Spatial distribution, build-up, and annealing of radiation defects in silicon implanted by high-energy krypton and xenon ions

An x-ray diffraction study of defect formation in silicon irradiated by Kr⁺ (210 MeV, 8×10¹²−3×10¹⁴ cm⁻²) and Xe⁺ (5.6 BeV, 5×10¹¹−5×10¹³ cm⁻²) ions is reported. It has been established that irradiation produces a defect structure in the bulk of silicon, which consists of ion tracks whose density of material is lower than that of the host. The specific features of defect formation are discussed taking into account the channeling of part of the ions along the previously formed tracks and the dominant role of electron losses suffered by the high-energy ions. It is shown that the efficiency of incorporation of stable defects by irradiation with high-energy ions is lower than that reached by implanting medium-mass ions with energies of a few hundred keV. Fiz. Tverd. Tela (St. Petersburg) 40, 1627–1630 (September 1998)     

Effect of ion sputtering on the statistical properties of a surface

The modification of a gallium arsenide surface during irradiation by heavy cesium ions Cs⁺ is investigated by measuring the surface height distribution with an atomic force microscope. Both increases and decreases in the rms height σ, an integral parameter of the surface, are observed to occur. It is established that for all experimental samples the roughness of the gallium arsenide surface increases in a 1–100 nm lateral range. Analysis of the structure function yields an estimate of the characteristic lateral dimensions of the surface structures arising during ion etching. Zh. Tekh. Fiz. 69, 107–111 (February 1999)     

Luminescence detection of multiphoton ionization-fragmentation of the molecular CrO 4 2− anions adsorbed on the surface of dispersed SiO2

It is shown that luminescence detection of multiphoton ionization-fragmentation of the molecular CrO ₄ ²⁻ anions adsorbed on the surface of dispersed SiO₂ is possible under excitation with the fundamental frequency of a Nd:YAG pulsed laser (λ=1.064 μm). The structure and the process of formation of the adsorbed complexes under thermal activation of the surface and the nature of luminescence transitions in CrO ₄ ²⁻ anions are studied in detail. It is shown that luminescence is excited as a result of the recombination of photoelectrons and ionized chromate ions. Multiphoton ionization of the ions occurs under three-photon resonance conditions. The resonance level is an antibonding state of the adsorption complex formed with the participation of an oxygen vacancy on the SiO₂ surface. The dynamics of the multiphoton luminescence excitation process includes autoionization (stimulated by intercomplex electronic excitation) in superexcited states, fragmentation of chromate anions, and annealing of surface oxygen vacancies. The rate equations for three-photon-resonance multiphoton ionization are studied. The cross sections for two-and one-photon transitions on the nonresonance steps of multiphoton absorption are obtained. It is concluded that the nonlinear polarizability of the donor-acceptor adsorption bond in “chromate anion-oxygen vacancy” complexes is very important. Zh. éksp. Teor. Fiz. 111, 1748–1774 (May 1997)     

Mechanoluminescence and submicrorelief of a copper surface

Copper plates are irradiated with pulsed laser light on one side, and the opposite side is investigated with a scanning tunneling microscope. It is found that the submicrorelief of the back surface changes after irradiation. During irradiation it emits a light pulse. It is established that a relation exists between the luminescence intensity and the magnitude of the change in the surface submicrorelief. Zh. Tekh. Fiz. 69, 102–104 (December 1999)     

Phase transitions in erbium-doped silicon exposed to laser radiation

The dynamics of phase transitions induced by nanopulsed ruby laser radiation (80 nsec, 2 J/cm²) both in silicon layers doped with erbium ions and in those containing doped erbium and oxygen have been studied by an optical probing method. It is shown that the reflectivity behavior of structures under pulsed irradiation is governed by phase transitions (melting and crystallization) of implanted silicon and also by interference effects at the interfaces of the resulting phases. It is established that the profiles of erbium distribution change under nanosecond laser irradiation and that the dopant is forced out to the surface due to a segregation effect at small implantation doses. As the implanatation dose increases, diffusion deep into the sample tends to prevail over segregation. A considerable increase in the photoluminescence peak intensity at 0.81 eV is found after both the pulsed laser processing and thermal post-annealing of doped samples as opposed to spectra of samples subjected either to thermal annealing or to pulsed laser irradiation. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 225–231, March–April, 2009.     

