Dose Of Si Ions Research Articles

Electrical performance study of Schottky barrier diodes using ion implanted β-Ga2O3 epilayers grown on sapphire substrates

β-Ga2O3 epilayers with a 210 nm thickness were successfully grown on c-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD). Highly resistive unintentionally doped (UID) epilayers are studied, as are Si ion-implantated samples with doses of 1✕1014, 6✕1014 and 1✕1015 cm−2 at 30 keV to improve β-Ga2O3 epilayer conductivity. Schottky barrier diodes (SBDs) were fabricated using optimized growth parameters and electrical measurements performed for both UID and Si-implanted β-Ga2O3 material. The forward current density (J) of an UID SBD at 2 V was 62 nA/cm2 with breakdown voltage (Vbr) of 1.03 kV and leakage J of 10 μA/cm2. The forward J improved by eight orders of magnitude after Si implantation. In this case, Vbr reduced to 680 V combined with a high leakage J of ∼A/cm2 for doses of 1✕1015cm−2. A hard breakdown of 553 V was achieved with a Si-ion dose of 1✕1014 cm−2 with comparatively less leakage than samples with higher dose amounts.

Ion implantation effects on the characteristics of β-Ga2O3 epilayers grown on sapphire by MOCVD

In this study, the Si-ions implantation technique with different doses from 1 × 1014 to 1 × 1015 cm−2 and dose energy 30, 40 and 50 keV was used to tune the electrical properties in unintentionally doped (UID) β-Ga2O3 epilayers grown on the sapphire substrates by metalorganic chemical vapor deposition (MOCVD). A high quality UID β-Ga2O3 epilayers were fabricated using the optimized growth parameters of MOCVD. The UID and Si-ions implanted β-Ga2O3 epilayers were examined and results were compared with the help of X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. Si-ions implantation parameters were also simulated by stopping and range of ions in matter software (SRIM) and actual Si-ions concentration was measured by secondary ions mass spectroscopy. The electrical properties of the implanted β-Ga2O3 epilayers were measured by transmission length method and Hall measurements. The sheet resistivity for the β-Ga2O3epilayers with Si-ion dose of 1 × 1014, 6 × 1014 and 1 × 1015 cm−2 were found as 2.047, 0.158 and 0.144 Ω cm, respectively measured by Hall measurements and the electron carrier concentrations for the above doses were 4.39 × 1018, 6.86 × 1018 and 7.98 × 1019 cm−3. From the above results, the ion implantation was demonstrated to effectively reduce the resistivity with the high carrier concentrations.

Synthesis, Characterization and Wettability of Cu-Sn Alloy on the Si-Implanted 6H-SiC

The wettability of the metal/SiC system is not always excellent, resulting in the limitation of the widespread use of SiC ceramic. In this paper, three implantation doses of Si ions (5 × 1015, 1 × 1016, 5 × 1016 ions/cm2) were implanted into the 6H-SiC substrate. The wetting of Cu-(2.5, 5, 7.5, 10) Sn alloys on the pristine and Si-SiC were studied by the sessile drop technique, and the interfacial chemical reaction of Cu-Sn/SiC wetting couples was investigated and discussed. The Si ion can markedly enhance the wetting of Cu-Sn on 6H-SiC substrate, and those of the corresponding contact angles (θ) are raised partly, with the Si ion dose increasing due to the weakening interfacial chemical reactions among four Cu-Sn alloys and 6H-SiC ceramics. Moreover, the θ of Cu-Sn on (Si-)SiC substrate is first decreased and then increased from ~62° to ~39°, and ~70° and ~140°, with the Sn concentration increasing from 2.5%, 5% and 7.5% to 10%, which is linked to the reactivity of Cu-Sn alloys and SiC ceramic and the variation of liquid-vapor surface energy. Particularly, only a continuous graphite layer is formed at the interface of the Cu-10Sn/Si-SiC system, resulting in a higher contact angle (>40°).

Sleep Fragmentation Exacerbates Executive Function Impairments Induced by Low Doses of Si Ions.

