Se Implantation Research Articles

Broad infrared absorption band through ion beam hyperdoping of silicon with selenium

In this work, we present the formation of silicon layers hyperdoped with selenium through Se implantation followed by pulsed laser annealing. The concentration depth distribution of Se atoms was investigated by Rutherford backscattering and X-Ray photoelectron spectroscopies. Scanning tunneling spectroscopy confirmed the formation of intermediate sub-band within Si band gap. The crystallinity of the doped silicon layer and the fraction of Se atoms in Si lattice sites were determined using backscattering yield analysis. Experimental and theoretical sub-band properties were compared and discussed. Notably, a significant increase in light absorption across a wide spectral region (0.2–23.0 μm) was observed, demonstrating the potential of selenium hyperdoping for enhancing infrared absorption in silicon.

Excitonic Dynamics in Janus MoSSe and WSSe Monolayers.

We report here details of steady-state and time-resolved spectroscopy of excitonic dynamics for Janus transition metal dichalcogenide monolayers, including MoSSe and WSSe, which were synthesized by low-energy implantation of Se into transition metal disulfides. Absorbance and photoluminescence spectroscopic measurements determined the room-temperature exciton resonances for MoSSe and WSSe monolayers. Transient absorption measurements revealed that the excitons in Janus structures form faster than those in pristine transition metal dichalcogenides by about 30% due to their enhanced electron-phonon interaction by the built-in dipole moment. By combining steady-state photoluminescence quantum yield and time-resolved transient absorption measurements, we find that the exciton radiative recombination lifetime in Janus structures is significantly longer than in their pristine samples, supporting the predicted spatial separation of the electron and hole wave functions due to the built-in dipole moment. These results provide fundamental insight in the optical properties of Janus transition metal dichalcogenides.

Effect of heat treatment on the migration behaviour of selenium implanted into polycrystalline SiC

This study reviews the migration behaviour of selenium in polycrystalline SiC, which acts as the main diffusion barrier in the coated fuel particles for Very High Temperature Reactors. Se ions of 200 keV were implanted into polycrystalline SiC wafers to a fluence of 1 × 1016 cm−2 at three temperatures, which were room temperature, 350 °C and 600 °C. The implanted samples were annealed at temperatures ranging from 1000 to 1500 °C in steps of 100 °C for 10 h. The migration of implanted Se was monitored by Rutherford backscattering spectrometry (RBS) while structural and morphological changes were monitored by Raman spectroscopy and scanning electron microscopy (SEM). Implantation of Se at room temperature amorphized the near surface region of the SiC substrates, while in samples implanted above the critical amorphization temperature the crystal structure was retained with some radiation damage. Annealing at 1000 °C resulted in the recrystallization of the amorphized SiC layer. In the case of room temperature implantation, the broadening of the implanted Se profile in RBS spectra was observed to occur after annealing at 1300 °C and became significant with an increase in annealing temperature. This broadening was accompanied by a peak shift towards the surface and loss of implanted Se. No broadening was observed in samples implanted above the critical amorphization temperature, but the peak shift towards the surface began after annealing at 1300 °C in samples implanted at 350 °C and 600 °C.

Effect of sequential isochronal annealing on the structure and migration behaviour of selenium-ion implanted in glassy carbon

In a view to further study the diffusion properties of glassy carbon for its applicability as a diffusion barrier for fission products found in high-level nuclear waste, glassy carbon samples were implanted with 150 keV Se ions to a fluence of 1 × 1016 ion/cm2 at room temperature. Some of the implanted samples were subjected to sequential isochronal annealing at two temperature regimes (300–700 °C and 1000–1200 °C) for 5 h under vacuum. Raman spectroscopy was used to investigate the structural changes while Rutherford backscattering spectrometry (RBS) was used to monitor the migration of implanted Se. Implantation of Se amorphized glassy carbon resulting in an increase in density (from 1.42 to 2.1 gcm−3). No notable diffusion of Se in the glassy carbon occurred after annealing at the low-temperature regime (300–700 °C). Raman spectroscopy shows that limited recrystallization occurred after annealing at the low-temperature regime. Appreciable recrystallization coupled with some diffusion occurred at the high-temperature regime, 1000–1200 °C. The original structure of glassy carbon was not achieved after annealing at 1200 °C. Diffusion coefficients of 5.9 × 10−20 m2s−1 and 4.79 × 10−20 m2s−1 were obtained for Se in defective glassy carbon at 1000 and 1100 °C, respectively.

