Ion-doped Layers Research Articles

Effect of О<sub>2</sub><sup>+</sup> Ion Implantation on the Elemental and Chemical Composition of the Si(111) Surface

Using the methods of secondary ion mass spectrometry, elastic peak electron spectroscopy and Auger electron spectroscopy, the elemental and chemical composition of the surface, concentration profiles of the distribution of atoms over the depth of silicon implanted with O2+ ions with energy E0 = 1 keV at a dose of D = 6 × 1016 cm–2 were studied. It was found that oxides and suboxides of Si (SiO2, Si2O and SiO0.5) were formed in the ion-doped layer, and it also contained unbound O and Si atoms. Post-implantation annealing at 850–900 K led to the formation of a stoichiometric SiO2 layer ~25–30 Å thick.

STUDY OF THE DISTRIBUTION PROFILE OF ION- IMPLANTED IN SILICON AND INFLUENCE THERMAL ANNEALING ON THE STRUCTYRE OF IRON SILICIDES

The paper presents the results of studies of the distribution profiles of implanted iron atoms in silicon depending on the irradiation dose and annealing temperature by the RBS method. The obtained results confirm similar data obtained by SIMS. The influence of thermal annealing on the distribution of iron and other impurities, in particular oxygen, has been studied. The possibility of using the RBS method for the analysis of the concentration distribution and the interaction of impurities with each other is presented. At the same time, the crystal structure of the surface and the electrophysical properties of ion-doped layers were studied.

Study of the synergy effect of high-intensity aluminum ions implantation into titanium and energy impact on the surface

The work studies the synergy effect of high-intensity implantation of aluminum ions and thesubsequent impact of a powerful pulsed ion beam on the microstructure and properties of titanium.Specimens of titanium were implanted for one hour at a temperature of 1170 K with an ion fluenceof 1021 ions/cm2. Layers with a thickness of about 150 μm were obtained. The energy impact wascarried out by a powerful nanosecond pulsed ion beam with an ion current density on the targetof 100 A/cm2. The paper presents data on changes in the elemental composition, surface morphology,and microstructure of ion-doped and energy-modified layers. It has been established that the additionalenergy impact on the ion-doped layer of a powerful pulsed beam improves microstructure at depthsgreater than 3.4 μm. The synergistic of high-intensity ion implantation of aluminum and the energyimpact of a pulsed ion beam improves the wear resistance of titanium by eighteen folds.

Electrical properties of silicon-implanted β-Ga2O3:Fe crystals

Ion implantation is a promising method for the development of β-Ga2O3-based technologies and devices. However, the physical principles of ion implantation for this particular semiconductor are still at the early stage of development. One of the primary tasks is the study of electrical properties of the ion-doped layers. In this work, we have investigated the electrical parameters of layers produced by ion implantation of a shallow donor impurity—silicon—into a semi-insulating β-Ga2O3 doped with iron and having a surface orientation of (−201). It is established that the activation efficiency of the implanted impurity significantly exceeds unity after post-implantation annealing at high temperatures. This indicates that not only silicon itself contributes to conductivity, but also defects formed with its (and, probably, iron) participation are involved. The temperature dependence of electron mobility is consistent with the theoretically calculated one under the assumption that, apart from shallow donors, there are also deep defect-associated donors and acceptors. It is assumed that the established properties are specific for the case of direct Si implantation into β-Ga2O3 doped with Fe.

Influence of Surface Sputtering during High-Intensity, Hot Ion Implantation on Deep Alloying of Martensitic Stainless Steel

This article is devoted to the study of the effect of ion sputtering on the alloy surface, using the example of martensitic stainless steel AISI 420 with ultrahigh-dose, high-intensity nitrogen ion implantation on the efficiency of accumulation and transformation of the depth distribution of dopants. Some patterns of change in the depth of ion doping depending on the target temperature in the range from 400 to 650 °C, current density from 55 to 250 mA/cm2, and ion fluence up to 4.5 × 1021 ion/cm2 are studied. It has been experimentally established that a decrease in the ion sputtering coefficient of the surface due to a decrease in the energy of nitrogen ions from 1600 to 350 eV, while maintaining the ion current density, ion irradiation fluence and temperature mode of target irradiation increases the ion-doped layer depth by more than three times from 25 μm to 65 µm. The efficient diffusion coefficient at an ion doping depth of 65 μm is many times greater than the data obtained when stainless steel is nitrided with an ion flux with a current density of about 2 mA/cm2.

