MeV Implantation Research Articles

Effect of Silver Nanoparticles on the Photoluminescence of Silicon Nanocrystals

ABSTRACT In this article, we report the photoluminescence of three different systems produced by ion implantation: a high-purity silica substrate with silicon nanocrystals and two samples containing silicon nanocrystals in the vicinity of silver nanoparticles. The silicon nanocrystals were formed inside silica matrix by 1.5MeV implantation of silicon ions and annealing. Subsequent implantations with silver ions at different energies were performed to vary the distance between the previously formed silicon nanocrystals and newly aggregated silver nanoparticles. The samples were studied by photoluminescence, Rutherford backscattering spectrometry, m-line, and optical absorption. The enhancement of photoluminescence is well evidenced at the lowest implantation energy of silver, but at higher energies, a decrease in intensity is observed.

3D-microscopy of hydrogen in tungsten

Abstract The mapping of hydrogen distributions in 3 dimensions and its correlation with structural features allow further insight into mechanisms of hydrogen trapping in tungsten. We studied hydrogen distributions in 25 μm thick polycrystalline tungsten foils by 3D hydrogen microscopy using a proton–proton-scattering method. Two types of tungsten samples were prepared: (i) at 1200 K annealed foils and using 1.8 MeV implantation energy (ii) at 2000 K annealed foils using 200 eV implantation energy. It has been found that large variations of surface hydrogen contamination occur within different samples. Nevertheless, a statistically significant variation of the hydrogen content across grain boundaries has been observed.

Nonlinear optical properties of MeV and keV ion beam synthesized Ag nanoclusters

Ag nanoclusters embedded in silica glass matrix have been synthesized by high fluence ion implantation using both keV and MeV ion beams. In keV implantation case, optical absorption shows an intense surface plasmon resonance (SPR) peak corresponding to the Ag clusters formed in the matrix. Transmission electron microscopy (TEM) measurements carried out on identically implanted SiO2 thin films on a TEM catcher grid shows the presence of Ag nanoclusters of size around 4nm in the matrix. However, for the MeV implantation case, the SPR peak appears in the optical absorption spectra only after air annealing the sample at 500°C for one hour. For the annealed samples, TEM measurements show the presence of 6nm sized Ag nanoclusters. On the other hand the as-implanted sample shows smaller nanoclusters with a lower particle density in the matrix. Interestingly, open aperture z-scan measurements carried out on keV implanted samples did not show any nonlinear absorption, while the MeV as-implanted as well as annealed samples showed nonlinear absorption. The nonlinear absorption coefficient of the MeV annealed sample is extracted from a fit to the z-scan data considering a three photon like absorption process.

Raman Scattering Studies of InP Nanostructures Created by MeV Sb Ion Implantation

We have investigated the nanostructures created via MeV implantations by utilizing the techniques of Raman scattering and scanning probe microscope (SPM). SPM demonstrates that a large number of nanostructures are smaller than 100 nm in size and lower than 4 nm in height. SPM and Raman scattering techniques have been combined to show that although InP surfaces initially become rougher with increasing fluence, they become smoother after critical fluence when the crystalline/amorphous phase transition takes place. Raman spectroscopy further suggests an increase in tensile stress on the InP surface with increasing ion fluences. Phonon confinement model (PCM) has been applied to investigate the correlation length of the crystalline nano-zones in the InP lattice. Results indicate that crystalline nano-zones of 35 A may be embedded in the InP lattice at high fluences.

