Low-energy Implantation Research Articles

Spatially selective p-type doping for constructing lateral WS2 p-n homojunction via low-energy nitrogen ion implantation

The construction of lateral p-n junctions is very important and challenging in two-dimensional (2D) semiconductor manufacturing process. Previous researches have demonstrated that vertical p-n junction can be prepared simply by vertical stacking of 2D materials. However, interface pollution and large area scalability are challenges that are difficult to overcome with vertical stacking technology. Constructing 2D lateral p-n homojunction is an effective strategy to address these issues. Spatially selective p-type doping of 2D semiconductors is expected to construct lateral p-n homojunction. In this work, we have developed a low-energy ion implantation system that reduces the implanted energy to 300 eV. Low-energy implantation can form a shallow implantation depth, which is more suitable for modulating the electrical and optical properties of 2D materials. Hence, we utilize low-energy ion implantation to directly dope nitrogen ions into few-layer WS2 and successfully realize a precise regulation for WS2 with its conductivity type transforming from n-type to bipolar or even p-type conduction. Furthermore, the universality of this method is demonstrated by extending it to other 2D semiconductors, including WSe2, SnS2 and MoS2. Based on this method, a lateral WS2 p-n homojunction is fabricated, which exhibits significant rectification characteristics. A photodetector based on p-n junction with photovoltaic effect is also prepared, and the open circuit voltage can reach to 0.39 V. This work provides an effective way for controllable doping of 2D semiconductors.

Synthesis of cobalt-oxide nanoparticles embedded in silicon nanotubes via low-energy cobalt implantation

Silicon nanotubes (Si NTs) show a unique structure compared to other silicon nanostructures, such as porous silicon, silicon nanoparticles, and silicon nanowires. Si NTs' well-defined structure in terms of silicon shell thickness, inner diameter, and length with a high surface area makes them useful in myriad applications. In this work, we fabricate Si NTs by using ZnO nanowires as templates; the Si NTs have a shell thickness of ∼13 nm, inner diameter of ∼80 nm, and a length in the range of 1–2 μm with embedded Co3O4 nanoparticles (NPs), which are formed by annealing the cobalt ion-implanted Si NTs. The cobalt ion implantation was carried out at 50 keV with a fluence of 7.5 × 1015 ions/cm2. The morphology and composition of the cobalt-NP decorated Si NTs are characterized by using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM), and x-ray photoemission spectroscopy (XPS). TEM, HRTEM, XPS, and Raman spectroscopy studies confirm the formation of Co3O4 nanoparticles in the NTs. The temperature-dependent zero-field-cooled (ZFC), and field-cooled (FC) magnetization for the Co implanted Si NTs before and after annealing is also measured and shows little magnetic response due to the low concentration of cobalt in the nanotubes. The fabrication process is compatible with the current semiconductor industry methods and may find potential applications in magnetic drug delivery and devices.

Orientation-dependent ion-irradiation responses in molybdenum and molybdenum-rhenium alloys

Helium ion-irradiation responses in molybdenum (Mo) and molybdenum-rhenium (Mo-Re) alloys at room temperature were evaluated via micro-pillar compression. Irradiation-induced hardening is closely dependent on orientation in Mo-Re alloys with low Re content, while is weak orientation-dependence on high Re alloys. Irradiated pillars with [100] orientation all shows higher flow stresses than pillars with [110] orientation after yield, which is distinguishing from pillars before irradiation that has been shown in our previous work. High density of dislocation loops and helium bubbles after irradiation at room temperature induces severe hardening in Mo. Voids / small loops induced by irradiation lead to less hardening in Mo-Re alloy than in Mo. No precipitation is observed in all samples, which may be attributed to low irradiated temperature and implantation energy.

Measurement and Simulation of Ultra-Low-Energy Ion-Solid Interaction Dynamics.

