Post-implantation Thermal Annealing Research Articles

Formation of β-Be3N2 nanocrystallites in Be-implanted GaN

A small Be ion dose of 5 × 1014 cm−2 was implanted in a 2 μm thick GaN epilayer at an energy of 50 keV. The sample was characterized by high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy techniques after a post-implantation rapid thermal annealing (RTA) treatment. The HRTEM images show the crystallographic (1 1 0) and (0 0 2) planes of β-Be3N2. Two characteristic parallelograms drawn in Fast Fourier transform (FFT) image support the formation of β-Be3N2 nanocrystallites in RTA treated sample. Two Raman peaks at 168 and 199 cm−1 are observed in the Raman spectrum of the sample that are assigned to β-Be3N2 on the basis of group theory and HRTEM data. The Raman peak at 168 cm−1 is found close to the K point in the first Brillouin zone of β-Be3N2 while the peak at 199 cm−1 is assigned as a combination mode of the fundamental Raman modes of β-Be3N2.

Growth of nanocrystalline graphite on sapphire by implantation of large carbon clusters from SNICS source

Nano-crystalline graphite (NCG) structures on insulating layers have been grown via implantation of kilo-electron-volt (keV) energetic carbon clusters (Cn) on sapphire (Al2O3) and post-implantation thermal annealing conditions. The clusters were produced using a source of negative ion using Cesium sputtering (SNICS) with graphite and carbon nanotubes (CNT) as cathode materials. The Graphite cathode exhibited high currents for most of the cluster sizes. However, the CNT cathodes showed higher yields for relative heavy clusters (n = 16, 18, and 20). Also, carbon clusters as large as n ~ 56 were observed from the SNICS source. The Sapphire substrates were implanted with carbon cluster (Cn, n = 18) ions at 11 keV (~611 eV per carbon atom) with fluences of 1.1 × 1015 C18-clusters/cm2 (~2 × 1016 carbon atoms/cm2). Ion impact craters and surface build-ups were observed. Further, we have studied the carbon bonding characteristics by Raman Spectroscopy (RS) on as-implanted and annealed implanted samples. We have observed well-developed disorder (D), graphite (G), and 2D peaks from the optimized samples, indicating the formation of nano-crystalline graphite (NCG) structures on the surface. The ratio of D and G peaks in the RS spectra suggests that the nano-crystalline cluster diameter or in-plane correlation length is about 10–16.5 nm. The Crystal size approaches a maximum value with increasing post-implantation thermal annealing temperature. We have studied the growth of NCG by X-ray Photoelectron Spectroscopy (XPS) for the chemical bonding and distribution. The average sizes of crystalline NCGs were also estimated using Grazing Angle X-ray Diffraction (GAXRD) Spectrometry. The surface morphology of the implanted samples was investigated using Atomic Force Microscopy (AFM).

Correlations between the structural transformations and concentration quenching effect for RE-implanted ZnO systems

In this paper, we present optical, structural and electrical studies of the phenomenon called concentration quenching effect occurring in ZnO doped with Rare Earth (RE) ions. For this purpose, the epitaxial ZnO layers grown by the Atomic Layer Deposition (ALD) are doped by ion implantation with Yb and Er elements with fluencies ranging from 5 × 1013 to 1 × 1016/cm2. In order to activate optically the implanted RE and to remove defects, the post-implantation thermal annealing was performed at 800 °C for 10 min in the O2atmosphere using aRapid Thermal Annealing (RTA) system. Two-step processed samples, before and after annealing, were evaluated by Rutherford Backscattering Spectrometry (RBS/c) to investigate the damage build-up process in the ZnO lattice after RE ion bombardment and the lattice site location of RE. The annealed samples were examined using the photoluminescence (PL) spectroscopy and Hall effect measurements. Our studies show that the luminescence quenching effect, as well as the electrical resistivity response to the increased RE concentration, are strongly connected with the threshold of the structural transformation due to defects accumulation. It suggests that during structural transformations the RE-ion centers are sufficiently close together to be able to interact and transfer the excitation energy between each other, increasing ipso facto the probability to lose the excitation energy by non-radiative processes. Moreover, in contrast to the popular belief, that the concentration quenching effect in RE-doped ZnO depends strongly on the kind of RE-doped ion, the presented results do not provide any evidence to support such an assumption.

