P-type conversion of n−-GaN by Mg-ion implantation was successfully performed using high quality GaN epitaxial layers grown on free-standing low-dislocation-density GaN substrates. These samples ...showed low-temperature PL spectra quite similar to those observed from Mg-doped MOVPE-grown p-type GaN, consisting of Mg related donor–acceptor pair (DAP) and acceptor bound exciton (ABE) emission. P–n diodes fabricated by the Mg-ion implantation showed clear rectifying I–V characteristics and UV and blue light emissions were observed at forward biased conditions for the first time.
Mg-ion-implanted layers in a GaN substrate after annealing were investigated. Implanted Mg atoms precipitated along the edges of crystal defects were observed using 3D-APT. The breakdown ...characteristics of a GaN double-diffused vertical MISFET (DMISFET) fabricated via triple ion implantation are presented. A DMISFET with Si-ion-implanted source regions was formed in Mg-ion-implanted p-base regions, which were isolated from adjacent devices by N-ion-implanted edge termination regions. A threshold voltage of -0.5 V was obtained at a drain voltage of 0.5 V for the fabricated vertical MISFET with an estimated Mg surface concentration of 5 × 10
cm
. The maximum drain current and maximum transconductance in a saturation region of V
= 100 V were 2.8 mA/mm and 0.5 mS/mm at a gate voltage of 15 V, respectively. The breakdown voltage in the off-state was 417 V. The breakdown points were determined by the boundary regions between the N- and Mg-implanted regions. By improving heat annealing methods, ion-implanted GaN DMISFETs can be a promising candidate for future high-voltage and high-power applications.
Ion implantation is a widely used doping technique for Si MOSFETs, but there have been few reports that demonstrate the formation of p-type GaN layer. We have succeeded to make the p-n junction by ...implanting Mg ions into n-type GaN layer, but Mg implanted layer showed inhomogeneity including p and n-type regions. Evaluation methods of homogeneity of Mg ion implanted GaN layer by mapping technique using current-voltage characteristics are demonstrated.
•Mg ion implanted layer on GaN substrate showed inhomogeneity including p and n-type regions.•New mapping method of IV characteristics was developed to determine p- or n-type regions in the layer w/o Ohmic contacts.•Mg ion implanted layer has an almost homogeneous p-type behavior, however, it contains small areas with n-type character.
Nitrogen-ion-implantation damage on SiC has been clearly imaged using scanning internal photoemission microscopy (SIPM). Ni Schottky contacts were formed on selectively N-ion-implanted n-SiC surfaces ...at 80keV with an ion dose of 1×1015cm−2. A photocurrent, Y (photoyield; defined as photocurrent per incident photon), was detected by focusing and scanning a laser beam over the contacts. The N-ion-implanted regions were clearly imaged with Y measurements. Y was detected even where the implanted region is protruding out of the electrode in the unannealed sample. We also found significant increase of Y in the periphery of the ion-implanted region. We confirmed that SIPM is a powerful tool for mapping damages due to ion implantation.
The realization of molecular devices via metal–molecule–metal junctions necessitates the fabrication of a steady molecular bridging structure, where the number of bridging structures should be fixed. ...This study investigated a new molecular bridging method using migrations of gold atoms on static nanogap electrodes. First, static nanogap electrodes with a large gap size were fabricated for bridging molecules, and the gap size was controlled through the applied bias voltage after the electrodes were coated with molecules. Similar to a mechanically controlled break junction (MCBJ), nanogap electrodes coated with thiol or dithiol molecules were continuously elongated and contracted under applied bias voltages. As the size of the nanogap varied, the electric properties of a single Au–benzene-dithiol (BDT)–Au junction, which have been previously evaluated using the MCBJ method, were clearly determined. Although MCBJ and scanning tunneling microscopy break junctions have been used to measure the electric properties of single molecules, these techniques are difficult to apply in integrated molecular devices. The proposed method is expected to be applicable to minuscule molecular devices with its ability to control gap sizes in static nanogap structures.
A normally-off GaN double-implanted vertical MOSFET (DMOSFET) with an atomic layer deposition (ALD)-Al₂O₃ gate dielectric film on a free-standing GaN substrate fabricated by triple ion implantation ...is presented. The DMOSFET was formed with Si ion implanted source regions in a Mg ion implanted p-type base with N ion implanted termination regions. A maximum drain current of 115 mA/mm, maximum transconductance of 19 mS/mm at a drain voltage of 15 V, and a threshold voltage of 3.6 V were obtained for the fabricated DMOSFET with a gate length of 0.4 μm with an estimated p-type base Mg surface concentration of 5 × 10
cm
. The difference between calculated and measured V
s could be due to the activation ratio of ion-implanted Mg as well as Fermi level pinning and the interface state density. On-resistance of 9.3 mΩ·cm² estimated from the linear region was also attained. Blocking voltage at off-state was 213 V. The fully ion implanted GaN DMOSFET is a promising candidate for future high-voltage and high-power applications.
This report describes the fabrication and characteristics of GaN p–n junction diodes on free‐standing GaN substrates with low dislocation density. We have demonstrated GaN p–n junction diodes with a ...unique field‐plate (FP) structure. The breakdown voltage VB is further improved due to the FP structure and the low dislocation density. The breakdown voltage of a diode of 60 µm in diameter with the FP structure is over −1000 V, and the leakage current is below 10−9 A until reaching the breakdown voltage. Even in larger diodes (100 and 200 µm in diameter) with FP, the breakdown voltage is over −800 V. However, the specific on‐resistance Ron is high due to damage by the plasma process of sputtering. The specific on‐resistance is further improved due to using a low damage passivation film. As a result, a specific on‐resistance of 1.2 mΩ · cm2 is obtained.
Variations in molecular electronic structures related to conformational change are exceedingly attractive because of their key role in the understanding and development of functional processes in ...molecular electronics and biology. We observed, for the first time, the novel phase switching of a photoactive isomeric molecule, N-(2-mercaptoethyl)-4-phenylazobenzamide (Azo molecule) at a single-molecule level, which exhibits a distinctive change in the conductive characteristic under scanning tunneling microscope (STM) measurement. In comparison with the results obtained by the measurement of photoactive isomerization of the isolated Azo molecule, which was performed also for the first time, the observed characteristics are attributed to the results of the trans and cis phase transformation of the Azo molecule, under the condition of an external electric field and current flow. A specific point is that the potential landscape of the system is controllable by the electric field and provides a conformational stability with asymmetric bias dependence resulting in rectification.
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