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Presents a study which examined over-passivation films of silicon nitride and silicon dioxide on (NH[sub4])[sub2]S[subx]-treated gallium arsenide deposited by various kinds of systems with photoluminescence measurements. Influence of annealing on over-passivation; Effect of the gallium arsenide etchant before the treatment; Effect of the precleaning process with nitrogen before the deposition of silicon nitride.

An evaluation of p + high pressure and high temperature (HPHT) substrates as the seed crystals of p + substrates for power devices was carried out. The crystallinity measured by Raman spectroscopy showed a poor distribution, such as a standard deviation of 0.44 cm − 1 for the 1332 cm − 1 diamond peak in a 3 × 3 mm 2 area, whereas the undoped crystal had a standard deviation of only 0.02 cm − 1 . B doping distribution mapping was carried out for the first time using B-related peaks that appear because of crystallographic symmetry breaking due to B incorporation into the diamond lattice. High B concentration was observed in the [ 1 − 11 ] and [ 1 1 − 1 ] growth sectors and low B concentration was observed in the [111] and [ 1 − 1 − 1 ] growth sectors. This result presumably depends on the instrumental pressure and temperature control in the HPHT equipment. [ABSTRACT FROM AUTHOR]

Diamond styluses have long been used for long play (LP) phonographs, and remain favored by fans because of their higher fidelity to original sounds compared with compact disk (CD) digital media. In this paper, we report the fabrication and characterizations of a whole diamond stylus integrating the shaft and tip using a large single crystal diamond plate by sophisticated laser machining. This is the first moving magnet (MM) type LP cartridge comprising a whole diamond including the tip and cantilever. According to the frequency response measurements, whole diamond stylus has a lower crosstalk than the conventional stylus; that is, a far larger separation of the right and left channels e.g., 36 dB @1 kHz. For the 3rd harmonic distortion, which is the most important factor affecting the audio noise characteristics, the whole diamond stylus exhibits significant improvements compared with the conventional aluminum shaft cantilever; a 4 dB improvement is observed in the frequency range of 500–800 Hz, and a 3–5 dB improvement is observed in the frequency range of 1300–1700 Hz. Further improvements are expected to yield a well- designed cone-shaped tip over a wide range of frequencies including > 20 kHz, which was recently identified as the “audible” range for human. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated phase transformation, optical and electrical properties of diamond implanted with high dose (up to ∼1021 cm−3) B, P and N acted as donor or acceptor elements in diamond, at elevated temperatures in the medium energy range (30 to several 100eV) followed by post-implantation annealing. Unlike a typical semiconductor such as Si, the high dose ion implantation over critical dose D c to diamond below about room temperature results in phase transformation to a thermally stable graphitic phase after a post-implantation annealing process. In this study, it was found that any diamonds B-, N- and P-implanted at high doses at elevated temperatures (∼400°C) maintain diamond structures (graphite transformation does not occur) after annealing, from the results of optical absorption spectra, Raman scattering and temperature dependence of electrical properties. In the case of B and N, not only graphitization was avoided but also resistivities were reduced after annealing. In particular, in the B doped samples high electrical activation of B acceptors occurred, and heavily B doped (∼2.5×1021 cm−3) diamond became a p-type degenerate semiconductor with low resistivity due to a metal-like band structure. In the N doped sample, the resistivity was ∼103 times as high as that in the B doped sample, but the value was much lower than normal diamond as an insulator. This suggests that in the N doped sample only impurity band conduction occured unlike the B dope samples. On the other hand, the resistivity of the P doped sample was ∼106 times as high as that of the N doped sample. This result most likely means that graphitization was avoided, also in the P doped sample, while the high mass number element P compared with B and N induced many radiation defects (not annealed out) in diamond acting as carrier trapping, and the resultant resistivity became very high. [Copyright &y& Elsevier]

