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The p-to-n-type conversion of particular B-doped homoepitaxially grown diamond layers upon deuterium plasma treatment was discovered three years ago. However, many questions regarding the reproducibility of the effect for samples of different origins remain unanswered up to now, in particular the role of the electrical contacts and the possibility of a surface inversion layer being responsible for the n-type conductivity, the thermal stability and origin of the donor. Here we address the above questions. We show that the p-to-n conversion is closely related to the presence of defects, which can vary, on a macroscopic scale, in different regions of the same sample. The p-type regions containing a small concentration of defects are found to be converted to n-type upon deuteration. In contrast, the regions counting a high defect density exhibit very low p-type conductivity related to passivation of the boron acceptors by deuterium accompanied by a large uptake of D on defects. We show that the n-type conversion can be equally observed with three different kinds of contacts (silver paint, implanted and evaporated). We prove that the n-type conversion is a bulk effect and not a surface effect. We find that the thermal stability of the n-type complex is limited to temperatures lower than 200 °C. The temperature dependence of the carrier concentration measured by the Hall effect at different stages of the conversion process is fitted following the formalism describing the conduction mechanisms in a partially compensated semiconductor. The fact that the donor concentration in the as-deuterated state is very close to the boron concentration strongly suggests that the new-formed donor complexes contain both D and B.

From the high ionization energy Ei = 0.368 eV and high solid solubility ≥ 1.4 × 1022 cm− 3 of boron in diamond, metallic conductivity is expected on the boron impurity band within the band gap (Mott model). On the contrary, the numerical models used to describe the superconductivity of metallic diamond mainly use the Bardeen model with a Fermi level within the valence band. Taking into account the decrease to zero of Ei through the high [B] range and the band gap narrowing through the high and heavy [B] ranges, both specific of the Bardeen model, we discuss the validity of the Mott and Bardeen models from the literature and cathodoluminescence and Raman experiments. They agree with the Mott rather than the Bardeen model. Several experiments independently show the coupling of boron related levels with the zone centre optical phonons which soften for heavy [B]. The Mott model might explain the similar range of the superconductivity temperature of homoepitaxial and polycrystalline films from the similarity of their boron impurity band.

As-grown (100) homoepitaxial diamond films with boron concentrations [B] from 4.6x10 16 to 1.5 x 102' cm -3 have been analysed using X-ray photoelectron spectroscopy (XPS). Their C Is core levels contain a dominant component around 284.17 ± 0.2 eV ascribed to sp 3 C and a main secondary component around 284.88 ± 0.2 eV ascribed to CH x (x ≥ 2) on surface defects. Their relative concentration decreases and increases, respectively, as [B] increases. A significant component around 286.4 ± 0.2 eV ascribed to ether group (C-O-C) remains nearly constant up to [B] ≈ 3 x 1020 cm -3 , then increases for greater boron concentrations. Other components around 283.0 ± 0.2, 287.69 ± 0.2 and 288.76 ± 0.2 eV ascribed, respectively, to sp 2 C, carbonyl (C=O) and carboxyl (HO-C=O) on surface defects remain with low concentrations. The occurrence of these XPS components, their assignments and their relative concentrations are satisfactorily compared to those previously found for IIb crystals with (100) surface and for polycrystalline films with [B] around 10 19 and 7 x 10 20 cm -3 .

About 20 μm thick films were deposited in the same run by MPCVD at 900 °C on Si substrates and then hydrogenated in situ during 30 min with a hydrogen plasma at the same temperature. Their surfaces were kept as prepared or more or less strongly oxidized by annealing at 600 °C under ambient atmosphere or by sulphochromic acid or aqua regia treatments. Raman spectra were excited at 325 and 632.8 nm. Spectra of the as-prepared sample exhibit structures around 2835 and 2895 cm–1 from monohydride carbon–hydrogen ascribed to the atomically flat (111) and (100) areas, respectively, on the facets of the sample surface crystallites. The decrease of these structures in the normalized spectra after the various oxidation treatments confirms these assignments. The decrease is smaller for the aqua regia treatment than for the two other treatments which give similar effects. Other Raman signals from sp2 C around 1589 cm–1 and CHx bonds around 2930, 2952, 3025 and 3050 cm–1 originate from species at the surface and within the films. Their variation with the oxidizing treatments indicates a significant contribution from the surface species. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A general view of the key issues which have to be surmounted for building elementary devices such as Schottky diodes on homoepitaxial p-type diamond layers is presented. The growth process of double homoepitaxial layers, comprising a stack of both high and low boron doped films, is described and boron concentrations are analysed by means of cathodoluminescence. The methods used for masking, performing lithography on 3 × 3 mm 2 samples and etching are delineated. Several ohmic contacts are compared. Surface treatments necessary for the Schottky diode technology are analysed and discussed. Two methods for achieving adherent Schottky contacts are compared and the electrical characteristics of diodes are studied as a function of the morphology, defect content and doping of the diamond layer, metal stack which is used, temperature history of the sample and passivation post-processes such as dry etching.