Study of the influence of a powerful pulsed ion beam on titanium deeply-doped with aluminum

The work studies the synergy effect of high-intensity implantation of aluminum ions and the subsequent impact of a powerful pulsed ion beam on the microstructure and properties of titanium. Specimens of titanium were implanted for 1 h at a temperature of 1170 K with an ion fluence of 1021 ions/cm2. Layers with a thickness of about 150 μm were obtained. The energy impact was carried out by a powerful nanosecond pulsed ion beams with an ion current density on the target of 100 A/cm2. The paper presents data on changes in the elemental composition, and microstructure of ion-doped and energy-modified layers. It has been established that the additional energy impact on the ion-doped layer of a powerful pulsed beam improves microstructure at depths of about 4.31 μm. The synergistic of high-intensity ion implantation of aluminum and the energy impact of a pulsed ion beam improves the wear resistance of titanium by eighteen folds.

Особенности фотоэлектронных спектров Ge, имплантированного ионами Na-=SUP=-+-=/SUP=-

Using the methods of Auger electron and photoelectron spectroscopy and light absorption spectroscopy, the composition, densities of state of electrons in the valence band, and parameters of the energy bands of Ge (111) implanted with Na+ ions with an energy of E0 = 0.5 keV at a dose of D = Dsat = 6·1016 cm-2 and a thin layer of NaGe2 obtained by heating ion-implanted Ge. It is shown that a narrow n-type band (~0.2 eV) appears in the Ge valence electron spectrum after ion implantation near the bottom of the conduction band, which is explained by the presence of a large number of unbound Na atoms in the ion-doped layer. NaGe2 nanofilms with a band gap of ~0.45 eV was obtained for the first time by heating ion-implanted Ge.

Simulation and experimental studies on the formation of high-power titanium ion beams for the synergy of ion implantation and energy impact on the surface

The development of a material modification method based on synergy of high-intensity ion implantation and simultaneous energy impact on the surface is aimed at creating deep ion-doped layers. To implement this method, the high power density of pulsed and repetitively-pulsed beams of metal and gas ions with micro-submillisecond duration are required. The paper presents the results of numerical simulation and experimental studies on the formation of pulsed high-intensity metal ion beams from vacuum arc plasma. The ballistic focusing of heavy ions at injection currents from 0.1 to 1 A has been studied. The influence of the ion current density, accelerating voltage, and conditions for neutralizing the beam space charge on the transport and focusing of a high power density ion beam has been studied. The possibility of ballistic formation of submillisecond titanium ion beams with a pulse power density of a hundred kilowatts per square centimeter has been experimentally shown.

Численное моделирование динамики температурных полей в монокристаллическом кремнии при импульсно-периодической высокоинтенсивной ионной имплантации и энергетическом воздействии пучка на поверхность

Methods to modify surface and near-surface layers of materials and coatings by ion beams are used in many fields of science and technology. The method of high-intensity implantation by high-power density ion beams with submillisecond duration involves significant pulsed heating of the irradiated target’s near-surface layer, followed by its rapid cooling due to heat transfer into the material due to thermal conductivity and the implementation of repetitively-pulsed radiation-enhanced diffusion of atoms to depths exceeding the projective ion range. Using the numerical simulation, this work studies the dynamics of changes in temperature fields into silicon wafer under single-pulse and repetitively-pulsed exposure to submillisecond titanium ion beam with a pulsed power density in the range up to 109 W/m2. The conditions are determined under which the temperature in the ion-doped layer will correspond to the conditions of radiation-stimulated diffusion of the implanted element, and the temperature in the matrix material will not deteriorate its microstructure and properties.

Формирование мощных импульсных пучков ионов титана субмиллисекундной длительности из плазмы вакуумной дуги

The development of a method to improve performance properties of various materials, based on the synergy of high-intensity ion implantation and simultaneous energy impact on the surface, is aimed at creating deep ion-doped layers. Repetitively-pulsed high-power density beams of metal and gas ions with submillisecond duration are required to implement this method. This article presents the results of experimental studies on the forming pulsed high-intensity titanium ion beams from vacuum arc plasma. The effect on focusing and transport efficiency of the cell sizes of the grid focusing electrode in the form of a part of a sphere has been studied. The possibility of ballistic focusing of a titanium ion beam with a pulse duration from 150 to 500 μs with a power density of up to 100 kW/cm2 has been experimentally shown.

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.

