Vanadium Ion Implantation Research Articles

Vanadium supersaturated silicon system: a theoretical and experimental approach

The effect of high dose vanadium ion implantation and pulsed laser annealing on the crystal structure and sub-bandgap optical absorption features of V-supersaturated silicon samples has been studied through the combination of experimental and theoretical approaches. Interest in V-supersaturated Si focusses on its potential as a material having a new band within the Si bandgap. Rutherford backscattering spectrometry measurements and formation energies computed through quantum calculations provide evidence that V atoms are mainly located at interstitial positions. The response of sub-bandgap spectral photoconductance is extended far into the infrared region of the spectrum. Theoretical simulations (based on density functional theory and many-body perturbation in GW approximation) bring to light that, in addition to V atoms at interstitial positions, Si defects should also be taken into account in explaining the experimental profile of the spectral photoconductance. The combination of experimental and theoretical methods provides evidence that the improved spectral photoconductance up to 6.2 µm (0.2 eV) is due to new sub-bandgap transitions, for which the new band due to V atoms within the Si bandgap plays an essential role. This enables the use of V-supersaturated silicon in the third generation of photovoltaic devices.

Modifications of reactively sputtered titanium nitride films by argon and vanadium ion implantation: Microstructural and opto-electric properties

Polycrystalline titanium nitride (TiN) layers of 240nm thickness and columnar microstructure were deposited at 150°C by d.c. reactive sputtering on Si(100) wafers and then irradiated at room temperature with either 80keV V+ ions (at fluences of up to 2×1017ions/cm2) or 200keV Ar+ ions (at fluences of 5×1015–2×1016ions/cm2). Rutherford backscattering spectroscopy, cross-sectional (high-resolution) transmission electron microscopy and X-ray diffraction were used to characterize ion-induced changes in the structural properties of the films. Their optical and electric properties were analyzed by infrared reflectance (IR) and electric resistivity measurements. After deposition, the stoichiometric TiN films had a (111) texture. Ion implantation generated a damaged surface layer of nanocrystalline structure, which extended beyond the implantation profile, but left an undamaged bottom zone of (111) orientation. This layer geometry determined from transmission electron microscopy was inferred in the analysis of IR reflectance data using the Drude model, and the variation of the electric and optical resistivity with the irradiation was deduced. The results were compared to those recently gained for ion-implanted reactively sputtered chromium nitride films.

Microstructural and opto-electrical properties of chromium nitride films implanted with vanadium ions

We report on modifications of 280-nm thin polycrystalline CrN layers caused by vanadium ion implantation. The CrN layers were deposited at 150°C by d.c. reactive sputtering on Si(100) wafers and then implanted at room temperature with 80-keV V+ ions to fluences of 1×1017 and 2×1017 ions/cm2. Rutherford backscattering spectroscopy, cross-sectional transmission electron microscopy, and X-ray diffraction were used to characterize changes in the structural properties of the films. Their optical and electrical properties were analyzed by infrared spectroscopy in reflection mode and electrical resistivity measurements. CrN was found to keep its cubic structure under the conditions of vanadium ion implantation used here. The initially partially non-metallic CrN layer displays metallic character under implantation, which may be related to the possible formation of Cr1−x V x N.

Effects of vanadium ion implantation on microstructure, mechanical and tribological properties of TiN coatings

TiN coatings were deposited on the substrates of cemented carbide (WC–TiC–Co) by Magnetic Filter Arc Ion Plating (MFAIP) and then implanted with vanadium through Metal Vacuum Vapor Arc (MEVVA) ion source with the doses of 1×1017 and 5×1017 ions/cm2 at 40kV. The microstructures and chemical compositions of the V-implanted TiN coatings were investigated using Glancing Incidence X-ray Diffraction (GIXRD) and X-ray Photoelectron Spectroscopy (XPS), together with the mechanical and tribological properties of coatings were characterized using nano-indentation and ball-on-disk tribometer. It was found that the diffraction peaks of the V-implanted TiN coatings at the doses of 5×1017 ions/cm2 shifted to higher angles and became broader. The hardness and elastic modulus of TiN coatings increased after V ion implantation. The wear mechanism for both un-implanted and V-implanted TiN coatings against GCr15 steel ball was adhesive wear, and the V-implanted TiN coatings had a lower friction coefficient as well as a better wear resistance

Electrical and optical characteristics of vanadium in 4H-SiC

A semi-insulating layer is obtained in N-type 4H-SiC by vanadium-ion implantation. A little higher resistivity is obtained by increasing the annealing temperature from 1450 to 1650 °C. The resistivity at room temperature is as high as 7.6 × 106 Ω.cm. Significant redistribution of vanadium is not observed even after 1650 °C annealing. Temperature-dependent resistivity and optical absorption of V-implanted samples are measured. The activation energy of vanadium acceptor level is observed to be at about EC- 1.1 eV.

Enhancement of photocatalytic activity of P25 TiO 2 by vanadium-ion implantation under visible light irradiation

An ion-implantation method was used to prepare V-ion-implanted P25 TiO 2 photocatalysts. Their photocatalytic activity for the degradation of formic acid under visible light irradiation ( λ > 450 nm ) was investigated. Upon implantation of V ions into the lattice of P25 TiO 2, the photoactivity was remarkably enhanced. HRTEM images showed that the implanted V ions existed in the form of VO 2(T) in the lattice of P25 TiO 2. The intensity of photoluminescence (PL) spectra of V-ion-implanted P25 TiO 2 decreased with the increase of the amount of implanted V ions, indicating the decrease of electron–hole pair recombination. It was also observed that the lower the PL intensity of V-ion-implanted P25 TiO 2, the higher the photoactivity.

Modification of TiO2 photocatalytic films by V+ ion implantation

TiO2 photocatalytic films produced by the sol–gel method were modified by vanadium ion implantation. The absorption edge of the modified films was broadened from UV to visible region. The photo-degradation of methyl orange (MO) in aqueous solutions catalyzed by these films was found to vary with the amounts of implanted vanadium ions. The maximum degradation of MO was found for a V+ ion implantation fluence of 1×1016 ions/cm2.

IMPATT oscillation in SiC p+-n−-n+ diodes with a guard ring formed by vanadium ion implantation

SiC impact avalanche and transit time (IMPATT) diodes with a guard ring formed by vanadium ion implantation showed a peak output power of 1.8 W at 11.93 GHz. The guard ring reduced the electric field near the diode's periphery and reduced the device temperature.

Planar 6H-SiC MESFETs with vanadium implanted channel termination

We use vanadium ion implantation to form a highly resistive surface layer in the wide bandgap semiconductor silicon carbide (SiC). MESFETs are successfully fabricated using this highly resistive layer to isolate gate metal extensions along the channel width from the p-type epilayer. Fabrication and characterization of these devices are described in this paper.

Formation of semi-insulating 6H-SiC layers by vanadium ion implantations

Vanadium ion (V+) implantation has been successfully applied to the formation of semiinsulating 6H-SiC layers. The resistivity of V+-implanted layers strongly depended on the conduction type of initial 6H-SiC crystals. The resistivity at room temperature exceeded 1012 Ω cm and 106 Ω cm for p- and n-type samples, respectively. Compensation mechanism is discussed based on the temperature dependence of resistivity. This technique will be useful for device isolation, edge termination, and reduction of parasitic impedance of SiC devices.