Implantation Dose Research Articles

A Novel Nitrogen Ion Implantation Technique for Turning Thin Film "Normally On" AlGaN/GaN Transistor into "Normally Off" Using TCAD Simulation.

This study presents an innovative, low-cost, mass-manufacturable ion implantation technique for converting thin film normally on AlGaN/GaN devices into normally off ones. Through TCAD (Technology Computer-Aided Design) simulations, we converted a calibrated normally on transistor into a normally off AlGaN/GaN transistor grown on a silicon <111> substrate using a nitrogen ion implantation energy of 300 keV, which shifted the bandgap from below to above the Fermi level. In addition, the threshold voltage (Vth) was adjusted by altering the nitrogen ion implantation dose. The normally off AlGaN/GaN device exhibited a breakdown voltage of 127.4 V at room temperature because of impact ionization, which showed a positive temperature coefficient of 3 × 10−3 K−1. In this study, the normally off AlGaN/GaN device exhibited an average drain current gain of 45.3%, which was confirmed through an analysis of transfer characteristics by changing the gate-to-source ramping. Accordingly, the proposed technique enabled the successful simulation of a 100-µm-wide device that can generate a saturation drain current of 1.4 A/mm at a gate-to-source voltage of 4 V, with a mobility of 1487 cm2V−1s−1. The advantages of the proposed technique are summarized herein in terms of processing and performance.

Electrical characteristics of silicon differential photoreceivers

The volt-ampere curve of silicon differential photodiodes were measured. It was found that the current-voltage curve of the photodiodes of the main and additional channels had a similar shape, without revealing a significant dependence on the implantation dose of the additional channel. The main parameters of the equivalent circuits of photodiodes are determined. In the reverse branch, the dominant impact was exerted by the surface leakage conductivity with a differential resistance of about 10 GΩ. Measurements from minus 60 °C to 60 °C showed that when using amplifiers with an input impedance of about 103 Ω, differential photoreceivers can be successfully used as selective short-wavelength and two-color ones.

Study of Concentration-depth Profiles of the Titanium and Nitrogen Ions by SRIM/TRIM Simulation

In this research, the concentration-depth profiles reached by titanium and nitrogen particles, on the surface of AISI/SAE 1020 carbon steel substrates, by using of ion implantation technique, are studied. The ions are surface deposited by means of high voltage pulsed discharges and electric arc discharge under high vacuum conditions. The concentration and position distribution of the metallic and non-metallic species are obtained by simulation of the interaction of ions with the matter, stopping and ranges of ions in the matter, by the computer program transport of ions in matter. The implantation dose is calculated from the discharge data and the previously established study parameters in this work. From the simulation results, the depth profiles demonstrated that titanium and nitrogen ions may reach up to 300 Å and 600 Å and concentrations of 1.478 x 1016 ions⁄cm2 and 2.127 x 1016 ions⁄cm2, respectively. The formation of titanium microdroplets upon the surface of the substrates is identified from the micrographs obtained by the scanning electron microscopy technique; furthermore, the presence of titanium and nitrogen implanted on the surface of the substrate is verified through the elemental composition analysis by the energy dispersive spectroscopy, validating the effect of ion implantation on ferrous alloys.

Local metal segregation as root cause for electrical shorts in highly doped pressure sensor devices

The fabrication of pressure sensor dies for precise and stable industrial applications requires a critical high dose implantation process strongly affecting the manufacturing yield of these devices. This paper describes a specific critical process related failure mechanism caused by this implantation process generating local electrical shorts within the piezo resistive structures in-built in the doped silicon substrate surface. The defect signature was investigated by applying site specific localization, advanced target preparation strategy and high-resolution electron microscopy to understand its process related root cause. The electrical shorts could be localized by Lock-in Thermography (LIT) and then were prepared by advanced laser and focused ion beam (FIB) based preparation in both cross-section and plan-view direction for in-depth investigation of the crystal defect signature by high resolution transmission electron microscopy (TEM) analysis in combination with energy dispersive X-ray spectroscopy (EDXS). As a result, the defect mechanism could be identified as segregation of embedded metal residues caused by Fe and Ni contamination from the high dose implantation equipment.

