Sequential Ion Implantation Research Articles

Hyperdoped Si nanocrystals embedded in silica for infrared plasmonics.

We present the experimental realization of plasmonic hyperdoped Si nanocrystals embedded in silica via a combination of sequential low energy ion implantation and rapid thermal annealing. We show that phosphorus dopants are incorporated into the nanocrystal cores at concentrations up to six times higher than P solid solubility in bulk Si by combining 3D mapping with atom probe tomography and analytical transmission electron microscopy. We shed light on the origin of nanocrystal growth at high P doses, which we attribute to Si recoiling atoms generated in the matrix by P implantation, which likely increase Si diffusivity and feed the Si nanocrystals. We show that dopant activation enables partial nanocrystal surface passivation that can be completed by forming gas annealing. Such surface passivation is a critical step in the formation of plasmon resonance, especially for small nanocrystals. We find that the activation rate in these small doped Si nanocrystals is the same as in bulk Si under the same doping conditions.

Process engineering of GaN power devices via selective-area p-type doping with ion implantation and ultra-high-pressure annealing

P-type doping in selected areas of gallium nitride (GaN) using magnesium (Mg)-ion implantation and subsequent ultra-high-pressure annealing (UHPA) are investigated to improve the performance of vertical GaN power devices. UHPA allows a high-temperature process without decomposition of the GaN surface and virtually complete activation of the implanted Mg ions in GaN. In the present paper, we provide an overview of recent challenges in making UHPA more realistic as an industrial process. Instead of UHPA at more than 1400 °C for a short duration, prolonged UHPA at 1300 °C demonstrates a comparable acceptor activation of Mg-ion-implanted GaN. This can reduce the annealing pressure to approximately 300 MPa and enlarge the processable wafer diameter. The second challenge is controlling the doping profiles in the lateral and vertical directions. We demonstrate fine patterning of the p-type regions, which indicates the limited lateral diffusion of Mg through UHPA. However, controlling the vertical doping profile is challenging. The nitrogen vacancies formed by ion implantation reduce the effective acceptor concentration near the surface, which can be compensated for by sequential nitrogen ion implantation. Defect-assisted Mg diffusion to the deeper region causes a redistribution of the Mg atoms and should be considered in the design of a device. Such anisotropic diffusion of Mg to the c-axis has potential applications in the fabrication of unique vertical device structures such as super junctions.

Synthesis of bimetallic AuAg nanoparticles by sequential ion implantation for modifying surface-plasmon-resonance properties

Bimetallic AuAg (Au (80%) and Ag (20%)) nanoparticles (NPs) have been synthesized in fused quartz matrix using sequential ion implantation and post-annealing in air at 600 °C, 700 °C, 800 °C and 900 °C. X-ray diffraction (XRD) results confirm the formation of crystalline Au80Ag20 bimetallic NPs after annealing. Transmission electron microscopy (TEM) investigations have confirmed presence of spherical AuAg alloyed and few AuAg alloy core- Ag shell/satellite NPs. Rutherford backscattering spectra, along with fittings, revealed the mixing of Au and Ag atoms after annealing and movement of elements towards the surface. The peak position of the surface plasmon resonance (SPR) feature of Au has been shifted towards higher energy after sequential Ag implantation. The SPR peak position and intensity is further modified after annealing of Au80Ag20 NPs. The mechanism of modified SPR properties is mechanistically discussed by considering the diffusion, alloying, segregation and redistribution of Au/Ag in the host matrix.

A Novel Hierarchical Nanostructure for Enhanced Optical Nonlinearity Based on Scattering Mechanism.

Surface modification of nonlinear optical materials (NOMs) is widely applied to fabricate diverse photonic devices, such as frequency combs, modulators, and all-optical switches. In this work, a double-layer nanostructure with heterogeneous nanoparticles (NPs) is proposed to achieve enhanced third-order optical nonlinearity of NOMs. The mechanism of modified optical nonlinearity is elucidated to be the scattering-induced energy transfer between adjacent NPs layers. Based on the LiNbO3 platform, as a typical example, double layers of embedded Cu and Ag NPs are synthesized by sequential ion implantation, demonstrating twofold magnitude of near-infrared enhancement factor and modulation depth in comparison with a single layer of Cu NPs. With the elastic collision model and thermolysis theory being considered, the shift of the localized surface plasmon resonance (LSPR) peak reveals the formation mechanism of the double-layer nanostructure. Utilizing the enhanced optical nonlinearity of LiNbO3 as modulators, a Q-switched mode-locked waveguide laser at 1µm is achieved with shorter pulse duration. It suggests potential applications to improve the performance of nonlinear photonic devices by using double-layer metallic nanostructures.

