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International audience; High electron mobility transistors (HEMTs) based on AlGaN/GaN heterostructures on silicon are stateof-the-art commercial power devices on the basis of nitrides. Performance and reliability of suchdevices are hampered by the presence of various defects. However, the relation between the natureof those defects and device characteristics is often not understood from a microstructural and physicalpoint of view. In this work we compare two nominally identical HEMT layer stacks that were grownunder different nucleation conditions, but differ significantly in vertical breakdown voltage. By defectselective etching it is shown that this phenomenon is not due to a different dislocation density. Insteada Conductive Atomic Force Microscopy study reveals locally strong electrical conductivity within thebuffer, which results in the formation of discrete vertical leakage paths that were identified tocorrespond to V-shaped defects at interfaces of the layer stack, also called V-pits. A detailed analysisby Cathodoluminescence (CL) mappings and CL-spectroscopy allows an identification of V-pits actingas centers of strongly reduced carbon and increased donor incorporation. Depending on growthconditions of the nucleation layer V-pits within the buffer occure in different sizes and densities acrossthe structure. The V-pits are closed by overgrowth sooner or later and are filled by the material of thefollowing layer. If such pits reach the upper buffer region, column-like areas of locally higher n-typebehavior are formed and disrupt the vertical device breakdown strength. The breakdown voltage isshown to be strongly dependent on the density of those V-pit induced n-type columns underneath theactive device region. An optimized nucleation layer growth was able to enhance the breakdownvoltage by nearly 600V.

A novel GaN trench gate (TG) MOSFET with P-type floating islands (FLI) in drift region, which can suppress the electric field peak at bottom of gate trench during the blocking state and prevent premature breakdown in gate oxide, is proposed and investigated by TCAD simulations. The influence of thickness, position, doping concentration and length of the FLI on breakdown voltage (BV) and specific on-resistance (Ron_sp) is studied, providing useful guidelines for design of this new type of device. Using optimized parameters for the FLI, GaN FLI TG-MOSFET obtains a BV as high as 2464 V with a Ron_sp of 3.0 mO cm2. Compared to the conventional GaN TG-MOSFET with the same structure parameters, the Baliga figure of merit (BFOM) is enhanced by 150%, getting closer to theoretical limit for GaN devices.

The Motion Decoupled Hydraulic Delivery System (MDHDS) is a new downhole tool delivery system that is deployed by wireline and uses drillstring pressure to advance a penetrometer (or other downhole tool) into the formation at the bottom of offshore boreholes. After hydraulic deployment of the penetrometer, it is completely decoupled from the BHA; this eliminates the adverse effects of ship heave. We tested the MDHDS at Site U1402 (the location of Site 1073, ODP Leg 174A), offshore New Jersey, during two days of ship time during Integrated Ocean Drilling Program (IODP) Expedition 342. In one deployment we emplaced a penetrometer successfully and documented that it was decoupled from drillstring movement. Based on this successful field test, the MDHDS has been certified by the U.S. Implementing Organization (USIO) for shipboard use. The MDHDS will replace the previous deployment system, the Colletted Delivery System. The MDHDS is an IODP-funded engineering development led by The University of Texas at Austin, in conjunction with the USIO and Stress Engineering Services. This sea trial was the culmination of a seven-year development effort that included extensive engineering design and fabrication. doi:10.2204/iodp.sd.15.07.2013

Metastable cobalt nitrides Co4N, Co3N, Co2N, and cobalt oxide nitride CoO0.74N0.24 were synthesized by ammonolysis of one single metastable azide precursor, [Co(NH3)5N3]Cl2, in high purity by controlled variation of the reaction conditions (temperature, duration, gas atmosphere, and flow rate). The alternative route towards cobalt nitrides by ammonolysis of CoBr2 proceeds via [Co(NH3)6]Br2 and Co(NH3)2Br2 to exclusively yield Co3N. For Co3N1.1 a complex magnetic behavior is observed: dominating ferromagnetic ordering at low temperatures and a small coercive field of 10 mT. Co2N orders antiferromagnetically below 10 K. Electronic structure calculations [DFT, generalized-gradient approximation (GGA)+U] on CoO0.75N0.25 reveal that the experimentally observed rock-salt structure is less stable than the sphalerite-type polymorph by about 30 kJ mol-1 and possesses an antiferromagnetically ordered ground state.

Three different synthetic routes to chromium nitrides were investigated using in situ neutron diffraction (SPODI, FRM-II) and thermal analysis in ammonia: (i) The direct conversion of chromium powder in ammonia, (ii) the ammonolysis of chromium(III) chloride CrCl3, and (iii) the ammonolysis of chromium(III) sulfide Cr2S3. During the direct conversion of chromium first -CrN was formed above 385 degrees C, above 567 degrees C additionally -Cr2N was detected. Finally, a complete conversion of -CrN to -Cr2N was observed at 1080 degrees C. The ammonolysis of chromium(III) compounds (CrCl3 and Cr2S3) revealed a so far in 3d metal nitride synthesis unprecedented redox sequence: The compounds are reduced to chromium(II) chloride CrCl2 and chromium(II, III) sulfide Cr3S4, respectively, prior to the reoxidation of those intermediates to -CrN. In contrast to the ammonolysis of 3d metal(II) halides, for chromium(III) chloride no temporary formation of ammoniates was observed. Since formation of -CrN was detected only after annealing chromium(III) sulfide in flowing ammonia for 4 h to 5 h at maximum temperature, the formation of sufficient amounts of chromium(II, III) sulfide as the rate-determining step for the nitride formation appears likely.

The Motion Decoupled Hydraulic Delivery System (MDHDS) is a new downhole tool delivery system that is deployed by wireline and uses drillstring pressure to advance a penetrometer (or other downhole tool) into the formation at the bottom of offshore boreholes. After hydraulic deployment of the penetrometer, it is completely decoupled from the BHA; this eliminates the adverse effects of ship heave. We tested the MDHDS at Site U1402 (the location of Site 1073, ODP Leg 174A), offshore New Jersey, during two days of ship time during Integrated Ocean Drilling Program (IODP) Expedition 342. In one deployment we emplaced a penetrometer successfully and documented that it was decoupled from drillstring movement. Based on this successful field test, the MDHDS has been certified by the U.S. Implementing Organization (USIO) for shipboard use. The MDHDS will replace the previous deployment system, the Colletted Delivery System. The MDHDS is an IODP-funded engineering development led by The University of Texas at Austin, in conjunction with the USIO and Stress Engineering Services. This sea trial was the culmination of a seven-year development effort that included extensive engineering design and fabrication.