ion implantation of bismuth into GaP. I. photoluminescence

Photoluminescence from the bismuth isoelectronic trap implanted into GaP is investigated for various ion doses and annealing conditions. A thin coating of silicon oxide is found to be essential to prevent thermal decomposition of the implanted surface during annealing. In isochronal anneal studies the intensity of the Bi luminescence increases rapidly between 650 and 800°C. For 200 keV implants, the dose for maximum luminescence is ～3.5 × 10¹² ions/cm², corresponding to an average concentration of ～10¹⁸/cm³. However, for the optimum dose and anneal, one observes only ～10 per cent of the light intensity expected from the estimated number of substitutional ions, and the emitting ions are situated in lattice sites with strong local strain. This strain is evident in the photoluminescence spectrum by the appearance of a strong no-phonon line which results from an otherwise forbidden transition when strain or an external field are present. The luminescence data are correlated with channeling experiments reported in a companion paper.     

Lattice disorder in germanium by boron ion bombardment

Abstract

The lattice disorder produced in germanium by 56keV boron-ion bombardment has been measured using the channeling-effect technique. The dependence on dose (10¹⁴-10¹⁶ ions/cm²) and implantation temperature (?90 °C to +130°C) has been studied. It is found that at room-temperature, each incident boron ion creates ?10 times more disorder in germanium than in silicon. It is remarked that, contrary to the present results, previously established anneal stages generally occur at significantly lower temperatures in germanium than in silicon.     

Blistering of rhenium irradiated with 21keV helium ions

This paper describes blistering of rhenium following 21 keV He⁺-ion irradiation at temperatures between 300 K and 1200 K. Blistering starts at 300 K at a dose of 3×10¹⁷ ions/cm². The most probable blister diameter varies from 4400 ? at 300 K to 10100 ? at 1200 K. The blister depth τ _bl , the blister diameter φ _bl and the blister heighth _bi show a distribution. From the observations one could derive the following relationships:h _bl = 0.35φ _bl ; τ _bl =3.43φ _bl ^2/3 . The erosion yieldE _y due to blistering is function of doseE _y =0.51 atoms/ion at 3×10¹⁷ ions/cm²,E _y =0.56 atoms/ion at 6×10¹⁷ ions/cm² andE _y =0.14 atoms/ion at 3×10¹⁸ ions/cm². The sputtering yieldS (21 keV) is estimated to be ∼0.1 atom/ion. The corresponding surface regression is 44? at 3×10¹⁷ ions/cm² and 1323 ? at 9×10¹⁸ ions/cm². Surface regression has therefore little influence on the observations at low doses. Work performed at the Mathematicals Science Department of S.C.K./C.E.N. at Mol (Belgium)     

implantation of Bi into GaP. II. channeling studies

The channeling technique has been used to investigate the properties of Bi-implanted Gap. Measurements of the crystal disorder for 100 keV room temperature implants indicate a damage vs dose curve corresponding to ～13000 displacements/ion in the linear region and saturation at ～1.5 × 10¹³ Bi ions/cm². Annealing of the radiation damage has been observed and indicates two annealing steps at ～450°C for light damage and ～750°C for implants in the 1 × 10¹⁴/cm² range. Difficulties associated with the thermal decomposition of the implanted area have been overcome with the use of SiO _x coatings. The experimental details associated with the use of the SiO _x layer and with the use of a C¹² beam to obtain better depth and mass resolution in the backscattering spectrum are discussed. The lattice location measurements of the Bi impurity show ～50 per cent of the Bi atoms to be along the 〈110〉 string after a 900°C anneal for a 7.5 × 10¹³/cm² implant. In addition, the spectra show ～25 per cent of the Bi atoms have diffused to the surface. Correlations of these lattice location results with measurements of the photoluminescent intensity of the GaP (Bi) isoelectronic trap show an agreement in trend with anneal temperature but indicate a factor of ～10 more substitutional ions in the channeling measurement as compared to the photoluminescence results.     