Gallium nitride nanocrystal formation in Si3N4 matrix by ion synthesis

Synthesis of nanoparticles in insulators attracts tremendous attention due to their unique electrical and optical properties. Here, the gallium (Ga) and gallium nitride (GaN) nanoclusters have been synthesized in the silicon nitride matrix by sequential ion implantation (gallium and nitrogen ions) followed by either furnace annealing (FA) or rapid thermal annealing (RTA). The presence of Ga and GaN nanoclusters has been confirmed by Fourier-transform infrared, Raman and X-ray photoelectron spectroscopy. Thereafter, the effect of RTA and FA on the conduction of charge carriers has been studied for the fabricated devices. It is found from the current–voltage measurements that the carrier transport is controlled by the space charge limited current conduction mechanism, and the observed values of parameter m (trap density and the distribution of localized state) for the FA and RTA devices are ~2 and ~4.1, respectively. This reveals that more defects are formed in the RTA device and that FA provides better performance than RTA from the viewpoint of opto- and nano-electronic applications.

Nanostructured c-Si surfaces obtained by sequential ion implantation of C+ and Ti+: Tribophysical and structural characterization

The effect of the sequential implantation of C+ and Ti+ ions on the microstructure and tribophysical properties of smooth crystalline silicon surfaces (c-Si) is evaluated. Microstructural characterization of the samples was performed by scanning electron microscopy, grazing incidence X-ray diffraction and by Rutherford backscattering spectrometry. The surface free energies of the implanted surfaces were also determined and their nanotribological response was evaluated by atomic force microscopy (AFM). It is shown that the sequential implantation of these ions, followed by annealing treatments at proper temperatures, results in thin modified nanolayer formed by a dense dispersion of SiC and TiSi2 nanoparticles in a recrystallized Si matrix that leads to a decrease of the surface energy of the samples, with enhanced nanowear response. These results strongly suggest that this approach can be used to improve the surface properties of Si wafers enlarging its application performance, namely in what concerns NEMS and MEMS devices.

Formation of Au-Ag alloy nanoparticles in amorphous silicon using sequential ion implantation

Au-Ag alloy nanoparticles were formed into amorphous silicon by sequential ion implantation of Au and Ag. Monocrystalline Si was amorphized at the initial moment of implantation with 1 × 1016 ions/cm2 gold ions, and then different silver fluences were applied in the range of 1 × 1016–1 × 1017 ions/cm2. After implantations the samples were investigated by means of Rutherford backscattering spectrometry and transmission electron microscopy. The nanoparticles were found to be formed at surface and sub-surface regions of the Si substrate, at depths corresponding to the maximum distribution of Au and Ag ions. The particles are crystalline in nature with sizes from 2 nm to 30 nm in diameter, increasing with silver ion fluence. Although the lattice constants of gold and silver are too close to be distinguished by measuring the characteristic interplanar spacings, imaging in scanning transmission mode confirms the formation of Au-Ag bimetallic nanoparticles, presenting a solid-solution alloy of gold and silver.

Optical changes in silica by sequential ion implantation of Au and Ag

Optical changes in silica by sequential ion implantation of Au and Ag

Synthesis of AuAg@Ag core/shell bimetallic nanoparticles in titanium nitride thin films by sequential ion implantation

In this study, we demonstrated the formation of a new type of AuAg@Ag nanostructure in titanium nitride (TiN) thin films using sequential implantation of Au and Ag ions. The TiN films deposited by DC reactive sputtering were sequentially implanted with 200 keV gold ions at fluences of 0.5 × 1016 and 1 × 1016 ions/cm2 and 150 keV silver ions at fluences of 1 × 1016, 2 × 1016, 3 × 1016, and 4 × 1016 ions/cm2. Formation of spherical-like particles with dimensions below 10 nm, homogeneously distributed along the ion track of implanted ions is verified by high resolution transmission electron microscopy. Specific nanostructure containing AuAg alloy in the center of the particle and only silver on the periphery was found in the TiN sample sequentially implanted with 1.0 × 1016 ions/cm2 of Au and 4 × 1016 ions/cm2 of Ag using high angle annular dark field scanning electron microscopy together with elemental mapping analysis. On the other hand, for the sample implanted with 0.5 × 1016 ions/cm2 of Au and 4 × 1016 ions/cm2 of Ag only formation of AuAg alloy was observed. A mechanism for the formation of a new type core/shell nanostructure in ion implanted TiN thin films is proposed. By varying the implantation fluence of the gold and silver ions properly, the optimized experimental parameters for creation of a specific AuAg@Ag core/shell nanoparticles were achieved.