A set of MPCVD films was prepared from 0.5% CH 4 /H 2 and B 2 H 6 with B/C in the gas phase from 0 to 8000 ppm. When the excitation wavelength of their Raman spectra is switched from 632.8 to 325 nm: The Fano induced dip switches from high to low wave number side of the “1332 cm − 1 ” signal. The deformation and the downward shift of this signal decrease. The G band, diamond second order, CH x bands appear. The evolution of these bands with increasing B / C is reported and discussed.

Homoepitaxial films containing from 2 × 10 16 to 1.75 × 10 21 B−cm − 3 are deposited by Microwave Plasma Chemical Vapor Deposition on Ib substrates. From their full continuity for all [B] with those found for the lower [B], the high energy structures in their cathodoluminescence spectra originate from recombination of free and boron bound excitons, with no signal from band to band transitions. Therefore, the metallic conduction takes place on a boron impurity band with a Fermi level outside the valence band in metallic diamond, in agreement with the original Mott model. The energy for the recombination of the boron bound exciton assisted by the TO phonon decreases from 5.211 to 5.036 eV when [B] increases from ≈ 1.5 × 10 19 to 6 × 10 20 cm − 3 , then remains constant. An interpretation of the results somewhat similar to that used for GaP:N might account for the excitons bound to the boron atoms of the impurity band.

Heavily boron doped 1.8 to 2.4 µm thick homoepitaxial diamond films with 1.5 × 1021 cm–3 ≤ [B] ≤ 1.75 × 1021 cm–3 have been deposited directly on their (100) Ib substrates at 830 °C. Their cathodoluminescence spectra probe the controlled thicknesses from 0.28 to 2.8 µm, therefore the bulk of the films as well as their interfaces with their substrates. The bulk of these films exhibit a band with shoulders ascribed to BETO (5.036 eV), FETO (5.094 eV) and BENP (5.184 eV) excitons whose energies are downward shifted by about 180 meV in comparison with monocrystalline diamond with low [B] < 5 × 1018 cm–3. This large shift allows the appearance of narrow peaks around 5.216, 5.271 and 5.357 eV ascribed to BETO, FETO and BENP from interfacial layers with low [B]. From their BETO to FETO ratio, their concentration of boron on isolated substitutional sites is significantly lower than their total low [B] content measured by SIMS. A tentative model is proposed to explain the characteristics of these 40 to 160 quasihomogeneous interfacial layers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Diamond is a very large bandgap material arising high expectations either for optoelectronic applications or for active semiconducting layers in specific electronic devices to be used under extreme conditions of pressure, temperature, wear or radiation, as well as in chemically aggressive environments. Unintentionally boron-doped diamond layers were grown by microwave plasma-assisted chemical vapour deposition (CVD) on {001}-oriented undoped Ib substrates with the addition of oxygen gas during growth. The relative quantities of nitrogen and boron incorporated in the diamond lattice are evaluated by cathodoluminescence (CL) spectra recorded at 5 K. Two different effects are shown to limit nitrogen incorporation: the substrate crystalline quality and the addition of oxygen into the precursor during the growth. First, the CL spectra are shown to change strongly near the edges of the substrate in the regions corresponding to different bulk crystal growth modes. Some regions show a luminescence governed by UV emission while in other regions, where the H3 defect-related luminescence of the substrate is much stronger, the film UV emission is reduced. Second, the relative importance of the free exciton emission with respect to those from the nitrogen-related H3 centre and from the boron-bound exciton is shown to increase with the addition of oxygen during growth. Such observations are of first importance to improve the spectral emission and absorption threshold of the diamond material in the deep UV range. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The lack of a shallow donor in diamond with reasonable room temperature conductivity has been a major obstacle, until now, for the realization of many diamond based electronic devices. Most recently it has been shown that exposure of p-type (B doped) homoepitaxial diamond layers to a deuterium plasma can result in the formation of n-type diamond with a shallow donor state (Ea=0.34eV) and high room temperature mobility (430cm2∕Vs) [Z. Teukam et al., Nat. Mater. 2, 482 (2003); C. Saguy et al., Diamond Relat. Mater. 13, 700 (2004)]. Experimental results, based on the comparison of secondary ion mass spectrometry profiles of B and D and Hall effect measurements at different temperatures are presented. They confirm the previous speculation that some deuterium related complex is responsible for the donor activity in diamond. These donors are shown to be formed in a two-step process. First, deuterium diffuses into the entire B containing layer rather slowly, being trapped by the boron acceptors and passivating t...

