As-implanted Samples Research Articles

Synthesis of crystalline phases in space silicate analogues with helium ion irradiation

Silicate minerals such as “Mg-Fe-Si-O” compounds, are found in asteroids, planets, and cosmic dust grains in the interstellar medium. As the silicate dust grains traverse regions of space, they are irradiated by energetic ions, such as alpha particles, which can modify the crystalline phase of the mineral dust. Silicate dust grain analogues were synthesized using multiple low energy (<60 keV) ion (Fe−, Mg−, O−) implantations into a silicon wafer. The low energy ion beam as-implanted samples were cut into several smaller sections. Some of these low-energy as-implanted samples were further irradiated with a 600 keV helium ion beam at varying current densities (ions/unit area/unit time) and subsequent furnace annealed at 1000 °C temperature in Ar gas environment. The crystalline phases of the post annealed samples were monitored and reported as a function of current densities using x-ray diffraction (XRD). The XRD results showed an increase in the crystalline phases of olivine by the high-energy helium ion irradiation processing with a beam of current density of 500 nA/cm2. This work is relevant for space weathering processes as well as solid material evolution in astrophysical environments, especially asymptotic giant branch stars with an oxygen rich outflow.

Conversion mechanism of conductivity and properties of nitrogen implanted ZnO single crystals induced by post-annealing

In this paper, the conversion mechanism of conductivity and properties of nitrogen (70 keV, 1 × 1016 cm−2) implanted ZnO single crystals induced by post-annealing in a temperature ranging from 500 °C to 800 °C have been investigated by Hall, Raman, X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and low temperature photoluminescence (PL) measurements. The results indicate that the sample converts to p-type conductivity as annealed at 650 °C. For the as-implanted sample, different type of nitrogen (N) local states are detected, including substitutional N atom and N2 molecules on O site [No and (N2)o], N–O, N–H, and N–C complexes. However, their thermal stabilities display significant difference upon thermal annealing. Differing from the initial ZnO bulk, the low-temperature PL spectrum of the post-annealed N implanted ZnO sample consists of two dominant peaks located at 3.105 eV and 3.220 eV, respectively. The former is attributed to radiative electron transition from the conduction band to the Zn vacancy (VZn) acceptor level, and the latter is assigned to recombination of the donor–acceptor pair (DAP). Our results suggest that the VZn together with the No acceptors are responsible for p-type conductivity of N doped ZnO.

Thermal stability of F ion-implant isolated AlGaN/GaN heterostructures

The thermal stability of F ion-implanted isolated AlGaN/GaN heterostructures was investigated, with B ion-implanted isolation shown for comparison. The sheet resistance of as-implanted samples with F ions was lower than that with B ions due to enhanced hopping conduction. The leakage current for both implanted samples initially decreased and then increased with increases in post-annealing temperature, indicating a damage-induced isolation mechanism. Leakage reached a minimum value after 400°C annealing, which was over 108 times lower than the saturated current (Isat) of the as-grown structure, suggesting a successful isolation. After relatively high-temperature annealing, the leakage for F implantation showed a small change, whereas that for B implantation showed significant increase, suggesting that F-implanted isolation exhibited excellent thermal stability. Leakage current measured at 300°C for F ion-implantation was 103 times lower than the Isat of the as-grown structure, demonstrating that F ion isolation was applicable up to 300°C. Differences in current and activation energy (Ea) between the high-resistance GaN layer and F or B ion-implanted samples indicated that the leakage current originated from the region above the high-resistance GaN layer. Variation in Ea revealed that the optimal contributing states for conduction changed with operating temperature, annealing temperature, and ion species.

Damage formation and Er structural incorporation in m-plane and a-plane ZnO

The various crystallographic orientations in semiconductors as ZnO exhibit different resistivity under the ion beam irradiation/implantation. Study of the various crystallographic orientations is mandatory for nano-structured semiconductor system development. This paper reports on the implantation damage build-up, structural modification and Er dopant position in a-plane and m-plane ZnO implanted with Er+ 400 keV ions at the ion fluences 5 × 1014, 2.5 × 1015, 5 × 1015 cm−2 and subsequently annealed at 600 °C in O2 atmosphere using Rutherford Back-Scattering spectrometry (RBS) in channelling mode as well as using Raman spectroscopy. Strongly suppressed surface damage formation was observed in both crystallographic orientations compared to the deep damage growth with the increased ion implantation fluence. More progressive damage accumulation appeared in m-plane ZnO compared to a-plane ZnO. Simultaneously, the strong Er out-diffusion depth profile in m-plane ZnO accompanied by the damage accumulation at the surface was observed after the annealing. Contrary, the surface recovery accompanied by Er concentration depth profiles keeping a normal distribution with a small maximum shift to the surface was observed in a-plane ZnO. Different structure recovery and Er behaviour was evidenced in a-plane and m-plane ZnO by RBS-C, moreover Raman spectroscopy proved a lower damage at higher ion fluences introduced in a-plane ZnO compared to m-plane. The structure modifications were discussed in connection with a damage accumulation and Er concentration depth profile shape in various ZnO crystallographic orientations in as-implanted and as-annealed samples.