Sequential nitrogen ion implantation in Si-based GaAs matrix and subsequent thermal annealing process: electrical characterization

Sequential nitrogen ion implantation in Si-based GaAs matrix and subsequent thermal annealing process: electrical characterization

Room-temperature photoluminescence lifetime for the near-band-edge emission of (0001¯) p-type GaN fabricated by sequential ion-implantation of Mg and H

Photoluminescence (PL) spectra of (0001¯) N-polar p-type GaN fabricated by using the sequential ion-implantation of Mg and H with subsequent high temperature annealing exhibited the near-band-edge (NBE) emission at 300 K. The longest PL lifetime (τPL) for the NBE emission of the sample with Mg and H concentrations of 1 × 1019 and 2 × 1020 cm−3, respectively, annealed at 1230 °C was 18 ps at 300 K. This value is almost comparable to that of the (0001) Ga-polar p-type Mg-doped GaN (p-GaN:Mg) homoepitaxial film of the same Mg concentration. By correlating τPL and the concentration of major vacancy-type defects quantified using positron annihilation spectroscopy, the electron capture-cross-section (σn) of the major nonradiative recombination centers (NRCs), namely, clusters of Ga vacancies (VGas) and N vacancies (VNs) such as (VGa)3(VN)3, is estimated at a few times 10−13 cm2. This σn value is also comparable to that of the major NRCs in p-GaN:Mg epilayers, namely, VGa(VN)2 or VGa(VN)3, although the clustering sizes of the defects are different. These σn values are commonly larger than the hole capture-cross-section (σp = 7 × 10−14 cm2) of the major NRCs, VGaVN divacancies, in n-type GaN.

Ultra-low-energy ion-beam synthesis of nanometer-separated Si nanoparticles and Ag nanocrystals 2D layers

2D networks of Si and Ag nanocrystals have been fabricated in the same SiO2 matrix by Ultra-Low-Energy Ion-Beam-Synthesis. Our synthesis scheme differs from a simple sequential ion implantation and its key point is the control of the matrix integrity through an appropriate intermediate thermal annealing. Si nanocrystal layer is synthesised first due to high thermal budget required for nucleation, while the second Ag nanocrystal plane is formed during a subsequent implantation due to the high diffusivity of Ag in silica. The aim of this work is to show how it is possible to overcome the limitation related to ion mixing and implantation damage to obtain double layers of Si-NCs and Ag-NCs with controlled characteristics. For this, we take advantage of annealing under slight oxidizing ambient to control the oxidation of Si-NCs and the Si excess in the matrix. The nanocrystal characteristics and in particular their position and size can be adjusted thanks to a compromise between the implantation energy, the implanted dose for both Si and Ag ions and the intermediate annealing conditions (atmosphere, temperature and duration).

A method to determine the pressure and densities of gas stored in blisters: Application to H and He sequential ion implantation in silicon

H and He sequential ion implantation of silicon followed by annealing leads to the formation of gas pressurized cavities. When close enough to the surface, they elastically deform this surface and generate blisters. Gaining knowledge of the characteristics and thermal behavior of these blisters is mandatory for the optimization of the Smart Cut™ process. In this paper, we develop the idea and demonstrate that the pressure and the concentrations of the gases inside a blister can be inferred from its actual dimensions and depth location by using simulations based on Finite Element Method (FEM) modelling. We apply this method to initiate a study on the influence of the respective fluences of H and He ions used in a sequential implantation on blistering efficiency.

Impact of He and H relative depth distributions on the result of sequential He+ and H+ ion implantation and annealing in silicon

Sequential He++H+ ion implantation, being more effective than the sole implantation of H+ or He+, is used by many to transfer thin layers of silicon onto different substrates. However, due to the poor understanding of the basic mechanisms involved in such a process, the implantation parameters to be used for the efficient delamination of a superficial layer are still subject to debate. In this work, by using various experimental techniques, we have studied the influence of the He and H relative depth-distributions imposed by the ion energies onto the result of the sequential implantation and annealing of the same fluence of He and H ions. Analyzing the characteristics of the blister populations observed after annealing and deducing the composition of the gas they contain from FEM simulations, we show that the trapping efficiency of He atoms in platelets and blisters during annealing depends on the behavior of the vacancies generated by the two implants within the H-rich region before and after annealing. Maximum efficiency of the sequential ion implantation is obtained when the H-rich region is able to trap all implanted He ions, while the vacancies it generated are not available to favor the formation of V-rich complexes after implantation then He-filled nano-bubbles after annealing. A technological option is to implant He+ ions first at such an energy that the damage it generates is located on the deeper side of the H profile.