Crystalline to amorphous transformations in ion implanted GaP

Abstract

The amorphization process of GaP by ion implantation is studied. The samples of 〈111〉 oriented GaP were implanted at 130 K with various doses 5 × 10¹³-2 × 10¹⁶ cm^?2 of 150 keV N⁺ ions and with the doses of 6 × 10¹²-1.5 × 10¹⁵ cm^?2 of 150 keV Cd⁺ ions. Room temperature implantations were also performed to see the influence of temperature on defect production. Rutherford backscattering and channelling techniques were used to determine damage in crystals. The damage distributions calculated from the RBS spectra have been compared with the results of Monte-Carlo simulation of the defect creation.

The estimated threshold damage density appeared to be independent on ion mass and is equal 6.5 × 10²⁰ keV/cm³. It is suggested that amorphization of GaP is well explained on the basis of a homogenous model.     

Low temperature channeling measurements of ion implantation lattice disorder in single crystal silicon

Lattice disorder for 200-keV Sb implantations into silicon has been studied by channeling effect analysis using 400 keV proton backscattering. Implantation and analysis were performed at low temperatures in the same system without warmup. In the temperature region between 85°K and room temperature the disorder production per incident ion at low doses is implantation temperature dependent. Approximately 18,000 silicon scattering centers per incident 200-keV Sb ion are observed for 90°K implantations, and this value is nearly a factor of three greater than at room temperature. Isochronal anneal curves of low fluence, low temperature implantations show, significant annealing below room temperature. The observed disorder production per incident ion decreases with increasing implantation temperature at temperatures 50 to 100°K lower than annealing occurs following 85 or 90°K implants. Strong similarities of the implantation temperature dependence and anneal behavior of the disorder exist for Sb and B implantations into silicon and suggest that much of the lattice disorder produced by ion implantation can be understood in terms of the basic properties of the silicon target material.     

The energy dependence and depth distribution of lattice disorder in ion-implanted silicon

Silicon single crystals were implanted at room temperature with Xe and I ions in the energy range 20 to 150 keV and with 20 to 50 keV P ions. The lattice disorder induced by these implants was measured by a combination of the channeling and Rutherford backscattering techniques. The disorder produced by implanting I and Xe ions exhibited a similar relationship with implantation energy to that previously established for bismuth implants. The P ion implants induced less lattice disorder per incident ion in the energy range studied. Integral depth distributions of the implanted ions and of the lattice disorder were obtained by combining a layer removal technique with radiotracer implants of 110 keV ¹³³Xe and 40 keV ³²P. The depth distributions showed that in both cases the ions penetrate deeper into the crystal than the damage they produce but that the separation is significantly greater for the P implant than for the Xe implant.     

Electrical properties of Cd,Zn and S ion-implanted layers in GaAs

The electrical properties of cadmium, zinc, and sulfur ion-implanted layers in gallium arsenide have been measured by the van der Pauw-Hall technique. Ion implantation was performed with the substrates held at room temperature. The dependence of sheet resistivity, surface carrier concentration, and mobility on ion dose and on post-implantation anneal temperature was determined. In the case of 60 keV Cd⁺ ions implanted into n-type substrates, a measurable p-type layer resulted when samples were annealed for 10 minutes at a temperature in the range 600—900°C. After annealing at 300—900°C for 10 minutes, 100 per cent electrical activity of the Cd ions resulted for ion doses ≤ 10¹⁴/cm².

The properties of p-type layers produced by implantation of 85 keV Zn⁺ ions were similar to those of the 60 keV cadmium-implanted layers, in that no measurable p-type behavior was observed in samples annealed below a relatively high temperature. However, in samples implanted with 20 keV Zn⁺ ions a p-type layer was observed after annealing for 10 minutes at temperatures as low as 300°C.

Implantation of sulfur ions into p-type GaAs substrates at room temperature resulted in the formation of a high resistivity n-type layer, evcn before any annealing was performed. Annealing at temperatures up to 200°C or above 600°C lowered the resistivity of the layer, while annealing in the range 300—500°C eliminated the n-type layer.     

Annealing of arsenic-and antimony-implanted silicon single crystals using A CW xenon arc lamp

Abstract

Continuous, incoherent light from a xenon arc lamp has been used to anneal radiation damage in <100> silicon single crystals produced by implantation of 30?keV arsenic or antimony ions to doses between 1×10¹⁵ cm^?2 and 1×10¹⁶ cm^?2. The recrystallized layers have been characterized by Rutherford-backscattering spectroscopy, ion-channeling, Transmission Electron Microscopy, and sheet-resistivity measurements.     