Ion implantation is a key capability for the semiconductor industry. As devices shrink, novel materials enter the manufacturing line, and quantum technologies transition to being more mainstream. Traditional implantation methods fall short in terms of energy, ion species, and positional precision. Here, we demonstrate 1 keV focused ion beam Au implantation into Si and validate the results via atom probe tomography. We show the Au implant depth at 1 keV is 0.8 nm and that identical results for low-energy ion implants can be achieved by either lowering the column voltage or decelerating ions using bias while maintaining a sub-micron beam focus. We compare our experimental results to static calculations using SRIM and dynamic calculations using binary collision approximation codes TRIDYN and IMSIL. A large discrepancy between the static and dynamic simulation is found, which is due to lattice enrichment with high-stopping-power Au and surface sputtering. Additionally, we demonstrate how model details are particularly important to the simulation of these low-energy heavy-ion implantations. Finally, we discuss how our results pave a way towards much lower implantation energies while maintaining high spatial resolution.

Emergent Magnetism with Continuous Control in the Ultrahigh-Conductivity Layered Oxide PdCoO2.

The current challenge to realizing continuously tunable magnetism lies in our inability to systematically change properties, such as valence, spin, and orbital degrees of freedom, as well as crystallographic geometry. Here, we demonstrate that ferromagnetism can be externally turned on with the application of low-energy helium implantation and can be subsequently erased and returned to the pristine state via annealing. This high level of continuous control is made possible by targeting magnetic metastability in the ultrahigh-conductivity, nonmagnetic layered oxide PdCoO2 where local lattice distortions generated by helium implantation induce the emergence of a net moment on the surrounding transition metal octahedral sites. These highly localized moments communicate through the itinerant metal states, which trigger the onset of percolated long-range ferromagnetism. The ability to continuously tune competing interactions enables tailoring precise magnetic and magnetotransport responses in an ultrahigh-conductivity film and will be critical to applications across spintronics.

Low energy ion-solid interactions: a quantitative experimental verification of binary collision approximation simulations

Ultra-low energy ion implantation has become an attractive method for doping of two-dimensional materials and ultra-thin films. The new dynamic Monte Carlo program IMINTDYN based on the binary collision approximation allows a reliable prediction of low energy implantation profiles and target compositional changes, as well as efficient simulation of high energy light ion scattering. To demonstrate the quality of these predictions and simulations, we present a model case experiment where we implanted W ions into tetrahedral amorphous carbon with low (10 keV) and ultra-low (20 eV) ion energies and analyzed the W implantation profiles with high resolution Rutherford backscattering spectrometry (HR-RBS). This experiment is compared with a complete simulation of all aspects of ion-solid-interactions of the experiment using the new IMINTDYN program. A unique novel simulation option, also relevant for implantation into 2D materials, is the inclusion of the vacancy as target species with dynamic vacancy generation and annihilation. Whereas simulations neglecting vacancy formation cannot reproduce the measured implantation profiles, we find excellent agreement between simulated and measured HR-RBS spectra. We also demonstrate the important role of simultaneous weak collisions in the binary collision approximation at low projectile energies.

A Superior Reverse Characteristics of 1.2 kV 4H-SiC Planar JBS Diode Employing Channeling Implantation

This paper presents a study on improving the reverse characteristics of 1.2 kV 4H-SiC JBS diodes by employing a deep P+ grid structure. To achieve a deep junction with low implantation energy, channeling implantation was implemented. Diodes with different junction depths of the P+ grid were fabricated to compare the forward and reverse I-V characteristics; depth of 0.8 μm, 1.4 μm, and 2.2 μm. Almost identical forward I-V characteristics were achieved regardless of the P+ grid depth. However, the leakage current was significantly suppressed by the deeper P+ grid junction depth; 60 μA, 1.5 μA, and 1.7 nA (at 1200V for 0.8, 1.4, 2.2 μm deep P+ grids, respectively). Although the deep junction was implemented with channeling implantation, high breakdown voltages similar to that of the shallow junction are achieved in the proposed JBS diode. This is due to the relatively low doping concentration in the deep junction. Moreover, the edge termination structures with different main junction depths were discussed. For a near ideal breakdown voltage insensitive to the JTE dose, Hybrid-JTE was employed. It was demonstrated that the high breakdown voltage with the drastically reduced leakage current of the proposed JBS diodes, was achieved using identical edge termination technology to the conventional shallow junction. To better understand the effect of the deep junction, 2D simulation was conducted.