Cracks and blisters formed in nanocrystalline tungsten films by helium implantation

Tungsten is regarded as a potential plasma facing material (PFM) in nuclear fusion reactors owing to its high melting point, good thermal conductivity, and low sputtering yield. However, various types of defects such as interstitial atoms, vacancies, dislocation rings, cavities, helium bubbles, and “fuzz” occur in W under helium irradiation. In this study, we obtained α- and β-phase W films with nanochannels and used a helium ion microscope to conduct helium ion implantation experiments on the films. The implantation dose and energy were 1.5 × 1022 ions/m2, and 30 keV, respectively. There was no helium bubble formation in the β-W film until the completion of the implantation. The uniformly distributed columnar crystals growing perpendicular to the substrate constitute remarkable nanochannels. These effectively inhibit the aggregation of helium atoms. For α-W films prepared at high temperatures, the escape efficiency of the implanted helium atoms was reduced owing to the chaotic and reduced number of nanochannels, and helium bubbles are eventually formed. Cross-sectional images revealed that helium atoms tended to gather near the grain boundaries and gradually followed the nanochannels formed by the grain boundaries. The expansion eventually formed numerous longitudinal fissures. The results show that grain boundaries play a decisive role in the radiation resistance of nanostructured materials. Furthermore, the preparation of regular nanochannels that reach the sample surface is an effective method to improve the helium escape capability.

Effect of hydrogen implantation on low-temperature activation of boron in silicon

Understanding the behavior of dopant activation at low temperatures is necessary for three-dimensional integration of transistors. In this work, the impact of hydrogen coimplantation on boron activation was investigated at implantation doses below the amorphization threshold. The carrier depletion effect due to substrate doping was simulated to accurately characterize the initial activation behavior of boron. At temperatures higher than 400 °C, the boron activation level decreased as the hydrogen dose increased. The deactivation caused by hydrogen diminished after extended annealing at 500 °C. This indicated the passivation of boron by hydrogen. However, the boron activation in the sample implanted with hydrogen at a dose of 1 × 1015 cm−2 was first degraded and then enhanced during annealing at 300 °C. The time-dependent activation behavior suggested the elimination of isolated defects via reactions associated with hydrogen migration.

Nano material removal mechanism of 4H-SiC in ion implantation-assisted machining

As a third-generation semiconductor material, four-hexagonal silicon carbide (4H-SiC) finds wide application in industries. The high efficiency and performance machining of 4H-SiC ceramics have attracted researchers’ more attention. Ultra-precision diamond cutting is generally used to machine high-quality nanoscale surfaces. As a typical hard-to-cut brittle material, 4H-SiC causes significant tool wear during machining. It is necessary to study the effective process parameters and machining methods to improve the machining performance. In this study, the molecular dynamic (MD) analysis was used to comparatively investigate the effect of 4H-SiC by implanted different Ga ion implantation doses. The lattice damage, hydrostatic stress, radial distribution function (RDF), and selected area electron diffraction (SAED) were analyzed in detail. The cutting effect of implanted 4H-SiC with different implantation ions was then compared with unimplanted 4H-SiC. The machining properties were characterized by removed material morphological structure, temperature, coordination number, and stress distribution. The results provided an understanding of the mechanism of ion implantation-assisted nano-cutting. Besides, the effect of ion implantation-assisted and stress-assisted combined nano-cutting 4H-SiC was also investigated. The results demonstrated that the combination of ion implantation-assisted and stress-assisted could effectively decrease the cutting force and stresses, thus improving the machining efficiency and machinability of 4H-SiC.

Simplified process flow for the fabrication of PERC solar cells with ion implanted emitter

Ion implanted PERC cells have already achieved power conversion efficiencies of about 20.0%. The process flows reported in the literature for the ion implanted PERC cells with commonly utilized Al2O3/SiNx rear passivation stack, which has the benefit of being less sensitive to surface roughness than SiO2/SiNx stack passivation, notably suffer from the additional process steps such as single side polishing and single side protection. Here, we present a simplified process flow for the fabrication of ion implanted PERC cells having Al2O3/SiNx stack passivation at the textured rear surface without any rear side processing, leading to a power conversion efficiency of 20% at large area. In this context, we show the sensitivity of solar cell efficiency to firing peak temperature, implantation dose, and Al2O3 thickness. The results of the present research will provide a basis for high efficiency implanted PERC cells with significantly reduced workload and cost.

