High-energy Implantation Research Articles

Modeling of Wound Coaxial Blumlein Pulsers

Blumlein pulsers are well-suited devices for high-voltage pulse generation in nanosecond and microsecond ranges. These generators have been used with great success in several areas such as in breakdown tests, X-ray generation, lasers, and high-energy plasma implantation. They consist of lengths of transmission lines charged in parallel and synchronously discharged in series into the load by using single or multiple switches at the opposite line endings. The main problem with the device performance is the presence of the shield cable impedance contributing to the Blumlein power loss especially when using only one switch. The very well known technique used for minimizing these losses consists of winding the transmission lines to increase the line shielding inductance if coaxial cables are used. Therefore, herein, circuit models are presented to assess theoretically the temporal response of the wound coaxial Blumlein pulsers by using a SPICE circuit simulator. For model assessment, the authors used the experimental results produced by a wound coaxial Blumlein pulser of 100 kV/200 A with 1.0 mus of pulse duration constructed for applications in surface treatment of polymers and aluminum with high-energy ions

Low Noise Junction Field Effect Transistors in a Silicon Radiation Detector Technology

We report on n-channel Junction Field Effect Transistors fabricated on high resistivity silicon by means of a specially tailored radiation detector technology. This research activity is being carried out in the framework of a project aiming at the integration of read-out circuits in the same detector substrate. Possible applications are in the field of medical/industrial imaging, space and high energy physics experiments. The pre-existent fabrication process has been modified in several respects to enhance the device noise behavior. In particular, the new process features a high-energy (1 MeV) Boron implantation to obtain a deep p-well which ensures an effective isolation of the transistor from the substrate and a strong modulating effect on the current. Selected results from the experimental characterization of transistors and charge sensitive amplifiers are presented, showing a sizable enhancement in the noise performance with respect to previously available devices

Modulation of the human bone cell cycle by calcium ion-implantation of titanium

Ca ion implantation of Ti surfaces has previously been reported to enhances osseointegration in vivo. Although the mechanisms underlying the response of bone cells to these novel surfaces still remain unclear, it is possible that Ca ion-implanted Ti (Ca-Ti) may influence the growth of new bone by modulating the progression of the cell cycle. In the present study we have, therefore, examined the precise effects of Ca ion-implantation of Ti on the bone-like MG-63 cell line in vitro. The results of flow cytometry analysis showed that this surface markedly enhanced the proportion of cells which expressed Ki-67, a cell proliferation-associated nuclear antigen, compared with cells grown on the non-implanted Ti (control) surface. In addition, cultures grown on Ca-Ti and synchronized at the G1/S boundary by hydroxyurea more rapidly re-entered and progressed through the S and G2/M phases of the cell cycle than their counterparts on Ti. Ca ion-implantation also significantly increased the numbers of mitotic cells. These results thus show that alteration of the surface chemistry of Ti by high-energy implantation with Ca ion was able to substantially modulate the progression of the bone cell cycle, and suggest a possible means of enhancing the response of bone cells to implant materials.

Intelligent anvils applied to experimental investigations: state-of-the-art

Since a long time, efforts have been made to improve the accuracy of pressure and temperature measurements in diamond anvil cell experiments performed in experimental petrology and high-pressure physics. Here, we report on the state-of-the-art of the research carried out during past few years with the diamond anvils carrying implanted electronic structures (‘intelligent’ anvils, iAnvils). The electronic structures are inserted a few microns below the diamond surface into the diamond lattice by high-energy implantation of boron. These structures can be used as pressure- and temperature-sensitive devices. Another useful application is the fabrication of micro-heaters integrated in the anvils. Pressure- and temperature-induced responses of the sensors (change of resistance) are quantified by low-current measurement equipment. Calibrations against pressure–temperature parameters are performed using well-known phase transitions or by using equation of state of pure substances. Results of in situ measurements performed on iAnvils under pressure and temperature are presented, together with calibration curves for pressure and temperature. Future experiments on in situ measurements of the conductivity dependence of the sensor structures are discussed.