Stimulation of secondary negative ion emission by implantation of alkaline ions into the surface layer of a solid followed by heating

A new method of stimulating secondary negative ion emission is suggested that is based on implantation of alkaline ions into the surface layer of a solid with subsequent heating to a temperature providing optimal coverage of the surface (about half a monolayer) by activator (alkaline) ions. It is shown that, by appropriately selecting the implantation dose (10¹⁸–10¹⁹ cm⁻³) and surface temperature (500–900°C), one can reach such a degree of coverage of the sample surface by activator ions that its work function eφ becomes minimal: 1.9 eV for molybdenum and 2.1 eV for copper. It is found that, with the implantation (irradiation) dose and surface temperature chosen properly, one can, by means of outdiffusion of cesium atoms, achieve such a degree of surface coverage that remains unchanged during the continuous sputtering of the surface by a cesium ion beam.     

Self-assembly of germanium islands under pulsed irradiation by a low-energy ion beam during heteroepitaxy of Ge/Si(100) structures

The effect of pulsed irradiation by a low-energy (50–250 eV) ion beam with a pulse duration of 0.5 s on the nucleation and growth of three-dimensional germanium islands during molecular-beam heteroepitaxy of Ge/Si(100) structures is investigated experimentally. It is revealed that, at specific values of the integrated ion flux (less than 10¹² cm^?2), pulsed ion irradiation leads to an increase in the density of islands and a decrease in their mean size and size dispersion as compared to those obtained in the case of heteroepitaxy without ion irradiation. The observed phenomena are explained in the framework of the proposed model based on the concept of a change in the diffusion mobility of adatoms due to the instantaneous generation of interstitial atoms and vacancies under pulsed ion irradiation. It is assumed that the vacancies and interstitial atoms give rise to an additional surface strain responsible for the change in the binding energy of the adatoms. Under certain conditions, these processes bring about the formation of centers of preferential nucleation of three-dimensional islands at the places where the ions impinge on the surface. The model accounts for the possibility of annihilating vacancies and interstitial atoms on the surface of the growing layer. It is demonstrated that the results obtained from the Monte Carlo calculations based on the proposed model are in good agreement with the experimental data.     

Influence of Cr<Superscript>+</Superscript> ion implantation and pulsed ion-beam annealing on the formation and optical properties of Si/CrSi<Subscript>2</Subscript>/Si(111) heterostructures

The effect of pulsed ion-beam annealing on the surface morphology, structure, and composition of single-crystal Si(111) wafers implanted by chromium ions with a dose varying from 6 × 10¹⁵ to 6 × 10¹⁶ cm⁻² and on subsequent growth of silicon is investigated for the first time. It is found that pulsed ion-beam annealing causes chromium atom redistribution in the surface layer of the silicon and precipitation of the polycrystalline chromium disilicide (CrSi₂) phase. It is shown that the ultrahigh-vacuum cleaning of the silicon wafers at 850°C upon implantation and pulsed ion-beam annealing provides an atomically clean surface with a developed relief. The growth of silicon by molecular beam epitaxy generates oriented 3D silicon islands, which coalesce at a layer thickness of 100 nm and an implantation dose of 10¹⁶ cm⁻². At higher implantation doses, the silicon layer grows polycrystalline. As follows from Raman scattering data and optical reflectance spectroscopy data, semiconducting CrSi₂ precipitates arise inside the silicon substrate, which diffuse toward its surface during growth.     

Mechanism of structural changes of Si(111) surfaces subjected to low-energy ion pulses during molecular-beam epitaxy

Reflected high-energy electron diffraction (RHEED) and detection of the intensity oscillations of the specular reflection have been used to investigate morphological changes in Si(111) associated with the two-dimensional layer-by-layer mechanism of silicon growth from a molecular beam under conditions of pulsed (0.25–1 s) bombardment with low-energy (80–150 eV) Kr ions in the interval of small total radiative fluxes (10¹¹–10¹² cm²²), for which the density of radiation-generated defects is small in comparison with the surface density of the atoms. After pulsed ion bombardment an increase in the intensity of the specular reflection is observed if the degree of filling of the monolayer satisfies 0.5<θ<1. No increase in the intensity occurs during the initial stages of filling of the monolayer. The maximum amplitude increment of the oscillations is reached at θ≈0.8. The magnitude of the amplitude increment of the RHEED oscillations increases with temperature up to 400°C and then falls. At temperatures above 500°C amplification of the reflection intensity essentially vanishes. Experiments on multiple ion bombardment of each growing layer showed that the magnitude of the amplitude increment of the oscillations decreased as a function of the number of deposited layers (the order of the RHEED oscillation). A mechanism for the observed phenomena is proposed, based on the concept of surface reconstruction by pulsed ion bombardment accompanied by formation of a (7×7) superstructure, which corresponds to a decrease of the activation energy of surface diffusion of the adatoms. Within the framework of the proposed mechanism the results of Monte Carlo modeling agree with the main experimental data. Zh. éksp. Teor. Fiz. 114, 2055–2064 (December 1998)     