Eu-Doped AlGaN/GaN Superlattice-Based Diode Structure for Red Lighting: Excitation Mechanisms and Active Sites

In this work, we have established the effects of postgrowth annealing and Eu implantation, followed by annealing on an AlGaN/GaN superlattice-based diode structure, containing Mg-doped GaN top p-cap layers. The study is based on the combined information from different optical techniques, such as Raman, photoluminescence, and photoluminescence excitation. We have shown that the diode structure exhibits a stable crystalline quality even after annealing under high temperature and high pressure (HTHP) conditions (1400 °C in 1 GPa N2). Furthermore, we have demonstrated that the implanted Eu ions reached the first quantum wells of the diode structure and that the postimplantation thermal annealing partly removed the implantation defects, recovering some of the as-grown luminescence and optically activating the Eu3+ in the diode structure. An in-depth study of the Eu3+ population mechanisms was realized through room temperature photoluminescence excitation. A model was built based on the different excitation bands originated from the materials present in the diode structure, demonstrating that an energy transfer between the AlGaN/GaN superlattice excitons and the Eu3+ ions occurs, therefore enlarging the excitation pathways for the ion’s red luminescence. In addition, Eu3+ luminescence was observed not only with above but also with below GaN bandgap excitation. The temperature dependent study of the 5DJ → 7FJ transitions allowed to tentatively provide the Eu3+ intraionic assignments of the diode structure. We have demonstrated that at least three nonequivalent active sites are created by the Eu implantation in the diode structure: Eu1, Eu2, and Eu–Mg defect in both configurations Eu0 and Eu1(Mg).

Luminescence of silicon nanoparticles from oxygen implanted silicon

Oxygen with a kinetic energy of 20 keV is implanted in a silicon wafer (100) at different fluences, followed by post-implantation thermal annealing (PIA) performed at temperatures ranging from 1000 to 1200 °C, in order to form luminescent silicon nanoparticles (SiNPs) and also to reduce the damage induced by the implantation. As a result of this procedure, a surface SiOx layer (with 0 < x < 2) with embedded crystalline Si nanoparticles has been created. The samples yield similar luminescence in terms of peak wavelength, lifetime, and absorption as recorded from SiNPs obtained by the more conventional method of implanting silicon into silicon dioxide. The oxygen implantation profile is characterized by elastic recoil detection (ERD) technique to obtain the excess concentration of Si in a presumed SiO2 environment. The physical structure of the implanted Si wafer is examined by grazing incidence X-ray diffraction (GIXRD). Photoluminescence (PL) techniques, including PL spectroscopy, time-resolved PL (TRPL), and photoluminescence excitation (PLE) spectroscopy are carried out in order to identify the PL origin. The results show that luminescent SiNPs are formed in a Si sample implanted by oxygen with a fluence of 2 × 1017 atoms cm−2 and PIA at 1000 °C. These SiNPs have a broad size range of 6–24 nm, as evaluated from the GIXRD result. Samples implanted at a lower fluence and/or annealed at higher temperature show only weak defect-related PL. With further optimization of the SiNP luminescence, the method may offer a simple route for integration of luminescent Si in mainstream semiconductor fabrication.

