The transient enhanced diffusion (TED) of As in silicon samples implanted at 35 keV with dose 5×1015 cm−2 has been investigated in the temperature range between 750 and 1030 °C by comparing experimental and simulated profiles. For temperatures higher than 900 °C the phenomenon is of modest entity and vanishes after a few seconds, whereas at lower temperatures diffusivity enhancements of some order of magnitude have been observed. The anomalous shift of the junction depth, evaluated at 2×1018 cm−3, is about 12 nm at 900 °C and increases up to 45 nm at 750 °C. It has been verified that the two are the contributions, that generate the interstitial excess responsible for the TED: (i) the implantation damage and (ii) the aggregation in clusters of the As atoms. From an experiment that allows us to separate the two contributions, we estimate that about one third of the TED observed in the first 20 min of annealing at 800 °C is due to the defects produced by clustering. The influence of clustering on the shape of the As profiles after diffusion at different temperatures is also discussed.

CuFeO 2 is a p-type semiconductor that has been recently identified as a promising photocathode material for photoelectrochemical water splitting. CuFeO 2 can absorb solar light and promote the hydrogen evolution reaction (HER), even though the photocurrents achieved so far are still well below the theoretical upper limit. While several experimental and theoretical works have provided a detailed characterization of the bulk properties of this material, surfaces have been largely unexplored. In this work, we perform firstprinciples simulations based on DFT to investigate the structure, electronic properties, and thermodynamic stability of CuFeO 2 surfaces both in vacuum and in an electrochemical environment. To estimate the alignment of the band edges on the electrochemical scale, we perform ab initio molecular dynamics in explicit water, unraveling the structure of the solid/liquid interface for various surface terminations. We consider the system both in the dark and under illumination, showing that light absorption can induce partial reduction of the surface, giving rise to states in the gap that can pin the Fermi level, in agreement with recent measurements. Using the free energy of adsorption of atomic hydrogen as a descriptor of the catalytic activity for the HER, we show that hydride species formed at oxygen vacancies can be highly active and could therefore be an intermediate of reaction.

CuFeO 2 has been recently identified as a promising photocathode material for photoelectrochemical water splitting cells. In spite of the first encouraging results, improvements in the catalytic activity and charge separation are required and an adequate theoretical characterization is currently not available to complement experimental results. We present a firstprinciples investigation of the bulk properties of CuFeO 2 , focusing in particular on its stability in air and in an aqueous environment. Here, we show that while the material is in a metastable phase in air at ambient conditions, the electrochemical environment strongly stabilizes it. In fact, at conditions of applied bias and pH used in the experiments, the material operates within its region of thermodynamic stability, thus explaining its remarkable resistance to corrosion. We investigated the formation energy of native point defects in the stability region, predicting a small formation energy for an antisite defect, which could be detrimental for the performance of CuFeO 2 as a photocathode, since defect states lying inside the gap may favor the electron−hole recombination.

A pyrolyzed photoresist film is commonly used as a protective cap of the surface of ion-implanted 4H-SiC wafers during the postimplantation annealing process with the aim to prevent Si sublimation and step bunching formation. Such a film that is called carbon-cap ͑C-cap͒ is always removed after postimplantation annealing and before any other processing step of the SiC wafer. Here, we show that this C-cap is a continuous, hard, black, mirrorlike, and planar thin film that can be patterned by a reactive ion etching O 2 -based plasma for the fabrication of ohmic contact pads on both Al + -and P + -implanted 4H-SiC. This C-cap material has an electrical resistivity of 1.5 ϫ 10 −3 ⍀ cm and a good resistance against scratch. Al ͑1% Si͒ wires can be ultrasonically bonded on the C-cap pads. Such a bonding and the C-cap adhesion to the implanted 4H-SiC surface are stable for electrical characterizations in vacuum between room temperature and 450°C. The measured specific contact resistance of the C-cap on a 1 ϫ 10 20 cm −3 P + -implanted 4H-SiC is 9 ϫ 10 −5 ⍀ cm 2 at room temperature. Micro-Raman characterizations show that this C-cap is formed of a nanocrystalline graphitic phase.Pyrolyzed photoresist films are carbonaceous materials that are the object of intensive studies for numerous and very different applications, among which the more recent ones are coating layers for large-area optoelectronics devices 1 and carbon microelectromechanical systems. [2][3][4][5] In the processing of silicon carbide ͑SiC͒ wafers for microelectronic devices fabrication, a pyrolyzed photoresist film is largely used as a protective cap on the surface of the implanted SiC wafers for preventing Si sublimation and step bunching formation during the mandatory postimplantation annealing at a temperature in the range 1300-1900°C. 6,7 After this annealing and before any other processing step, this cap called carbon-cap ͑C-cap͒ is removed.Taking into account the 6 eV work function of graphite 8 and the electron affinity of SiC, which is 3.45 and 3.17 eV for ͑0001͒ 6H-and 4H-SiC, respectively, 9 ohmic contacts between graphite and SiC would be hard to form. But the presence of carbonaceous phases at the interface metal/SiC has been detected so often that the effect of an interface graphite layer on the electronic properties of metal/ SiC contacts has been studied. 10 These studies have shown that the Schottky barrier height ͑⌽ B ͒ of graphite on the Si-face ͑0001͒ of every SiC polytype are lower for the n-type material than for the p-type one. More precisely, depending on the measurement technique, ⌽ B ranges between 0.3 and 0.6 eV for n-type ͑0001͒ 6H-SiC and between 1.23 and 2.7 eV for p-type ͑0001͒ 6H-SiC and between 0.4 and 0.6 eV for n-type ͑0001͒ 4H-SiC and between 1.25 and 2.58 eV for p-type ͑0001͒ 4H-SiC. 10 It can be remarked that for graphite on n-type SiC, these experimental ⌽ B values are lower than the theoretical value hypothesized by the classical Schottky-Mott theory, i.e., ⌽ B equals to the difference between the metal work functio...