Towards Sic-Based VUV Pin-Photodiodes - Investigations on 4H-SiC Photodiodes with Shallow Implanted Al Emitters

4H silicon carbide (SiC) based pin photodiodes with a sensitivity in the vacuum ultraviolet spectrum (VUV) demand newly developed emitter doping profiles. This work features the first ever reported 4H-SiC pin photodiodes with an implanted p-emitter and a noticeable sensitivity at a wavelength of 200 nm. As a first step, Aluminum doping profiles produced by low energy ion implantation in 4H-SiC were characterized by secondary-ion mass spectrometry (SIMS). Photodiodes using these shallow emitters are compared to one with a deep p-emitter doping profile employing IV characteristics and the spectral response. SIMS results demonstrate the possibility of shallow Alimplantation profiles using low implantation energies with all emitter profiles featuring characteristic I-V results. For some shallow doping profiles, a meassurable signal at the upper limit of the VUV spectrum could be demonstrated, paving the way towards 4H-SiC pin photodiodes with sensitivities for wavelengths below 200 nm.

Low Energy Measurements in Low-Energy µSR

In the context of µSR studies on magnetic materials in the ordered state, often a strong initial depolarization is found in the zero field spectra. For transverse field measurements this is often referred to as a loss in asymmetry. In case of the low-energy µSR (LE-µSR) setup this needs a more detailed discussion since effects such as time-of-flight distribution of impinging muons, back scattering, and muon reflection will change the spectra at early times and low implantation energies (E < 3keV). These effects are well understood and reproducible allowing to correct for in any given experiment. We will discuss them and show how to correct for in experiments at low implantation energies.

Characterization of magnesium channeled implantation layers in GaN(0001)

The effect of Mg channeled implantation into epitaxially grown gallium nitride (GaN) was studied using Hall-effect measurements, photoluminescence (PL), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and Rutherford backscattering spectroscopy (RBS). In the channeled implantation, deeper profiles were obtained with lower implantation energy and less damage compared to random implantation. The donor–acceptor pair signal at ∼3.28 eV, suggesting that Mg is activated, was confirmed by PL measurement when the ion dose and implantation energy are 1 × 1014 cm−2 and 20 keV, respectively. However, even with channeled implantation, several types of defects including point defects and oblong defects as seen in the random implantation were observed by TEM/STEM analysis. RBS analysis showed slightly worse crystal qualities in channeled implantation compared to non-implanted samples. Mg channeled implantation is useful to achieve deeper profiles (>1 μm), but further condition tuning of process will be necessary for practical application.

Bonding, retention and thermal stability of shallow nitrogen in diamond (100) by low-energy nitrogen implantation

We investigate the sub-surface bonding, retention, and thermal stability of nitrogen in diamond (100) implanted with 200 and 800 eV N2+ at room temperature (RT) and 600 °C at an ion dose of 3.4×1014 ions/cm2. Upon 200 eV N2+ implantation at RT and 600 °C, nitrogen is incorporated in the diamond lattice mainly in a C-N/C=N bond bonding configuration alongside a small CN(nitrile-like) component. 800 eV N2+ implantation at both RT and 600 °C, the implanted nitrogen can occupy multiple bonding configurations, including C-N/C=N and CN(nitrile-like) bonds. Implantation at 600 °C resulted in higher thermal stability of the implanted nitrogen compared to RT implantation due to dynamic annealing assisted defect curing and desorption of weekly bonded species (possibly nitrogen bonded to defects) during the high temperature implantation. The long-range order of the N2+ implanted diamond surfaces was also investigated using low-energy electron diffraction measurements.