In the 1980s, zirconia was introduced for THA with the expectation of lower polyethylene wear and better clinical results. However, several studies have reported poor survivorship of zirconia-polyethylene THA. We performed a systematic review and meta-analysis of zirconia-polyethylene THA to confirm or refute the theoretical advantages of this combination. Of 163 studies identified by a comprehensive search, seven met our selection criteria. These involved 769 hips of 586 patients with a mean age of 56.8 years and a minimum followup of 60 months (mean, 89.2 months; range, 60-155 months). The consolidated revision rate of zirconia-polyethylene THA at 89.2 months was higher than that of nonzirconia-polyethylene THA by 5% (risk difference, 0.05; 95% confidence interval, 0.02-0.08). Subgroup meta-analysis suggested THAs with zirconia heads from Ceraver had more revision surgery than nonzirconia heads (risk difference, 0.08; 95% confidence interval, 0.03-0.14), whereas zirconia heads from DePuy did not (risk difference, 0.02; 95% confidence interval, -0.01-0.06). The meta-analysis for annual linear polyethylene wear (which did not involve zirconia heads from Ceraver because of insufficient descriptions) showed no difference between zirconia and control groups. Collectively, THAs with high-quality zirconia heads appear to have prosthesis survivorship and polyethylene wear equivalent to those of THAs with traditional materials, but differing quality among zirconia heads could lead to poor survivorship of prostheses. [ABSTRACT FROM AUTHOR]

Abstract: A proposed new type of diamond-based frequency device has been fabricated for the first time through the use of nano-crystalline diamond as the thin film component of a Film Bulk Acoustic Resonator (FBAR) device. The new fabrication process uses Si MEMS-based fabrication techniques on 200 nm thick nano-crystalline diamond deposited on a 4 inch silicon wafer. After completely removing the silicon substrate below the device by the BOSCH process, one port resonators with a diaphragm structure have been fabricated. All the devices produced in the first fabrication run operated successfully with a high frequency response of 3.5 GHz. [Copyright &y& Elsevier]

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]

Presents information on the application of ammonium sulphate surface treatment to the aluminum-gallium-arsenic/gallium arsenide heterojunction bipolar transistor. Suppression of the emitter size effect on the current gain of the aluminum compounds; Current voltage ideality factor at low current; Dependence of current gain on periphery to area ratio.

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]

Presents a correction to the article 'Suppression of the Emitter Size Effect on the Current Gain of AlGaAs/GaAs Heterojunction Bipolar Transistor by Utilizing (NH[sub4])[sub2]S[subx] Treatment,' by S. Shikata, H. Okada and H. Hayashi, which appeared in the 1991 issue of the 'Journal of Applied Physics.'

Presents a study that examined the annihilation characteristics of positrons in various types of diamonds. Measurements of two-dimensional angular correlation of positron annihilation; Amount of defects in type Ib synthesized diamond; Results of the double x-ray measurements.

The effect of substrate polishing on the surface morphology of epitaxially grown diamond films was investigated using conventional mechanical polishing and polishing with vacuum ultra-violet (VUV) light assistance. In addition, the influence of dry-etching treatment before epitaxial film growth was examined. An approximately 7 μm epitaxial film deposited on a polished diamond substrate with VUV assisted polishing had a very smooth surface roughness average up to 1.5 nm. The Schottky barrier diodes (SBDs) fabricated on the epitaxial layer exhibited favorable electrical characteristics. However, the pre-etching process resulted in roughening of the epitaxial layer surface and degraded the surface properties of SBDs. In contrast, the epitaxial layers deposited on mechanically polished diamond substrates exhibited rough surface morphologies and poor SBD electrical characteristics, regardless of pre-etching. Polishing assisted by VUV irradiation without pre-etching can be considered an excellent treatment of diamond substrate surfaces before epitaxial growth compared to conventional mechanical polishing. [Display omitted] [ABSTRACT FROM AUTHOR]

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]