Astronauts on deep space missions will be required to work autonomously and thus their ability to perform executive functions could be critical to mission success. Ground-based rodent experiments have shown that low (<25 cGy) doses of several space radiation (SR) ions impair various aspects of executive function. Translating ground-based rodent studies into tangible risk estimates for astronauts remains an enormous challenge, but should similar neurocognitive impairments occur in astronauts exposed to low-SR doses, a Numbers-Needed-to-Harm analysis (of the rodent data) predicts that approximately 30% of the astronauts could develop severe cognitive flexibility decrements. In addition to the health risks associated with SR exposure, astronauts have to contend with other stressors, of which inadequate sleep quantity and quality are considered to be major concerns. We have shown that a single session of fragmented sleep uncovered latent attentional set-shifting (ATSET) performance deficits in rats exposed to protracted neutron radiation that had no obvious defects in performance under rested wakefulness conditions. It is unclear if the exacerbating effect of sleep fragmentation (SF) only occurs in rats receiving protracted low-dose-rate-neutron radiation. In this study, we assessed whether SF also unmasks latent ATSET deficits in rats exposed to 5 cGy 600 MeV/n 28Si ions. Only sham and Si-irradiated rats that had good ATSET performance (passing every stage of the test on their first attempt) were selected for study. Sleep fragmentation selectively impaired performance in the more complex IDR, EDS and EDR stages of the ATSET test in the Si-irradiated rats. Set-shifting performance has rarely been affected by SR exposure in our studies conducted with rats tested under rested wakefulness conditions. The consistent SF-related unmasking of latent set-shifting deficits in both Si- and neutron-irradiated rats suggests that there is a unique interaction between sleep fragmentation and space radiation on the functionality of the brain regions that regulate performance in the IDR, EDS and EDR stages of ATSET. The uncovering of these latent SR-induced ATSET performance deficits in both Si- and neutron-irradiated rats suggests that the true impact of SR-induced cognitive impairment may not be fully evident in normally rested rats, and thus cognitive testing needs to be conducted under both rested wakefulness and sleep fragmentation conditions.

Effects of silicon ion irradiation on the interface properties of SiCf/SiC composites

Continuous silicon carbide fiber–reinforced silicon carbide matrix composites (SiCf/SiC) are promising candidate materials for nuclear applications. In this paper, three–dimensional SiCf/SiC composites were fabricated using polymer infiltration and pyrolysis method. Interface properties of SiCf/SiC composites that were irradiated with 3MeV Si ions to 1dpa and 5dpa at room temperature were studied using single-fiber push–out test, Raman spectroscopy, and transmission electron microscopy. Results indicate that, after being irradiated with different doses of Si ions, SiCf/SiC composites have weaker interfacial shear strength compared to that of samples before irradiation. The greater that the ion irradiation damage is, the lower that the interfacial shear strength is. With an increase in ion irradiation dose, the strength of the disordered (D) and graphitic (G) characteristic peaks in Raman spectra of SiCf/SiC composite decreases, and full width at half–maximum broadens. TEM micrographs show that ion irradiation damaged the continuity of SiCf/SiC composites, and microcracks appeared at pyrocarbon interface between the fiber and matrix. The crystallinity of SiC was lowered, the grain size shrank, and the ordered C phase became amorphous noncrystalline structure.

Effects of high-energy Si ion-irradiations on optical responses of Ag metal nanoparticles in a SiO2 matrix

Optical responses of pristine Ag metal nanoparticles in a SiO2 matrix have changed drastically upon high-energy Si ion-irradiations. Systematic blueshifts of the quantum surface plasmon resonances and concomitant decrease in the optical absorption resonance intensities with increase of ion dose of Si ions are thought to be due to decrease in size of Ag nanoparticles. Observed shrinking of sizes of Ag metal nanoparticles due to irradiation effects of high-energy Si ions has been elucidated using model calculations. Transmission electron microscopy as well as Raman scattering spectroscopy confirms decrease in size of Ag nanoparticles caused by the Si ion-irradiations.

Relative enhancement of photoluminescence intensity of passivated silicon nanocrystals in a silicon dioxide matrix

Photoluminescence (PL) intensity of passivated silicon nanocrystals (Si NCs) embedded in a SiO2 matrix is compared with that of unpassivated Si NCs. We investigate the relative enhancement of PL intensity (IR) as a function of annealing temperature and implanted Si ion dose. The IR increases simultaneously with the annealing temperature. This demonstrates an increase in the number of dangling bonds (DBs) with the degree of Si crystallization varying via the annealing temperature. The increase in IR with implanted Si ion dose is also observed. We believe that the near-field interaction between DBs and neighboring Si NCs is an additional factor that reduces the PL efficiency of unpassivated Si NCs.

