An assessment of contact metallization for high power and high temperature diamond Schottky devices

Different metals W, Al, Ni and Cr were evaluated as Schottky contacts on the same p-type lightly boron doped homoepitaxial diamond layer. The current–voltage (I–V) characteristics, the series resistance and the thermal stability are discussed in the range of RT to 625 K for all Schottky devices. High current densities close to 3.2 kA/cm2 are displayed and as the series resistance decreases with increasing temperature, proving the potential of diamond for high power and high temperature devices. The thermal stability of metal/diamond interface investigated with regards to the Schottky barrier height (SBH) and ideality factor n fluctuations indicated that Ni and W are thermally stable in the range of RT to 625 K. Current–voltage measurements at reverse bias indicated a maximum breakdown voltage of 70 V corresponding to an electric field of 3.75 MV/cm. Finally, these electrical measurements have been completed with mechanical adhesion tests of contact metallizations on diamond by nano-scratching technique. These studies clearly reveal Ni as a promising contact metallization for high power, high temperature and good mechanical strength diamond Schottky barrier diode applications

Surface production of negative ions from pulse-biased nitrogen doped diamond within a low-pressure deuterium plasma

International audienceThe production of negative ions is of significant interest for applications including mass spectrometry, materials surface processing, and neutral beam injection for magnetic confined fusion. Neutral beam injection sources maximise negative ion production through the use of surface production processes and low work function metals, which introduce complex engineering. Investigating materials and techniques to avoid the use of low work function metals is of interest to broaden the application of negative ion sources and simplify future devices. In this study, we use pulsed sample biasing to investigate the surface production of negative ions from nitrogen doped diamond. The use of a pulsed bias allows for the study of insulating samples in a preserved surface state at temperatures between 150 ∘ C and 700 ∘ C in a 2 Pa, 130 W, (n e ∼ 10 9 cm −3 , T e ∼ 0.6 eV) inductively coupled deuterium plasma. The negative ion yield during the application of a pulsed negative bias is measured using a mass spectrometer and found to be approximately 20% higher for nitrogen doped diamond compared to non-doped diamond. It is also shown that the pulsed sample bias has a lower peak negative ion yield compared to a continuous sample bias, which suggests that the formation of an optimum ratio of defects on its surface can be favourable for negative ion production

Enhancing surface production of negative ions using nitrogen doped diamond in a deuterium plasma

The production of negative ions is of significant interest for applications including mass spectrometry, particle acceleration, material surface processing, and neutral beam injection for magnetic confinement fusion. Methods to improve the efficiency of the surface production of negative ions, without the use of low work function metals, are of interest for mitigating the complex engineering challenges these materials introduce. In this study we investigate the production of negative ions by doping diamond with nitrogen. Negatively biased ($-20$ V or $-130$ V), nitrogen doped micro-crystalline diamond films are introduced to a low pressure deuterium plasma (helicon source operated in capacitive mode, 2 Pa, 26 W) and negative ion energy distribution functions (NIEDFs) are measured via mass spectrometry with respect to the surface temperature (30$^{\circ}$C to 750$^{\circ}$C) and dopant concentration. The results suggest that nitrogen doping has little influence on the yield when the sample is biased at $-130$ V, but when a relatively small bias voltage of $-20$ V is applied the yield is increased by a factor of 2 above that of un-doped diamond when its temperature reaches 550$^{\circ}$C. The doping of diamond with nitrogen is a new method for controlling the surface production of negative ions, which continues to be of significant interest for a wide variety of practical applications

Elaboration de films épais de diamant monocristallin dopé au bore par MPAVCD pour la réalisation de substrats de diamant P +

L objectif principal de ce travail de thèse est la synthèse de films épais (>100 m) de dia-mant monocristallin fortement dopés au bore permettant la fabrication de substrats de diamant et le développement de composants verticaux pour des applications en électronique de puissance. Dans un premier temps, l effet des différents paramètres de croissance a été étudié. Il a ainsi été mis en évidence l existence d une fenêtre de DPMO (caractérisée par le couple pression/puissance) qui permet d assurer un bon compromis entre qualité, vitesse de croissance et efficacité de dopage per-mettant la croissance de films de plusieurs centaines de micromètres. Ensuite, afin d assurer un bon contrôle de la morphologie finale des cristaux, un modèle de croissance géométrique 3D développé au laboratoire, associé à des expériences de croissance dans un plasma H2/CH4/B2H6 a permis de montrer que les conditions déterminées précédemment entrainaient systématiquement l apparition de faces indésirables (110) conduisant à la rupture du cristal. L ajout de faibles quantités d oxygène dans la décharge a permis d interdire la formation de ces faces indésirables et de conserver l intégrité du cristal, condition indispensable pour le développement de substrats permettant la réali-sation de composants électroniques verticaux. Enfin, des substrats CVD à différentes concentration ont été fabriqués et caractérisés par SIMS, FTIR, spectroscopie Raman et diffraction des rayons X haute résolution. Cette étude a ainsi montré l excellente qualité cristalline des films réalisés y com-pris pour les dopages les plus élevés (>1020 cm-3 en bore). Des mesures de résistivité électriques ont par ailleurs montré que les substrats les plus dopés présentent des résistances suffisamment fai-bles pour être utilisés comme substrat pour des composants en électronique de puissance.The main objective of this thesis is the synthesis of thick films (> 100 microns) of monocrystalline diamond heavily doped with boron for the manufacture of diamond substrates and the development of vertical components for applications in power electronics. At first, the effect of different growth parameters was studied. It was thus demonstrated the existence of a window of DPMO (characterized by the pressure torque / power) which ensures a good compromise between quality, speed of growth and doping efficiency per-putting film growth several hundred micrometers. Then, to ensure proper control of the final morphology of the crystals, a 3D geometric model of growth developed in the laboratory, together with growth experiments in a plasma H2/CH4/B2H6 showed that the conditions determined previously resulted systematically the appearance of undesirable side (110) leading to the breakdown of the crystal. The addition of small amounts of oxygen in the discharge allowed to prohibit the formation of these side reactions and to maintain the integrity of the crystal, a prerequisite for the development of substrates for the realization of electronic components vertical. Finally, CVD substrates at various concentrations were fabricated and characterized by SIMS, FTIR, Raman spectroscopy and X-ray diffraction resolution. This study has shown the excellent crystalline quality of the films includ-ing for the highest doping (> 1020 cm-3 boron). Electrical resistivity measurements have also shown that most doped substrates have sufficiently low resistance-able to be used as a substrate for power electronics components.PARIS13-BU Sciences (930792102) / SudocSudocFranceF

