Shift in room-temperature photoluminescence of low-fluence Si+-implanted SiO2 films subjected to rapid thermal annealing

Abstract

We experimentally demonstrate the effect of the rapid thermal annealing (RTA) in nitrogen flow on photoluminescence (PL) of SiO₂ films implanted by different doses of Si⁺ ions. Room-temperature PL from 400-nm-thick SiO₂ films implanted to a dose of 3×10¹⁶ cm^?2 shifted from 2.1 to 1.7 eV upon increasing RTA temperature (950–1150 °C) and duration (5–20 s). The reported approach of implanting silicon into SiO₂ films followed by RTA may be effective for tuning Si-based photonic devices.     

Transmission electron microscopy of Li+ implanted Al films

Aluminium films implanted with 30 keV lithium ions of doses from 2.2 × 10¹⁶ to 1 × 10¹⁷ ions cm^?2 were studied by transmission electron microscopy. Samples implanted with 6 × 10¹⁶ and 1 × 10¹⁷ ions cm^?2 showed the presence of the Al-Li phase, while no change was observed in specimens implanted with 2.2 × 10¹⁶ ions cm^?. Microdiffraction patterns obtained from different areas of an aluminium film implanted with 2.0 × 10¹⁷ Li⁺ ions cm^?2 at 35 keV, revealed the presence of a stable Al-Li phase along with a metastable phase. Furthermore, on annealing the implanted samples at 200°C for 20 min an increase in ‘d’ values was noticed when compared with non-annealed specimens. However the annealed samples showed a very small lattice mismatch between the metastable phase and the Al matrix, thus indicating the presence of a metastable Al₃Li phase, responsible for hardening in binary Al-Li alloy.     

Rutherford backscattering analysis of oxide layers formed by ion implantation into single-crystal silicon

Single-crystal silicon was implanted with 40 keV and 60 keV oxygen ions. Rutherford backscattering (RBS) analysis was used to determine the oxygen profile, the ratio of oxygen to silicon in the implanted layer and the extent of radiation damage for doses up to 3 × 10¹⁸ ions cm^-2. The measured oxygen profiles appear to agree with theory at low doses. The radiation damage, as characterized by the damage peak and the yield _χmin behind the implanted layer, saturates at a dose of approximately 1 × 10¹⁶ ions cm^-2. The oxygen content of the layer is directly proportional to dose until the peak value of the oxygen:silicon ratio reaches 2.0. At higher doses the oxygen concentration only increases in the region between the peak and the surface, resulting in a uniform layer of thickness 2R_p (SiO₂). Infrared transmission measurements also indicate that stoichiometric SiO₂ is formed. Annealing at 900 °C has no effect on the RBS spectrum from the implanted layer but the area of the interfacial damage peak is reduced by 60%. Two interesting effects occur: (a) _χmin rises to a peak when the oxygen:silicon ratio is approximately unity; (b) the interfacial damage peak decreases with increasing dose once a uniform layer has been formed.     

Surface hardening in N<Superscript>+</Superscript> implanted polycarbonate

The influence of low energy nitrogen ions on the surface hardness of polycarbonate has been studied by implanting some of these specimens with 100 keV N⁺ ions at a beam current of 1 μA/cm² in the dose range of 1 × 10¹⁵ to 1 × 10¹⁷ ions cm^?2. Knoop microhardness has been found to be increased nearly 24 times at a load of 9.8 mN, for the dose of 1 × 10¹⁷ ions cm^?2. The structural changes occurred in implanted specimens were studied by Raman analysis, UV–Visible spectroscopy, and X-ray diffraction techniques. Raman studies point toward the formation of a structure resembling hydrogenated amorphous carbon. Disordering in the surface structure (I _D/I _G ratio) has also been found to increase with ion fluence using Raman technique. UV–Visible spectroscopic analysis shows a clear enhancement in Urbach energy (disorder parameter) from a value of 0.61 eV (virgin sample) to 1.72 eV (at a fluence of 1 × 10¹⁷ N⁺ cm^?2) with increasing ion dose. The increase in Urbach energy has been found to be correlated linearly with the increase in Knoop microhardness number. Results of X-ray diffraction analysis also indicate disordering in implanted layers as a result of implantation. In the present work, the possible mechanism behind the formation of harder surfaces due to implantation has been discussed in detail.     