Influence of implantation dose on electroluminescence from Si-implanted silicon nitride thin films

Strong visible electroluminescence (EL) with electrically tunable colors from violet to white has been observed from Si-implanted silicon nitride thin films. Influence of the implanted Si ion dose on both the current conduction and EL properties has been studied. With a larger excess Si concentration, the carrier transport is enhanced leading to a higher EL intensity, but the light emission efficiency is reduced. On the other hand, the increase of the excess Si concentration causes redshifts in the major EL bands and improves the transition of the EL colors with increasing current. The excess Si concentration is also found to have a significant influence on the EL degradation. These findings are important to the application of the Si-implanted thin films in light emitting devices.

Si nanoclusters generated in Si-SiO2 structures implanted with different doses of Si ions

Topography changes of a SiO2 surface and formation of Si nanoclusters, induced by high-energy electron irradiation of ion implanted Si-SiO2 structures, are studied by atomic force microscopy (AFM) measurements. Si ions with energy of 15 KeV and doses of 1012 or 1016 cm−2 are implanted in the Si-SiO2 structures with an oxide thickness of 20 nm. The ion energy is chosen to produce maximum ion damage at the Si-SiO2 interface. Some of the implanted samples are simultaneously irradiated by 20 MeV electrons with a flux of about 1×1015 cm−2. AFM measurements indicated that the SiO2 topography does not vary significantly only due to the ion-implantation. Si nanoclusters are observed in a SiO2 layer after MeV electron irradiation. The measurements show that the size and shape of the Si nanoclusters depend significantly on the dose of the previously implanted ions.

Radiation effect on the photoluminescence properties of Si/SiO2 thin films

Silicon ions were implanted into SiO2 thin films with various doses and energies. For the films implanted with various ion doses the photoluminescence (PL) intensity of 470nm firstly increased with the increase of Si ion dose, which is similar to the variation trend of displacement per atom (DPA) number during ion radiation. Further increasing Si ion dose the PL intensity of 470nm decreased gradually since the neutral oxygen vacancy centers were destroyed. For the samples implanted with different energy the variation trend of PL intensity for 470nm peak is similar to the result of DPA under different radiation energy according to SRIM2006 simulation. With the increase of radiation energy a new PL peak at 550nm appeared because of the variation of defect type. Combining with the simulation results and PL spectra the radiation effect on Si/SiO2 thin films were proposed.

Formation of light-emitting Si nanostructures inSiO2 by pulsed anneals

Intense excimer laser pulses, flash lamp annealing and rapidthermal annealing were used to form Si nanocrystals in thinSiO2 layers implanted with high doses of Si ions. The pulse durations were20 ns, 20 ms and 1 s, respectively. Laser annealing produced light sourcesluminescing in the wavelength range of 400–600 nm. They were attributed to theSi clusters formed as a result of the fast segregation of Si atoms from theSiO2 network. There were no indications of nanocrystal formation in the as-implanted layersafter 20 ns laser pulses; however, nanocrystals formed when, before the laser annealing, theamorphous Si nanoprecipitates were prepared in the oxide layers. Evaluations show thatthe crystallization may proceed via melting. A photoluminescence band near 800 nm,typical of Si nanocrystals, was found after 20 ms and 1 s anneals. Calculationsrevealed that the annealing times in both cases were too short to provide thediffusion-limited crystal growth if one uses the values of stationary Si diffusivity inSiO2. This points toward the existence of a transient rapid growth process at the very beginningof the anneals.