Effects of thermal annealing on structural and magnetic properties of Mn ions implanted AlInN/GaN films

In the search of functional diluted magnetic semiconductors, a study of effects of Mn ions implantation on structural and magnetic properties of AlInN/GaN/sapphire films is reported. Mn ions at 200 keV were implanted into the layers at three doses 5 × 1014 cm−2, 5 × 1015 cm−2 and 5 × 1016 cm−2. The as-implanted samples were thermally annealed and investigated by using X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS) and vibrating sample magnetometry (VSM). The structural analysis of the samples indicated that the sample implanted at dose of 5 × 1014 cm−2 and thermally annealed at 750 °C exhibited good crystalline recovery. The ferromagnetism of the samples was investigated by recording magnetization as a function of applied magnetic field. The magnetic characterizations exhibited well shaped hysteresis at room temperature which indicates presence of high temperature ferromagnetism in the samples. The findings of this work pointed out that AlInN/GaN samples implanted with Mn ions at dose of 5 × 1016 cm−2 and annealing at 750 °C exhibited maximum magnetization. On the basis of first principles calculations, it is predicted that p–d interaction is the mechanism of ferromagnetic ordering in the material.

Effects of phosphorus implantation time on the optical, structural, and elemental properties of ZnO thin films and its correlation with the 3.31-eV peak

To study the effects of implantation on ZnO thin films grown on Si substrates, we have subjected it to phosphorous ion implantation for 10, 40, and 70 s through plasma immersion ion implantation and rapid thermal annealing. Low-temperature photoluminescence spectra of the as-implanted samples exhibited a reduction in the donor-bound exciton peak at 3.36 eV with implantation time. The photoluminescence spectrum of the 70 s implanted 1000°C-annealed sample confirmed acceptor-type doping. X-ray diffraction measurements showed a reduction in the c-axis length along the <002> direction with implantation time, evidencing phosphorous-ion incorporation in the implanted films, which was further confirmed by the blue shifting of the E2 high peak in the Raman spectra. XPS measurements affirmed the presence of the P 2p peak, a signature of PO bond, and confirmed the substitution of Zn atoms by P atoms and the subsequent formation of the Pzn-2Vzn complex essential for acceptor-type conductivity.

Heavy doping of CdTe single crystals by Cr ion implantation

Abstract Implantation of bulk CdTe single crystals with high fluences of 500 keV Cr+ ions was performed to achieve Cr concentration above the equilibrium solubility limit of this element in CdTe lattice. The structure and composition of the implanted samples were studied using secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) to characterize the incorporation of chromium into the host lattice and to investigate irradiation-induced damage build-up. It was found that out-diffusion of Cr atoms and sputtering of the targets alter the depth distribution and limit concentration of the projectile ions in the as-implanted samples. Appearance of crystallographically oriented, metallic α-Cr nanoparticles inside CdTe matrix was found after implantation, as well as a strong disorder at the depth far beyond the projected range of the implanted ions.

Damage recovery and dopant migration of Eu+ ion implanted KTiOAsO4 crystals

Damage formation and annealing of Eu implanted KTiOAsO4 crystals is investigated. Ion implantation was done with 400 keV Eu2+ ions and an ion fluence of 5 × 1015 ions/cm2 at room temperature. The damage of as-implanted and annealed samples was analysed by Rutherford backscattering spectrometry in channelling configuration using 2.1 MeV He+ ions. After implantation, a thick RBS-amorphous layer is obtained. The damage in the Eu2+ implanted KTiOAsO4 layer decreases significantly after annealing at 700° C for 30 min in Ar atmosphere. Interestingly, the Eu peak firstly migrated to the surface after annealing at 600° C for 30 min, and then appeared narrower after annealing at 700° C for 30 min. Furthermore, arsenic loss by evaporation and titanium enrichment at the surface are observed during the annealing process.