Raman scattering characterization and electron phonon coupling strength for MeV implanted InP(111)

Structural modifications in InP(111) due to 1.5 MeV implantation of Sb have been characterized using first-order and second-order Raman spectroscopy. With both longitudinal optical (LO) and transverse optical (TO) modes allowed for InP(111), we have investigated the evolution of both these modes as a function of fluence. Investigations of both the first and second-order Raman modes indicate the presence of tensile stress in the lattice after implantation, which increases with fluence. Results show a coexistence of nanocrystalline InP regions and amorphous zones in the lattice. Consequently phonon confinement is observed and phonon confinement model (PCM) has been applied here to estimate the coherence length and the size of nanocrystalline zones in InP lattice after implantation. Nanocrystalline zones as small as 35 Å have been observed here. A LO phonon-plasmon coupled mode, due to the charge layer in the vicinity of the surface, has also been observed. This coupled mode becomes sharper and more intense with increasing fluence. For high fluences, crystalline to amorphous phase transition has also been observed. First and second-order LO modes have been utilized to estimate the electron-phonon coupling strengths. The coupling strength is observed to decrease as the nanocrystalline zones, in the implanted lattice, become smaller.

Is there an influence of ion-beam-induced interfacial amorphization on the a/c-interface depth in silicon at common implantation energies?

Ion-beam-induced interfacial amorphization (IBIIA) of Si, i.e. the growth of an existing amorphous layer upon ion bombardment, has previously been demonstrated for high-energy (MeV) heavy ions. Using transmission electron microscopy we show that IBIIA cannot be observed for sub-MeV energies at liquid nitrogen temperature, while it still exists at room temperature, in spite of the fact that for MeV implants the IBIIA rate increases with decreasing temperature. The experimental conditions investigated are 60keV Si and 560keV Ge implants. We corroborate the liquid nitrogen results by molecular dynamics simulations. The observation of IBIIA at room temperature for sub-MeV energies suggests that it should be considered for modeling the position of the a/c-interface in amorphizing implants.

Shape transition of nanostructures created on Si(1 0 0) surfaces after MeV implantation

We have studied the modification in the surface morphology of the Si(100) surfaces after 1.5MeV Sb implantation. Scanning probe microscopy has been utilized to investigate the ion implanted surfaces. We observe the formation of nanosized defect features on the Si surfaces for the fluences of 1×1013ions/cm2 and higher. These nanostructures are elliptical in shape and inflate in size for higher fluences. Furthermore, these nanostructures undergo a shape transition from an elliptical shape to a circular-like at a high fluence. We will also discuss the modification in surface roughness as a function of Sb fluence.

Pattern formation on InP(1 1 1) surfaces after ion implantation

We have investigated the formation of nanosized structures on InP(111) surfaces after 1.5MeV Sb implantation. Scanning probe microscope (SPM) has been utilized to investigate the size, height and the density distributions of the nanostructures as a function of ion fluence. We observe nanostructures smaller than 100nm and lower than 4nm at all fluences. Moreover in large nanostructures we observe agglomeration of several smaller structures. We have also investigated the rms surface roughness of the InP(111) surfaces after MeV implantations.

Application of high energy ion beam for the control of boron diffusion

For the purpose of optimizing the process of co-implantation of MeV Si ions to reduce boron transient enhanced diffusion and boron-enhanced diffusion in Si, multiple MeV implantations and annealing at different temperatures have been performed. A slight improvement on the suppression of B diffusion is observed by adding a low temperature annealing step after the MeV implantation. No differences in B diffusion are observed when the Si doses are increased from 1×1015 to 1×1016cm−2. This dose independent behavior is speculated to be a quasi-steady state of vacancy cluster evaporation.

Effect of substrate temperature on the radiation damage from MeV Si implantation in Si

We have investigated the radiation damage by MeV implantation of Si in Si and its evolution under thermal annealing. Si wafers were implanted with MeV Si at various substrate temperatures. Damages were characterized by Rutherford-backscattering (RBS) channeling and by transmission electron microscopy (TEM). Defect formation after post-implantation annealing is very sensitive to the substrate temperatures during implantation. When the substrate temperature was decreased to 200K, TEM revealed two distinct bands of damage after annealing: one around the mean projected ion range and another at half the projected range. Our study indicates that the formation of defects at half range results from the solid phase epitaxy growth of initial buried amorphous layers.