GaAs photodetectors prepared by high-energy and high-dose nitrogen implantation

The authors report on the fabrication and characterization of photodetectors based on nitrogen-ion-implanted GaAs and the annealing dynamics in these devices. An energy of 400keV was used to implant N ions in a GaAs substrate at an ion concentration of ∼1×1016cm−2. Dark current measurements as well as measurements under illumination show that the material properties rapidly change during the annealing process. Photodetectors based on nitrogen-implanted GaAs materials with annealing temperatures up to 400°C exhibit a subpicosecond carrier lifetime up to 0.6ps. These properties make nitrogen-ion-implanted GaAs an ideal material for ultrafast photodetectors, as alternative to low-temperature-grown GaAs.

Damage and recovery in boron doped silicon on insulator layers after high energy Si+ implantation

The effects of 2MeV Si+ implantation on silicon-on-insulator layers uniformly doped with B at concentrations 1.0 and 1.8×1020cm−3, and the kinetics of damage recovery were investigated by carrier density, mobility measurements, and transmission electron microscopy (TEM) observations. High energy implantation reduces the hole density by about 98%; the mobility is also reduced at an extent which increases with B concentration. Isochronal and isothermal annealings show that recovery of the hole density takes place in three stages: the first stage (α) is accompanied by a mobility decrease and is followed by the second stage (β) where mobility increases attaining values close to the ones of the reference undamaged samples. Mobility keeps nearly constant in the third recovery stage (γ), which takes place above 800°C. As a characterizing feature the mobility values for each B concentration only depend on the hole density, irrespective of the thermal history of the samples. Experiments and TEM observations allowed us to distinguish defect recovery from SiB3 precipitation, which can take place at temperatures higher than 700°C. Recovery stages are discussed, and it is concluded that dissolution of B rich clusters in stage (α) modifies the concentration, or the charge state, of the defects responsible of the second (β) stage. These defects are identified as boron interstitial clusters in consideration of their mobility behavior and of the activation energy Eβ for their recovery process, which results to be 3±0.2eV.

Identification of vacancy type defects in low and high energy nitrogen ion implanted InP

Depth resolved positron annihilation measurements were carried out on 85 keV and 1 MeV nitrogen ion implanted InP samples. The defect sensitive S-parameter and R-parameter values for the low energy implantations confirm the presence of monovacancies up to a dose of 1015 cm−2 and coexistence of monovacancies and divacancies for 1016 cm−2 dose sample. Corroborative glancing incidence x-ray diffraction measurements on the highest dose sample revealed that the sample is amorphized. For high energy implantation, it is found that vacancy-defects are present right from the near-surface region and these defects are identified to be monovancancies, based on the observed S- and R-parameters. A comparison of the results for the low and high energy implantations is made.

Realization of Low CoSi2/p+-Silicon Contact Resistance with Low Junction Leakage Current and Junction Capacitance Using Laser Thermal Process

In this paper we report source–drain engineering for the realization of low contact resistance between CoSi2 and p+ Si with low junction leakage current and low junction capacitance using laser thermal processing (LTP) and the optimization of ion implantation conditions. We first demonstrate the impact of pre-amorphization on the reduction of the contact resistivity of a CoSi2/p+ deep source–drain (deep-SD) interface using laser thermal processing (LTP). A highly activated dopant profile at the CoSi2/deep-SD interface is required to reduce the contact resistivity there. Dopant profile can be finely controlled by implanting heavy ions to preamorphize a region to the desired depth and then using an appropriate laser power to selectively melt the amorphous Si, which has a melting temperature lower than that of single-crystal Si. We can thus form a highly activated boxlike dopant profile suitable for a deep-SD by using LTP and relatively deep preamorphization. Then, we discuss how to suppress the leakage current and the capacitance of the junctions. The larger junction capacitance and junction leakage current due to the abrupt deep-SD profile can be greatly reduced by combining LTP with lower-dose, higher-energy implantation and RTA prior to preamorphization (predoping and pre-RTA) to form a graded deep-SD profile beyond the abrupt deep-SD profile and overwhelm the channel doping profile, resulting in a wide depletion layer.