Formation of graphitic and diamond-like carbon by low energy carbon ion implantation on c plane sapphire substrate

The present work reports the effect of 200 keV carbon ion implantation on the c-axis sapphire with different fluences: 4 × 1015, 8 × 1015 and 1.6 × 1016 ions/cm2. The electronic and nuclear energy losses and projected range were calculated using the Stopping and Range of Ions in Matter software. The Raman studies of as-implanted and post-implantation annealed samples showed the signatures of graphitic and diamond-like carbon materials. The structural studies were carried out using X-ray diffraction which showed the presence of carbon in different phases. The optical properties of the samples were studied using the room temperature Photoluminescence which confirms the formation of F-type color centers due to microstructural changes. The morphological studies by Atomic Force Microscopy revealed the surface modification in the samples. The Hall measurements were carried out on carbon ion implanted sapphire substrate and analyzed. The Hall measurements confirmed that the insulating c-sapphire becomes conducting after carbon ion implantation and subsequent annealing.

Deep level defects in 4H-SiC introduced by ion implantation: the role of single ion regime

We characterized intrinsic deep level defects created in ion collision cascades which were produced by patterned implantation of single accelerated 2.0 MeV He and 600 keV H ions into n-type 4H-SiC epitaxial layers using a fast-scanning reduced-rate ion microbeam. The initial deep level transient spectroscopy measurement performed on as-grown material in the temperature range 150–700 K revealed the presence of only two electron traps, Z1/2 (0.64 eV) and EH6/7 (1.84 eV) assigned to the two different charge state transitions of the isolated carbon vacancy, VC (=/0) and (0/+). C–V measurements of as-implanted samples revealed the increasing free carrier removal with larger ion fluence values, in particular at depth corresponding to a vicinity of the end of an ion range. The first DLTS measurement of as-implanted samples revealed formation of additional deep level defects labelled as ET1 (0.35 eV), ET2 (0.65 eV) and EH3 (1.06 eV) which were clearly distinguished from the presence of isolated carbon vacancies (Z1/2 and EH6/7 defects) in increased concentrations after implantations either by He or H ions. Repeated C–V measurements showed that a partial net free-carrier recovery occurred in as-implanted samples upon the low-temperature annealing following the first DLTS measurement. The second DLTS measurement revealed the almost complete removal of ET2 defect and the partial removal of EH3 defect, while the concentrations of Z1/2 and EH6/7 defects increased, due to the low temperature annealing up to 700 K accomplished during the first temperature scan. We concluded that the ET2 and EH3 defects: (i) act as majority carrier removal traps, (ii) exhibit a low thermal stability and (iii) can be related to the simple point-like defects introduced by light ion implantation, namely interstitials and/or complex of interstitials and vacancies in both carbon and silicon sub-lattices.

White luminescence emission from silicon implanted germanium

Abstract Germanium crystals were implanted with low-energy and high-dose silicon ions. The implantation led to amorphization of a near-surface layer due to the formation of many adatoms and vacancies. Adatoms can be absorbed in germanium by the amorphous matrix faster than vacancies. The excess of vacancies and their ability to cluster resulted in formation of a porous structure beneath the surface. Pores of different sizes and depths were observed experimentally. A subsequent thermal annealing was carried out at 973 K in order to repair the damage due to the implantation. The annealing resulted, among other things, in oxidation of the pores. Visible white luminescence was observed for the as-implanted samples at the 325 nm excitation wavelength; the photoluminescence intensity increased after the annealing. The optical properties were attributed to the combined effects of different defects and the formation of germanium oxides with oxygen deficiencies.

Synthesis of a GaN nanolayer on (001) GaAs by N ion implantation

N+ ions at 50keV were implanted up to a fluence of 3×1017cm−2 into a (001) GaAs substrate capped by a 125-nm Si3N4 layer obtained by sputtering deposition. The Si3N4/GaAs system was kept at 450°C during ion implantation. Nitrogen bubbles were present on both sides of the Si3N4/GaAs interface of the as-implanted sample, which showed a layered structure. In addition, the N-implanted region on the GaAs side was almost amorphous. By subsequent thermal annealing at 850°C for 5min under N2 flow, we were able to synthesize a GaN nanolayer with the wurtzite structure. We also identified cubic-structured GaN with a lattice parameter of (0.42±0.01) nm, which is significantly smaller than the one reported in the literature (0.45nm) for the GaN zinc-blend phase.

