Formation of high-quality Ag-based ohmic contacts to p-type GaN

Low resistance and high reflectance ohmic contacts on p-type GaN were achieved using an Ag-based metallization scheme. Oxidation annealing was the key to achieve ohmic behavior of Ag-based contacts on p-type GaN. A low contact resistivity of similar to 5x10(-5) Omega cm(2) could be achieved from Me (=Ni, Ir, Pt, or Ru)/Ag (50/1200 angstrom) contacts after annealing at 500 degrees C for 1 min in O(2) ambient. Oxidation annealing promoted the out-diffusion of Ga atoms from the GaN layer, and Ga atoms dissolved in the in-diffused Ag layer with the formation of Ag-Ga solid solution, resulting in ohmic contact formation. Using Ru/Ni/Au (500/200/500 angstrom) overlayers on the Me/Ag contacts, the excessive incorporation of oxygen molecules into the contact interfacial region, and the out-diffusion and agglomeration of Ag, were effectively prevented during oxidation annealing. As a result, a high reflectance of 87.2% at the 460 nm wavelength and a smooth surface morphology could be obtained simultaneously. (C) 2008 The Electrochemical Society.open111618sciescopu

Ferromagnetic properties of (Ga,Mn)N nanowires grown by a chemical vapor deposition method

Ferromagnetic (Ga,Mn)N nanowires were grown on sapphire substrates at 900 degrees C by a chemical vapor deposition. Synchrotron radiation photoemission spectroscopy revealed that no secondary phases were found in the grown nanowire, meaning the dissolution of Mn atoms to form a solid solution in GaN nanowire. Fermi level was apart by 3.0,eV in the GaN nanowire (n-type), and it shifted toward the valance band maximum with ammonia flow rate. The Ga-to-N ratio decreased with the increase of ammonia flow rate, leading to the increase of Ga vacancies. From this, it is suggested that both increases in magnetic moment and Curie temperature with ammonia flow rate originated from the solid solution of Mn and Ga vacancies.open4

Observation of inductively coupled-plasma-induced damage on n-type GaN using deep-level transient spectroscopy

The effects of inductively coupled plasma (ICP) etching on electrical properties of n-type GaN Schottky contacts were investigated by observing ion damage using deep-level transient spectroscopy. An electron trap, not previously seen, localized near the contact, as well as a pre-existing trap, was observed in the ICP-etched sample. The ICP-etched surface was found to be N-deficient, which means that N vacancies (V-N) were produced by ICP etching. From these, the origin of the ICP-induced electron trap was suggested to be V-N or a V-N-related complex of point defects. The ICP-induced traps provided a path for the transport of electrons, leading to the reduction of Schottky barrier height and increase of gate leakage current.open273

Degradation mechanism of Schottky diodes on inductively coupled plasma-etched n-type 4H-SiC

The degradation mechanism of Ta Schottky contact on 4H-SiC exposed to an inductively coupled plasma (ICP) was studied using deep-level transient spectroscopy and angle-resolved x-ray photoelectron spectroscopy (XPS). Four kinds of traps T1, T2, T3, and T4 were observed in the ICP-etched sample. The T4 trap was deep in the bulk, but the shallower levels, T1, T2 and T3, were localized near the contact. From angle-resolved XPS measurements, the ICP-etched surface was found to be carbon deficient, meaning the production of carbon vacancies by ICP etching. The activation energies 0.48 (T3 trap) and 0.60 eV (T4 trap) agreed well with the previously proposed energy level of V-C (0.5 eV). The ICP-induced traps provided a path for the transport of electrons at the interface of metal with Sic, leading to a reduction of the Schottky barrier height and an increase of the gate leakage current.open6

Insights from the U-238-th-234 method into the coupling of biological export and the cycling of cadmium, cobalt, and manganese in the southeast Pacific Ocean