Migration behaviour of selenium implanted into polycrystalline 3C–SiC

The migration behaviour of selenium (Se) implanted into polycrystalline SiC was investigated using Rutherford backscattering spectrometry (RBS), scanning electron microscopy (SEM) and Raman spectroscopy. Se ions of 200 keV were implanted into polycrystalline SiC samples to a fluence of 1 × 1016 cm−2 at room temperature. The implanted samples were isochronal annealed in vacuum at two different regimes. Initially, the samples were annealed from 1000 to 1500 °C in steps of 100 °C for 10 h. Another set, at 1300 °C, 1350 °C and 1450 °C for 20 h. Implantation of Se at room temperature amorphized the near-surface region of the SiC substrate. Annealing at 1000 °C already resulted in the recrystallization of the amorphous SiC. The SEM images showed that the polishing marks became less visible after implantation due to the sputtering and swelling effects. These crystallites became larger and more visible with increase in annealing temperature. No diffusion was observed for annealing up to 1200 °C. Slight peak broadening indicating diffusion was observed after annealing at 1300 °C. This broadening increased with increase in annealing temperature. In the second set of annealing, the diffusion coefficients at 1300 and 1350 °C were estimated to be 6.3 × 10−21 and 2.0 × 10−20 m2 s−1, respectively.

Formation of ZnSe nanoclusters in the layers of silicon dioxide by high-fluence ion implantation and annealing

In this work we used the method of hot implantation of zinc and selenium ions into SiO2/Si structures in combination with subsequent heat treatment in order to form nanosized phases. Implantation modes for ionic synthesis chosen in such a way that the concentration of the embedded impurity is maximum approximately at the middle of the thickness of the dielectric layer. For the subsequent clustering of the impurity, it is necessary to create a high concentration of the implanted impurity at the maximum of the depth profile. The computer stimulation to select Implantation modes was carried out using the SRIM- 2013 program. Also we calculated the thickness of the silicon dioxide layer sprayed during high-dose implantation of zinc ions was. In this way, we have studied the formation of ZnSe precipitates in silicon dioxide by means of Zn (150 keV, 4×1016 cm−2) and Se (170 keV, 4×1016 cm−2) implantation at 550 °C and subsequent annealing at 1000 °C for 3 min. From analysis of XTEM images it has been showen that the use of hot implantation leads to the formation of small nanoclusters with sizes from 2 to 15 nm. Subsequent annealing results in the redistribution of nanoclusters within the implanted layer and the formation of large crystallites (up to 80 nm). To analyze the distribution of the introduced impurity throughout the sample depth the Rutherford backscattering (RBS) method was used. The band at 251-256 cm-1 associated with LO phonons of crystal ZnSe was registered in Raman spectra.

NMOS contact resistivity reduction with implants into silicides

AbstractNMOS contact resistivity (ρc) for NiPtSi was reduced by up to 50% by implanting either Se or P into the silicide film, followed by thermally recrystallizing the silicide and activating the implanted species. The silicide module integration included use of plasma pre‐clean, a thin NiPt film, a low temperature soak anneal (RTP1), and millisecond laser anneals for post‐implant anneals (RTP2 and RTP3). Additionally, experiments with Se implants into TiSi2 achieved 60% reduction in ρc with exclusive use of laser anneals (for both RTP1 and RTP2). The test structures included van der Pauw, transmission line model (TLM) and diodes, all of which are testable after silicidation to extract of silicide phase and sheet resistance (Rs), silicide/SD external resistance (Rext), ρc, and junction breakdown (Vbj). In order to mimic realistic CMOS process flows, contact chain structures testable after metal‐1 were also used to obtain average resistance/contact and extract contact resistivity. The results in this work demonstrated adequate process window, while maintaining junction characteristics without degradation of Rs. Laser anneal steps were key enabler to achieve these results, and were designed to prevent dopant deactivation while minimizing diffusion of SD regions for USJ compatibility for sub‐20 nm CMOS nodes. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Deep Energy Levels Formed by Se Implantation in Si

To transfer a photon with a 1.55μm wavelength into an electron in an integrated optoelectronic silicon waveguide detector, selenium-doped silicon with deep energy levels is used. The deep levels in the silicon with implanted selenium are studied. Three levels are observed and their captured cross sections, concentrations and in-depth profiles are measured.

Effective Schottky Barrier Height Reduction Using Sulfur or Selenium at the NiSi/n-Si (100) Interface for Low Resistance Contacts

We explore a novel integration approach that introduces valence-mending adsorbates such as sulfur (S) or selenium (Se) by ion implantation and prior to nickel silicidation for the effective reduction of contact resistance and Schottky barrier (SB) height at the NiSi/n-Si interface. While a low SB height of ~0.12 eV can be obtained for NiSi formed on S-implanted n-Si, the insertion of a 1000degC anneal prior to silicidation leads to S out-diffusion and loss of SB modulation effects. We demonstrate that Se-implanted Si does not suffer from Se outdiffusion even after a 1000degC anneal, and subsequent Ni silicidation formed an excellent ohmic contact with a low SB height of 0.13 eV. Se segregation at the NiSi/n-Si (100) interface occurred. Implantation of Se and its segregation at the NiSi/n-Si interface is a simple and promising approach for achieving reduced SB height and contact resistance in future high-performance n-channel field-effect transistors.