The temperature dependence of stresses in aluminum films on oxidized silicon substrates

In situ measurements were carried out of stress at the AlSiO₂ interface at various temperatures (25–500 °C) and for various film thicknesses (0.2–1.6 microm). These data are complemented with microstructural studies by transmission electron microscopy.For the aluminum films studied, the intrinsic structural component was very small (less than 2 × 10⁸ dyn cm^?2). On heating, thermal mismatch led to a compressive stress, with dσ/dT ≈ ?2 × 10⁷ dyn cm^?2 °C; these films yielded at 6σ6 ; ? 5 × 10⁸ dyn cm^?2, primarily through diffusion creep and grain growth. On cooling from about 450–500 °C, thermal mismatch led to a tensile stress which was limited mainly by dislocation slip. The final room temperature value after thermal cycling ranged from 0.5 × 10⁹ dyn cm^?2 for a 1.5 microm film to 8 × 10⁹ dyn cm^?2 for a 0.2 microm film; these values are believed to represent the critical stress for the generation of dislocation loops within the grains.The grain size of cold-deposited aluminum films ranged from about 0.2 microm for films 0.45 microm thick to about 2 microm for films 1.5 microm thick. Thermal cycling led to an order-of-magnitude increase in the grain size together with the formation of dislocation networks within the grains.     

Formation of thin SiO2 films by high dose oxygen ion implantation into silicon and their investigation by IR techniques

The ion dose dependence of the infrared transmission spectra of SiO₂ layers formed by high dose ion implantation into silicon was investigated for ion doses ranging from $\text{10}{}^{16}\text{to}\text{2 × 10}{}^{18}\text{(}{}^{16}\text{O}{}_2\text{)}{}^{\mathrm{+}}\text{30}\text{kV ions cm}{}^{-2}$. The annealing temperature dependence of these spectra is also reported.The passivation properties of the SiO₂ layers and their dependence on annealing were investigated and monitored by IR techniques. It was found that an SiO₂ layer that is formed by implantation with 1 × 10¹⁸ ions cm^-2 and annealed at temperatures higher than 550 °C but not more than 800 °C is similar in its IR and passivation properties to thermally grown SiO₂ films.     

Thin SiO2 films formed by oxygen ion implantation in silicon: Electron microscope investigations of the Si-SiO2 interface structures and their c-v characteristics

Electron microscope reflection diffraction studies were carried out for silicon wafers implanted with different doses of oxygen ions. Structural changes were monitored both with increasing ion dose and with annealing temperature. The structural properties of the silicon substrate underlying the SiO₂ layers that were formed with the highest implant doses were also investigated and changes caused by annealing are reported. An anneal at 800 °C was found to re-establish good structural properties of the silicon underneath the SiO₂. C-V studies of MOS structures based on such SiO₂ layers indicated good interface properties for samples annealed at 800 °C.     

Effect of Hf ion implantation on grain growth in Ni nanocrystalline electrodeposits

Abstract

The microstructural stability of Ni nanocrystalline electrodeposits was investigated to verify general principles underlying the suppression of grain growth by microalloying with elements of very low solid solubility. Hf ions at 300 keV energy were implanted in Ni nanocrystalline foils at low (5·8 × 10¹⁵ ions cm^?2) and high (3·0 × 10¹⁶ ions cm^?2) doses. Their effects on grain growth at 550°C were studied in situ by transmission electron microscopy at 1·25 MeV and by selected area electron diffraction. Grains roughly doublled in size during implantation, but grain growth during subsequent heat treatment was dose dependent and significantly less than in specimens without implantation. Observation on implanted Ni single crystals revealed clustering and the formation of fine Ni₅Hf precipitates. A possible mechanism of grain growth suppression is discussed.     

