Mg-doped p-type gallium nitride (GaN) layers with doping concentrations in the range from 6.5 × 1016 cm−3 (lightly doped) to 3.8 × 1019 cm−3 (heavily doped) were investigated by Hall-effect measurement for the analysis of hole concentration and mobility. p-GaN was homoepitaxially grown on a GaN free-standing substrate by metalorganic vapor-phase epitaxy. The threading dislocation density of p-GaN was 4 × 106 cm−2 measured by cathodoluminescence mapping. Hall-effect measurements of p-GaN were carried out at a temperature in the range from 130 to 450 K. For the lightly doped p-GaN, the acceptor concentration of 7.0 × 1016 cm−3 and the donor concentration of 3.2 × 1016 cm−3 were obtained, where the compensation ratio was 46%. We also obtained the depth of the Mg acceptor level to be 220 meV. The hole mobilities of 86, 31, 14 cm2 V−1 s−1 at 200, 300, 400 K, respectively, were observed in the lightly doped p-GaN.

We present a vertical GaN planar metal-oxide-semiconductor field-effect transistor (MOSFET) fabricated by an all ion implantation process. The fabricated MOSFET shows an on-resistance of 2.78 mΩ cm 2 and a breakdown voltage of 1200 V, by applying the short cell pitch design to reduce the on-resistance and a Mg and N sequential implantation to improve the breakdown voltage of the pn-junction. By evaluating each on-resistance component in the fabricated vertical GaN planar MOSFET using the simultaneously formed test structures, an effective on-resistance of the active region excluding the source parasitic resistance is 1.4 mΩ cm 2 . Consequently, it was demonstrated that an all ion implantation process can fabricate a vertical GaN planar MOSFET with a high breakdown voltage and low on-resistance. This result will greatly contribute to the realization of GaN power devices.

The Hall effect is investigated for eight superconducting Fe(Se 0 (typically T c > 9 K), R H leaves almost unchanged down to T ≈ 100 K, and then starts decreasing toward a negative side. Around the temperatures when R H changes its sign from positive to negative, obvious nonlinearity is observed in the field-dependence of Hall resistance as to keep the low-field R H positive while the high-field R H negative. Thus the electronic state just above T c is characterized by n e (electron density) > n h (hole density) with keeping µ e < µ h . These results suggest the dominance of electron density to the hole density is an essential factor for the occurence of superconductivity in Fe-chalcogenide superconductors..

FeSe0.5Te0.5 thin films with a PbO-type structure are successfully grown on MgO(100) and LaSrAlO4(001) substrates from FeSe0.5Te0.5 or FeSe0.5Te0.75 polycrystalline targets by pulsed laser deposition. The film deposited on the MgO substrate (film thickness: ∼55 nm) shows superconductivity at 10.6 K (onset) and 9.2 K (zero resistivity). On the other hand, the film deposited on the LaSrAlO4 substrate (film thickness: ∼250 nm) exhibits superconductivity at 5.4 K (onset) and 2.7 K (zero resistivity). This suggests the strong effect of substrate materials and/or the c-axis length on the superconducting properties of FeSe0.5Te0.5 thin films.

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Lateral GaN double-implanted MOSFETs (DIMOSFETs) on Mg ion implanted GaN layers with different Mg ion implantation doses have been evaluated to investigate the impact of Mg dose on MOS channel properties. It is demonstrated that the threshold voltage (Vth) and the field effect mobility (μfe) depend on the Mg dose. A maximum μfe of 173 cm2 V−1 s−1 has been obtained with a Vth of 2.2 V on the Mg implantation layer with a dose of 4.2 × 1013 cm−2. The obtained results indicate that the channel characteristics of a GaN DIMOSFET can be designed by p-type ion implantation.

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Achieving efficient p-type conduction in Mg-implanted GaN depends largely on postimplantation annealing conditions. Here, we study the effect of postimplantation annealing on the evolution of defects and their interactions with implanted Mg ions by using scanning transmission electron microscopy and atom probe tomography. We found that Mg clusters start to form by annealing the implanted sample above 1000 °C. In addition to the Mg clusters, stacking faults form at an annealing temperature of 1300 °C. The Mg concentrations of about 2–3 orders of magnitude higher than implanted Mg were segregated at the stacking faults. Nanobeam electron diffraction analysis revealed no distinct phase other than GaN formed at the Mg-enriched defects, suggesting that Mg is substituted for Ga in the GaN lattice at the edge of the stacking faults.