Abstract: To obtain high current operation of the diamond SBDs, the device should be designed in a vertical type structure in order to minimize the device on-resistance. In this research, we have designed and developed the technology for fabrication of diamond vertical structure Schottky barrier diodes (vSBD) by utilizing Inductively Coupled Plasma etching technique. Free standing CVD grown epilayers (p+/p− =100μm/5μm) were obtained by removing the base Ib substrate on which the epi-layers were grown, using ICP etching process. After ICP etching, ohmic contact (Ti/Pt/Au) was made at the bottom of p+ layer, and Schottky contact (Mo) was made at top side on oxidized surface of p− layer, to realize Diamond/Mo vSBDs and were analyzed for their electrical characteristics. The SBDs showed a reproducible ideality factor close to 1.0, and a barrier height of 1.4eV, with a small standard deviation of 0.06 and 0.12eV respectively. Diodes in the vertical structure exhibited R on with a battery uniformity irrespective of their location on the wafer, compared the diodes in a pseudo-vertical structure. Room temperature I–V analysis of the fabricated vSBDs (70μm size) exhibited a high forward current density of 2980A/cm2 (=0.115A) with a low R onS of 8mΩcm2, which could be attained due to the vertical geometry of the diodes. At the high temperature operation, still higher current density could be obtained. Satisfactory reverse blocking characteristics also could be achieved with a breakdown field of 2.7MV/cm for small size diodes. [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]

Confinement of charge carriers in semiconductors by quantum wells is usually accomplished with layers that vary in elemental composition, such as aluminum gallium arsenide and gallium arsenide. We fabricated diamond superlattices by creating multilayer structures of isotopically pure carbon isotopes carbon-12 (12C) and carbon-13 (13C), which confine electrons by a difference in band-gap energy of 17 millielectron volts. Cathodoluminescence experiments performed at 80 kelvin showed that excitonic recombination in the higher-energy band of 13C vanishes in favor of increased recombination in the lower-energy 12C material. Carrier confinement was achieved in diamond superlattices made up of both thinner (30 nanometers) and thicker (up to 350 nanometers) layers. [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: Diamond nano-tips for measurements of living-cell activities have been fabricated from polycrystalline diamond/Si substrates using an inductively coupled plasma reactive ion etching (ICP-RIE) system. Mixtures of O2 and CF4 gas in a plasma was used as etching atmosphere. The etching properties of polycrystalline diamond film have been characterized. During etching of polycrystalline diamond, unintentional nano whiskers were formed due to the inhomogeneity of chemical bonds at grain boundaries. Finally, nano-tips longer than 10 μm and with an apex radius below 50 nm without nano whiskers have been realized. [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]

This research is focused on the development of a new technology for the fabrication of high-frequency surface acoustic wave (SAW) filters based on diamond and lithium niobate (LiNbO3) materials. LiNbO3 films are in situ deposited at 490 °C on polycrystalline diamond substrates by radio-frequency magnetron sputtering; a multistep growth process is proposed to deposit oriented LiNbO3 films with a smooth surface. Conventional interdigital transducers are fabricated on top of the piezoelectric LiNbO3 layer by standard optical lithography. We report experimental results for a SAW bandpass filter operating at a frequency above 2.30 GHz. We have observed that Rayleigh SAW modes are excited within this structure, with extremely high phase velocities (up to 12 000 m/s). This latter result illustrates the greatest advantage of using diamond as an acoustic substrate. It allows the fabrication of SAW devices operating in the gigahertz frequency range using standard optical lithography. [ABSTRACT FROM AUTHOR]

Strong modification of the optical spectra is apparent in nitrogen-doped chemical vapor deposited (CVD) diamonds. Nitrogen-vacancy (NV) defects in CVD diamond are effectively created by nitrogen doping with a high concentration of the gaseous phase. In particular, the 575 nm center and 637 nm centers are enhanced in intensity at a N doping level of around 1018 at./cm3, while nitrogen addition during CVD growth leads to quenching of both the exciton and H3 centers. The influence of nitrogen doping on the exciton and NV defect states in a homoepitaxial CVD diamond thin film was investigated by high-resolution cathodoluminescence experiment. In addition, Raman experiments were performed to detect the internal stress. The results show that the exciton and nitrogen-related defect emission spectra underwent a shift of the peak position to a longer wavelength by nitrogen doping. The characteristic Raman peak of diamond at 1332 cm-1 showed a shift toward lower wave numbers with increasing nitrogen incorporation. [ABSTRACT FROM AUTHOR]