The influence of the implantation dose and energy on the electroluminescence ofSi+-implantedamorphous SiO2 thin films

Visible and infrared (IR) electroluminescence (EL) has been observed from ametal–oxide–semiconductor-like (MOS-like) structure with Si nanocrystals (nc-Si) embedded inthe gate oxide fabricated with low-energy ion implantation. The EL spectra are found toconsist of four Gaussian-shaped luminescence bands with their peak wavelengths at∼460,∼600,∼740, and∼1260 nm, respectively,among which the ∼600 nm band is the dominant one. Different nanocrystal distributions are achieved by varyingthe implanted Si ion dose and implantation energy. The nanocrystal distribution is foundto play an important role in the EL. The influence of the applied voltage, theimplantation dose, and implantation energy on the luminescence bands has beeninvestigated.

Impact of Si+ implantation on reduction of contact resistance in Ti/Al contact to GaN

AbstractFor the Ti/Al contact to n‐type GaN, the impact of Si+ implantation on the reduction of contact resistance is investigated. The undoped GaN, grown on the sapphire substrate, is implanted by Si ions with the energy of 150 keV at the dose ranging from 5 x 1013 to 5 x 1014/cm2 and subsequently annealed at 1200 °C for 1 min in N2 gas flow. For the Ti(50 nm)/Al(200 nm) contacts annealed at 550 and 600 °C, as Si ion dose is increased, the specific contact resistance is decreased with the Schottky barrier height of 0.27 eV. The Ti/Al contact annealed at 600 °C reveals the exteremly low contact resistance as low as 1.2 x 10–7 Ωcm2 for the Si ion dose of 5 x 1014/cm2. Ti/Al contact annealed above 700 °C shows Rc in the order of 10–6 Ωcm2 even though Si ion dose increases. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Studies on the surface swelling of ion-irradiated silicon: Role of defects

Low-energy (keV) Si ions are implanted on mask-pattered Si wafer at doses above amorphization threshold for a variety of implantation conditions (ion dose, energy, temperature) and post-implantation annealing. Precise measurement of the surface swelling (step-height) on the amorphous Si layer was carried out using an atomic force microscope (AFM). Thickness and microstructure of the ion-damaged layer was evaluated by transmission electron microscopy (TEM) measurements. The measured step-height in excess to that contributed by implanted ions shows a cube root dependence on the Si ion dose. The swelling heights studied for two different energies of Si ions show identical step-heights. Implantation at low temperature (77 K) shows a reduced step-height, indicating possible contribution of migrated Si atoms in the swelling. We propose that excess swelling is caused by migration and segregation of the displaced Si atoms from the bulk to the surface leaving behind corresponding vacancies in the lattice. Ellipsometric studies of the similarly damaged layer profile provide supporting evidence for surface segregation of Si atoms over the amorphous layer.

Fabrication and electrical characteristics of Ti/Al ohmic contact to Si+ implanted GaN

AbstractTi/Al ohmic contact with an extremely low specific contact resistance has been formed by the deposition of Ti and Al films on Si+ lanted GaN. The ohmic contact formed by annealing at 600 o C of Ti film with a thickness of 50 nm and Al film with a thickness of 200 nm reveals the good smooth surface and uniform structure as compare to those of contacts formed above 700 °C, which is correlated to whether the Al-Ti alloy is melted during the annealing of ohmic contact or not. The specific contact resistance of 2 × 10-6Ω-cm2 is obtained for Si+ implanted GaN with a dose of 5 × 1013 cm-2. As Si ion dose increases to 5 × 1014 /cm2, the specific contact resistance is reduced to 2 × 10-8 Ω-cm2. It is revealed that the selective doping at high impurity concentration in the surface region by Si+ implantation is useful to reduce the contact resistance for Ti/Al contact to GaN.

Spectral responsivity and quantum efficiency of n-ZnO/p-Si photodiode fully isolated by ion-beam treatment

We report on the fabrication of a heterojunction photodiode for the visible range that consists of a transparent insulating ZnO overlayer and a transparent semiconducting n-ZnO layer on p-Si. For device isolation, we implanted Si+ ions into the n-ZnO layer. We have obtained a wide-range spectral responsivity curve for our isolated photodiodes, which showed a maximum quantum efficiency of 70% at 650 nm and a minimum of 10% at 420 nm. However, they exhibited an efficiency drop at 380 nm in the near-ultraviolet because the ZnO layers absorbed the photons of higher energy before they reached p-Si. The ion-beam-induced isolation considerably reduced dark leakage currents in our devices when the dose of Si ions was as high as 5×1015 cm−2.

