Peter P. Murmu

Observation of magnetism, low resistivity, and magnetoresistance in the near-surface region of Gd implanted ZnO

Ferromagnetic order is observed in Gd ion implanted ZnO crystals after annealing at 650 °C in a vacuum and we find that it is intrinsic and extends to depths of up to 40 nm. The ferromagnetic order is not affected by Gd for concentrations as high as 5% and possibly arises from defect clusters. Magnetoresistance is observed at low temperatures that may be due to spin-tunnelling between the defect clusters or spin-dependent scattering at the defect cluster interfaces. Gd implantation has an advantageous effect where it results in mΩ cm resistivities as well as significant electron doping.

Enhanced Power Factor and Increased Conductivity of Aluminum Doped Zinc Oxide Thin Films for Thermoelectric Applications

We report the structural, electrical and thermopower properties of un-doped and Al doped zinc oxide (ZnO) thin films. Al doping was carried out using 25 keV Al+ implantation with 0.1, 1 and 2% Al into ZnO. X-ray diffraction measurements showed that the lattice parameters were larger than the bulk values, which is consistent with the incorporation of Al atoms at interstitials. Al doping increased the electrical conductivity from 100 (Ωcm)-1 in the un-doped ZnO film to 598 (Ωcm)-1 in the 2% Al doped ZnO film. Electron doping by Al resulted in an increase in the carrier concentration and it had an advantageous effect on the mobility where it was highest for 2% doping. The absolute value of the Seebeck coefficient systematically increased for un-doped, 1% and 2% Al doped ZnO films where the room temperature values were -50.8, -60.9 and -66.3 μV/K, respectively. The power factor increased significantly from 2.58 × 10-5 W/mK2 in un-doped ZnO film to 2.63 × 10-4 W/mK2 in 2% Al doped ZnO film. Our results suggest that the ion beam method is a suitable technique to enhance the thermoelectric properties of ZnO.

Microstructural, Electrical and Magnetic Properties of Erbium Doped Zinc Oxide Single Crystals

We report the structural, electrical and magnetic properties of erbium (Er) implanted zinc oxide (ZnO) single crystals. Rutherford backscattering and channeling results showed that the majority of Er atoms resided in Zn substitutional lattice sites. Annealing led to a fraction of Er atoms moving into random interstitial sites. Transmission electron microscopy micrographs revealed that doped Er atoms were located in the near-surface region, consistent with the results obtained from DYNAMIC-TRIM calculations. A non-linear Hall-voltage was observed near 100 K, which is associated with inhomogeneous transport in the material. The Er implanted and annealed ZnO exhibited persistent magnetic ordering to room temperature. Ferromagnetism was likely from the presence of intrinsic defects in ZnO, which mediates the magnetic ordering in Er implanted and annealed ZnO.

Characterization of the Structural and Electrical Properties of Ion Beam Sputtered ZnO Films

We report the structural and electrical properties of ion beam sputtered ZnO films vacuum annealed at varying temperatures. XRD results revealed that the films grow along the c-axis. The crystallite sizes increase from ~8 to ~30 nm upon annealing at 800 ºC. Annealing aided to recover the compressive strain and regain the standard lattice parameter values. The RMS surface roughness increased to ~5.0 nm after annealing at 800 ºC as observed in AFM micrographs. Increased resistivity on the annealed films suggested that the oxygen vacancies are compensated by de-trapped oxygen at grain boundaries.

Correlation between microstructural and magnetic properties of Tb implanted ZnO

We report the results from microstructural and magnetic measurements on 40 keV Tb implanted ZnO single crystals. RBS and channeling measurements for 6.7 × 1014 cm−2 implanted ZnO showed that around 85% of the Tb atoms occupied Zn substitutional lattice sites. Annealing at 650 °C had a small effect on the Tb location where only 81% of the Tb atoms were located at substitutional lattice sites. Energy-filtered TEM micrographs showed that the Tb atoms were located at an average depth of ∼15 nm. Raman spectroscopy results indicated that annealing resulted in a reduction in the implantation induced disorder in the ZnO lattice. Room temperature ferromagnetic order was observed in ZnO:Tb annealed at 650 °C. Superparamagnetic behavior was observed with an average blocking temperature of °40 K for high Tb concentrations and a distribution in the blocking temperature for low Tb concentrations.

Thermally stable device isolation by inert gas heavy ion implantation in AlGaN/GaN HEMTs on Si

Multiple energies of heavy ion implantation with inert-gas ion (84Kr+) were carried out on AlGaN/GaN high-electron-mobility transistors (HEMTs) for planar device isolation. Thermal stability of the implantated samples were also investigated by isochronal annealing at 500, 600, 700, and 800 °C (each temperature for 1 h.). Due to the damages created by heavy ions (84Kr+) in the GaN lattice, the implant-isolated Al0.27Ga0.73N/GaN HEMT samples exhibited better thermal stability than 40Ar+-implant-isolation. This was also confirmed by Rutherford backscattering spectrometry in channeling condition and ultraviolet micro-Raman spectroscopy measurements. With reference to mesa-isolated AlGaN/GaN HEMTs, the buffer breakdown voltage is also stable in the implant-isolated AlGaN/GaN HEMTs. An enhanced OFF-state breakdown voltage was also realized in the implant-isolated AlGaN/GaN HEMTs. The inert gas heavy ion implantation (84Kr+) is a viable solution for the fabrication of thermally stable planar AlGaN/GaN HEMTs even...