Defect formation and optical activation of Tb implanted AlxGa1−xN films using channeled implantation at different temperatures

AlxGa1−xN (x = 0.20, 0.50, 0.63) films grown on (0001) sapphire substrates by metal organic chemical vapor phase deposition were implanted with Tb ions at 150 keV and a fluence of 7 × 1014 Tb cm−2. The implantation was carried out with the beam aligned with the c-axis and the implantation temperature was varied from room temperature (RT) to 550 °C. Additionally, post-implantation rapid thermal annealing was performed at 1200 °C during 120 s. The impact of implantation temperature on the damage accumulation is investigated. Rutherford backscattering spectrometry/channeling (RBS/C) measurements show that two damage regions are forming and the damage is not decreasing monotonically with the increase of implantation temperature. Bulk damage follows the same trend for all AlxGa1−xN compositions, increasing when the temperature is raised up to ~100 °C, and then decreasing for higher temperatures. A good agreement is observed between the damage accumulation obtained from RBS/C and the strain profile derived from symmetric (0002) 2θ-ω X-ray diffraction scans. Transmission electron microscopy results show the suppression of basal stacking faults after implantation at 550 °C. Tb lattice site location studies revealed two preferential sites: the substitutional cation site and a site displaced from that by 0.2 Å along the c-axis. A higher substitutional fraction of Tb ions is obtained for implantation temperature of 550 °C. The optical activity investigated by photoluminescence showed that after thermal annealing, the 5D4 → 7FJ intra-4f8 transition is detected in all the samples.

Defects in Arsenic Implanted р+–n- and n+–p- Structures Based on MBE Grown CdHgTe Films

Complex studies of the defect structure of arsenic-implanted (with the energy of 190 keV) Cd x Hg 1–x Te (x = 0.22) films grown by molecular-beam epitaxy are carried out. The investigations were performed using secondary-ion mass spectroscopy, transmission electron microscopy, optical reflection in the visible region of the spectrum, and electrical measurements. Radiation donor defects were studied in n+–p- and n+–n-structures obtained by implantation and formed on the basis of p-type and n-type materials, respectively, without activation annealing. It is shown that in the layer of the distribution of implanted ions, a layer of large extended defects with low density is formed in the near-surface region followed by a layer of smaller extended defects with larger density. A different character of accumulation of electrically active donor defects in the films with and without a protective graded-gap surface layer has been revealed. It is demonstrated that p+–n- structures are formed on the basis of n-type material upon activation of arsenic in the process of postimplantation thermal annealing with 100% activation of impurity and complete annihilation of radiation donor defects.

Significantly Enhanced Visible Light Photoelectrochemical Activity in TiO₂ Nanowire Arrays by Nitrogen Implantation.

Titanium oxide (TiO2) represents one of most widely studied materials for photoelectrochemical (PEC) water splitting but is severely limited by its poor efficiency in the visible light range. Here, we report a significant enhancement of visible light photoactivity in nitrogen-implanted TiO2 (N-TiO2) nanowire arrays. Our systematic studies show that a post-implantation thermal annealing treatment can selectively enrich the substitutional nitrogen dopants, which is essential for activating the nitrogen implanted TiO2 to achieve greatly enhanced visible light photoactivity. An incident photon to electron conversion efficiency (IPCE) of ∼10% is achieved at 450 nm in N-TiO2 without any other cocatalyst, far exceeding that in pristine TiO2 nanowires (∼0.2%). The integration of oxygen evolution reaction (OER) cocatalyst with N-TiO2 can further increase the IPCE at 450 nm to ∼17% and deliver an unprecedented overall photocurrent density of 1.9 mA/cm(2), by integrating the IPCE spectrum with standard AM 1.5G solar spectrum. Systematic photoelectrochemical and electrochemical studies demonstrated that the enhanced PEC performance can be attributed to the significantly improved visible light absorption and more efficient charge separation. Our studies demonstrate the implantation approach can be used to reliably dope TiO2 to achieve the best performed N-TiO2 photoelectrodes to date and may be extended to fundamentally modify other semiconductor materials for PEC water splitting.