Nitrogen ion induced CdS clusterization: Structural, morphological, and optoelectrical properties

Semiconducting nanostructures are unique system to study the nanoscale phenomenon for diverse applications in new generation electronic devices. Ion implantation is a promising approach for producing nanoscale crystals or clusters in the near-surface region for doping of semiconductors which repair the respective optical and electrical properties. In the present study, cadmium sulfide (CdS) thin films are grown on a glass substrate via an easy and economical chemical bath deposition method. Thereafter, CdS thin films are implanted with 80 keV nitrogen (N+) ions with different fluences. Implanted thin films are characterized with the support of various characterization techniques. X-ray diffraction (XRD) analysis indicates that the hexagonal phase of CdS nanoflakes remains consistent while scanning electron microscopy (SEM) imaging reveals the formation of defect clusterization after implantation. The defect clusterization in CdS thin films is explained on the basis of local heating after the transmission of implantation energy. Optical properties such as absorption and emission spectra of implanted CdS thin films also get affected on the account of the generation of donor and acceptor level owing to Cd and S vacancies. Furthermore, a considerable increase in the magnitude of the electric current is observed as compared to the pristine sample with the implantation dose.

Acoustical emission and fractoluminescence from the Ar+-implanted fused SiO2

Chemically inert 40 keV Ar+ ions were implanted into fused SiO2 with doses in the range of 1×1014 to 1×1016 ion/cm2. The implanted specimens were subjected to the localized impact damaging by a pointed striker. The acoustic emission method was applied to assess the dependence of the microcracking process on the implantation dose. The fractoluminescence method showed the generation of non-bridged oxygen hole centers (NBOHC) [Si–O–] in newly formed microcracks. The performed experiments revealed a critical fluence, which affected in a non-linear manner the fractoluminescent activity due to changes in the mechanical properties of the Ar+-treated surface layer. An interplay between random and correlated damage accumulation at various structural levels was demonstrated.

Enhancement in Corrosion Resistance and Hardness of AZ91D Magnesium Alloy by Carbon Ion Implantation

To improve the mechanical and corrosion resistance of AZ91D magnesium alloy, carbon ion implantation technique has been carried out using 2 MV Pelletron accelerator on the polished magnesium alloy surface. Vickers hardness test, particle induced X-ray emission (PIXE) analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD) and corrosion tests are employed to analyse the properties. Vickers hardness tests revealed the improvement in surface hardness which we infer is due to the enhancement in dislocation density, as a consequence of carbon ion implantation with varied dose from 1.26×1013 to 8.4×1014 ions-cm-2. That is, the increase in hardness is directly related to the ion dose, variation in lattice parameters, crystallite size, and change in peak intensity, all due to the increase in ion fluence. The non-destructive elemental analysis, PIXE, gave the elemental profile before and after ion implantation. SEM results indicated that singly ionized carbon ion implantation has modified the surface of AZ91D Mg-alloy. XRD results showed that the unexposed and treated samples include ?-Mg and ?-Mg17Al12 phases. XRD results also revealed that after the carbon ion implantation the diffraction peak position and intensity of all the phases shifted. The corrosion tests were carried out using two methods, namely, weight loss method and electrochemical test. The results guided that for a higher dose of ion implantation, the corrosion resistance increased and loss of mass of exposed surface of specimens decreased, which reflect the enhancement of corrosion resistance.

Effect of Low-Energy Nitrogen Ion Implantation on Friction and Wear Properties of Ion-Plated TiC Coating

To further improve the performance of the coated tools, we investigated the effects of low-energy nitrogen ion implantation on surface structure and wear resistance for TiC coatings deposited by ion plating. In this experiment, an implantation energy of 40 keV and a dose of 2 × 1017 to 1 × 1018 (ions/cm2) were used to implant N ions into the TiC coatings. The results indicate that the surface roughness of the coating increases first and then decreases with the increase of ion implantation dose. After ion implantation, the surface of the coating will soften and reduce the hardness, and the production of TiN phase will gradually increase the hardness. Nitrogen ion implantation can reduce the friction coefficient of the TiC coating and improve the friction performance. In terms of wear resistance, the coating with an implant dose of 1×1018 ions/cm2 has the greatest improvement in wear resistance. Tribological analysis shows that the improvement in the performance of TiC coatings implanted with N ions is mainly due to the effect of the lubricating implanted layer. The implanted layer mainly exists in the form of amorphous TiC, TiN phase, and sp2C–C phase.