Radiation damage by implanted ions in GaAs and GaP

Abstract

The production of lattice disorder in GaAs and GaP by Te ions up to 40 keV has been investigated. For GaAs the build up of damage with implanted ion dose is linear until a saturation level is reached. For Gap, two linear regions are evident; a slow build up of damage to ?15 per cent of the saturation level, followed by a faster rate of increase up to the final 100 per cent level. Radiation annealing, for GaP samples, both by the heavy ion beam during implantation and by the helium beam during back-scattering measurements has been observed. The annealing temperatures required for re-ordering the lattice depend on the percentage of damage present. Samples damaged up to the saturation level require annealing at ?500°C, whilst 300°C is sufficient for samples damaged to ?50 per cent of the saturation value.     

Damage anneal of antimony/phosphorus double implants in silicon

A method is presented for avoiding the dislocation generation in (100) silicon implanted with phosphorus doses up to 5×10¹⁵ ions/cm² at 50 keV. The residual defects after the damage anneal are considerably reduced if the phosphorus implant is combined with a low dose, e.g. 1×10¹⁴ ions/cm², antimony implant which produces a deeper surface layer of amorphous silicon. It is essential that the phosphorus ions are implanted shallower than the antimony ions, and come to rest within the amorphous layer. Subsequent thermal annealing proceeds by a solid phase epitaxial regrowth mechanism.     

Combined field ion microscopy and transmission electron microscopy of heavy ion damage in tungsten

Abstract

A field ion microscopy (FIM) and transmission electron microscopy (TEM) investigation of radiation damage in tungsten after heavy ion bombardment has been carried out. Field ion specimens of tungsten were irradiated with 180–230 keV Xe⁺ ions. The irradiation doses were varied between 4 × 10¹¹ and 4 × 10¹² ions/cm². The irradiated specimens were examined in FIM. Experiments combining both TEM and FIM were performed in order to compare the results obtainable by these two methods. The distribution of defects visible by TEM was inhomogeneous. The influence of the imaging field in FIM on the defects visible in TEM is discussed.     

Radiation damage of material surfaces under prolonged irradiation with He+ and Ar+ ions with broad energy spectra

The results of studying the redistribution of Be, Al, Ti, Fe, Cu, Zr, Mo, and W atoms incorporated in polycrystalline metal samples under irradiation with He⁺, (He⁺ + Ar⁺), and Ar⁺ ion beams with a broad energy spectrum and an average energy of 10 keV at irradiation doses of 1 × 10²¹ ion/cm² are studied. It is discovered that irradiation at doses exceeding 1 × 10¹⁹ ion/cm² results in local small-crystal formations being produced in a near-surface substrate layer. Their typical dimensions are less than 1–5 μm, and their the density is up to 1–100. They contain incorporated atoms and impurity atoms with a concentration of 0.1–10 at %. Subsequent irradiation at a dose of 1 × 10²⁰ ions/cm² or more leads to disappearance of these formations, mainly because of sputtering processes.     

Effet elastique en volume dans le nickel irradie aux electrons a tres basse temperature

Abstract

Experiments designed to determine the damage distribution produced by energetic heavy ions in Si are described. For low ion doses (10¹¹ to 10¹³ cm^?2), the location of the damage peak was determined by changes, which were produced by ion damage, in the electrical properties of thin (0.6 μ), uniformly doped Si layers as a function of depth. The ratio of the peak position in the damage distribution to the peak position in the ion distribution was determined to be approximately 0.6 ± 0.1 for Si²⁹ (150 keV), P³¹ (70, 140, 200 keV), B¹¹ (60 keV), and As⁷⁵ (280 keV). A comparison of carrier removal rates and the number of displaced lattice atoms previously reported from back-scattering experiments with He ions indicates that the nature of damage produced by Si²⁹ and B¹¹ are different. In the former case, cluster damage (amorphous disordered regions) appears to be an important form of radiation damage, while in the latter case, isolated defects are the dominant form of radiation damage for room temperature implantations. Isochronal annealing studies of Si²⁹ and B¹¹ ion damage provide further support for the different nature of radiation defects produced by these species. For high doses (10¹⁴ to 10¹⁶ cm^?2), the growth of a continuous amorphous Si layer was studied with ESR, optical transmission, and visual observation and stripping studies. The ratio of the location of the damage peak to that of the peak ion concentration was determined to be approximately 0.7 for P³¹ (140, 280 keV) and 0.8 for As⁷⁵ (280 keV). From the ESR studies, the number of displaced atoms in amorphous clusters was estimated to be 2800 per 280 keV P³¹ ion.     