To investigate electrically-active deep levels in high-resistivity single-crystalline diamond, particle-induced charge transient spectroscopy (QTS) techniques were performed using 5.5 MeV alpha particles and 9 MeV carbon focused microprobes. For unintentionally-doped (UID) chemical vapor deposition (CVD) diamond, deep levels with activation energies of 0.35 eV and 0.43 eV were detected which correspond to the activation energy of boron acceptors in diamond. The results suggested that alpha particle and heavy ion induced QTS techniques are the promising candidate for in-situ investigation of deep levels in high-resistivity semiconductors. [ABSTRACT FROM AUTHOR]

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]

A neutron bang time and burn history monitor in inertial confinement fusion with fast ignition are necessary for plasma diagnostics. In the FIREX project, however, no detector attained those capabilities because high-intensity X-rays accompanied fast electrons used for plasma heating. To solve this problem, single-crystal CVD diamond was grown and fabricated into a radiation detector. The detector, which had excellent charge transportation property, was tested to obtain a response function for intense X-rays. The applicability for neutron bang time and burn history monitor was verified experimentally. Charge collection efficiency of 99.5% ± 0.8% and 97.1% ± 1.4% for holes and electrons were obtained using 5.486 MeV alpha particles. The drift velocity at electric field which saturates charge collection efficiency was 1.1 ± 0.4 x 107 cm/s and 1.0 ± 0.3 x 107 cm/s for holes and electrons. Fast response of several ns pulse width for intense X-ray was obtained at the GEKKO XII experiment, which is sufficiently fast for ToF measurements to obtain a neutron signal separately from X-rays. Based on these results, we confirmed that the single-crystal CVD diamond detector obtained neutron signal with good S/N under ion temperature 0.5-1 keV and neutron yield of more than 109 neutrons/shot. [ABSTRACT FROM AUTHOR]

We present measurements of spin relaxation times (T1, T1 ρ, T2) on very shallow (≲5??nm) nitrogen-vacancy centers in high-purity diamond single crystals. We find a reduction of spin relaxation times up to 30 times compared to bulk values, indicating the presence of ubiquitous magnetic impurities associated with the surface. Our measurements yield a density of 0.01-0.1μB/nm2 and a characteristic correlation time of 0.28(3) ns of surface states, with little variation between samples and chemical surface terminations. A low temperature measurement further confirms that fluctuations are thermally activated. The data support the atomistic picture where impurities are associated with the top carbon layers, and not with terminating surface atoms or adsorbate molecules. The low spin density implies that the presence of a single surface impurity is sufficient to cause spin relaxation of a shallow nitrogen-vacancy center. [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]

We synthesized a mosaic diamond wafer 2 in. in size (40×60mm²), which consisted of 24 single-crystal diamond (SCD) plates 10×10mm² in area, by using microwave plasma chemical vapor deposition. Even by using a cloning technique, cracking frequently occurred and the non-uniformity was remarkable for wafers that were larger than 1 in. in size. This has not been observed in smaller samples before. Appropriate crystallographic directions could avoid the cracking and is one of the predominant factors in fabricating large area SCD wafers. Comparison with numerical simulations highlighted the importance of uniformity of the substrate temperature distribution on the uniformity of the growth. [ABSTRACT FROM AUTHOR]