실리콘에 고에너지 안티몬이온주입의 실험과 개선된 모델에 관한 연구

Antimony profiles by MeV implantation are measured by secondary ion mass spectrometry (SIMS) and spreading resistance (SR). The moments of SIMS and simulated profiles are calculated and compared for the exact range in MeV energy. SRIM, DUPEX, ICECREM, and TSUPREM4 simulation programs are used for the calculation of range 1D, 2D. SRIM is a Monte Carlo simulation program and different inter-atomic potentials can be used for the calculation of nuclear stopping power cross-section (Sn) and range moments. Nevertheless, the range parameters were not influenced from nuclear stopping power in MeV. Through the modification of electronic stopping power cross-section (Se), the results of simulation are remarkably improved and matched very well with SIMS data. The values of electronic stopping power are optimized for Sb high energy implantation. For the electrical activation, Sb implanted samples are annealed under <TEX>$N_2$</TEX> and <TEX>$O_2$</TEX> ambient. Finally, Oxidation retard diffusion(ORD) effect of Sb implanted sample are demonstrated by SR measurements and ICECREM simulation.

Using point defect engineering to reduce the effects of energy nonmonochromaticity of B ion beams on shallow junction formation

We have shown that energy contamination introduced by deceleration technology, for increasing the beam currents available for low energy boron implants, can affect fabricated junctions adversely. Energy contamination at a level of 0.1% can extend the profile of 0.5 keV B implants 10 nm deeper after a 1050 °C spike annealing. A highly monoenergetic beam with energy contamination less than 0.1% is required for submicron devices. Furthermore, we have used MeV implantation as a technique of point defect engineering (PDE) to control boron diffusion. PDE can reduce boron clustering and enhance boron activation. Diffusion of B in the tail region has been reduced significantly and the boron profile is much sharper. PDE lowers the critical requirement for beam purity. We conclude that shallower and sharper box-like boron junctions can be achieved by PDE with sub-keV B implants with highly monoenergetic beams.

Recovery of the carrier density in arsenic-doped silicon after high energy (2 MeV) Si+ implantation

Carrier density and mobility measurements were performed on heavily arsenic-doped silicon-on-insulator specimens after 2 MeV implantation of Si+ ions. It is found that implantation induces a marked reduction of the electron density, which increases with the concentration of active dopant, and approaches saturation for a Si+ fluence of 5×1015 cm−2. Recovery of the carriers was studied by isothermal annealing at temperatures in the range of 550–800 °C. It is shown that this phenomenon can be separated by As deactivation, which takes place at the same time, and that the kinetics of carrier recovery can be expressed by the rate equation: −dn/dt=nγC exp(−Ea/kT), with Ea=2.3 eV and γ=2.32. The recovery rate increases with As concentration, and values of C that account for this phenomenon are reported. These results and the annealing behavior of the carrier mobility in the damaged and undamaged reference samples indicate that the decrease of the carrier density upon irradiation can be attributed to acceptor centers, probably due to point defects clusters.

Continuous-wave laser action at λ=1064.3 nm in proton- and carbon-implanted Nd:YAG waveguides

This work reports continuous laser oscillation at λ=1064.3 nm at room temperature in Nd:YAG planar waveguides fabricated by two different techniques: proton implantation with a multi-implant of energies around 1 MeV and carbon implantation with a single-implant at an energy of 7 MeV. Threshold powers of 11 and 22 mW and slope efficiencies of 7% and 9% were achieved in the proton- and carbon-implanted guides, respectively. The laser outputs show a very high stability operating in cw regime at room temperature.

Using point-defect engineering to increase stability of highly doped ultrashallow junctions formed by molecular-beam-epitaxy growth

Stability of p+/n junctions remains a critical issue for device performance. We report that the technique of point-defect engineering (PDE) can substantially increase the stability of ultrashallow junctions formed by molecular-beam epitaxy. It is shown that an as-grown 15 nm, 2×1020/cm3 B-doped Si layer becomes unstable during 10 min thermal anneal above 650 °C. The thermal stability can be increased by performing a 5×1015/cm2 1 MeV Si ion implantation. The B profile with the MeV Si implant does not show significant diffusion during annealing up to 750 °C, and the final junction depth after an 800 °C/10 min anneal is about half that of an annealed unimplanted sample. Although with Mev implantation the as-implanted B profile becomes slightly deeper due to recoil implantation, and some of the B has been electrically deactivated by the MeV implantation, PDE is advantageous for postgrowth thermal processes above 700 °C. The mechanism causing the instability is discussed.