Atomic layer deposited ZnO films implanted with Yb: The influence of Yb location on optical and electrical properties

Epitaxial ZnO films implanted with ytterbium have been studied by combination of channeling Rutherford backscattering spectrometry and Hall measurements. This approach is able to shed more light onto the difficult problem of optical activation of Yb implanted into the ZnO lattice. ZnO films grown by atomic layer deposition on a GaN/Al2O3 substrate were implanted with Yb+ ions to the fluences of 5×1014, 1×1015 and 5×1015at./cm2. RBS/c spectra show that for as implanted samples the fraction of implanted Yb ions occupying substitutional lattice positions amounts to 72%, 54% and 22%, respectively. Annealing under an ambient atmosphere at 800°C leads to a partial recovery of the crystal lattice but also substantially reduces substitutional fraction of Yb atoms. Photoluminescence studies on the as-implanted samples revealed a very weak luminescent peak in the near-infrared region, which slightly increases with a fluence. The annealing process leads to optical activation of Yb3+ ions and significantly increases the previously observed the near-infrared inter-ionic emission. The results obtained from Hall measurements indicate that after implantation Yb ions are mainly in the 2+ state and are transformed to the optically active 3+ state as a result of annealing. It suggests that the process of optical activation via annealing is related not only to lattice recovery, but also to Yb diffusion from substitutional to interstitial positions, where Yb ions are in the optically active 3+ state.

Surface insulating properties of titanium implanted alumina ceramics by plasma immersion ion implantation

The insulating property of the alumina ceramic in vacuum under high voltage is mainly limited by its surface properties. Plasma immersion ion implantation (PIII) is an effective method to modify the surface chemical and physical properties of the alumina ceramic. In order to improve the surface flashover voltage of the alumina ceramic in vacuum, titanium ions with an energy of about 20keV were implanted into the surface of the alumina ceramic using the PIII method. The surface properties of the as-implanted samples, such as the chemical states of the titanium, morphology and surface resistivity, were characterized by X-ray photoelectron spectroscopy, scanning electron microscope and electrometer, respectively. The surface flashover voltages of the as-implanted alumina samples were measured by a vacuum surface flashover experimental system. The XPS spectra revealed that a compound of Ti, TiO2 and Al2O3 was formed in the inner surface of the alumina sample. The electrometer results showed that the surface resistivity of the implanted alumina decreased with increased implantation time. In addition, after the titanium ion implantation, the maximum hold-off voltage of alumina was increased to 38.4kV, which was 21.5% higher than that of the unimplanted alumina ceramic.

High-Temperature Annealing Induced He Bubble Evolution in Low Energy He Ion Implanted 6H-SiC**Supported by the National Natural Science Foundation of China under Grant No 11475229.

Bubble evolution in low energy and high dose He-implanted 6H-SiC upon thermal annealing is studied. The -oriented 6H-SiC wafers are implanted with 15 keV helium ions at a dose of 11017 cm−2 at room temperature. The samples with post-implantation are annealed at temperatures of 1073, 1173, 1273, and 1473 K for 30 min. He bubbles in the wafers are examined via cross-sectional transmission electron microscopy (XTEM) analysis. The results present that nanoscale bubbles are almost homogeneously distributed in the damaged layer of the as-implanted sample, and no significant change is observed in the He-implanted sample after 1073 K annealing. Upon 1193 K annealing, almost full recrystallization of He-implantation-induced amorphization in 6H-SiC is observed. In addition, the diameters of He bubbles increase obviously. With continually increasing temperatures to 1273 K and 1473 K, the diameters of He bubbles increase and the number density of lattice defects decreases. The growth of He bubbles after high temperature annealing abides by the Ostwald ripening mechanism. The mean diameter of He bubbles located at depths of 120–135 nm as a function of annealing temperature is fitted in terms of a thermal activated process which yields an activation energy of 1.914+0.236 eV.

The microstructure of Si surface layers after plasma-immersion He+ ion implantation and subsequent thermal annealing.

The structural changes in the surface layer of p-type Cz-Si(001) samples after high-dose low-energy (2 keV) He+ plasma-immersion ion implantation and subsequent thermal annealing were studied using a set of complementary methods: high-resolution X-ray reflectometry, high-resolution X-ray diffraction, transmission electron microscopy and atomic force microscopy. The formation of a three-layer structure was observed (an amorphous a-SiO x layer at the surface, an amorphous a-Si layer and a heavily damaged tensile-strained crystalline c-Si layer), which remained after annealing. Helium-filled bubbles were observed in the as-implanted sample. The influence of annealing on the evolution of the three-layer structure and the bubbles is considered. The bubbles are shown to grow after annealing. Their characteristic size is determined to be in the range of 5-20 nm. Large helium-filled bubbles are located in the amorphous a-Si layer. Small bubbles form inside the damaged crystalline Si layer. These bubbles are a major source of tensile strain in the c-Si layer.