The modification behaviour for Si implanted PET

Polyethylene terephthalate (PET) has been modified by Si ion implantation with a dose ranging from 1 × 10 16 to 2 × 10 17 ions /cm 2 using a metal vapor vacuum arc（MEVVA）source. The surface morphology was observed by atomic force microscopy (AFM). The change in the microstructure of Si implanted PET was observed with a transmission electron microscope (TEM). It is believed that the change would improve the conductive properties and wear resistance. The electrical properties of PET have been improved via Si ion implantation. The resistivity of implanted PET decreased obviously with an increase in ion dose. When Si ion dose was 2 × 10 17 cm -2 , the resistivity of PET could be less than 7.9 W·m. The surface hardness and modulus increased obviously. The mechanical property of the implanted PET has been modified greatly. The hardness and modulus of Si implanted PET with a dose of 2 × 10 17 /cm 2 are 12.5 and 2.45 times greater than those of pristine PET, respectively. The area of cutting groove for Si implanted PET is narrower and shallower than those of the unimplanted PET. So the wear resistance is greatly raised. In comparison with metal ion implantation, the improvement of mechanical properties is obvious in ion implantation into PET. Si ion beam modification mechanism of PET is discussed.

Erbium-doped optical waveguide materials based on Si nanocrystals formed bymetal vapour vacuum arc ion implantation

Dual implantation of erbium and silicon into thermally grown SiO2 film on Siwas performed using a metal vapour vacuum arc ion source; this wasfollowed by rapid thermal annealing at 500–1100°C for 20 s. 1.54 μ mphotoluminescence (PL) was observed at 77 K. Rutherford backscatteringspectrometry shows that Er ions mainly distribute within 80 nm of thesurface. The highest Er peak concentration obtained exceeded 5 × 1021 cm−3,which is the highest Er concentration reported in Si-based materials.Transmission electron microscopy demonstrates that nanocrystallinesilicon (nc-Si) embeds in SiO2 matrices. The Er3 + excitation energy isobtained from the electron–hole pairs nonradiatively combining at defectsand impurities in SiO2 matrices or at the interface of the nc-Si/SiO2(or c-Si/SiO2), and energy transferring to Er3 + ions results in 1.54 μ mlight emission. The dependence on the Si-ion dose and annealing temperature ofthe PL intensity has also been investigated.

Optimum silicon ion dose for 1540 nm photoluminescence from erbium-doped silica thin films formed by MEVVA implantation

In this work, SiO 2 thin films containing Er and Si nanocrystals were prepared by implantation with a metal vapor vacuum arc (MEVVA) ion source. Photoluminescence (PL) properties of the films at 77 K and at room temperature (RT) were studied as functions of the Si ion dose. The PL intensities were strongly enhanced by the incorporation of nanocrystalline Si (nc-Si) in the SiO 2 films. The intensity of the 1.54 μm luminescence peak first increased with increasing Si dose, arriving at a maximum at a Si dose of 5×10 17 cm −2, then decreased with further increase in Si dose. These results are discussed and understood in terms of the role of nc-Si in Er luminescence mechanisms in silica containing nc-Si.

The Influence of Annealing Temperature and Doping on the Red/Near-Infrared Luminescence of Ion Implanted SiO2:nc-Si

AbstractThe results of an experimental research of the dependence of photoluminescence (PL) intensity in region about 800 nm for silicon nanoinclusions (quantum dots) obtained by Si ion implantation in SiO2 on the dose of Si ions at two temperatures of an annealing ?ann = 1000 and 1100° ? are presented. It is established that in both cases the dependences have the shape of the curves with a maximum. For 1100° ? the maximum is shifted to the lower dose. The influence of an additional ion doping by the phosphorus on intensity of PL is investigated depending on the dose (concentration) of P and the dose of the silicon at ?ann = 1000° ?. It is shown, that in all the investigated region of P doses, the presence of P enhances the PL. The degree of the enhancement increases with the P dose, but the rate of the intensity enhancement goes down. With the growth of Si dose at the constant dose of P, the degree of the enhancement decreases. In an approximation of an effective mass, the energy spectra of a quantum dot are calculated at the presence of one or several P atoms for various their arrangement.