We show that deuteration of a series of boron-doped (100) diamond epitaxial layers can lead to a p-type to n-type conversion. The n-type diamond epilayers have electrical conductivities of a few S/cm at 300 K. These values are a factor 10 3 -10 5 higher than the n-type conductivities achieved with phosphorus doping. This is a consequence of the shallow donor character of the deuterium-related donors inducing the conversion (ionization energy of 0.34 eV) and of the high donor concentrations. We also show that these donors are formed in a two-step process. First, all the acceptors form (B, D) complexes with one deuterium per boron atom. Then, the presence of excess and more mobile deuterium triggers the formation of the shallow donors.

We study the signals from excitons and defects from the cathodoluminescence spectra (CL) of the p - /pseudo substrate sample. The CL from the p - film are determined from the variation of the CL of the sample as the voltage of the exciting electron beam increases. At the lower voltages, it probes the p - film. The CL is dominated by the free exciton associated with the TO phonon (FE TO , FWHM = 6 meV), but shows also small signals (ratio = 5 x 10 -2 ) mainly from the A band (and other 2.6, 3.6 and 4.05 eV wide bands) and tiny signals from the 5 RL defect. At the higher voltages it probes also the Ib substrate and is dominated by the signals of the H3 defects in the Ib substrate. The p - film appears almost homogeneous, and of good quality from the characteristics of its exciton.

The conversion of the conductivity of B-doped homoepitaxially grown diamond layers from p- to n-type upon deuteration and its reconversion to p-type following annealing is extensively studied. Several B doped samples have been converted to n-type when exposed to a deuterium plasma at approximately 500 °C. The n-type features are related to D uptake of the samples. The donors, thus formed, have an ionization energy of approximately 0.34 eV below the conduction band edge and a high RT (room temperature) mobility (up to 430 cm2/V s), as determined by Hall effect measurements as a function of temperature. In the B-doped layers that do convert to n-type upon deuteration, the D to B concentration ratio is found to be in the range of one to two. Higher D uptake (D to B ratio ≫2) must be connected to B-doped layers containing a large amount of growth defects, which trap the D. The exact nature of the donor is yet unknown. However, the reversibility of the effect and its relationship with the D concentrations suggest that deuterium is involved in the formation of some complex with B or with some other defects.

We study the Raman spectra of heavily boron ([B]>3×1020 cm−3) polycrystalline and homoepitaxial diamond films. A detailed comparison of the structures of these spectra can be done only after normalizations. As [B] increases in polycrystalline and homoepitaxial films, (i) the ‘1225 cm−1’ appear identical (ii) the maximum of the ‘500 cm−1’ band shifts to lower wavenumbers while its intensity increases (ii) the overall shapes of the ‘500 cm−1’ bands remain similar while their full widths at half maximum are higher in the polycrystalline films. From these characteristics and previous works, the ‘500 cm−1’ band is proposed to originate from local vibrational modes of boron pairs.

Diamond deposition is performed at 900 °C on Ib substrates in the middle of the plasma ball from gas mixtures containing 1% CH 4 and 0, 0.125, 0.25, 0.375 and 0.5% O 2 at a pressure of 50 Torr. Smooth homogeneous homoepitaxial films of good quality whose characteristic depends systematically on the percentage of O 2 are obtained on the backside of the substrates. Weak structures (in the 10 −5 –10 −3 range compared to the 1332 cm −1 peak) appear in their Raman spectra excited by 632.8 or 514.5 nm lasers. They correspond to (i) N-vacancy centers (2.156 eV luminescence), but no Si-vacancy center (no 1.681 eV luminescence) (ii) Ultra nanocrystalline (diameter 4–6 nm) diamond and micro crystalline graphite residual phases which are detected from their specific signals. Lower concentrations of both residual parasitic phases and N complexes are obtained in the 0.125–0.375% O 2 film.

