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Abstract: The use of diamond as the extraction window membrane for electron beam (EB) irradiation systems has been investigated by preliminary experiments and static simulations. The EB transmission characteristics of a fabricated 1.1 μm thick poly-crystalline diamond membrane were evaluated. A very high EB transmittance was observed, up to 70% at a 28 KeV accelerating voltage. Static simulations of EB extraction through a diamond membrane with a Si support have been carried out, under conditions from vacuum to atmosphere. Compared with Si, diamond/Si suffers a higher stress and strain, but, the displacement of a diamond film is much smaller. These results form a basis for the application of thin film, nanocrystalline and ultranano crystalline diamond on Si in the realization of the next generation miniature EB irradiation systems. [Copyright &y& Elsevier]

X-ray topography is an effective tool for investigating dislocations in semiconductor crystals. Owing to the low X-ray absorption coefficients of light element materials such as diamond, X-rays can penetrate deep into the crystal. Thus, deep three-dimensional dislocations are projected onto a two-dimensional film, which makes dislocation analysis particularly challenging. The dislocation vectors from the films obtained using a set of the same diffraction vectors were identified using topographical and geometrical analyses. The depth and position of the dislocations in a three-dimensional crystal that was projected onto a two-dimensional film were determined using geometrical relationships. The proposed analysis method was verified by analyzing many dislocations using four <404> diffraction films. [Display omitted] • The dislocation vectors of X-ray topography images were identified using geometrical analyses. • The depth and position of the dislocations were determined using geometrical relationships. • The proposed analysis method was verified by analyzing a Ib substrate using four <404> diffraction films. [ABSTRACT FROM AUTHOR]

Abstract: Diamond superlattices were fabricated by producing multilayer structures of isotopically pure carbon-12 (12C) and carbon-13 (13C), which confine charge carriers through a difference in band-gap energy. 12C/13C homojunctions of a diamond layer in which isotopic composition modulation occurred were grown via a microwave plasma-assisted chemical vapor deposition on diamond substrates. Secondary ion mass spectrometry (SIMS) and imaging measurements were employed to characterize the isotopic composition of the diamond superlattices. Layers between 2 and 30nm thick were designed and fabricated. [Copyright &y& Elsevier]

Etch pits formed on (001)-oriented single crystal diamond surfaces by O/H plasma etching have been investigated using optical microscopy. Shapes of the formed pits are basically inverted-pyramidal hollows with the edge directions of the 〈110〉, but central areas of these pits have two types of shapes, point-bottom and flat-bottom ones. Depth profiles of the number densities of these two-type pits showed that at an early stage of the etching, a large number of the flat-bottom pits are observed, but disappear to a depth shallower than ~ 10 μm. Compared with the other etching experiment using ion beam sputtering, such flat-bottom pits most likely correspond to the dislocations or microfractures introduced around the surface during surface polishing of the diamond substrates. On the other hand, point-bottom pits still continue to appear even in a deeper region. These correspond to “intrinsic” dislocations included originally inside the diamond substrate. All the tilt angles of the pit between the slope of the pit and top face of the substrate, characterizing the pit shape, were within the range of 3–7° and independent of their sizes in many pits investigated. It was found that the tilt angle and the activation energy of the etch rate obtained in this study are similar to that of an oxygen-gas related etching process. [ABSTRACT FROM AUTHOR]

In this study, we applied dislocation analysis to X-ray topography images to identify the complete dislocation information for two typical high-pressure high-temperature diamond crystals, IIa and Ib. Almost all dislocation line vectors of both crystals were identified for the first time. For IIa crystal, it was confirmed that up to 84% of the dislocations have 〈101〉 vectors. For Ib crystal, up to 71% of the dislocations have 〈112〉, 〈121〉, and 〈211〉 vectors. Both [110] and [1-10] with zero components of the c-axis are the major Burgers vectors. Regarding the types of dislocation, the major types were edge types, which were approximately 47% and 65% for IIa and Ib crystals, respectively. In addition, screw, 60° and 73° type on the IIa, and 30°, 35°, and 73° type on Ib were identified. Complete analysis of dislocations will give important information for the diamond growth and reduction of the dislocations. [Display omitted] • Complete dislocation analysis by X-ray topography were carried out for IIa and Ib type HPHT crystals. • Up to 84% of the dislocations of IIa crystal are <101> vectors, and 71% of Ib crystal are <112>, <121>, and <211> vectors. • Screw, 60° and 73° types were identified for IIa, and 30°, 35°, and 73° types for Ib. [ABSTRACT FROM AUTHOR]

Abstract: The superior material properties of diamond power semiconductor devices make them a crucial technology. For high-voltage applications, optimized structures such as electric field edge termination are required for devices. In this paper, we have investigated the optimization of electric field relaxation techniques in oxygen-terminated p-type diamond Schottky barrier diodes and made comparisons with regard to electric field crowding and breakdown in oxides. Due to the low dielectric constant of diamond, Al2O3 is appropriate for the fabrication of field plate structures in diamond power devices. [Copyright &y& Elsevier]

Abstract: The annealing induced effects on hydrogen (H)- and oxygen (O)-terminated P-doped (111) diamond surfaces were investigated by X-ray photoelectron spectroscopy (XPS). Thermally triggered systematic shift of carbon 1s (C1s) peaks was observed for both the surface terminations. The shift is characterized by H- and O-desorption kinetics until a clean surface is produced and then by the non-diamond carbon layer formation on the diamond surface. Desorption induced shift of binding energy (BE) in H-terminated surface is larger than O-terminated diamond surface since the surface bonding configuration of H and O is different. The clean surface emerges at a lower temperature for O-terminated surface than it turned out in H-terminated surface. The growth of non-diamond carbon layer was analysed through loss spectrum of C1s core levels. [Copyright &y& Elsevier]