SIMS as a new methodology to depth profile helium in as-implanted and annealed pure bcc metals?

Reliable He profiles are highly desirable for better understanding helium behavior in materials for future nuclear applications. Recently, Secondary Ions Mass Spectrometry (SIMS) allowed the characterization of helium distribution in as-implanted metallic systems. The Cs+ primary ion beam coupled with CsHe+ molecular detector appeared to be a promising technique which overcomes the very high He ionization potential.In this study, 4He depth profiles in pure body centered cubic (bcc) metals (V, Fe, Ta, Nb and Mo) as-implanted and annealed, were obtained by SIMS. All as-implanted samples exhibited a projected range of around 200nm, in agreement with SRIM theoretical calculations. After annealing treatment, SIMS measurements evidenced the evolution of helium depth profile with temperature. The latter SIMS results were compared to the helium bubble distribution obtained by Transmission Electron Microscopy (TEM).This study confirmed the great potential of this experimental procedure as a He-depth profiling technique in bcc metals. Indeed, the methodology described in this work could be extended to other materials including metallic and non-metallic compounds. Nevertheless, the quantification of helium concentration after annealing treatment by SIMS remains uncertain probably due to the non-uniform ionization efficiency in samples containing large bubbles.

Annealing effects on the migration of ion-implanted cadmium in glassy carbon

The migration behaviour of cadmium (Cd) implanted into glassy carbon and the effects of annealing on radiation damage introduced by ion implantation were investigated. The glassy carbon substrates were implanted with Cd at a dose of 2×1016ions/cm2 and energy of 360keV. The implantation was performed at room temperature (RT), 430°C and 600°C. The RT implanted samples were isochronally annealed in vacuum at 350, 500 and 600°C for 1h and isothermally annealed at 350°C up to 4h. The as-implanted and annealed samples were characterized by Raman spectroscopy and Rutherford backscattering spectrometry (RBS). Raman results revealed that implantation at room temperature amorphized the glassy carbon structure while high temperature implantations resulted in slightly less radiation damage. Isochronal annealing of the RT implanted samples resulted in some recrystallization as a function of increasing temperature. The original glassy carbon structure was not achieved at the highest annealing temperature of 600°C. Diffusion of Cd in glassy carbon was already taking place during implantation at 430°C. This diffusion of Cd was accompanied by significant loss from the surface during implantation at 600°C. Isochronal annealing of the room temperature implanted samples at 350°C for 1h caused Cd to diffuse towards the bulk while isothermal annealing at 500 and 600°C resulted in the migration of implanted Cd toward the surface accompanied by a loss of Cd from the surface. Isothermal annealing at 350°C for 1h caused Cd to diffuse towards the bulk while for annealing time >1h Cd diffused towards the surface. These results were interpreted in terms of trapping and de-trapping of implanted Cd by radiation damage.

Magnetic and Mössbauer effect studies of ZnO thin film implanted with iron ions to high fluence

We present the results of magnetic and Mössbauer effect studies of zinc oxide thin film obtained by RF magnetron sputtering and implanted with 40 keV iron ions to a fluence of 1.5·1017 ion/cm2. As-implanted and post-annealed sample shows ferromagnetic properties at room temperature and consists of paramagnetic and ferromagnetic phases according to Mössbauer spectroscopy.

Effects of 200 keV Ar-ions irradiation on the structural and optical properties of reactively sputtered CrN films

Modification in structural and optical properties of chromium-nitride (CrN) films induced by argon ion irradiation and thermal annealings were investigated using various experimental techniques. CrN films deposited by d. c. reactive sputtering on Si substrate were implanted with 200 keV argon ions, at fluences of 5–20 × 1015 ions/cm2. As-implanted samples were then annealed in vacuum, for 2 h at 700 °C. Rutherford backscattering spectrometry, X-ray diffraction, cross-sectional (high-resolution) transmission electron microscopy and spectroscopic ellipsometry (SE) measurements were carried out in order to study structural and optical properties of the layers. After irradiation with 200 keV Ar ions a damaged surface layer of nanocrystalline structure was generated, which extended beyond the implantation profile, but left an undamaged bottom zone. Partial loss of columnar structure observed in implanted samples was recovered after annealing at 700 °C and CrN started to decompose to Cr2N. This layer geometry determined from transmission electron microscopy was inferred in the analysis of SE data using the combined Drude and Tauc-Lorentz model, and the variation of the optical bandgap was deduced. The results are discussed on the basis of the changes induced in the microstructure. It was found that the optical properties of the layers are strongly dependent on the defects' concentration of CrN.