A Novel Nitrogen Ion Implantation Technique for Turning Thin Film “Normally On” AlGaN/GaN Transistor into “Normally Off” Using TCAD Simulation

This study presents an innovative, low-cost, mass-manufacturable ion implantation technique for converting thin film normally on AlGaN/GaN devices into normally off ones. Through TCAD (Technology Computer-Aided Design) simulations, we converted a calibrated normally on transistor into a normally off AlGaN/GaN transistor grown on a silicon <111> substrate using a nitrogen ion implantation energy of 300 keV, which shifted the bandgap from below to above the Fermi level. In addition, the threshold voltage (Vth) was adjusted by altering the nitrogen ion implantation dose. The normally off AlGaN/GaN device exhibited a breakdown voltage of 127.4 V at room temperature because of impact ionization, which showed a positive temperature coefficient of 3 × 10−3 K−1. In this study, the normally off AlGaN/GaN device exhibited an average drain current gain of 45.3%, which was confirmed through an analysis of transfer characteristics by changing the gate-to-source ramping. Accordingly, the proposed technique enabled the successful simulation of a 100-µm-wide device that can generate a saturation drain current of 1.4 A/mm at a gate-to-source voltage of 4 V, with a mobility of 1487 cm2V−1s−1. The advantages of the proposed technique are summarized herein in terms of processing and performance.

Effect of Nitrogen Ion Implantation Energy on the Mechanical and Chemical Properties of AISI M50 Steel

Nitrogen ion implantation has shown its role in enhancing steel surface properties. In this work, AISI M50 steel was implanted with nitrogen ions by using the metal vapor vacuum arc technique with a dose of 2 × 1017 cm−2, and corresponding implanted energies were at 60 keV, 80 keV, and 100 keV, respectively. The distribution of implanted nitrogen ions was calculated, and the samples were tribologically tested and examined. As shown by the results, the microhardness in implanted samples was 1.17 times greater relative to that of the unimplanted sample. The implantation of the nitrogen ion leads to a change in the friction coefficient of the AISI M50 steel. Adhesive wear mechanism occurs in the unimplanted sample, and adhesion resistance tends to increase when nitrogen-implanted energy increases. The formation of oxides α-Fe2O3 and Fe3O4 further enhanced the tribological properties for implanted samples.

Effect of Low-Energy Nitrogen Ion Implantation on Friction and Wear Properties of Ion-Plated TiC Coating

To further improve the performance of the coated tools, we investigated the effects of low-energy nitrogen ion implantation on surface structure and wear resistance for TiC coatings deposited by ion plating. In this experiment, an implantation energy of 40 keV and a dose of 2 × 1017 to 1 × 1018 (ions/cm2) were used to implant N ions into the TiC coatings. The results indicate that the surface roughness of the coating increases first and then decreases with the increase of ion implantation dose. After ion implantation, the surface of the coating will soften and reduce the hardness, and the production of TiN phase will gradually increase the hardness. Nitrogen ion implantation can reduce the friction coefficient of the TiC coating and improve the friction performance. In terms of wear resistance, the coating with an implant dose of 1×1018 ions/cm2 has the greatest improvement in wear resistance. Tribological analysis shows that the improvement in the performance of TiC coatings implanted with N ions is mainly due to the effect of the lubricating implanted layer. The implanted layer mainly exists in the form of amorphous TiC, TiN phase, and sp2C–C phase.

Effect of Nitrogen Ion Implantation on the Cavitation Erosion Resistance and Cobalt-Based Solid Solution Phase Transformations of HIPed Stellite 6