Nitrogen ion implantation effects on the structural,optical and electrical properties of CdSe thin film

In the present study, thin films of cadmium selenide (CdSe) are deposited on ITO substrate by electrodeposition method using aqueous solution of 3CdSO₄·8H₂O and SeO₂. These films are implanted with 40 keV N⁺ ions with different fluencies i.e. 1?×?10¹⁵, 5?×?10¹⁵, 1?×?10¹⁶ and 5?×?10¹⁶ ions/cm² using a beam current of 0.9 µA. The structural, morphological, optical and electrical properties of pristine and nitrogen ion-implanted CdSe thin films are analyzed using XRD, SEM, AFM, UV-PL Spectrophotometer and I–V four probes setup. XRD analysis revealed the effects of nitrogen ions on the structural parameters such as grain size, FWHM, micro strain and dislocation density etc. Crystallanity of the material increased with increase in implantation dose. SEM and AFM analysis show decrease in the surface roughness with implantation. From the optical studies, band gap value decreased from 2.50 to 2.29 eV with increase in N⁺ implantation doses. Noticeable changes in the electrical properties are also reported. The effect of N⁺ ion implantation on the properties of CdSe thin films are discussed on the basis of lattice disorder.     

IR and x-ray studies of ion-beam-synthesized aluminium nitride films

IR transmission spectroscopy in conjunction with X-ray diffraction was used to characterize the phase composition of aluminium films after nitrogen ion implantation. Aluminium films deposited onto single-crystal silicon and implanted with 30 keV nitrogen ions (¹⁴N₂⁺) to a dose of 10¹⁷-10¹⁸ ions cm^-2 were subsequently characterized for aluminium nitride (AIN) formation by IR spectroscopy. The formation of a stoichiometric AIN layer was evident from the IR absorption band observed at 648 cm^-1. Furthermore, X-ray diffraction of an aluminium foil after nitrogen implantation at 110 keV to a dose of 5.0 × 10¹⁷ ions cm^-2 on each side revealed the presence of a polycrystalline AIN phase. A thermal treatment at 700°C did not yield any new crystalline phases.     

The Effect of Dose of Nitrogen-Ion Implantation on the Concentration of Point Defects Introduced into GaAs Layers

Secondary-ion mass spectrometry and Rutherford proton backscattering have been used to measure the concentration profiles of nitrogen atoms and examine the defect structure of epitaxial GaAs layers implanted with 250-keV N⁺ ions at doses of 5 × 10¹⁴–5 × 10¹⁶ cm^–2. It was found that no amorphization of the layers being implanted occurs at doses exceeding the calculated amorphization threshold, a concentration of point defects that is formed is substantially lower than the calculated value, and a characteristic specific feature of the defect concentration profiles is the high defect concentration in the surface layer.     

The chemical vapour deposition and characterization of ZrO2 films from organometallic compounds

ZrO₂ films were deposited on silicon substrates by oxygen-assisted decomposition of zirconium-β-diketonates at temperatures of 400–550°C. The deposits, fine-grained nearly stoichiometric monoclinic ZrO₂, were hard and showed strong adherence to the substrate. The films were characterized by transmission electron microscopy, X-ray diffraction and electron microprobe analysis and by measuring their dielectric and optical properties. The index of refraction was found to be 2.18, and the optical energy band gap was found to be 5.16 eV. The dielectric constant at 1 MHz was 17–18, and the dielectric strength varied between 1 × 10⁶ and 2.0 × 10⁶ V cm^?1. Capacitance-voltage measurements at 1 MHz indicated the presence of effective surface states with a concentration in the range (1.0?6.0) × 10¹¹cm^?2 for films deposited at temperatures above 500°C or for films deposited at 400–450°C and annealed at above 750°C. The flat-band voltages were between ?0.6 and + 0.2 V. The films showed satisfactory bias-temperature stability. The current-voltage characteristic followed an I ∝ V² dependence for negative bias and an I ∝ V^2.6 to I ∝ V^3.4 dependence for positive bias.     