Diffusion of Ag, Au and Cs implants in MAX phase Ti3SiC2

MAX phases (M: early transition metal; A: elements in group 13 or 14; X: C or N), such as titanium silicon carbide (Ti3SiC2), have a unique combination of both metallic and ceramic properties, which make them attractive for potential nuclear applications. Ti3SiC2 has been considered as a possible fuel cladding material. This study reports on the diffusivities of fission product surrogates (Ag and Cs) and a noble metal Au (with diffusion behavior similar to Ag) in this ternary compound at elevated temperatures, as well as in dual-phase nanocomposite of Ti3SiC2/3C-SiC and polycrystalline CVD 3C-SiC for behavior comparisons. Samples were implanted with Ag, Au or Cs ions and characterized with various methods, including X-ray diffraction, electron backscatter diffraction, energy dispersive X-ray spectroscopy, Rutherford backscattering spectrometry, helium ion microscopy, and transmission electron microscopy. The results show that in contrast to immobile Ag in 3C-SiC, there is a significant outward diffusion of Ag in Ti3SiC2 within the dual-phase nanocomposite during Ag ion implantation at 873K. Similar behavior of Au in polycrystalline Ti3SiC2 was also observed. Cs out-diffusion and release from Ti3SiC2 occurred during post-implantation thermal annealing at 973K. This study suggests caution and further studies in consideration of Ti3SiC2 as a fuel cladding material for advanced nuclear reactors operating at very high temperatures.

Modeling the effects of ion dose and crystallographic symmetry on the morphological evolution of embedded precipitates under thermal annealing

Thermal annealing is one of the most common techniques to synthesize embedded precipitates by ion implantation process. In this study, an anisotropic phase field model is presented to investigate the effects of ion dose and crystallographic symmetry on the morphological formation and evolution of embedded precipitates during post-implantation thermal annealing process. This theoretical model provides an efficient numerical approach to understand the phenomenon of faceted precipitates formation by ion implantation. As a theoretical analysis, the interfacial energy and diffusion kinetics play prominent roles in the mechanism of atomic diffusion for the precipitates formation. With a low ion dose, faceted precipitates are developed by virtue of the anisotropic interfacial energy. As an increase of ion dose, connected precipitates with crystallographic characters on the edge are appeared. For a high ion dose, labyrinth-like nanostructures of precipitates are produced and the characteristic morphology of crystallographic symmetry becomes faint. These simulation results for the morphological evolutions of embedded precipitates by ion implantation are corresponded with many experimental observations in the literatures. The quantitative analyses of the simulations are also well described the consequence of precipitates formation under different conditions.

Damage properties in ion-implanted YbVO4 crystals using RBS/Channeling study

YbVO4 crystals are implanted with 3.0MeV Ni ions and 600keV H ions with fluences of 2.0–10.0×1014cm−2 and 6.0×1016cm−2, respectively. In addition, post-implantation thermal annealing is performed at selected temperatures. The disorder induced by implantation and the effect of the annealing on the recovery of the crystal lattice are investigated by RBS/Channeling measurements with the help of simulation code RUMP.

Effects of the surface oxide layer on platelet growth in H2+-implanted Si

The effect of a surface oxide layer on platelet growth in H2+-implanted Si was investigated. Samples of p-type Cz Si (100) and the same Si covered with a 170 nm thick thermal oxide layer were implanted with H2+ ions to a fluence of 2.5 × 1016 H2+/cm2 at room temperature. Post-implantation thermal annealing at temperatures between 773 K and 973 K for 30 min was performed in a flow of N2. Optical microscopy, cross-sectional transmission electron microscopy (XTEM) and micro-Raman spectroscopy were performed to investigate the effect of the oxide layer on platelet evolution upon annealing. Optical microscopy observations show that blisters and half-open blisters occur on the surface of Si with the oxide layer, but craters and half-open blisters occur on the pure Si surface. XTEM observations show that the growth rate of platelets in the defect band of Si with the oxide layer is slower than that in the pure Si sample, due to the lower concentration of vacancy-type defects in the Si with the oxide layer. The density of frank loops increases with increasing annealing temperature in the Si with the oxide layer.