Computational Study of Low-Energy Pt-Ion Implantation into Graphene for Single-Atom Catalysis

Single-atom catalysts (SACs) represent the ultimate goal of nanocatalysis fields. However, complex synthesis processes and pyrolysis inactivation problems are the two main challenges that plague the development of SACs. In this work, we propose that the ultralow-energy ion-implantation (ULEII) method could be utilized to simply and efficiently synthesize stable SACs. Our simulation results of Pt-ion implantation into graphene indicate that the total doping efficiency, including direct displacement doping and indirect trap doping, can be effectively optimized by delicately adjusting the energy of incident ions. Further systematic molecular dynamics simulations and first-principles calculations demonstrate that irradiation-induced vacancy defects can effectively capture and anchor adsorbed metal atoms on the graphene surface. The stability and migration characteristics of various defects are also clearly elucidated. Theoretically, by selecting an optimal ion energy, the ULEII method can achieve a doping efficiency as high as 73.4% .

Radiation tolerance of GaN: the balance between radiation-stimulated defect annealing and defect stabilization by implanted atoms

Realization of radiation-hard electronic devices that are able to work in harsh environments requires deep understanding of the processes of defect formation/evolution occurring in semiconductors bombarded by energetic particles. In the present work we address such intriguing radiation phenomenon as high radiation tolerance of GaN and analyze structural disorder, employing advanced co-irradiation schemes where low and high energy implants with different ions have been used. Channeling analysis revealed that the interplay between radiation-stimulated defect annealing and defect stabilization by implanted atoms dominates defect formation in the crystal bulk. Furthermore, the balance between these two processes depends on implanted species. In particular, strong damage enhancement leading to the complete GaN bulk amorphization was observed for the samples pre-implanted with fluorine ions, whereas the co-irradiation of the samples pre-implanted with such elements as neon, phosphorus and argon leads to a decrease of the bulk damage.

Modification of stainless steel based on synergistic of low-energy high-intensity ion implantation and high-current electron beam impact on the surface layer

The results of experiments on low-energy implantation of AISI 321 stainless steel by nitrogen ions are presented. The treatment was carried out by a pulsed beam of nitrogen ions obtained using a ballistic ion focusing system. The surface modification occurs with the formation of a two-layer structure, which is typical for ion-plasma nitriding processes of stainless steels. The thickness of the modified layer can reach 27 μm after 1 hour of ion-plasma treatment. The influence of subsequent modification of the ion-doped layer by the action on the surface of the pulsed high-current electron beam of microsecond duration is studied. The work presents the results of the studying the regularities of changes in the depth distribution of dopants, microstructure and phase composition of the modified and matrix layers by optical metallography, diffraction analysis and transmission electron microscopy.

(Invited) History of Micro-/Nano-Electronics Development; Breakthroughs and Innovations