Memory effects in optically active CdSe nanocrystal doped MOS structures

We present a first study of the synthesis of CdSe nanocrystals embedded in 50 nm thick thermally grown SiO 2 on p-type silicon by sequential ion implantation of Cd (30 keV) and Se (26 keV) followed by a rapid thermal annealing step. A metal-oxide-semiconductor (MOS) capacitor structure was fabricated by evaporation of an optically transparent thin Au gate electrode on top of the nanocluster doped SiO 2 layer. The observed band edge emission of CdSe is fully intensity tuneable by applying a high electric field over the MOS structure. Strong hysteretic electric field enhancement and quenching of the photoluminescence (PL) was observed when sweeping the electric field strength between ±1 MV/cm. Further an electro optical memory effect was observed in this device and investigated upon its long time stability. Possible mechanisms for this behavior are discussed.

INFLUENCE OF ION IMPLANTATION ON OXIDATION BEHAVIOR OF TiAl

The influence of alloying elements on oxidation behavior of TiAl has been investigated using an ion-implantation technique and the mechanisms were discussed. The influence can be classified into several groups according to their effects. The implantation of β-forming elements, halogens, Cu and Zn results in a significant improvement of the oxidation behavior through formation of Al 2 O 3 layer in the initial stage of oxidation. The improvement by Zn is attributed to the formation of complex oxide of Zn and selective oxidation of Al beneath the layer. The implantation of Al , Si or P is also effective. On the other hand, implantation of Ag , Se and other several elements enhance the oxidation. The deterioration by Ag or Se is explained in terms of Al depletion in the implanted layer.

N-type ion implantation doping of AlxGa1−xAs (0⩽x⩽0.7)

Si-implant activation characteristics in AlxGa1−xAs for Al compositions of 0%–70% AlAs are presented for doses of 5.6×1012 and 2.8×1013 cm−2 at 100 keV. For both doses, the effective activation efficiency (ηeff) is relatively constant from 0% to 20% AlAs (ηeff=64% for 5.6×1012 cm−2 and 37% for 2.8×1013 cm−2 for 20% AlAs), goes through a minimum at 35% AlAs (ηeff=6.6% for 5.6×1012 cm−2 and 2.5% for 2.8×1013 cm−2), and then increases towards 70% AlAs (ηeff=52.8% for 5.6×1012 cm−2 and 31.1% for 2.8×1013 cm−2). The results are explained based on the compositional dependence of the ionization energy and conduction band density-of-states of AlGaAs. The effects of P coimplantation is also studied but demonstrates no significant enhancement of the activation efficiency of Si implantation for 0%–70% AlAs. Finally, data are presented for Se implantation in Al0.2Ga0.8As with a maximum effective activation efficiency of 5.6% achieved.

Ion-beam modification of ISFET membranes for copper ion detection

The sensibilization of a silicon-insulator system for Cu 2+ ion measurement is reported. This aim is realized by (i) coupling of sputtered arsenic selenide (As 2Se 3) layers to the insulator top layer and (ii) direct ion implantation of As, Se and Cu into the SiO 2 matrix. Conditions for the arsenic selenide ion-beam synthesis have been elaborated, consisting of alternating implantation at different energies and thermal treatment with short time pulses. Cu 2+ sensitivities near the theoretical value of 30 mV pCu − have been measured between pCu = 1 and pCu - 5.

Ion implantation effects in GaSb

The effects of ion implantation of Zn, Mg, Si, C, S and Se into n- and p-type GaSb have been studied. It is shown that low dose (5 × 10 13 cm −2) implantations of acceptor impurities, Zn, Mg and C at 60 keV are suitable for preparing good quality p-n GaSb diodes.

Characterization of vacancy-type defects in Se-implanted GaAs by means of a slow positron beam

Variable-energy (0–30 keV) positron beam studies have been carried out on 200 keV Se-implanted GaAs specimens before and after annealing for the electrical activation. From the measurements of Doppler broadened profiles of the positron annihilation as a function of the incident positron energy, it was found that vacancy clusters with high concentration were introduced especially in the annealed specimens after Se implantation. From the parallel measurement of electric characteristics, the higher activation efficiency was found to be obtained for the higher concentration of vacancy clusters. This fact implies that electrons supplied by the activation of Se also convert the charge state of As vacancies from positive to negative.