Depth Profiling of Electronic Transport Parameters in n-on-p Boron-Ion-Implanted Vacancy-Doped HgCdTe

We report results of a detailed study of electronic transport in n-on-p junctions formed by 150-keV boron-ion implantation in vacancy-doped p-type Hg0.769Cd0.231Te without postimplantation thermal annealing. A mobility spectrum analysis methodology in conjunction with a wet chemical etching-based surface removal approach has been employed to depth profile the transport characteristics of the samples. In the as-implanted samples, three distinct electron species were detected which are shown to be associated with (a) low-mobility electrons in the top 220-nm surface-damaged layer (E1: μ80K = 2940 cm2/Vs), (b) the B-ion implantation region in the top 500-nm region (E2: μ80K = 7490 cm2/Vs), and (c) high-mobility electrons in the n-to-p transition region at a depth of 600 nm to 700 nm (E3: μ80K = 25,640 cm2/Vs). Due to the maximum magnetic field employed (2 T), hole carriers from the underlying vacancy-doped p-type region were detected only after the removal of the top 220 nm of the profiled sample (μ80K = 126 cm2/Vs), revealing fully p-type character 800 nm below the original sample surface. A comparison of the extracted E2 electron concentration and calculated B-impurity profile suggests that the n-type region is due primarily to near-surface implantation-induced lattice damage.

Effects of implantation temperature and thermal annealing on the Ga+ ion beam induced optical contrast formation in a-SiC:H

The effects of implantation temperature and post-implantation thermal annealing on the Ga+ ion beam induced optical contrast formation in hydrogenated silicon–carbon alloy films have been studied. As a result of the implantation a well-expressed “darkening” effect (i.e. absorption edge shift to the longer-wavelength/lower-photon-energy region) has been registered. It is accompanied by a remarkable increase of the absorption coefficient up to 2 orders of magnitude in the measured photon energy range (1.5–3.1eV). The optical contrast thus obtained (between implanted and unimplanted regions of the film material) has been made use of in the form of optical pattern formation by computer-operated Ga+-focused ion beam. Possible applications of this effect in the area of submicron lithography and high-density optical data storage have been suggested with regard to the most widely spread focused micro-beam systems based on Ga+ liquid metal ion sources. The fact that Ga has a very low melting point (Tm=29.8°C) and an unusual feature of volume contraction on melting are factors which favour Ga incorporation upon ion-implantation as dispersed clusters, or small nanoparticles. It has been previously noted that Ga precipitation into nanoparticles can vary dramatically (in terms of particle size) with Ga concentration and small changes in surface implant temperature, thus affecting the optical properties of the target. The precise role of implantation temperature effects, i.e. the target temperature during Ga+ ion irradiation, on the optical contrast obtainable, has been therefore a key part of this study. Appropriate post-implantation annealing treatments were also studied, since these are expected to offer further benefits in reducing the required ion dose and enhancing contrast, thus increasing the cost-effectiveness of the bit-writing method.

Direct observation of substitutional Ga after ion implantation in Ge by means of extended x-ray absorption fine structure

We present an experimental lattice location study of Ga atoms in Ge after ion implantation at elevated temperature (250°C). Using extended x-ray absorption fine structure (EXAFS) experiments and a dedicated sample preparation method, we have studied the lattice location of Ga atoms in Ge with a concentration ranging from 0.5 at. % down to 0.005 at. %. At Ga concentrations ≤0.05 at.%, all Ga dopants are substitutional directly after ion implantation, without the need for post-implantation thermal annealing. At higher Ga concentrations, a reduction in the EXAFS amplitude is observed, indicating that a fraction of the Ga atoms is located in a defective environment. The local strain induced by the Ga atoms in the Ge matrix is independent of the Ga concentration and extends only to the first nearest neighbor Ge shell, where a 1% contraction in bond length has been measured, in agreement with density functional theory calculations.