We present experimental results on the band-gap energies of homoepitaxial diamond films with isotopic compositions ranging from nearly pure carbon- 12 (12C) to nearly pure carbon- 13 (13C). Diamond crystals were grown by microwave plasma-assisted chemical vapor deposition, which controls the isotope composition and minimizes the density of impurities and defects. We find that the isotope substitution of 12C by 13C increases the band-gap energy in diamond by up to 15.4 meV at 79 K. The increase at room temperature is estimated from the temperature dependence of the band-gap renormalization due to electron-phonon interaction and is found to be even larger than that at low temperatures. These results unambiguously demonstrate the possibility of band-gap engineering of diamond via control of the isotopic composition. [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: Thick (∼100μm) undoped diamond films were grown homoepitaxially on single crystal (SC) diamond substrates by microwave plasma chemical vapor deposition (CVD). To form a freestanding SC diamond film (plate), the substrate was pre-ion-implanted with high-energy ion beams before the film growth, and after the thick-film deposition, the substrate was eliminated using a lift-off method, resulting in fabrication of a SC CVD diamond plate. Two samples were prepared; sample 1 was grown on a (001) oriented, nitrogen doped CVD SC diamond at ∼900°C with the input microwave power of 1.7kW, while sample 2 was grown on a (001) oriented, high-pressure high-temperature synthesized type-Ib SC diamond at ∼900°C with the input microwave power of 1.25kW. The formed SC plates have high optical transparencies, indicating no remarkable optical absorptions seen in the wavelength from ultraviolet to near infrared. The photoluminescence (PL) spectra of both samples show strong free exciton FE peaks, while in sample 2 relatively strong optical emissions corresponding to nitrogen related centers were observed in the visible region. After the metal electrodes were formed on both faces of the SC diamond plate to fabricate a sandwich-type diamond particle detector, the energy spectra of 5.486MeV α-particles from 241Am were measured. The charge collection efficiencies (CCEs) of sample 1 were CCE=98% for a hole transport and CCE=89% for an electron transport, respectively, while CCEs of sample 2 were CCE=80% for a hole transport and CCE=78% for an electron transport, respectively. These results indicate that both holes and electrons in sample 2 were trapped much more than those in sample 1. Possible candidates of carrier capture centers are nitrogen and/or nitrogen-vacancy centers observed in PL, nonradiative defect (complex) centers, extended defects such as threading dislocations observed in micrographs taken with polarizers. The different growth conditions most likely affected crystallinity and responses to α-particles of the samples. [Copyright &y& Elsevier]

Abstract: Crystallinity of a freestanding large (size: ~9×7mm) undoped single crystal (SC) diamond film grown by plasma chemical vapor deposition (CVD) and radiation response of a sandwich-type radiation detector made from this SC plate to α particles were investigated. The freestanding SC film was formed by elimination of a substrate using a so-called “lift-off method” after the growth of a thick-film on a pre-ion-implanted substrate. The formed SC plate has a high optical transparency, indicating no remarkable optical absorption seen in the wavelength from ultraviolet to near-infrared region. In the energy spectra of 5.486MeV α-particles, relatively sharp peaks were observed for both hole and electron transits. For the hole transit, the peak resolution of the pulse height distribution and charge collection efficiency (CCE) were ~0.7% and 98%, respectively. On the other hand, for the electron transit, the peak resolution and CCE obtained were ~4.4% and 89%, respectively. In the photoluminescence spectrum at room temperature, a strong sharp peak around 235nm corresponding to free exciton and a weak visible band mainly related to nitrogen-vacancy complex were observed. The spectral width of the (004) plane X-ray rocking curve was 16.5″. The micrograph taken using crossed-polarizers demonstrated that there are some white regions and four-petaled patterns, originating from internal strain and most likely threading dislocations, respectively. [Copyright &y& Elsevier]

Abstract: In this article, we present a study of surface stress measurements of a thick single-crystal diamond (SCD) layer (110μm) deposited onto a high-temperature high-pressure (HTHP) Ib substrate. The measurement is based on observations of the deformation of the backside of the HTHP substrate due to internal stress that varies as the thickness of the SCD layer is modified by ion-beam etching. The deformation is obtained from the height-distribution analysis of interference microscopy (IM) observation. The results show that the tensile surface stress σ increases linearly with SCD-layer thickness with t f according to σ =0.065tf MPa/μm. The tensile surface stress may be attributed to the intrinsic stress that originates from the lattice mismatch between the CVD-diamond layer and the HTHP-Ib substrate. The increased internal stress is a principle cause of crack formation of the crystal. [ABSTRACT FROM AUTHOR]