Profiles of ion-doped layers on gallium arsenide

We studied the concentration profiles of charge carriers that are characteristic for ion-doped layers (IDL) used in the manufacturing of field-effect transistors with a Schottky barrier (FTS) on gallium arsenide. Silicon was used as a dopant in the formation of n- and n+ -n layers on GaAs. During annealing of the IDL, SiO2 films were used as protective coatings. The impurity content and silicon distribution in the IDL were estimated by the SIMS method. Profiles of ion-doped layers were calculated by the LSB method. The method for measuring of surface concentration consists in the constant chemical etching of thin layers of gallium arsenide and the measurement of surface electrophysical characteristics. The experimental concentration profiles for GaAs are not Gaussian, but have wide “tails” due to channeling effects in crystals and the influence of chromium. The modes of ion implantation are considered, which form IDL with a sharper profile of the concentration of charge carriers in the “tail”.

Distributions of silicon implanted in GaN epitaxial layers

Ion-doped layers of n+ - GaN were formed with a high degree of activation of the embedded impurity. Si+ ion implantation was performed in GaN epitaxial layers grown by MOCVD. Profiles of embedded silicon in gallium nitride were calculated. The experimental profile obtained by secondary ion mass spectrometry is compared with the calculated one. Optimal implantation modes were determined, the implantation dose is 1015 cm−2, and the energy is 50 keV. Activation of the embedded impurity was performed by high-temperature photon annealing in a nitrogen medium using SiO2 and Si3N4 protective coatings. The influence of the annealing temperature on the morphology of protective coatings is considered. The SRIM program was used to simulate the process of ion implantation of silicon at the interface of the AlGaN/GaN heterostructure through SiO2 dielectric films of different thickness. Ohmic contacts were formed on the ion-doped basis of the Ti/Al/Ni/Au metallization system. The calculation of the contact resistance of ohmic contacts showed that the use of ion doping through a 50 nm thick silicon dioxide film reduces the contact resistance from 1.2 Ω·mm to 0.8 Ω·mm. The use of ion implantation technology in the manufacture of diode structures reduces the direct voltage drop and the minimum voltage drop is achieved when using implantation through a 50 nm SiO2 mask, this is due to the location of the maximum distribution of the implanted impurity at a depth corresponding to the occurrence of a two-dimensional electron gas.

Modification of the microstructure and properties of martensitic steel during ultra-high dose high-intensity implantation of nitrogen ions

In this work, we report a study of the chemical and phase composition, structural modifications and mechanical properties of martensitic stainless steel surface layers modified by high-intensity nitrogen ion implantation using a high current beam of low-energy nitrogen ions. The effect of ultrahigh-dose implantation of nitrogen ions into steel using a high-intensity repetitively pulsed beam of nitrogen ions with a current of 0.6 A (at an ion energy of 1.2 keV) and a sample temperature of 500 °C is investigated. The fluence of ion irradiation in the range from 6 × 1021 ions/cm2 to 2.25 × 1021 ions/cm2 varied by changing the current density and implantation time. The studies performed using transmission electron microscopy and X-Ray diffraction analysis of the microstructure and phase composition of the implanted samples showed that the surface-doped layer formed up to 75 μm thick and contains ferrite, iron nitride Fe4N, and chromium nitride CrN (α-phase – 70.88 vol.%, γ'-Fe4N – 16.30 vol.%, CrN – 12.82 vol.%). The obtained values of the coherent scattering region size of the formed chromium nitride and iron nitride indicate a very high dispersion of the elements in the ion-doped layer substructure. The data on changes in the surface morphology and microhardness of the near-surface layers are presented.

Ohmic Contacts to Gallium Nitride-Based Structures

Studies of the characteristics of ohmic contacts to epitaxial and ion-doped gallium-nitride layers, based on the Cr/Pt/Au metallization system, are reported. The possibility of forming low-resistance contacts without the application of high-temperature treatment is shown. It is demonstrated, for AlGaN/GaN-based heterostructures, that the characteristics of Ti/Al/Ni/Au ohmic contacts are improved upon using ion implantation through a silicon-dioxide mask.

Improving the performance properties of titanium alloy VT6 after ion implantation with copper and aluminum ions

The objective of this work was to study the processes occurring on the surface of VT6 titanium alloy samples when implanting with copper and aluminum ions. Elemental composition, structural-phase state, mechanical and tribological properties of VT6 titanium alloy surface layers modified by aluminum and copper ions was being researched. As can be seen from the undertaken studies, the mode of high-intensity ion-implantation process makes it possible to obtain ion doped surface layers of VT6 alloy containing finely dispersed intermetallic phases and a solid solution of aluminum and copper in titanium of a composition varying in depth. The thickness of the ion-doped layer, the average grain size of the intermetallic phases and their conglomerates increases with the increase in implantation dose while aluminum implantation is in progress. It has been shown that the implantation of aluminum and copper ions into VT6 alloy leads to a considerable increase in its microhardness and wearability. Based on the research results, a conclusion on the positive effect of a structural-phase state of ion-doped titanium layers on their mechanical and tribological properties of VT6 titanium alloy has been drawn.

