We have demonstrated for the first time a remarkable reduction of current collapse in AlGaN/GaN highelectron-mobility transistors (HEMTs) by high-pressure water vapor annealing (HPWVA). The device subjected to HPWVA exhibited considerably low dynamic ON-resistance (R ON ), suggesting highly improved performance of these devices. Analyses of the results on normalized dynamic R ON experiments have shown the elimination of deeper traps by HPWVA, leading to the substantially reduced current collapse. X-ray photoelectron spectroscopy (XPS) studies revealed a significant increase in the oxygen core-level O 1s peak. Moreover, angleresolved XPS suggested the formation of surface oxide layer. These results indicate that the effective reduction of current collapse in the HPWVA-processed samples is likely due to the incorporation of active oxygen species generated by the HPWV into the AlGaN surface. These oxygen atoms eventually fill up near-surface nitrogen vacancies and promote the formation of Ga 2 O 3 native oxide and possibly Ga 2 O suboxide, which is known to be an excellent III-V surface passivant. HPWVA is a relatively simple, low-damage, and low-temperature process, and hence, it is found to be a highly feasible and promising alternative for realizing AlGaN/GaN HEMTs with improved performance.Index Terms-AlGaN/GaN high-electron-mobility transistor (HEMT), current collapse, high-pressure water vapor annealing (HPWVA), normalized dynamic R ON (NDR), ON-resistance, X-ray photoelectron spectroscopy (XPS).

We investigated the effects of the passivation layer on the characteristics of amorphous InGaZnO4 thin-film transistors (a-InGaZnO TFTs) by comparing AlOx film by thermal atomic layer deposition (TALD-AlOx) with SiOx film by plasma enhanced chemical vapor deposition (PECVD-SiOx). The PECVD-SiOx TFTs before and after final annealing exhibited conductive and hump characteristics, respectively. In contrast, both TALD-AlOx TFTs before and after final annealing exhibited enhancement characteristics. From secondary ion mass spectroscopy analysis, we found that TALD-AlOx effectively suppresses H injection into the underneath of the a-InGaZnO layer compared with PECVD-SiOx. We believe such suppression of H injection leads to the enhancement characteristics of TALD-AlOx TFTs. On the other hand, the conductive and hump characteristics of PECVD-SiOx TFTs may be attributed to a higher concentration of H injected into the a-InGaZnO layer and ion bombardment due to PECVD. From these results, we argue that plasma-free TALD-AlOx is effective for achieving good characteristics in a-InGaZnO TFTs.

This paper briefly reviews the characterizations of Al2O3 gate dielectric deposited by plasma‐assisted atomic layer deposition (PA‐ALD) on n‐GaN. We report on insulating and physical properties of PA‐ALD Al2O3 film from I‐V characteristics of metal‐insulator‐semiconductor (MIS) diodes and analysis of X‐ray photoelectron spectroscopy (XPS), respectively. Compared to Al2O3 film deposited by thermal ALD method, the PA‐ALD Al2O3 film exhibited higher breakdown field and several orders of magnitude lower leakage current density. Analysis of the current conduction mechanism reveals that the gate leakage current of PA‐ALD Al2O3/n‐GaN MIS diode consisted of Schottky emission (SE) and Fowler‐Nordheim tunneling (FNT). In contrast, it is suggested that trap‐assisted tunneling (TAT) mechanism was dominant in the gate leakage of T‐ALD Al2O3 sample at the middle field range. From the XPS analysis, the band gap of PA‐ALD Al2O3 was estimated about 6.7 eV. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper reports an effect of post annealing technique for the deposited dielectric films utilizing high pressure deuterium oxide. Al2O3 deposited on Si thermal oxide film by plasma-assisted atomic layer deposition (PA-ALD), which can have the advantage of low temperature process. For reforming qualities of the ALD–Al2O3, high pressure deuterium oxide annealing (HPDOA) was carried out at 0.3 MPa for 60 min while keeping at 300ºC. The leakage current and the breakdown field of metal-insulator-semiconductor (MIS) diodes with the Al2O3 gate dielectrics were improved by the HPDOA treatment. The HPDOA is found to be useful for reforming the Al2O3 thin film even if it was deposited by PA-ALD.

We have been interested in behaviors of suspended particles in a volatile droplet placed on a smooth substrate. It is known that the particles gather and deposit in the vicinity of the macroscopic contact line of the droplet, which is generally called 'coffee stain problem'. A convective flow induced by nonuniform evaporation through the interface brings suspended particles toward the pinned contact line in the drying droplet, which forms a ring stain. We have focused on the dynamics of the droplet with/without suspended particles spreading on the solid substrate and on the behaviors of particles in the evaporating droplet. Spreading process of the droplet is significantly affected by the suspended particles. We indicate flow patterns in the droplet, in which the flow exhibits a modal structure with a mode number in the azimuthal direction, and indicate particles depositions after the dryout of the droplet. Three-dimensional particle tracking velocimetry is applied to reconstruct such unique flow patterns in the spreading process of the droplet. Resultant patterns of the particles depositing on the substrate are introduced.