Photoelectrical detection of nitrogen-vacancy centers by utilizing diamond lateral p–i–n diodes

We demonstrate a photoelectrical readout of negatively charged nitrogen-vacancy (NV−) centers by utilizing a lateral diamond p–i–n diode structure. We found that the photocarriers generated at NV centers are efficiently extracted in the depletion layer even at zero voltage. The transport mechanism for photoexcited minority carriers was investigated by varying the nitrogen ion implantation dose. The minority carrier diffusion length decreased when the photocarriers passed through the implantation region, particularly at a high nitrogen ion dose. From photoelectrically detected magnetic resonance (PDMR) measurements, the photocurrent was found to exhibit a minimum at approximately 2.87 GHz upon microwave irradiation with a contrast of 12%, while this dip was observed to split upon the application of a static magnetic field. The PDMR signal was found to depend on the measurement position. This study paves the way for efficient electrical detection for quantum sensors based on device technologies.

The microstructure and tribological properties of M50 steel surface after titanium ion implantation

Titanium ions with different energies and doses were implanted into the M50 steel surface. In addition, titanium and nitrogen ion co-implantation was applied for comparison. The tribological properties and wear resistance of the implanted samples were characterized using a sliding friction tester, grazing incidence angle X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, surface profiler, Raman spectrometer, and nanoindentation tests. The results indicated that the compounds of the titanium ion–implanted samples mainly consisted of titanium and TiO2, CrN interstitial compounds formed after titanium and nitrogen ion co-implantation, thus generating an implantation layer that exhibited high nano-hardness and low wear rates. The linear contact sliding friction coefficient curves for the implantation samples were composed of an initial stage, ascent stage, and stable stage. The tribological properties effectively improved with increasing titanium ion implantation energies and doses. In addition, this beneficial effect became much more significant at a higher titanium ion dose. The titanium and nitrogen ion–co-implanted samples formed Fe2O3 and Fe3O4 tribo-oxide layers after the wear test, which were partially responsible for reducing the wear. The dominant wear mechanisms of the implanted samples were abrasive wear and oxidative wear.

Annealing temperature effect on optical properties of Cr-implanted ZnO nanostructure

Room temperature ferromagnetism was observed in Cr-implanted ZnO nanowires annealed at 500, 600, and 700 °C. The implantation dose for Cr ions was 1 ×1016 cm−2 , while the implantation energies were 100 keV. Except for ZnO (100), (002), and (200) orientations, no ex- tra diffraction peaks from Cr-related secondary phase or im- purities were observed. With the increasing of annealing temperatures, the intensity of the peaks increased while the FWHM values decreased. The Cr 2p1/2 and 2p3/2 peaks, with a binding energy difference of 10.6 eV, appear at 586.3 and 575.7 eV, can be attributed to Cr3+ in ZnO nanowires. For the Cr-implanted ZnO nanowires without annealing, the band energy emission disappears and the defect related emission with wavelength of 500–700 nm dominates, which can be attributed to defects introduced by implantation. Cr- implanted ZnO nanowires annealed at 500 °C show a saturation magnetization value of over 11.4 × 10−5 emu and a positive coercive field of 67 Oe. The origin of ferromagnetism behavior can be explained on the basis of electrons and defects that form bound magnetic polarons, which over- lap to create a spin-split impurity band.

Accelerated in vitro release testing method for a long-acting peptide-PLGA formulation

Poly (lactic-co-glycolic acid) (PLGA), a biocompatible and biodegradable polymer, is one of the most commonly used vehicles for controlled-release (CR) implantable dosage forms. Drug molecules formulated in such CR vehicles are released slowly over an extended period of time – often months to years – posing challenges for batch release and quality control testing. Thus, reliable and reproducible accelerated testing methods are required to bridge this gap during early formulation development. This work describes the development of an accelerated in vitro release testing method to predict the real-time in vitro release of a synthetic peptide from a 6-month CR PLGA implant formulation. While accelerated methods have been previously reported for PLGA-based formulations, this work describes a unique case of an aggregation-prone peptide, which required careful attention to the impact of different conditions on both release kinetics and peptide stability. This method describes a suitable combination of release conditions that could help in understanding the release profiles of such peptides prone to aggregation. Parameters including pH, buffer species, temperature, and addition of organic co-solvents and surfactants were evaluated separately and in combination for their ability to achieve complete peptide release within 2 weeks while accurately recapitulating release rate, profile and peptide stability. The accelerated release method that gave the best agreement with real-time release was a mixed media of co-solvent (5% tetrahydrofuran), surfactant (5% TritonX-100) and elevated temperature (50 °C) in a neutral buffer (PBS pH 7.4). This optimized accelerated release method achieved complete release of the peptide load within 14–21 days compared to 3- to 6-months of real-time release and could discriminate critical differences in release behavior between different CR formulations to guide formulation and process development.