By hot-filament (HF) chemical vapor deposition (CVD), heavily boron (B)-doped single-crystal diamond (100) films were fabricated and their structural and electrical properties were studied. We did not observe the soot formation, which is frequently observed and limits the performances in the case of microwave plasma (MWP) CVD. The B concentration was successfully controlled over the range from 10 19 to 10 21 cm − 3 . Hillock-free films were obtained, whose mean surface roughness measured by atomic force microscopy (AFM) was less than 0.1 nm. From the reciprocal space mapping (RSM) around 113 diamond reflection, it was revealed that the films possess the smaller lattice expansion than that expected from the Vegard's law. The room-temperature resistivity was decreased lower than 1 mΩ·cm for B concentration ~ 10 21 cm − 3 . These results indicate that the HFCVD possesses large potential for fabricating the device-grade p + diamond. [ABSTRACT FROM AUTHOR]

Pyramidal and flat-type hillocks, both known for having a threading dislocation in the center, are utilized to examine the effect of surface irregularities on the characteristics of Schottky barrier diodes (SBDs). By performing RAMAN mapping on both hillocks, crystalline imperfections in three dimensions with clear strain are observed. Surface scanning images obtained via atomic force microscopy show an extremely large surface protrusion with a maximum height of approximately 15 nm in the pyramidal hillock. Owing to crystalline imperfections in the threading dislocation region, the SBDs fabricated on the dislocations exhibit inferior forward characteristics. However, high reverse leakage currents are only observed in dislocations on pyramidal hillocks with surface protrusions, whereas low reverse currents are observed in the flat hillock region without surface irregularities. The phenomenon above is consistent with the characteristics of wide bandgap semiconductors such as silicon carbide. [Display omitted] • Effects of surface irregularities on the characteristics of Schottky barrier diodes are studied. • SBDs fabricated on the dislocations exhibit inferior forward characteristics. • High reverse leakage currents are only observed in dislocations on pyramidal hillocks with surface protrusions. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present planar mesa termination structure with high k dielectric Al2O3 for high-voltage diamond Schottky barrier diode. Analysis, design, and optimization are carried out by simulations using finite element technology computer-aided design (TCAD) Sentaurus Device software. The performances of planar mesa termination structure are compared to those of conventional field plate termination structure. It is found that optimum geometry of planar mesa terminated diode requires shorter metal plate extension (1/3 of the field plate terminated diode). Consequently, planar mesa terminated diode can be designed with bigger Schottky contact to increase its current carrying capability. Breakdown performance of field plate termination structure is limited at 1480V due to peak electric field at the corner of Schottky contact (no oxide breakdown occurs). In contrast, peak electric field in planar mesa termination structure only occurs in the field oxide such that its breakdown performance is highly dependent on the oxide material. Due to Al2O3 breakdown, planar mesa termination structure suffers premature breakdown at 1440V. Considering no oxide breakdown occurs, planar mesa termination structure can realize higher breakdown voltage of 1751V. Therefore, to fully realize the potential of planar mesa terminated diode, it is important to choose suitable high k dielectric material with sufficient breakdown electric field for the field oxide. [Copyright &y& Elsevier]

Abstract: In this study, we investigated non-ideal characteristics of a diamond Schottky barrier diode with Molybdenum (Mo) Schottky metal fabricated by Microwave Plasma Chemical Vapour Deposition (MPCVD) technique. Extraction from forward bias I–V and reverse bias C −2–V measurements yields ideality factor of 1.3, Schottky barrier height of 1.872eV, and on-resistance of 32.63mΩ·cm2. The deviation of extracted Schottky barrier height from an ideal value of 2.24eV (considering Mo workfunction of 4.53eV) indicates Fermi level pinning at the interface. We attributed such non-ideal behavior to the existence of thin interfacial layer and interface states between metal and diamond which forms Metal-Interfacial layer-Semiconductor (MIS) structure. Oxygen surface treatment during fabrication process might have induced them. From forward bias C–V characteristics, the minimum thickness of the interfacial layer is approximately 0.248nm. Energy distribution profile of the interface state density is then evaluated from the forward bias I–V characteristics based on the MIS model. The interface state density is found to be uniformly distributed with values around 1013 eV−1·cm−2. [Copyright &y& Elsevier]

Abstract: The microscopic surface morphology of “lifted-off” surfaces, produced via ion implantation was observed by atomic force microscopy. A polished single-crystal diamond substrate with an average surface roughness of less than 0.1nm was used for precise observations. After the lift-off process, the lifted-off surface became rough with pits appearing. Hydrogen plasma treatment close to the chemical vapor deposition conditions for diamond (1150°C, 160Torr) completely removed these pits and the surface was subsequently covered by a strip-like structure consisting of atomic steps. The surface roughness, however, was not further influenced by the plasma treatment. The observed morphological evolution reflects the graphite/diamond interface formed by the lift-off. [Copyright &y& Elsevier]

Abstract: Diamond pseudo-vertical structure Schottky barrier diodes (PVSBD) have been fabricated by developing a simple and efficient fabrication technology, in which 14 µm thick p− layer was selectively etched out and ohmic contact was made onto the low resistive p+ layer from topside. The electrical characteristics were evaluated by fabricating Mo/Diamond Schottky barrier diodes in pseudo-vertical structure. With the fabricated structure, a high blocking voltage of 1.6 kV with a low leakage current density in order of 10−7 ~10−6 A/cm2 could be obtained, without any edge termination. The reverse characteristics of the SBDs exhibited a hard breakdown at 1.6 kV, and causing breakdown of the diamond surface itself in a particular case. The later case indicated the presence of sub-surface leak path causing current leakage in one direction in near surface region, and a model has been proposed to explain this. [Copyright &y& Elsevier]