Zinc diffusion in YBa2Cu3O7−x ceramics

The process of zinc diffusion in YBa₂Cu₃O_7?x ceramics with a porosity of 20–30% was studied in the temperature interval from 110 to 450°C using a ⁶⁵Zn radioactive tracer. The temperature dependence of the tracer diffusion coefficient is described by the relation D=5×10^?9 exp(?0.25 eV/kT) cm²/s. It is concluded that zinc migrates predominantly via pores and intergranular layers in the ceramics.     

Structural and optical properties of sulfurized Cu2ZnSnS4 thin films from Cu–Zn–Sn alloy precursors

This study reports the preparation of Cu₂ZnSnS₄ (CZTS) thin films by magnetron sputtering deposition with a Cu–Zn–Sn ternary alloy target and sequential sulfurization. The effects of substrate temperatures on the structural, morphological, compositional as well as optical and electrical properties were characterized. The results showed the CZTS thin films prepared by sulfurization at substrate temperature of 570 °C yielded secondary phases along with CZTS compound. The relatively good properties of CZTS thin film were obtained after sulfurization at substrate temperature of 550 °C. This CZTS film showed compact structure with large grain size of 900 nm, direct optical band gap of 1.47 eV, optical absorption coefficient over 10⁴ cm^?1, resistivity of 4.05 Ω cm, carrier concentration of 8.22 × 10¹⁸ cm^?3, and mobility of 43.38 cm² V^?1 S^?1.     

Conductivity of Sm<Subscript>2</Subscript>TiO<Subscript>5</Subscript> and Sm<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

The oxygen-ion conductivity of porous materials, the coarse-grained pyrochlore-like Sm₂Ti₂O₇ and fine-grained Sm₂TiO₅ compounds, produced by mechanical activation of initial oxides is studied at 400–1000 °C. The Sm₂TiO₅ samples contain ～15 wt % of the nanosized pyrochlore-like Sm₂TiO₅ phase in addition to the rhombic phase. As determined by impedance spectroscopy, the ionic conductivities of Sm₂TiO₅ and Sm₂Ti₂O₇ at 1000°C are 1.3 × 10^?3 and 1.8 × 10^?4 S cm^?1, and the activation energies of the bulk and grainboundary conductivities of the materials are 1.04 and 1.24 eV for Sm₂TiO₅ and 1.69 and 1.80 eV for Sm₂Ti₂O₇.     

Deep levels in GaN studied by deep level transient spectroscopy and Laplace transform deep-level spectroscopy

In this study we present the results of investigations on Schottky Au-GaN diodes by means of conventional DLTS and Laplace DLTS methods within the temperature range of 77–350 K. Si-doped GaN layers were grown by Molecular Beam Epitaxy technique (MBE) on sapphire substrates. DLTS signal spectra revealed the presence of four majority traps: two hightemperature and two low-temperature peaks. Using LDLTS method and Arrhenius plots the activation energy and capture cross sections were obtained. For two high-temperature majority traps they are equal to E1 = 0.65 eV, σ₁ = 8.2 × 10^?16cm² and E2 = 0.58 eV, σ₂ = 2.6 × 10^?15 cm² whereas for the two low-temperature majority traps E3 = 0.18 eV, σ₃ = 9.72 × 10^?18 cm² and E4 = 0.13 eV, σ₄ = 9.17 × 10^?18 cm². It was also found that the traps are related to point defects. Possible origin of the traps was discussed and the results were compared with the data found elsewhere [1–5].     