Long-acting implantable dosage forms containing paliperidone palmitate obtained by 3D printing

In this work, the versatility of pressure extrusion-based printing (PEBP) was used as 3D printing process to create long-acting implantable dosage forms. Different release profiles were achieved based on the drug concentration, the way of preparation and the design of the final implants. Polycaprolactone (PCL) was used as the polymer to sustain the release of the loaded drug. Paliperidone palmitate (PP), a BCS Class II drug, used in the treatment of schizophrenia, was used as the model drug. Two PP concentrations (e.g. 5 and 10% w/w) as well as two methods of preparation before the 3D printing process, mortar and pestle and cryogenic milling, were evaluated. The amorphous state of PP was obtained by using cryogenic milling and it was maintained after printing. Two designs were printed by PEBP, a ring and a disk, to evaluate their impact on the release profile of PP. During the in vitro dissolution tests, the implant design, the amount of PP, as well as the crystalline or amorphous state of PP have shown to influence the drug release profile. During the successive steps of preparation of the long-acting implants, blends and raw materials were characterized by DSC and XRD.

Analysis of the titanium ions concentration implanted in low alloy steel

In the surface modification processes obtained by high voltage electric discharges and cathodic arc at low pressures its of great interest to estimate the concentration of ions that are implanted on the surfaces of metallic substrates. The employment of computational tools to estimate the concentrations of implanted ions on the surface of materials as a function of the depth allows to optimize the experimental processes reducing costs and time. In the present research, a software that simulates the mobility, stopping and range of ions in matter by means of the Monte Carlo method is used, in order to obtain the ratio between the concentration and the dose of ions regarding to depth in a titanium ion implantation process on the surface of chromium molybdenum low alloy carbon steel; then, using experimental parameters, the implantation dose is calculated and an estimated profile of ion concentration is obtained as a function of the depth. The results showed that titanium ions implanted at 10 KV for 5 minutes and 10 minutes had projected ion ranges until depths of 250 Å and the highest concentration is located around 50 Å; the concentration of the implanted ions increases with the exposure time of the surface because the implantation dose is proportional to the discharge time. Furthermore, it is observed that the location of the highest concentration region and the range of the implanted ions is invariant.

Influence of dual Ge/C pre-amorphization implantation on the Ni1−xPtxSi phase nucleation and growth mechanisms

The impact of dual Ge/C pre-amorphization implantation (PAI) processes on the Ni0.9Pt0.1(7 nm)/Si system phase sequence has been investigated by advanced X-ray diffraction techniques and transmission electron microscopy (TEM). Using a high carbon implantation dose, it is found that the expected development of Ni-rich phases is not observed: a thick amorphous Ni1−xPtxSi layer developed until Ni0.9Pt0.1 full consumption, followed by the development of a thin crystalline Ni1−xPtxSi layer along the TiN interface. By increasing the temperature further, this last one abruptly thicken, creating the final silicide layer. An alternative model to grain boundary diffusion is discussed, accounting for the final distribution of the foreign species within the silicide layer. The use of Ge in dual Ge/C PAI processes is proposed to impact the growing mechanisms by alloying to fine-tune the carbon distribution in the substrate sub-surface.

Phosphorus implantation into 4H-SiC at room and elevated temperature

Phosphorus implantation is essential to create localized n-type doped regions in 4H-SiC. The realized profiles may, however, deviate from the desired ones, affecting device properties. In order to characterize typical process parameters and to enable correct prediction of the desired structures, phosphorous implantation into 4H-SiC with a variety of doses and energies is performed at room and elevated temperature. Exemplary post-implantation annealing shows no significant influence on the phosphorus distribution. The as-implanted profiles, analyzed by secondary ion mass spectrometry, show a clear dependence on implantation dose and temperature. High sample temperature at implantation suppresses channeling in case of low and medium doses due to increased lattice vibrations, while crystal damage is restored in case of high doses leading to increased opportunities for channeling, pointing toward different crystal damage and energy loss mechanisms. Finally, the Monte Carlo profiles of the simulation tools stopping and range of ions in matter (SRIM) and Sentaurus Process are critically compared with the experimental profiles.