Effect of the bombarding-ion mass in alloy sputtering

It is shown experimentally that a change in the mass of bombarding ions from ⁴⁰Ar⁺ to ⁴He⁺ has a strong effect on the spatial distributions of the components sputtered from the alloy NiMoRe. A mechanism of sputtering by backscattered ions is proposed to describe the observed preferential ejection of the light component in the direction normal to the surface of the sample under bombardment by ⁴He⁺ ions. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 7, 507–510 (10 April 1996)     

Magnetic resonance of metallic nanoparticles in vitreous silicon dioxide implanted with iron ions

Silica glasses exposed to steady-state and pulsed irradiation with Fe⁺ ions are studied using magnetic resonance. The irradiation doses used in experiments are equal to 1 × 10¹⁵, 1 × 10¹⁶, and 1 × 10¹⁷ cm^?2. It is found that, under both steady-state and pulsed irradiation conditions, glass samples exposed at a dose of 1 × 10¹⁷ cm^?2 exhibit a broadband orientation-dependent signal. The shape of inclusions is evaluated under the assumption that the observed spectrum is caused by the ferromagnetic resonance induced in a new phase of metallic iron.     

Systematic field-theory for the hard-core one-component plasma

A continuous liquid flow in a vacuum (a liquid beam) of an aqueous solution of adenine salt containing hydrochloric acid or sodium hydroxide was irradiated with an intense pulsed IR laser at 3 μm, which is resonant to a vibrational mode related to the OH stretch vibration of H₂O. Neutral species isolated into the vacuum were ionized by a pulsed UV laser at 270 nm, and the product ions were mass-analyzed by a time-of-flight mass spectrometer. It is found that AH ₂ ^{2 + .} 2Cl^- and [A-iH] ^{i - .} iNa⁺ (i = 1-3) are isolated in the vacuum from the aqueous acidic and alkaline solutions, respectively, under irradiation of the IR laser, and undergo four-photon ionization involving decomposition and proton transfer of the intermediate species under irradiation of the UV laser. Received 1st May 2002 Published online 13 September 2002     

Luminescence of short-lived color centers induced in LiF crystals by a pulsed microwave discharge

A new phenomenon — intense luminescence of noncolored lithium fluoride (LiF) crystals excited by an electrodeless pulsed microwave discharge at the prebreakdown stage of development — is observed. This luminescence consists of the luminescence of short-lived aggregate F₂ and F ₃ ⁺ color centers at room temperature. It is shown that the density of short-lived color centers induced in the surface layer of LiF crystals by a microsecond microwave discharge reaches values of ∼10¹⁹−10²⁰ cm⁻³. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 3, 163–167 (10 August 1997)     

Influence of electron irradiation of the NOVER-1 vacuum resist on its resistance to ionbeam etching

The influence of electron irradiation on the resistance of the NOVER-1 resist to ion-beam etching is studied. Etching is carried out by argon ions with energies between 300 and 2500 eV. It is found that, depending on the energy and angle of incidence of the ions on the surface of the resist, electron irradiation may either speed up or slow down the NOVER-1 etching. A clear correlation is observed between the penetration depth of the ions in the resist and the influence of the electron irradiation on the resistance of the resist to etching. At ion energies higher than 500 eV (ion penetration depth ≳3.5 nm) the resistance decreases, passes through a minimum at low electron irradiation doses, and returns to the etching rate of the initial resist at high doses. For glancing etching angles (∼ 70° to the surface normal) and low ion energies (300 eV), i.e., small ion penetration depths (≲2.5 nm), an electron-irradiated resist is etched more slowly than the initial resist at all the electron irradiation doses studied. This effect may be used to enhance the resistance of resist structures whose height exceeds their width, which in this case is determined mostly by the rate of etching of the inclined facets. Zh. Tekh. Fiz. 68, 140–142 (January 1998)     

TEM study of ion implanted GaAs after pulsed electron beam annealing

Abstract

(001) GaAs single crystals were implanted with 150 keV Cr⁺ ions using a dose of 5 × 10¹⁵ ions cm^?2. The amorphized surface layers were subjected to pulsed electron beam annealing at energy densities in the range 0–1.3 J cm^?2. A detailed TEM investigation of the damaged and annealed surface layer was conducted. These observations were correlated with backscattering results.     