High-energy Au implantation of GaAs at 16 K

GaAs was irradiated with 10MeV or 17.5MeV Au ions at 16K and subsequently measured at the same temperature. Under these conditions ion-beam induced processes can be studied whilst thermal effects are widely excluded. It is found that the measured defect concentration scales with the number of displacements per lattice atom (representing the nuclear energy deposition) independent of the ion energy and of the depth. This result demonstrates that, for the chosen ion energies, the electronic energy deposition itself does not influence the damage production in GaAs. Contrary in GaAs implanted with high-energy ions (10MeV range) and analysed at room temperature, the defect concentration close to the surface was found to be lower than expected from theoretical simulations. The explanation for this previously observed effect is a preferred annealing of lightly damaged areas during warming the samples to room temperature for measurement.

Resonant Raman scattering in ion-beam-synthesizedMg2Siin a silicon matrix

Resonant Raman scattering by ion beam synthesized in silicon matrix ${\mathrm{Mg}}_{2}\mathrm{Si}$ phase is studied. The samples are prepared with the implantation of $^{24}\mathrm{Mg}^{+}$ ions with dose $4\ifmmode\times\else\texttimes\fi{}{10}^{17}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ and with two different energies 40 and $60\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ into (100)Si substrates. The far infrared spectra are used as criteria for the formation of the ${\mathrm{Mg}}_{2}\mathrm{Si}$ phase. The Raman spectra are excited with different lines of ${\mathrm{Ar}}^{+}$ laser, with energies of the lines lying in the interval from $2.40\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}2.75\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The resonant scattering can be investigated using these laser lines, as far as according to the ${\mathrm{Mg}}_{2}\mathrm{Si}$ band structure, there are direct gaps with energies in the same region. The energy dependences of the scattered intensities in the case of the scattering by the allowed ${F}_{2g}$ and the forbidden LO-type modes are experimentally obtained and theoretically interpreted. On the base of the investigation energies of the interband transitions in the ${\mathrm{Mg}}_{2}\mathrm{Si}$ are determined. It is found also that the resonant Raman scattering appears to be a powerful tool for characterization of a material with inclusions in it. In the particular case it is concluded that the ${\mathrm{Mg}}_{2}\mathrm{Si}$ phase is present in the form of a surface layer in the sample, prepared with implantation energy $40\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ and as low-dimensional precipitates, embedded in the silicon matrix, in the sample, prepared with the higher implantation energy.

Room-temperature defect tolerance of band-engineered InAs quantum dot heterostructures

Using photoluminescence (PL) at 77–420K and high-energy proton implantation (1.5MeV, dose up to 3×1014cm−2) we have studied the thermal quenching of PL and defect tolerance of self-assembled shape-engineered InAs quantum dots (QDs) embedded into GaAs quantum wells (QWs). At room temperature, QDs appeared to withstand two orders of magnitude higher proton doses than QWs without PL degradation. A simple dynamic model was used to account for both dose and temperature dependence of PL efficiency. At low temperatures, the defect-related quenching is mainly controlled by a reduction in the density of defect-free QDs. At and above room temperature, both thermal and defect-related quenching of PL are due to the escape of carriers from dots to wells that act as barriers with low damage constants. A relatively large barrier for escape (450meV) as well as low nonradiative recombination rate in QDs is shown to account for unsurpassed room-temperature defect tolerance and high PL efficiency at room and elevated temperatures.