A novel radial anode layer ion source for inner wall pipe coating and materials modification—Hydrogenated diamond-like carbon coatings from butane gas

We report a new ion source development for inner wall pipe coating and materials modification. The ion source deposits coatings simultaneously in a 360° radial geometry and can be used to coat inner walls of pipelines by simply moving the ion source in the pipe. Rotating parts are not required, making the source ideal for rough environments and minimizing maintenance and replacements of parts. First results are reported for diamond-like carbon (DLC) coatings on Si and stainless steel substrates deposited using a novel 360° ion source design. The ion source operates with permanent magnets and uses a single power supply for the anode voltage and ion acceleration up to 10 kV. Butane (C4H10) gas is used to coat the inner wall of pipes with smooth and homogeneous DLC coatings with thicknesses up to 5 μm in a short time using a deposition rate of 70 ± 10 nm min(-1). Rutherford backscattering spectrometry results showed that DLC coatings contain hydrogen up to 30 ± 3% indicating deposition of hydrogenated DLC (a-C:H) coatings. Coatings with good adhesion are achieved when using a multiple energy implantation regime. Raman spectroscopy results suggest slightly larger disordered DLC layers when using low ion energy, indicating higher sp(3) bonds in DLC coatings. The results show that commercially interesting coatings can be achieved in short time.

Improved device isolation in AlGaN/GaN HEMTs on Si by heavy Kr + Ion implantation

GaN high-electron-mobility transistor (HEMT) based technology demonstrated excellent high-frequency, high microwave power and power switching device applications that exceeded the existing Si technology limits. Inter device isolation of GaN-based HEMTs are typically achieved with either plasma mesa etching or ion implantation. The advantage for the ion implantation-based isolation approach is that it can offer device planarity and thus improve the fabrication yield. In addition, the planarity will avoid the gate from touching the 2DEG channel at the mesa-sidewall thus reduces the gate leakage current. For device isolation, different ion species (N+, O+, Ar+, Fe+ and Zn+) have been utilized for AlGaN/GaN HEMTs [1-5]. Except Fe+, no ion species have been proven to maintain the high resistivity of the the GaN buffer layer after high-temperature annealing. Recently, Umeda et al. reported thermally stable device isolation by Fe+ implantation [5]. However, Fe+-ions may create deep levels. In this work, we have selected inert Kr+-ions which can provide heavy damage to the crystal lattice. As Kr+ has ~2×, ~1.5× and 1.2× heavier atomic mass than Ar+, Fe+, and Zn+ ions, respectively. it is expected that the heavy Kr+-ion induced lattice damages/disorders will be hard to recover completely by high-temperature thermal annealing. To investigate the thermal stability of Kr+ implant-isolation, we have investigated thermal stability of implant-isolated samples by isochronal annealing process. To-date, there are also very few reports on the effect of the blocking voltage of implant-isolated AlGaN/GaN HEMT structures with SiN passivation [2], which has significant impact on their high breakdown voltage characteristics. Hence, in this work, we have also investigated the influence of SiN passivation in the device isolation current (i.e. buffer leakage current, Ibuff) on implant-isolated and mesa-isolated devices.

Depth Profiling of N and C in Ion Implanted ZnO and Si Using Deuterium Induced Nuclear Reaction Analysis

Nuclear Reaction Analysis (NRA) with deuteron ion beams has been used to probe for ion implanted nitrogen and carbon with high sensitivity in zinc oxide and silicon single crystals. The ion implanted N was measured using 1.4 MeV deuteron ion beams and was found to be in agreement with calculated values. The limit of detection for N in ZnO is 8×1014 ions cm−2. Raman measurements of the ion implanted samples showed three additional modes at 275, 504, and 644 cm−1 compared to the un‐implanted ZnO crystals. The NRA and Raman results provided information on the N concentration, depth distribution, and structural changes that occur in dependence on the nitrogen ion fluences. The deuterium induced 12C(d,p)13C reaction was used to measure the carbon impurity/dose in ion implanted silicon. It was found that the use of a large cold shield (liquid nitrogen trap) in the ion implanter chamber greatly reduces the amount of carbon impurity on the surface of ion implanted silicon. Various implantations with N2, O2, NO, N...

Microstructure Evolution in Nitrogen Implanted Sapphire

Low-energy 14N+ ions were implanted with 23 keV under normal incidence into C-axis (0001) sapphire at room temperature. DYNAMIC-TRIM calculations were performed to calculate the N depth profiles for the various fluences from 1x1016 to 1017 cm-2. Electron Beam Annealing (EBA) was performed at a sample temperature of 700 °C for 10 min to allow the implanted and substrate atoms in the implanted layer to move to energetically preferable positions. Nuclear Reaction Analysis revealed the implanted nitrogen ion concentrations. Atomic Force Microscopy and Scanning Electron Microscopy show some nanostructures at the surface of the sapphire substrate exhibiting an average width of 139 ± 25 nm and height of 37 ± 7 nm using the lowest fluence of 1x1016 ions cm-2. Notably for samples implanted with the highest fluence of 1x1017 ions cm-2, bubble/holes like structures appeared after EBA due to out-diffusion of nitrogen that causes blistering and exfoliation effects.