Sputtering of highly oriented pyrolytic graphite with 30 keV Argon ions

The influence of the incidence angle of 30 keV Ar⁺ ions, ion fluence and target temperature on the sputtering yield and surface microgeometry of highly oriented pyrolytic graphite (UPV-1T) samples was experimentally studied. It was found that at fluences more than 5 × 10¹⁹ ion cm^?2 the sputtering yield at room temperature in the range of the ion incidence angle from 0° to 80° is twice as small as the corresponding experimental data for both polycrystalline graphite and glassy carbon. The analysis of ion-induced relief permits us to suppose the topographical suppression mechanism of highly oriented pyrolytic graphite sputtering.     

Raman scattering in a near-surface n-GaAs layer implanted with boron ions

Structure in the Raman scattering spectra of near-surface n-GaAs layers (n=2×10¹⁸ cm⁻³) implanted with 100 keV B⁺ ions in the dose range 3.1×10¹¹–1.2×10¹⁴ cm⁻² is investigated. The qualitative and quantitative data on the carrier density and mobility and on the degree of amorphization of the crystal lattice and the parameters of the nanocrystalline phase as a result of ion implantation are obtained using a method proposed for analyzing room-temperature Raman spectra. Fiz. Tverd. Tela (St. Petersburg) 41, 1495–1498 (August 1999)     

Effect of bombardment with iron ions on the evolution of helium,hydrogen, and deuterium blisters in silicon

The effect of bombardment with iron ions on the evolution of gas porosity in silicon single crystals has been studied. Gas porosity has been produced by implantation hydrogen, deuterium, and helium ions with energies of 17, 12.5, and 20 keV, respectively, in identical doses of 1 × 10¹⁷ cm^–2 at room temperature. For such energy of bombarding ions, the ion doping profiles have been formed at the same distance from the irradiated surface of the sample. Then, the samples have been bombarded with iron Fe¹⁰⁺ ions with energy of 150 keV in a dose of 5.9 × 10¹⁴ cm^–2. Then 30-min isochoric annealing has been carried out with an interval of 50°C in the temperature range of 250–900°C. The samples have been analyzed using optical and electron microscopes. An extremely strong synergetic effect of sequential bombardment of silicon single crystals with gas ions and iron ions at room temperature on the nucleation and growth of gas porosity during postradiation annealing has been observed. For example, it has been shown that the amorphous layer formed in silicon by additional bombardment with iron ions stimulates the evolution of helium blisters, slightly retards the evolution of hydrogen blisters, and completely suppresses the evolution of deuterium blisters. The results of experiments do not provide an adequate explanation of the reason for this difference; additional targeted experiments are required.     

Surface disorder in c-Si induced by swift heavy ions

The disorders induced in crystalline silicon (c-Si) through the process of electronic energy loss in the swift heavy ion irradiation were investigated. A number of silicon <1 0 0> samples were irradiated with 65 MeV oxygen ions at different fluences, 1×10¹³ to 1.5×10¹⁴ ions/cm², and characterized by the Raman spectroscopy, the optical reflectivity, the X-ray reflectivity, the atomic force microscopy (AFM) and the X-ray diffraction (XRD) techniques. The intensity, redshift, phonon coherence length and asymmetric broadening associated with the Raman peaks reveal that stressed and disordered lattice zones are produced in the surface region of the irradiated silicon. The average crystallite size, obtained by analyzing Raman spectrum with the phonon confinement model, was very large in the virgin silicon but decreased to<100 nm dimension in the ion irradiated silicon. The results of the X-ray reflectivity, AFM and optical reflectivity of 200–700 nm radiation indicate that the roughness of the silicon surface has enhanced substantially after ion irradiation. The diffusion of oxygen in silicon surface during ion irradiation is evident from the oscillation in the X-ray reflectivity spectrum and the sharp decrease in the reflectivity of 200–400 nm radiation. The rise in temperature, estimated from the heat spike model, was high enough to melt the local silicon surface. The results of XRD indicate that lattice defects have been induced and a new plane <2 1 1> has been formed in the silicon <1 0 0>after ion irradiation. The results of the present study show that the energy deposited in crystalline silicon through the process of electronic energy loss ～0.944 keV/nm per ion is sufficient to induce disorders of appreciable magnitude in the silicon surface even at a fluence of ～10¹³ ions/cm².     