Phase formation after nitrogen implantation into molybdenum

High fluence nitrogen ion implantation into molybdenum is compared for low energies of 30keV and below and high energies of 1MeV at a total fluence between 0.5 and 2.7×1018at./cm2. For the low energy implantation, a transformation from cubic Mo2N towards tetragonal Mo2N is observed around 580°C with ex situ X-ray diffraction (XRD), whereas high energy implantation leads to the simultaneous formation of tetragonal Mo2N and hexagonal MoN in the same temperature range, as observed with in situ XRD. Additionally, ion beam analysis was employed to measure the local atomic concentrations, which can be used for determining the phase formation threshold and the diffusion constant.

Structural and compositional characterization of X-cut LiNbO3 crystals implanted with high energy oxygen and carbon ions

High energy implantation of medium-light elements such as oxygen and carbon was performed in X-cut LiNbO3 single crystals in order to prepare high quality optical waveguides. The compositional and damage profiles, obtained by exploiting the secondary ion mass spectrometry and Rutherford back-scattering techniques respectively, were correlated to the structural properties measured by the high resolution X-ray diffraction. This study evidences the development of tensile strain induced by the ion implantation that can contribute to the decrease of the ordinary refractive index variation through the photo-elastic effect.

Low-temperature epitaxial Ni silicidation: The role of hyperthermal species

We present the results of Ni silicidation on a Si111 surface employing a mass-selected hyperthermal ion beam at 100 eV and discuss the reaction mechanism compared with the conventional Ni silicidation process. It is found that the Ni silicide formation using this technique is different from that achieved by conventional methods such as high-energy Ni-ion implantation or evaporation with thermal species. Namely, the Ni silicide phase formed at 230 degrees C using hyperthermal ions in this study is Ni-rich Ni2Si, in contrast to Si-rich disilicide NiSi2, ordinarily formed when high-energy Ni ions or thermal Ni beams react with Si at elevated temperatures. In addition, this layer is formed epitaxially on Si in spite of a low substrate temperature of 230 degrees C, while a polycrystalline Ni silicide layer is formed with conventional Ni-rich silicidation. This suggests that the reaction mechanism of the silicide formation with hyperthermal Ni particles is different from that using higher- or thermal-energy Ni particles. The atomic rearrangement induced by the thermal spikes most likely plays an important role in the Ni silicidation process employing hyperthermal species.

Photoluminescence signature of silicon interstitial cluster evolution from compact to extended structures in ion-implanted silicon

Low temperature photoluminescence (PL) studies have been carried out on ion-implanted silicon in order to elucidate upon the structure evolution of the self-interstitial (I) clusters as a function of implantation dose, energy, species and post-implantation annealing conditions. PL measurements on as-implanted and low temperature annealed (up to 450 °C) Si show a sharp X band and a W band at 1200 nm and 1218 nm, respectively. The W band shows gradual quenching of PL above ∼60 K with a characteristic activation energy of 59 meV. We argue that the W band originates from a compact di-interstitial cluster in Si. Short duration annealing at 600 °C results in multiple sharp peaks in the range of 1228–1400 nm for the high energy (MeV) and high dose (⩾1 × 1012 cm−2) implantation, while low energy (keV) or low dose ions induce two broad peaks in the same wavelength range. Prolonged annealing at 600 °C induces primarily two broad peaks centred at 1322 nm and 1392 nm. These broad, but distinct, PL signatures are attributed to a chain of I-clusters, while the multiple sharp peaks possibly result from multiple configurations/excited states of the compact but bigger I-clusters. For annealing at and above 680 °C and dose of ⩾1 × 1013 cm−2, the sharp PL peak observed at 1376 is attributed to {3 1 1} rod-like defects. We argue that the changing line shape and energy of the PL spectra with processing temperature is a possible indicator of the shape evolution of the clusters from compact to extended structures as predicted recently from simulation.

Formation of radiation defects in silicon at high-energy implantation

The processes of defect formation in silicon following high-energy ion implantation were studied using the Hall effect and IR absorption spectroscopy. Point radiation defects were found far beyond the region of typical ion projected ranges. It is suggested that the defects were formed as a result of diffusion of interstitials and vacancies from the implanted region further into the substrate. The efficiency of the formation of these defects was found to decrease with increase of the mass of implanted ions and is thought to be related to the increase in concentration of the interstitial and vacancy traps.