VT6 TITANIUM ALLOY WEARABILITY INCREASE VIA IMPLANTATION OF COPPER AND ALUMINUM IONS

The relevance of the article is due to the fact that the use of titanium alloys within friction joints is restrained by their low resistance to wear while traditional methods of increasing their wear resistance are ineffective. The objective of this work was to study the processes occurring on the surface of VT6 titanium alloy samples when implanting with copper and aluminum ions, as well as in friction. Elemental composition, structural-phase state, mechanical and tribological properties of VT6 titanium alloy surface layers modified by aluminum and copper ions during the high-intensity ion-implantation process was being researched. As can be seen from the undertaken studies, the mode of the high-intensity ion-implantation process makes it possible to obtain ion doped surface layers of VT6 alloy containing TiAl, Ti3Al, Ti3Cu, Ti2Cu, TiCu finely dispersed intermetallic phases and a solid solution of aluminum and copper in titanium of composition varying in depth. The thickness of the ion-doped layer, the average grain size of the intermetallic phases (from 18 to 55nm) and their conglomerates (from 45 to 280 nm) increases with the increase in implantation dose from 2⋅1017 to 1.2⋅1019 ion/cm2 while aluminum implantation (from 0.42 to 2.1 μm) is in progress. It has been shown that the implantation of aluminum and copper ions into VT6 alloy leads to a considerable increase in its microhardness and wearability. Based on the research results, a conclusion on the positive effect of a structural-phase state of ion-doped titanium layers on their mechanical and tribological properties of VT6 titanium alloy has been drawn.

Redistribution of impurity in ion-doped layers during fast heat treatment of gate dielectric

Redistribution of impurity in ion-doped layers during fast heat treatment of gate dielectric

Physicochemical fundamentals of phase formation in silicon layers implanted with oxygen and carbon

The thermodynamic and kinetic regularities of processes occurring during heat treatment in silicon layers implanted with oxygen and carbon ions have been considered. We have analyzed the regularities of silicon deformation, impurity distribution and defect formation after different annealing modes. Diffusion smearing of implanted impurities in these layers has not been observed during carbon and oxygen implantation. As-annealed carbon does not occupy sites of the silicon lattice, in contrast to the implantation behavior of other impurities, e.g. boron and phosphorus. Phase formation regularities in implanted layers during subsequent heat treatment have been analyzed. Changes in the free energy of the system during heterogeneous and homogeneous precipitate nucleation have been compared. Sequential implantation with carbon and oxygen ions has been found to initiate diffusion flows of carbon and oxygen toward the center of the ion doped layer (the uphill diffusion phenomenon). The possibility of uphill diffusion has been analyzed from the standpoints of the Onsager theory. We show that the contribution of the chemical interaction between oxygen and carbon is far greater than the entropy contribution to the diffusion flux. We have demonstrated the high efficiency of ion doping with oxygen and carbon for gettering of uncontrolled impurities from active regions of silicon structures. The efficiency of this gettering process has been assessed for epitaxial structures in which layers had been grown on silicon wafers implanted with these impurities. Uphill diffusion in the layers after double doping with carbon and oxygen has led to the formation of more defects which may provide for efficient gettering. We have found the optimal oxygen and carbon implantation dose ratio for maximal gettering efficiency.

An Optical Diffraction Method for Controlling the Solid-Phase Recrystallization and Heating of Implanted Semiconductors during Pulse Light Annealing

t—The results of the improvement of the method of laser diagnostics for investigating the heating dynamics, solid-state recrystallization, and melting of implanted semiconductors directly during a pulse light annealing procedure are presented. This technique is based on recording Fraunhofer diffraction patterns from special periodic structures; it allows investigations of structural–phase transitions in ion-doped semiconductor layers simultaneously with sample temperature measurements with a high time resolution. For this purpose, two measuring diffraction gratings were preliminarily formed on the surface of a silicon wafer: a phase grating and an amplitude grating. The solid-phase recrystallization and melting processes were studied via the kinetics of the disappearance and appearance of the diffraction maxima from the amplitude grating. The sample temperature was monitored by the deflection of the diffraction angle of the probe laser beam from the phase diffraction grating. This deflection is caused by a change in the grating period due to its thermal expansion.