Structure analysis of bimetallic Co–Au nanoparticles formed by sequential ion implantation

Co–Au alloy Metallic nanoparticles (MNPs) are formed by sequential ion implantation of Co and Au into silica glass at room temperature. The ion ranges of Au ions implantation process have been displayed to show the ion distribution. We have used the atomic force microscopy (AFM) and transmission electron microscopy (TEM) to investigate the formation of bimetallic nanoparticles. The extended X-ray absorption fine structure (EXAFS) has been used to study the local structural information of bimetallic nanoparticles. With the increase of Au ion implantation, the local environments of Co ions are changed enormously. Hence, three oscillations, respectively, Co–O, Co–Co and Co–Au coordination are determined.

Optical and structural properties of InAs nanoclusters in crystalline Si obtained through sequential ion implantation and RTA

Si (100) wafers were implanted at 500 °C with 250 keV As ions and 350 keV In ions in this order. The implantations were carried out with three different fluences, namely 1 × 1016, 2 × 1016, and 5 × 1016 cm−2. The samples were annealed with rapid thermal annealing (RTA) for 30 s at temperatures ranging from 800 up to 1000 °C. Different techniques like photoluminescence (PL) and Rutherford backscattering spectrometry (RBS) were employed to characterize the samples. Finally, scanning and transmission electron microscopy (SEM and TEM, respectively) provided further structural information of the InAs nanoclusters. The results indicate that InAs nanoprecipitates are formed after RTA treatment. Moreover, a broad photoluminescence peak was observed in all samples submitted to RTA. RBS results reveal that losses of implanted ions due to diffusion processes can be minimized through the use of RTA, depending of the fluence of ion implantation. Finally, the present results suggest that the photoluminescence yield depends on the degree of the radiation damage induced in the Si matrix during the implantation process.

Design of Step-Index Optical Waveguides by Ion Implantation

Step-index optical waveguides have been obtained by means of silver ion implantation on fused silica substrates. Step index profiles have been reached using a sequential multiple ion implantation process with energies of implantation from 4.3 to 9 MeV and fluences of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> ions/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Optical absorption spectra, propagation losses, intensity distribution, and effective refractive indices of the propagation modes of the waveguides are presented. An approach of refractive index profile of ion-implanted waveguides was fitted as function of polarizability, compaction, and stress.

Gold-based nucleation in implanted silica studied by x-ray absorption spectroscopy

Ion implantation into silica is used to produce Au subnanometer metal clusters, whose size can be finely tuned from few-atom to about 1nm by acting on the implantation fluence and post-implantation annealing conditions. The structural analyses rely basically on x-ray absorption spectroscopy that can investigate the metal site independently from long range order considerations. Besides the signal from the intermetallic coordination, a correlation of the dopant with oxygen atoms from the matrix is found, especially upon implantation at low fluence. The possibility of promoting the formation of subnanometer AuAg clusters by sequential ion implantation is also explored, with promising preliminary results. The control of the metal cluster nucleation, composition and first steps of growth have relevant consequences on the interpretation of the optical emission spectra of these molecule-like clusters and on their sensitizing action towards nearby rare-earth ions embedded in the same matrix.

Au-Ag nanoalloy molecule-like clusters for enhanced quantum efficiency emission of Er³⁺ ions in silica.

The occurrence of a very efficient non-resonant energy transfer process forming ultrasmall Au-Ag nanoalloy clusters and Er(3+) ions is investigated in silica. The enhancement of the room temperature Er(3+) emission efficiency by an order of magnitude is achieved by coupling rare-earth ions to molecule-like (Au(x)Ag(1-x))N alloy nanoclusters with N = 10-15 atoms and x = 0.6 obtained by optimized sequential ion implantation on Er-implanted silica. For comparison, AuN nanoclusters obtained by the same approach and with the same size and numerical density showed an enhancement by only a factor of 2 with respect to pure Er emission, demonstrating the beneficial effect of using nanoalloyed clusters. The temperature evolution of the energy transfer process is investigated by photoluminescence and exhibits a maximum efficiency at about 600 °C, where the clusters reach the optimal size and the silica matrix completely recovers the implantation damage. The nanoalloy cluster composition and size have been studied by EXAFS analysis, which indicated a stronger Ag-O interaction with respect to the Au-O one and a preferential location of the Ag atoms at the nanoalloy cluster surface.

Enhanced optical functionalities in silica by doping with Au-based nanostructures

The sensitization mechanism of Er ions by sub-nanometric Au aggregates formed in silica by sequential ion implantation has been investigated by room temperature photoluminescence characterizations. Er–Au co-implanted samples with different Au and Er relative concentrations have been studied. The results allowed to point out a correlation between the luminescence properties of the molecule-like Au nanoclusters and the Er sensitization effect and to definitely prove the short-range nature of the energy-transfer process. Efficient sensitization of the Er luminescence in silica is obtained by energy-transfer from ultra-small Au nanoclusters.