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 33(1), (2019): 15-36, doi:10.1029/2018GB005985.Better constraints on the magnitude of particulate export and the residence times of trace elements are required to understand marine food web dynamics, track the transport of anthropogenic trace metals in the ocean, and improve global climate models. While prior studies have been successful in constructing basin‐scale budgets of elements like carbon in the upper ocean, the cycling of particulate trace metals is poorly understood. The 238U‐234Th method is used here with data from the GP‐16 GEOTRACES transect to investigate the upper ocean processes controlling the particulate export of cadmium, cobalt, and manganese in the southeastern Pacific. Patterns in the flux data indicated that particulate cadmium and cobalt behave similarly to particulate phosphorus and organic carbon, with the highest export in the productive coastal region and decreasing flux with depth due to remineralization. The export of manganese was influenced by redox conditions at the low oxygen coastal stations and by precipitation and/or scavenging elsewhere. Residence times with respect to export (total inventory divided by particulate flux) for phosphorus, cadmium, cobalt, and manganese in the upper 100 and 200 m were determined to be on the order of months to years. These GEOTRACES‐based synthesis efforts, combining a host of concentration and tracer data with unprecedented resolution, will help to close the oceanic budgets of trace metals.This work was supported by the National Science Foundation (OCE‐1232669 and OCE‐1518110), and Erin Black was also funded by a NASA Earth and Space Science Graduate Fellowship (NNX13AP31H). The authors would like to thank the captain, crew, and scientists aboard the R/V Thomas G. Thompson. A special thanks to two anonymous reviewers and Virginie Sanial for providing the additional 228Ra‐based estimates for Cd. All original data have been made available in either the supporting information or through BCO‐DMO (see Website and Database References).2019-06-1

Fermi level pinning on Si0.83Ge0.17 surface by inductively coupled plasma treatment

Effects of inductively coupled plasma (ICP) treatment on Fermi level pinning on the surface of Si0.83 Ge0.17 was studied by current-voltage and x-ray photoemission spectroscopy measurements. ICP treatment induced the growth of silicon oxide, suggesting that Si vacancies are generated under the oxide. From linear fitting of Schottky barrier heights with metal work functions, it was found that surface state density increased from 6.60?? 1012 to 1.13?? 1013 cm2 eV by the ICP treatment, leading to the pinning of surface Fermi level about EC ???0.53 eV. From this, it is suggested that the Si vacancies are the main surface states in pinning Fermi level on the ICP-treated surface.open1

Water-Soluble Epitaxial NaCl Thin Film for Fabrication of Flexible Devices

We studied growth mechanisms of water-soluble NaCl thin films on single crystal substrates. Epitaxial growth of NaCl(100) on Si(100) and domain-matched growth of NaCl(111) on c-sapphire were obtained at thicknesses below 100 nm even at room temperature from low lattice mismatches in both cases. NaCl thin film, which demonstrates high solubility selectivity for water, was successfully applied as a water-soluble sacrificial layer for fabrication of several functional materials, such as WO3 nano-helix and Sn doped In2O3 nano-branches.111Ysciescopu

Enhanced black state induced by spatial silver nanoparticles in an electrochromic device

The use of three-dimensional (3D) hierarchical indium tin oxide (ITO) branches of electrochromic devices (ECDs) is an effective approach for increasing the optical properties via localized surface plasmon resonance compared with two- dimensional nanostructured electrodes. ECDs with 3D branches were designed to operate in transparent, mirror and black states. Finite- difference time- domain simulation was used to find the electrical field distributions in three types of ECD: glass/ITO with Ag film, glass/ITO branches and glass/ITO branches with Ag nanoparticles. The ECDs had an optical transmittance of 73.76% in the transparent state, a reflectance of 79.77% in the mirror state and a reflectance of 8.78% in the black state. We achieved an ECD with high stability that can show similar to 10 000 switching cycles among the three states.113Ysciescopu

Indium as an efficient ohmic contact to N-face n-GaN of GaN-based vertical light-emitting diodes

We propose indium (In), a low work function and nitride-forming element, as an efficient ohmic contact layer to N-face n-GaN. While conventional Al-based ohmic contacts show severe degradation after annealing at 300 C, In-based ohmic contacts display considerable improvement in contact resistivity. The annealing-induced enhancement of ohmic behavior in In-based contacts is attributed to the formation of an InN interfacial layer, which is supported by x-ray photoemission spectroscopy measurements. These results suggest that In is of particular importance for application as reliable ohmic contacts to n-GaN of GaN-based vertical light-emitting diodes.open3