From the wide range of engineering materials traditional Stellite 6 (cobalt alloy) exhibits excellent resistance to cavitation erosion (CE). Nonetheless, the influence of ion implantation of cobalt alloys on the CE behaviour has not been completely clarified by the literature. Thus, this work investigates the effect of nitrogen ion implantation (NII) of HIPed Stellite 6 on the improvement of resistance to CE. Finally, the cobalt-rich matrix phase transformations due to both NII and cavitation load were studied. The CE resistance of stellites ion-implanted by 120 keV N+ ions two fluences: 5 × 1016 cm−2 and 1 × 1017 cm−2 were comparatively analysed with the unimplanted stellite and AISI 304 stainless steel. CE tests were conducted according to ASTM G32 with stationary specimen method. Erosion rate curves and mean depth of erosion confirm that the nitrogen-implanted HIPed Stellite 6 two times exceeds the resistance to CE than unimplanted stellite, and has almost ten times higher CE reference than stainless steel. The X-ray diffraction (XRD) confirms that NII of HIPed Stellite 6 favours transformation of the ε(hcp) to γ(fcc) structure. Unimplanted stellite ε-rich matrix is less prone to plastic deformation than γ and consequently, increase of γ phase effectively holds carbides in cobalt matrix and prevents Cr7C3 debonding. This phenomenon elongates three times the CE incubation stage, slows erosion rate and mitigates the material loss. Metastable γ structure formed by ion implantation consumes the cavitation load for work-hardening and γ → ε martensitic transformation. In further CE stages, phases transform as for unimplanted alloy namely, the cavitation-inducted recovery process, removal of strain, dislocations resulting in increase of γ phase. The CE mechanism was investigated using a surface profilometer, atomic force microscopy, SEM-EDS and XRD. HIPed Stellite 6 wear behaviour relies on the plastic deformation of cobalt matrix, starting at Cr7C3/matrix interfaces. Once the Cr7C3 particles lose from the matrix restrain, they debond from matrix and are removed from the material. Carbides detachment creates cavitation pits which initiate cracks propagation through cobalt matrix, that leads to loss of matrix phase and as a result the CE proceeds with a detachment of massive chunk of materials.

Effect of Nitrogen Ion Implantation on the Cavitation Erosion Resistance and Cobalt-Based Solid Solution Phase Transformations of HIPed Stellite 6

From the wide range of engineering materials traditional Stellite 6 alloy exhibits excellent cavitation erosion (CE) resistance. In this work, the effect of nitrogen ion implantation of HIPed Stellite 6 on the improvement of CE resistance and both cobalt-rich matrix phase transformation due to nitrogen implantation and CE were stated. The CE resistance of stellites ion-implanted by 120 keV N+ ions two fluences: 5x1016 cm-2 and 1x1017 cm-2 were comparatively analysed with the unimplanted stellite and AISI 304 stainless steel. CE tests were conducted according to ASTM G32 with stationary specimen method. Erosion rate curves and mean depth of erosion confirm that the nitrogen implanted HIPed Stellite 6 two times exceeds the resistance to CE than unimplanted stellite, and has almost 10 times higher CE reference than stainless steel. The X-ray diffraction (XRD) confirms that HIPed Stellite 6 nitrogen ion implantation favours transformation of the ɛ(hcp) to &gamma;(fcc) structure. Unimplanted stellite ɛ-rich matirx is less prone to plastic deformation than &gamma; and consequently, increase of &gamma; phase effectively holds carbides in cobalt matrix and prevents Cr7C3 debonding. This phenomenon elongates three times the CE incubation stage, slows erosion rate and mitigates the material loss. Metastable &gamma; structure formed by ion implantation consumes the cavitation load for work-hardening and &gamma; &rarr; ɛ martensitic transformation. In further CE stages, phases transform as for unimplanted alloy namely, the cavitation-inducted recovery process, removal of strain, dislocations resulting in increase of fcc phase. The CE mechanism was investigated using a surface profilometer, atomic force microscopy, SEM-EDS and XRD. HIPed Stellite 6 wear behaviour relies on the plastic deformation of cobalt matrix, starting at Cr7C3/matrix interfaces. Once the Cr7C3 losing their restrain, are debonding and removed. Carbides detachment creates cavitation pits which initiate cracks propagation through cobalt matrix, the loss of matrix phase and CE proceeds with a detachment of massive chunk of materials.

N+-ion implantation induced enhanced conductivity in polycrystalline and single crystal diamond

The paper highlights the effect of nitrogen ion implantation on polycrystalline and single crystal diamond where we try to explain its structural and electrical transport behaviour in three different ion dose regimes: low, medium and high fluence respectively.