Introduction Although the first MOSFET-like device ideas were proposed about 90 years ago by J. E. Lilienfeld [1], it took 30 years for the first operational MOSFET to have been successfully fabricated by selecting Al/SiO2/Si as the MOS materials by D. Kahng and M. Attalla [2]. Then, another 10 years were necessary until it had evolved to Large Scale Integrated circuits (LSIs). Indeed ‘microelectronics’ started in early 1970’s with microprocessors fabricated on the LSI chips. At that time, the technology was 10 μm PMOS LSIs. Now, it has evolved to 10 nm-range CMOS LSIs. In the past 50 years, we have experienced 23 generations (each about 2.5 years) of the shrinkage, and the MOSFETs size has decreased by 1,000 times, resulting in an increase in integration density with 1 million times. The continuous increase with the constant rate is the Moore’s law [3], but no one including me could imagine its continuation of over 50 years. The downsizing of MOSFETs has been accomplished based on the scaling scheme proposed by R. Dennard [4], but we have encountered very serious problems at every new generation. Fortunately, however, we have so far succeeded in finding the solutions. This presentation explains some of the history of micro-/nano-electronics technology developments in the past 50 years based on my experience and memory. Technology development for the past 50 years In order to shrink the size, removing the misalignment space margin between the layers is effective, and 2 self-align techniques, Si-gate (between gate and source/drain) and LOCOS (between filed diffusion and oxide) were developed at the end of 1960’s. Then, at the beginning of 1970’s, the fabrication process was simple, with 5 masks for the lithography; field isolation, gate electrode, contact hole, Al interconnects, and bonding pad, with options of a few more masks; channel ion-implantation, or direct-contact between poly-Si lines and source/drain layers, etc.Another factor to reduce the size is to minimize the side-etching and side-diffusion, and anisotropic technologies (or 'dry-process'), such as reactive ion etching and heavy source/drain implantation, were developed at the beginning of 1980’s for the VLSI era. At the same time, stepper (step-and-repeat reduction-projection system) was introduced for higher-resolution lithography. The resolution of the lithography has been improved continuously by introducing a shorter optical wavelength and also by developing various resolution enhancement technologies. Recent introduction of the EUV is a big leap for the wavelength.Since the early 1970’s, short-channel effects (threshold voltage decrease and off-leakage current increase) have been the hurdle for the gate length reduction. The solution was to decrease source/drain junction depth and gate oxide thickness. In order to realize shallow source/drain diffused layers with low resistance, the diffusion element changed from P to As, and new technologies such as low-energy implantation, rapid thermal annealing, and silicided-source/drain were developed. For the thin gate oxide, rapid thermal oxidation, oxynitride gate insulator and finally high-k metal gate technologies were developed. In the early stage of the LSI in 1970s, the semiconductor chips were composed of only 3 major elements, i.e., Si, O, Al with 3 other ones, P, B and H, as additives, but now so many new elements are used for the gate, source, and drain of the MOSFETs, memory cells, and interconnects.Other problems were the degradations of yield and reliability. The mechanisms of the degradations were investigated and many new process/structure/material technologies have been developed as the solutions.In order to suppress the short-channel effects and also to increase the integration density, the structures of the MOSFETs and DRAM/flash memory cells have changed from flat to 3D. Conclusions So huge resources have been invested for the development of micro/nano-electronics in the past 50 years because of its impact to and demands from our modern society, and unbelievably huge progress in engineering and science has been achieved. Indeed, the scales of investment and impact were much bigger than those of the Apollo moon project. The dedication of so many people during the past 50 years has opened up a new smart society in the 21st century with AI, big data, internet and so on. Past 50 years have been really an exciting period. However, the next 50 years will be a more exciting period with a great leap on the base of the micro/nano-electronics.[1] J. Lilienfeld, US1900018A, filed March 28, 1928[2] M. Atalla, and D. Kahng, IRE-AIEE Solid State Device Research Conference, 1960[3] G. Moore, Electronics, Vol. 38, No. 8, April 19, 1965[4] R. Dennard et al., IEEE JSSC, Vol.SC-9, No.5, October, 1974

Influence of ion implantation on the charge storage mechanism of vanadium nitride pseudocapacitive thin films

The influence of microstructural or structural defects is seldom investigated in pseudocapacitive electrodes. Indeed, most of the synthesized materials do present defects at every scales which contribute to the improvement of the charge storage. In this study VN thin films were deposited by reactive magnetron sputtering. The as-deposited VN films were compared with similar films implanted with arsenide cations (As+) with energies ranging from 20 keV up to 150 keV. The influence of the ionic implantation on the structure and microstructure of the pristine films was characterized by several techniques. The initial curing of the internal stress of as-deposited VN films observed for low implantation energies was lost with increasing implantation energy. Concomitantly, the electrochemical behaviors of the VN films were investigated. All the VN films show a pseudocapacitive behavior at 2 mV.s−1. At low scan rates, the as-deposited film exhibits the highest areal capacitance (45 mF.cm−2) which drastically decreases upon increasing the scan rate. Only 30% of the initial capacitance is maintained at 100 mV.s−1. Despite lower capacitances at 2 mV.s−1, As+ implanted VN films exhibit better capacitance retention in the same conditions, i.e. up to 65% of the initial capacitance is maintained at 100 mV.s−1. The contributions coming from surface and subsurface reactions have been determined which enable to propose possible origins for the changes occurring in charge storage mechanisms upon ion implantation.

