phases in a locally deformed (Berkovich pyramid) region of unirradiated and beforehand irradiated Si single crystals are quantitatively estimated. Experimental data obtained by Raman spectroscopy and in situ detection of Si-I → Si-II silicon phase transformations under an indenter are used to calculate the volumes. The preliminary irradiation of silicon by β particles from a 90Sr–90Y source (fluence F = 3.24 × 1010 cm–2, intensity I = 1.8 × 105 cm–2 s–1) reduces the volume of these phases by a factor of more than 1.5.