High pressure vapour phase epitaxy of GaN

GaN epitaxial layers were grown on (1102) oriented sapphire substrates with the GaHClNH₃ technique at temperatures from 660 to 1000 °C under nitrogen pressures from 40 to 130 bar. The optimum growth temperature was 820 to 840 °C. Growth rates of 0.2 to 0.4 /um/min were obtained. The lattice constants of this material were $\text{a}\text{= 3.18}\text{A}\text{?}$ and $\text{c}\text{= 5.18}\text{A}\text{?}$, and single crystalline layers showed (1120) orientation. The layers were n-conducting with typical mobilities of 30 cm²/Vsec and with carrier concentrations from 2 · 10¹⁹ to 1 · 10²⁰ cm^?3, even when grown at 120 bar and 660 °C. Therefore, p-type conduction could not be achieved in GaN, even under these extreme conditions.     

Study of iron-ion implantation in rutile single crystals

TiO₂ crystals implanted with 100 keV ⁵⁷Fe⁺ ions at doses ranging from 10¹⁶ to 10¹⁷ ions.cm^?2 have been investigated with the conversion electron Mössbauer spectroscopy (CEMS), Rutherford backscattering (RBS) and transmission electron microscopy (TEM). Implanted samples of iron ions are mostly in a Fe²⁺ state and small precipitates of FeTi₂O₅ are observed using TEM. The migration of iron ions in a Fe³⁺ state occurs at about 600°C. Such a low temperature diffusion is thought to go along extended defects.     

Effect of rapid thermal annealing on Zn/ZnO layers

Zn/ZnO layers were deposited on SiO₂/Si substrate by magnetron sputtering at room temperature, and then these layers were annealed at various temperatures from 200 to 400 °C in nitrogen atmosphere for 1 min. The structural and electrical properties of the Zn/ZnO layers before and after annealing are systematically investigated by X-ray diffraction, scanning electron microscopy, current–voltage measurement system, and Auger electron spectroscopy. Current–voltage measurements show that the Zn/ZnO layers exhibit an Ohmic contact behavior. It is shown that, initially, the specific contact resistivity decreases with the increase of the annealing temperature and reaches a minimum value of 9.76 × 10^?5 Ω cm² at an annealing temperature of 300 °C. However, with a further increase of the annealing temperature, the Ohmic contact behavior degrades. This phenomenon can be explained by considering the diffusion of zinc interstitials and oxygen vacancies. It is also shown that Zn-rich ZnO thin films can be obtained by annealing Zn on the surface of ZnO film and that good Ohmic contact between Zn and ZnO layers can be observed when the annealing temperature was 300 °C.     

Fabrication and characterization of Ge nanocrystalline growth by ion implantation in SiO<Subscript>2</Subscript> matrix

Ge nanocrystallites (Ge-nc) have been formed by ion implantation of Ge⁺⁷⁴ into SiO₂ matrix, thermally grown on p-type Si substrates. The Ge-nc are examined by Raman spectroscopy, photoluminescence (PL) and Fourier transform infrared spectroscopy (FTIR). The samples were prepared with various implantation doses [0.5; 0.8; 1; 2; 3; 4] × 10¹⁶ cm⁻² with 250 keV energy. After implantation, the samples were annealed at 1,000 °C in forming gas atmosphere for 1 h. Raman intensity variation with implantation doses is observed, particularly for the peak near 304 cm⁻¹. It was found that the sample implanted with a doses of 2 × 10¹⁶ cm⁻² shows maximum photoluminescence intensity at about 3.2 eV. FTIR analysis shows that the SiO₂ film moved off stoichiometry due to Ge⁺⁷⁴ ion implantation, and Ge oxides are formed in it. This result is shown as a reduction of GeO_x at exactly the doses corresponding to the maximum blue-violet PL emission and the largest Raman emission at 304 cm⁻¹. This intensity reduction can be attributed to a larger portion of broken Ge–O bonds enabling a greater number of Ge atoms to participate in the cluster formation and at the same time increasing the oxygen vacancies. This idea would explain why the FTIR peak decreases at the same implantation doses where the PL intensity increases.