The Study of Si, Se and O-Implanted GaAs by Slow Positrons

ABSTRACTVariable-energy (0–30keV) positron beam studies have been carried out on 200 keV Se-implanted and 70 keV Si-implanted GaAs specimens before and after annealing for electrical activation. From the measurements of Doppler broadened profiles as a function of incident positron energy, it was found that vacancy clusters with high concentration were introduced in the annealed specimen after Se implantation. From the parallel measurement of electrical characteristics, a higher activation efficiency was found for the higher concentration of vacancy clusters. That fact implies that electrons supplied by the activation of Se also convert the charge state of As vacancies from positive to negative. In contrast, no vacancy clusters were introduced in the Si-implanted GaAs. On the other hand, oxygen clustering was found in annealed specimen after O implantation.

Damage induced in GaAs by high-energy Be, Si and Se implantation

Semi-insulating {100} GaAs wafers have been implanted with 3 MeV 9Be 2+, 7 MeV 28Si 2+ and 8 MeV 80Se 2+ ions to total doses ranging from 10 14 to 10 16 ions/cm 2 and the resulting damage has been profiled by channeling/Rutherford backscattering (RBS) spectroscopy with 5 MeV α-particles. The effect of different rapid thermal annealing (RTA) conditions has been studied. While it was possible to recover most of the original crystal structure, RTA processing could not eliminate a thin layer of secondary defects near the end of the projected range of the implanted ions. The density of defects after annealing has been calculated in the framework of a simple model and the depth profiles obtained by channeling/RBS have been compared with the profiles of chemically free as obtained by XPS, the secondary defects observed by XTEM and the vacancy distributions calculated by TRIM.

ChemInform Abstract: Luminescent Properties of Cadmium Sulfoselenide Electrodes Prepared by Ion Implantation.

AbstractInhomogeneous samples of n‐type CdSxSe1‐x are prepared by implantation of Se+ ions into single‐crystal n‐CdS substrates.

Luminescent Properties of Cadmium Sulfoselenide Electrodes Prepared by Ion Implantation

Inhomogeneous samples of n‐type have been prepared by implantation of Se+ ions into single‐crystal substrates. When thermally annealed, these samples exhibit photoluminescence (PL) and photoelectrochemical properties characteristic of alloy compositions. The spatial profile of Se has been examined by secondary ion mass spectroscopy (SIMS), electron microprobe analysis, and PL spectra, obtained after successive photoelectrochemical etching treatments. SIMS data indicate the presence of a Se‐containing surface layer, extending ∼0.5 μm into the sample with a peak Se content of about 50%. The PL spectra are dominated by contributions from compositions having up to ∼30% Se content. These samples can be used as photoanodes in photoelectrochemical cells (PEC's) employing aqueous, alkaline, (di) selenide electrolyte. Photoaction spectra are consistent with contributions from alloys of up to ∼35% Se content. The PL intensity of the samples is quenched in passing from open circuit (∼−1.5V vs. SCE) to a potential near short circuit (−1.0V), but the spectral distribution is unaffected. The electroluminescence (EL) of the samples, obtained in aqueous, alkaline, peroxydisulfate electrolyte, is similar to the PL in spectral distribution.

Optical Properties of Se+- and Zn+-Implanted GaAs: Photoluninescence Behavior at the Band-Edge

ABSTRACTIon implantation of Se+ and Zn+ ions into GaAs was carried out and characterization was performed by photoluminescence and Raman scattering at 2 K and room temperature, respectively. For comparison, implantation of Cd+ ions was also performed and further. a series of Si-doped GaAs samples were prepared by molecular beam epitaxy. In the Se+-implanted samples. with Se concentration between 1×1016 cm−3 and 5×1019 ca−3 the dominant radiative transition was the band-to-band emission, (B-B). No energy shift characteristic of (B-B) was observed but instead, the formation of a complex radiative center between donor impurities and implantation-induced damages, [D.LD] was revealed. This was in contrast to the Si-doped GaAs which displayed a pronounced energy shift of (B-B) towards higher energies with increasing Si concentration. The results suggest that (B-B) (reflecting the raising of the quasi Fermi-energy due to the increase of net free electron concentration) is significantly suppressed in the donor-ion implanted GaAs due to the presence of unremovable damages caused by implantation. In the Zn+ -implanted GaAs, the dominant emission was [g-g] which is formed just below the bound exciton emissions. The energy shift of [g-g] towards lower energies with increasing implanted Zn concentration was reproducibly observed. Thus clear differences in the PL spectra of donor- and acceptor-implanted samples were observed near the fundamental band edge. It was suggested that residual radiation damages suppress (B-B) but have little effect on acceptor-related emissions.