Performance Enhancement of Al 2 O 3 /H-Diamond MOSFETs Utilizing Vacuum Annealing and V 2 O 5 as a Surface Electron Acceptor

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Radiative lifetime of boron-bound excitons in diamond

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Synthesis of High Quality Transparent Nanocrystalline Diamond Films on Glass Substrates Using a Distributed Antenna Array Microwave System

Diamond is a material of choice for the fabrication of optical windows and for protective and anti-reflecting coatings for optical materials. For these kinds of applications, the diamond coating must have a high purity and a low surface roughness to guarantee a high transparency. It should also be synthesized at low surface temperature to allow the deposition on low melting-point substrates such as glasses. In this work, the ability of a Distributed Antenna Array (DAA) microwave system operating at low temperature and low pressure in H2/CH4/CO2 gas mixture to synthesize nanocrystalline diamond (NCD) films on borosilicate and soda-lime glass substrates is investigated aiming at optical applications. The influence of the substrate temperature and deposition time on the film microstructure and optical properties is examined. The best film properties are obtained for a substrate temperature below 300 °C. In these conditions, the growth rate is around 50 nm·h−1 and the films are homogeneous and formed of spherical aggregates composed of nanocrystalline diamond grains of 12 nm in size. The resulting surface roughness is then very low, typically below 10 nm, and the diamond fraction is higher than 80%. This leads to a high transmittance of the NCD/glass systems, above 75%, and to a low absorption coefficient of the NCD film below 103 cm−1 in the visible range. The resulting optical band gap is estimated at 3.55 eV. The wettability of the surface evolves from a hydrophilic regime on the bare glass substrates to a more hydrophobic regime after NCD deposition, as assessed by the increase of the measured contact angle from less than 55° to 76° after the deposition of 100 nm thick NCD film. This study emphasizes that such transparent diamond films deposited at low surface temperature on glass substrate using the DAA microwave technology can find applications for optical devices

Spin-Orbit Effects on Exciton Complexes in Diamond

International audienceUltrafine splittings are found in the optical absorption spectra of boron-doped diamond measured with high resolution. An analytical model of an exciton complex is developed, which permits assigning all absorption lines and sizing the interactions among the constituent charges and crystal field. We conclude that the entry of split-off holes in the acceptor-bound exciton fine structure yields two triplets separated by a spin-orbit splitting of 14.3 meV. Our findings thereby resolve a long-standing controversy [R. Sauer et al., Revised fine splitting of excitons in diamond, Phys. Rev. Lett. 84, 4172 (2000).; M. Cardona et al., Comment on “Revised fine splitting of excitons in diamond,”, Phys. Rev. Lett. 86, 3923 (2001).; R. Sauer and K. Thonke, Sauer and Thonke reply, Phys. Rev. Lett. 86, 3924 (2001).], revealing the underlying physics common in diverse semiconductors, including diamond

Phonon-assisted transitions of bound excitons in diamond: Analysis by mirror symmetry

International audienceThis study aims at a quantitative understanding of the optical spectra taken from bound excitons weakly coupled to phonons in indirect semiconductors, which had been missing for decades. Insights on the properties of excitons bound at neutral acceptor impurities are obtained by analyzing the spectra reported for diamond with appropriate boron doping [Y. Kubo, Appl. Phys. Lett. 114, 132104 (2019)APPLAB0003-695110.1063/1.5089894]. We focus on the mirror symmetry holding between phonon-assisted absorption and luminescence simultaneously regarding energies, linewidths, and intensities. New analytic expressions are proposed to reproduce the spectra of phonon-assisted recombination lines. The detailed analysis reveals the contribution from excited bound-exciton states whose origin is discussed and modeled. Taking them into account improves simulation of the bound-exciton optical spectra in indirect band-gap semiconductors up to a quantitative level

A route towards high quality p doped layers suitable for high power electronics: Improvement of dislocation density in single crystal CVD diamond

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