Thermal effects on the Ga+ ion beam induced structural modification of a-SiC:H

The effects of implantation temperature and post-implantation thermal annealing on the Ga+ ion beam induced optical contrast formation in hydrogenated silicon-carbon alloy (a-SiC:H) films and underlying structural modifications have been studied. The optical contrast formed (between implanted and unimplanted regions of the film material) has been made use of in the form of optical pattern formation by computer-operated Ga+-focused ion beam. Possible applications of this effect in the area of submicron lithography and high-density optical data storage have been suggested with regard to the most widely spread focused micro-beam systems based on Ga+ liquid metal ion sources. The implanted samples were structurally analysed using vibrational spectroscopies, like Raman and infra-red (IR) spectroscopy, to define optimum implantation conditions. The precise role of implantation temperature effects, i.e. the target temperature during Ga+ ion irradiation, on the structural modification obtainable has been therefore a key part of this study. Appropriate post-implantation annealing treatments were also studied, since these are expected to offer further benefits in reducing the required ion dose and enhancing the optical contrast, thus increasing the cost-effectiveness of the method.

Specificity of silver nanoparticle synthesis in quartz glass upon low-energy ion implantation

Silicabased composite materials with silver nano particles (NPs) were studied. Synthesis of the NPs was carried out using a lowenergy (30 keV) implantation of Ag + ions to high fluences. After the implan� tation, the samples were thermally annealed at 300°C for 1 hour in argon atmosphere. Synthesized NPs dem� onstrated an absorption band related to surface plasmon resonance (SPR). Shift of the SPR maximum towards longer wavelengths was found with an increase of ion fluence. This shift correlates with an enlarge� ment of the hemispherical protrusions observed on the sample surface using atomic force microscopy. The obtained results were interpreted as increase of the NPs in size. It was shown that the postimplantation ther� mal annealing leads to change of size of the NPs thus allowing to develop a technological approach for con� trolled synthesis of NPs in shallow dielectric layers.

Modeling spatially dependent kinetics of helium desorption in BCC iron following He ion implantation

One of the most important tasks in fusion materials research is to study the effect of helium on the microstructure and mechanical property evolution of structural materials. Thermal helium desorption spectrometry (THDS), through measuring the outward He surface flux as a function of temperature (or time), provides indirect information about the kinetics and energetics of helium transport and trapping/detrapping which is important for developing a predictive assessment for the life performance of fusion reactors. Nevertheless, THDS data interpretation is not straightforward, particularly when a broad temperature regime and a high He concentration are concerned. Here we present results from a spatially-dependent rate theory modeling framework in coordination with our previous THDS experiments on single crystal iron implanted with 4He + ions at 5 or 10 keV to fluences of 10 18 or 10 19 He/m 2. The model incorporates both temporally and spatially dependent diffusion, trapping, and detrapping (emission) kinetics for both implantation process and post-implantation thermal annealing. Possible desorption sequences/mechanisms are discussed.

He implantation in cubic zirconia: Deleterious effect of thermal annealing

This study investigates the microstructural modifications induced in cubic zirconia by He implantation at high concentration (∼4 at.%). The effect of post-implantation thermal annealing on the crystal stability is particularly addressed. For this purpose, three complementary analysis techniques, namely RBS/C, XRD and TEM, have been used. The structure of as-implanted crystals appears weakly defective, the damage very likely consisting of interstitial-type defects and helium-vacancy clusters. These defects induce a tensile elastic strain gradient with a depth distribution that overlaps the He depth profile. After annealing at 800 °C, a partial strain relaxation is observed, but the crystalline structure is strongly altered due to the formation of helium bubbles and elongated fractures.

Luminescence and Si and Ge nanocluster formation in silica

Cathodoluminescence (CL), high resolution transmission (HR-TEM) and scanning transmission electron microscopy (STEM), and energy dispersive X-ray analysis (EDX) have been used to investigate Si and Ge cluster formation in amorphous silicon dioxide layers and their respective luminescence behavior. In Ge+ ion implanted SiO2 an additional violet (V) Ge related emission band is identified at (410 nm). A postimplantation thermal annealing at temperatures Ta=700, 900, 1100 ∘C for 60 minutes in dry nitrogen or vacuum leads to a hugh increase of the violet luminescence up to 900 ∘C, followed by a decrease towards 1100 ∘C. The strong increase of the violet luminescence is associated with formation of low-dimension Ge aggregates like dimers, trimers and higher formation; the following decay of luminescence is due to further growing to Ge nanoclusters.