Matrix-seeded growth of nitride semiconductor nanostructures using ion beams

We have examined the matrix-seeded growth of narrow-gap nitride nanostructures in nitrogen ion implanted GaAs and InAs. Low-energy implantation followed by rapid thermal annealing (RTA) results in the formation of 2–3 nm sized amorphous precipitates in a crystalline matrix. On the other hand, high-energy implantation results in an amorphous layer, with or without crystalline remnants. When the ion-beam-synthesized amorphous matrix is a continuous amorphous layer, subsequent RTA leads to the formation of 4–5 nm zinc blende (ZB)-GaN-rich crystallites in an amorphous matrix. When this matrix contains crystalline remnants, subsequent RTA leads to the formation of 2–4 nm ZB-GaN-rich crystallites within the amorphous regions. These results suggest that the matrix plays an important role in the nucleation and growth of narrow-gap nitride nanostructures, and that matrix-seeded growth may provide an opportunity to control the structure and properties of the nanostructures.

A microspectroscopic study of cap damage in annealed RE-doped AlN-capped GaN

AbstractIntegrated AlN nanocaps are used to protect gallium nitride epilayers during high temperature annealing treatments following high-energy implantation of rare earth (RE) ions. Cracks formed in thicker caps due to the lattice mismatch between AlN and GaN lead to the creation of microscopic surface defects at annealing temperatures higher than around 1200 °C. GaN dissociates locally to produce holes in the caps. Simultaneous cathodoluminescence/wavelength dispersive X-ray microanalysis in a modified electron probe microanalyzer allows study of the compositional and light emission variations near these microscopic defects. The intensity of the 5D0 – 7F2 transition related emission is enhanced and spectral changes can be observed, which indicate changes in the structure and/or composition of a very thin layer that forms the walls of holes in the caps. We also report some preliminary observations on the influence of the annealing atmosphere (nitrogen or ammonia) on cap damage.

실리콘에 고에너지 안티몬이온주입의 실험과 개선된 모델에 관한 연구

Antimony profiles by MeV implantation are measured by secondary ion mass spectrometry (SIMS) and spreading resistance (SR). The moments of SIMS and simulated profiles are calculated and compared for the exact range in MeV energy. SRIM, DUPEX, ICECREM, and TSUPREM4 simulation programs are used for the calculation of range 1D, 2D. SRIM is a Monte Carlo simulation program and different inter-atomic potentials can be used for the calculation of nuclear stopping power cross-section (Sn) and range moments. Nevertheless, the range parameters were not influenced from nuclear stopping power in MeV. Through the modification of electronic stopping power cross-section (Se), the results of simulation are remarkably improved and matched very well with SIMS data. The values of electronic stopping power are optimized for Sb high energy implantation. For the electrical activation, Sb implanted samples are annealed under <TEX>$N_2$</TEX> and <TEX>$O_2$</TEX> ambient. Finally, Oxidation retard diffusion(ORD) effect of Sb implanted sample are demonstrated by SR measurements and ICECREM simulation.

Damage and recovery in doped SOI layers after high energy implantation

Silicon on insulator (SOI) substrates, uniformly n doped with As or P at different concentrations in the range between 1.9 and 8 × 10 20 cm −3, have been irradiated with increasing doses of high energy (2 MeV) Si + ions. The effects of irradiation and the subsequent recovery have been followed by electrical conductivity and carrier mobility measurements and transmission electron microscopy observations. Isothermal annealings have been performed at temperatures in the range 600–800 °C. It was found that recovery takes place in two distinct stages which have been evidenced by using rapid thermal annealing and furnace heating. Our results show a very similar behavior for the two donors and indicate that electron trapping is the responsible of the reduction of the carrier density upon irradiation both in As and P doped samples.