Dependences of HTS tape critical parameters on fluences under irradiation with heavy ions and high energy electrons

Experimental data on the study of modifications of two types of the YBCO(123)-based composite tape under irradiation with electrons with the energy of 23 MeV and ¹³²Xe²⁷⁺ (167 MeV), ⁸⁴Kr¹⁷⁺ (107 MeV), and ⁴⁰Ar⁸⁺ (48 MeV) ions in a wide range of irradiation doses are presented. It is shown that no changes in the HTS transition temperature and critical current occurred under electron irradiation up to the dose D ≈ 10⁻⁴ disp/a (displacements per atom). The threshold dose of irradiation with ¹³²Xe²⁷⁺ ions, at which superconductivity disappears, is determined. In comparison with the initial value, the critical current of ⁴⁰Ar⁸⁺ ions is found to increase by ≈18% in the zero magnetic field at T = 77 K. This effect can be explained by the pinning centers for Abrikosov vortices induced by relatively small ion irradiation doses. High doses of heavy ions lead to partial or complete amorphization of a superconductor, which results first in a decrease in the critical current and transition temperature and then in a total disappearance of superconductivity. X-ray diffraction is used to study the changes in the crystal structure of the YBCO(123) superconductor under ion irradiation.     

Spodumene and garnet luminescence excited by subnanosecond electron beams

Pulsed cathodoluminescence of spodumene and yttrium-aluminum garnet crystals activated by Mn²⁺ and Nd³⁺ ions, respectively, is investigated. The luminescence was excited upon crystal irradiation by electron beams with current densities of 35 and 100 A/cm² and average electron energy of ∼ 50 keV for 0.1, 0.25, and 0.65 ns. It is demonstrated that the electron beam duration decreased to several tenth of a nanosecond does not lead to essential changes of the mechanisms of pulsed cathodoluminescence excitation and character of its spectrum, but in this case, the intensity of luminescence of the hole centers increases compared with the intracenter luminescence.     

Depth distribution of point defects in Si bombarded by high-energy N5+ and Si5+ ions

Electron spin resonance has been used to study the depth distribution of point defects in Si samples bombarded by N⁵⁺ (E=16 MeV) and Si⁵⁺ (E=26.8 MeV) ions at 175 and 300 K in the dose range (4–8)×10¹⁵ cm⁻². It was established that unlike the implantation of moderate-energy Si ions (E ∼ 100 keV), the depth distributions of planar tetravacancies in samples bombarded by ions at 300 K under these conditions have two maxima. The experimental results indicate that the tetravacancy density maximum closer to the surface is formed as a result of secondary defect formation processes. No continuous amorphous layer was observed in the bulk of any of the Si samples. This experimental observation is evidence of defect annealing which takes place when high-energy ions are implanted in Si. Fiz. Tverd. Tela (St. Petersburg) 40, 217–222 (February 1998)     

Erosion of the GaAs target under irradiation by a high-power pulsed ion beam

The results of examination of the GaAs-target erosion under irradiation by a high-power pulsed ion beam are reported. In the experiments, use was made of a high-power pulsed ion source with the following parameters: ion energy — 250 keV, target current density — 350 A/cm², pulse duration — 80 ns, target energy density — up to 7 J/cm². The target erosion coefficient and its dependence on the number of successive pulses are measured. It is found that the surface roughness parameter is increased with the number of successive beam pulses. A regular structure of surface relief is observed to form in the case where the number of pulses > 20–40. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 66–70, January, 2007.     

Sputtering of AlxGa1−x As semiconductor targets by Ar+ ions with energies of 2–14 keV

Investigations of the sputtering of Al_xGa_1−x As semiconductor solid solutions by Ar⁺ ions with energies of 2–14 keV are performed. The dependence of the sputtering yield on the energy and angle of incidence of the ions are determined and the character of the surface relief formed during the sputtering is investigated. A comparison with theory shows that the best agreement between theory and experiment is achieved when the Haff-Switkowski formula is used together with Yudin’s stopping cross section. It is shown that the surface binding energies obtained differ from the atomization energies by an amount approximately equal to the amorphization energy. Zh. Tekh. Fiz. 67, 113–117 (June 1997)