Abstract: Crystallinity of freestanding large (size: ∼9×9mm) undoped single crystal (SC) diamond films grown by plasma chemical vapor deposition (CVD) was investigated using optical transmission spectroscopy, polarized optical microscope, X-ray rocking curves, X-ray topographs and photoluminescence. The production of the freestanding film was performed by elimination of the substrates using a so-called “lift-off method” after the growth of a homoepitaxial thick-film on a pre-ion-implanted substrate. The remarkable optical absorption in the wavelength from ultraviolet to near-infrared region (220–2500nm) was not seen, similarly to a high-pressure, high-temperature (HPHT) synthetic type-IIa diamond. The cross-nicol optical microscope image demonstrated that there are patchy white regions and many dotted patterns, originating from internal strain and threading dislocations, respectively, over the entire area of the sample. The dotted patterns, corresponding to threading dislocations observed in the cross-nicol image, were also observed in X-ray topographs. The full width at half maximum (FWHM) of the X-ray rocking curve was 19.8″. In photoluminescence spectra at room temperature, a strong sharp peak around 235nm corresponding to the recombination emission of free exciton was observed, while there were no remarkable emission peaks related to various defects typically observed in the visible region. [ABSTRACT FROM AUTHOR]

Abstract: Using lift-off method, we synthesized large self-standing plasma CVD diamond films on various substrates. Charge carrier transportation in diamond was measured using α particle measurements and TOF methods with a short-pulsed UV laser. The high-quality films were synthesized rapidly. We observed the maximum transit time of holes and electrons shorter than 5ns. The lift-off method is useful to fabricate the high-quality diamond with excellent drift velocities of the charge carrier. The charge transport characteristics of our diamond films are comparable to those of a commercially available (Element Six Ltd.) electronics grade IIa diamond single crystal. [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]

Abstract: We have investigated the crystallinity of a self-standing homoepitaxial diamond film grown at a high rate using a polarized optical microscope, X-ray rocking curves and X-ray topographs. The self-standing film was made by removing a synthetic type-Ib(001) substrate after the film growth using a “lift-off process”. The cross-nicol optical microscope image demonstrated that there exists strain spreading at a relatively large area in the film and the strain inherits over that in the substrate. From cross-sectional X-ray topographs, the dominant defects, observed as dotted patterns in plan-view topographs and micrographs, are dislocations extending along the film growth direction 〈001〉 and generating at the interface between the film and the substrate. The density of such defects counted from these measurements was ~1×103 cm−2. The dotted patterns observed in X-ray topographs of (220), (−220) and (400) diffraction planes are almost the same with each other, suggesting that dominant line defects along 〈001〉 are mixed dislocations with a burgers vector directing between 〈001〉 and in-plane of the sample. The high resolution X-ray rocking curve showed that the peak is very sharp with full width at half maximum of 7.56″, which indicates that imperfection of our single-crystal diamond plate is almost the same as that of high-quality high-pressure high-temperature, synthetic type-Ib diamond. [Copyright &y& Elsevier]

Abstract: We have carried out simulations of microwave plasmas inside a reactor for thick diamond syntheses. In a model reactor used in the calculation, a diamond substrate with finite thickness and area is taken into account. Distributions of electric field, density of microwave power absorbed by the plasma, temperatures and flow field of gas have been studied not only in a bulk region inside a reactor but also a local region around the substrate surface. Numerically predicted distributions of (1) microwave power density, (2) temperature on the top surface of the substrate, and (3) gas flow around the substrate imply that the adopted arrangement of the substrate is not desirable for continuous growth of large diamond crystals. [Copyright &y& Elsevier]

Abstract: Micro-Raman spectroscopy was used to evaluate the internal stress of the cross section of a large single crystal diamond (SCD) bulk of 9mm thickness, which was synthesized under a repetitive growth by using microwave plasma chemical vapor deposition (MWPCVD). The variation of internal stress estimated from Raman shift, is approximately 0.08GPa. In addition, the nitrogen effect on internal stress is evaluated approximately 4.05×10−2 GPa·ppm−1, which is based on our simplified model. [Copyright &y& Elsevier]