Post-Implantation Thermal Annealing Effect on the Gate Oxide of Triple-Well-Structure

In this work, we investigate the effect of post-implantation thermal annealing on the quality of thin gate oxides grown on MeV ion-implanted Si substrates for the triple-well structure. The thin gate oxide grown on the MeV ion-implanted Si substrates without post-implantation thermal annealing may contain pinholes, leading to oxide failure at a very low voltage; in addition, the gate oxide has a higher density of interface states, which may result in a low breakdown voltage. With appropriate post-implantation thermal annealing before the growth of the gate oxide, e.g., 1000°C for 30 min under the MeV implantation conditions employed in this work, the gate oxide is able to regain its integrity in terms of electrical breakdown voltage.

High-energy (MeV) Al and B ion implantations into 4H-SiC and fabrication of pin diodes

High-energy (MeV) implantation of Al+ or B+ into 4H-SiC epilayers has been investigated. A 3 μm deep pn junction was formed by multiple-step Al+ or B+ implantation with implantation energies up to 6.2 or 3.4 MeV, respectively. Rutherford backscattering channeling and cross-sectional transmission electron microscopy analyses have revealed residual damages in the implanted layers even after high-temperature annealing at 1600–1800 °C. Nevertheless, high electrical activation ratios over 90% have been achieved for both Al+- and B+-implanted layers by annealing at 1800 °C. Mesa pin diodes with a 15-μm-thick i layer formed by MeV implantation have exhibited high breakdown voltages of 2860–3080 V. The reverse characteristics of diodes have been substantially improved by increasing annealing temperature up to 1800 °C. The diode performance is discussed with the results of deep level analyses near the junctions.

Effect of ion beam irradiation on metal silicon junctions

The effect of MeV and low energy nitrogen implantation on the electrical properties of metal semiconductor junctions is studied. It is found that MeV implantation has better contact performance is comparison to keV nitrogen implantation. The defects introduced due to MeV implantation have very little effect on contact formation.

Vacancy Clusters at Nanoparticle Surfaces

The authors detect vacancy clusters at Au nanoparticle surfaces using a combination of positron lifetime spectroscopy, 1- detector, and 2-detector measurements of Doppler broadening of annihilation radiation. Gold nanoparticles are formed by MeV implantation of gold ions into MgO (100) followed by annealing. Clusters of two Mg and two O vacancies (v{sub 4}) are attached to the gold nanoparticle surfaces within the projected range (R{sub p}).

Track formation in KTiOPO 4 by MeV implantation of light ions

In order to investigate the damaging in KTiOPO 4 due to light ion irradiation with energies in the MeV region various light ions were implanted at room temperature. In the case of 4 MeV N and 3 MeV B implantation in the near-surface region, i.e. in the region of dominating electronic energy deposition, by means of RBS an ion-fluence dependent damage production up to the formation of amorphous layers at ion fluences N I=3×10 13 and 1.5×10 14 cm −2 , respectively, was found. Both XTEM and RBS measurements indicate that the accumulation of detectable damage requires a repeated overlap of individual damage cascades which leads to the formation of amorphous tracks. The diameter of the resulting tracks determined from XTEM images agrees well with that determined from the ion fluence dependence of the RBS minimum yield using the overlap damage model and a fourfold overlap of individual cascades. Contrary to that, 1 MeV Li-implantation does not result in a remarkable damage formation near the surface up to ion fluences in the order of 10 16 cm −2 . The results show that the near-surface damage in KTP is due to high electronic excitation and occurs only if the electronic energy deposition per ion and unit length exceeds a critical value around 100 eV/ion/Å.