“EXPERIMENTAL STUDY OF PHOTOELECTRONIC SPECTRA OF NIOBIUM-HAFNIUM-ZIRCONIUM ALLOY”

Crystals of niobium and its alloys obtained by low-energy implantation of hafnium and zirconium ions have been studied in a multifunctional experimental setup. Distribution profiles of implanted hafnium and zirconium atoms, energy distributions of photoelectrons N (E), and spectral dependences of the quantum yield of photoelectron emission before and before and after heating of the niobium-hafnium-zirconium alloy have been investigated. The contribution of surface states and bands formed by hafnium and zirconium atoms to photoelectron emission in the photon energy range of 8–10 eV is analyzed. The experimental results are discussed on the basis of theoretical calculations of the surface, photoelectron emission in which the dominant factors are indirect optical transitions. The experiments were carried out under ultrahigh vacuum conditions using photoelectron and Auger electron spectroscopy. Krypton and xenon resonance lamps were used as radiation sources.&#x0D;

Excitonic Dynamics in Janus MoSSe and WSSe Monolayers.

We report here details of steady-state and time-resolved spectroscopy of excitonic dynamics for Janus transition metal dichalcogenide monolayers, including MoSSe and WSSe, which were synthesized by low-energy implantation of Se into transition metal disulfides. Absorbance and photoluminescence spectroscopic measurements determined the room-temperature exciton resonances for MoSSe and WSSe monolayers. Transient absorption measurements revealed that the excitons in Janus structures form faster than those in pristine transition metal dichalcogenides by about 30% due to their enhanced electron-phonon interaction by the built-in dipole moment. By combining steady-state photoluminescence quantum yield and time-resolved transient absorption measurements, we find that the exciton radiative recombination lifetime in Janus structures is significantly longer than in their pristine samples, supporting the predicted spatial separation of the electron and hole wave functions due to the built-in dipole moment. These results provide fundamental insight in the optical properties of Janus transition metal dichalcogenides.

Investigation on the Electronic Structure of Nanosized Barium Monosilicide Films Produced by Low-energy Implantation of Ba&amp;lt;sup&amp;gt;+&amp;lt;/sup&amp;gt; Ions in Si

The processes of formation of nanoscale silicide films during the implantation of Ba⁺ ions into Si (111) and Si (100) and subsequent thermal annealing were studied by electron spectroscopy. It is shown that implantation of ions with a high dose D > 10¹⁶ cm^-2 and short-term heating leads to the formation of thin films of barium monosilicide with new surface superstructures. The optimal modes of formation and band-energy parameters of BaSi films obtained by low-energy high-dose implantation of barium ions in Si are determined. It is shown that BaSi films are a narrow-gap semiconductor with a band gap of 0.7 eV and have good emission and thermoelectric properties corresponding to the solar spectrum and have high photoelectric and thermoelectric characteristics. It should be noted that, in addition to the formation of a chemical compound, the narrowing of the Si band gap upon implantation of large doses of Ba⁺ ions also contributes to defects formed as a result of strong disordering of the crystal lattice.

Optimum technological modes of ion implantation and subsequent annealing for formation of thin nanosized silicide films

Using the methods of electron spectroscopy and slow electron diffraction, we studied the processes of the formation of nanosized metal silicide films in the near-surface region of Si (111) and Si (100) during low-energy implantation of Ba ions and alkaline elements. The optimal technological modes of ion implantation and subsequent annealing for the formation of thin nanoscale films of silicides were determined. The type of surface superstructures of thin silicide films has been established.