Combined MEIS/TEM study of structural defects in Si implanted with a high dose of 100 keV Si ions

Medium-energy ion scattering and transmission electron microscopy have been used to study the structural perfection of a Si single crystal implanted with 100 keV Si ions at a dose of 1×10¹⁷ cm^?2, which exceeds the amorphization threshold by two orders of magnitude. The implantation of Si ions was found to produce a high density of extended defects without amorphization of the Si layer. The increasing depth dependence of the full width at half-minimum of the dip in angular scans of backscattered protons, was observed in a Si layer containing a high density of extended defects, in contrast to the decreasing dependence in the perfect Si crystal.     

The optical and electrical effects of high concentrations of defects in irradiated crystalline gallium arsenide

The damage produced by fast neutron irradiation of gallium arsenide has been studied by a number of techniques. The electrical resistivity, which increases with dose at low doses to semi-insulating values, shows a remarkable, specimen-independent decrease for doses greater than 10¹⁷ n cm^-2 from values of ca. 10⁹ Ω cm to 3 Ω cm for the highest dose of 1.5 × 10²⁰ n cm^-2. In this high dose region the temperature dependence of the resistivity at low temperatures is given by exp [b/T ^1/4] and it is suggested that in this highly disordered state conduction occurs by tunnel-assisted hopping between defect levels in the band gap. The presence of such levels is indicated by the strong optical absorption tail which is produced from 0.1 eV to the crystalline edge at 1.5 eV.

Although at the highest doses the samples contain a high degree of disorder, X-ray diffraction shows that they are basically crystalline. Lattice parameter determinations show that it increases with dose, linearly at first, then tending to saturation for doses above 2 × 10¹⁸ n cm^-2. The dose dependence of the lattice parameter is the same as that of the integrated optical absorption and both effects may be expected to relate to the total defect concentrations.

The existence of small-angle neutron scattering at the highest dose shows that the defects are not uniformly distributed. It is shown that this state is the high dose manifestation of the production of defects by each primary knock-on atom in fairly localized regions. The overlap of the wings of these regions for doses greater than 10¹⁷ n cm^-2 provides a conducting path and a fairly constant b value with dose, while the resistivity decreases rapidly. The total defect concentration, which is heavily weighted to the central regions of the individually damaged volumes, does not show overlap until a higher dose, as observed for the optical absorption and lattice parameter.

Estimates of the total defect concentration have been obtained by measuring the total diffuse neutron scattering as well as from the small-angle scattering results. It is shown that each primary knock-on produces ca. 10³ atomic displacements. This means that the amount of damage in gallium arsenide is close to that predicted by radiation damage theory.

Measurements of photoconductivity show that the sharp photoconductivity edge is eliminated at quite low doses. At high doses the photoconductivity becomes very small and is much less than in unirradiated samples of similar resistivity. It appears that the ionized state lifetime of photo-induced carriers is very small in the high dose state.

The effects anneal more or less completely after heating to 700°C. The hopping conductivity effect anneals between room temperature and 400°C and the remaining electrical effects between 500 and 600°C. The optical effects anneal more or less continuously throughout the temperature range up to 700°C.

It is shown that the doses at which the tunnel-assisted hopping sets in are consistent with similar effects recently observed in ion implantation. We suggest that a similar mechanism applies in implanted layers for ion doses greater than 10¹²–10¹³ ions cm^-2.

Density measurements show an expansion identical with the lattice parameter expansion and indicate an expansion of 2.93 ų per defect. This is relatively small and is consistent with the tentative conclusion from the neutron-scattering data that the main defect is the close interstitial-vacancy pair in which the strain is minimized by being of opposite sign around each component.