Schottky contacts on the (1 0 0) surface of homoepitaxial boron-doped diamond films are investigated. The potential barrier height of a metallic interface build in a ultra-high vacuum (UHV) chamber by the deposition of one monolayer of titanium, subsequently covered with a thick film of silver, is studied. From X-ray photoelectron spectroscopy spectra, a barrier height of 1.7 eV is derived. However, after annealing in air, the current–voltage characteristics analysed at several temperatures allow the plot of a Richardson's diagram, which yields a 3.4 eV barrier height, higher than half the diamond bandgap. Annealing of the Ti layer at 400 °C in UHV induces carbide formation, which ensures a good adhesion of the metallic coating. Comparison of the series resistance of diodes implemented either only on a moderately doped diamond layer (a few 1017 cm−3) or on p/p+ double layer is done. In the former case, the 0.38 eV activation energy for boron acceptors ionisation is clearly identified while it decreases to 0.06 eV in the latter case, with an absolute value of the series resistance typically five orders of magnitude lower at ambient temperature. Consequences and applications of these findings are presented.

Diamond is a unique semiconductor for the fabrication of electronic and opto-electronic devices because of its exceptional physical and chemical properties. However, a serious obstacle to the realization of diamond-based devices is the lack of n-type diamond with satisfactory electrical properties. Here we show that high-conductivity n-type diamond can be achieved by deuteration of particularly selected homo-epitaxially grown (100) boron-doped diamond layers. Deuterium diffusion through the entire boron-doped layer leads to the passivation of the boron acceptors and to the conversion from highly p-type to n-type conductivity due to the formation of shallow donors with ionization energy of 0.23 eV. Electrical conductivities as high as 2omega(-1) x cm(-1) with electron mobilities of the order of a few hundred cm2 x V(-1) x s(-1) are measured at 300 K for samples with electron concentrations of several 10(16) x cm(-3). The formation and break-up of deuterium-related complexes, due to some excess deuterium in the deuterated layer, seem to be responsible for the reversible p- to n-type conversion. To the best of our knowledge, this is the first time such an effect has been observed in an elemental semiconductor.

BOLD (Blind to the Optical Light Detectors) est un projet regroupant plusieurs laboratoires, instituts, et industriels europeens ; il est dedie aux developpements et aux tests de nouveaux detecteurs pour l'observation du Soleil dans l'ultraviolet. Notre investigation repose sur les proprietes des solides a large bande interdite, tels que le diamant ou les nitrures d'aluminium et de gallium (AlGaN). L'initiative est proposee en vue des instruments UV du futur Orbiteur Solaire de l'Agence Spatiale Europeenne (ESA), mais plusieurs autres applications scientifiques ou industrielles en beneficieront. L'insensibilite au visible (solar-blindness) des nouveaux senseurs sera tres avantageuse. Elle permettra une plus grande sensibilite des instruments, et donc plus de resolution spatiale, et une plus haute cadence. Une technologie fondee sur le diamant ou sur les AlGaN plutot que sur le silicium autorisera aussi une resistance accrue aux rayonnements ionisants (rad-hardness), et donc la stabilite indispensable aux conditions extremes que connaitra l'Orbiteur Solaire. Nous presentons ensuite quelques resultats de campagnes de mesures entreprises dans le cadre du projet BOLD, et decrivons le programme envisage pour obtenir en quelques annees des cameras UV tres innovantes.

Hydrogen is a key impurity in diamond since it is unintentionally incorporated in all chemical vapor deposition (CVD) grown diamond layers.Its presence in the material can grossly affect its electrical and optical properties.Theoretically, hydrogen has been predicted to be present in diamond in one of the three charge states, H , H and H .Moreover it may form complexes q 0 y with impurities, native defects or with other hydrogen atoms.This paper is comprised of two parts: (a) a review of previous results of studies investigating different aspects of the diffusion of hydrogen (deuterium) in various kinds of diamonds.The diamonds studied are: undoped type IIa diamonds, undoped CVD diamond layers containing growth defects only, p-type B-doped homoepitaxially CVD grown diamond layers or B ion implanted type IIa diamonds and n-type P doped homoepitaxially CVD grown diamond or N-doped type Ib natural diamonds.Hydrogen is introduced in diamond by exposing the diamond surface to hydrogen plasma or by using hydrogen ion implantation.The following issues are discussed: (1) the influence of the interaction between H and the dopants and defects on the hydrogen diffusion. (2) The kinetic of (B, H), (P, H ) and (N, H) pair formation and dissociation. (3) The modification of the optical and electrical properties as a result of hydrogen incorporation and annealing. It is found that, under certain conditions, H diffuses into the B containing layer and it passivates B acceptors.In contrast, no H diffusion could be observed in n-type diamonds, up to 1000 8C. (b) Recent results of our group regarding other aspects related to the diffusion of H in diamond are presented.These include results on: (i) the influence of ion implantation related defects on the diffusion of deuterium.For this study type IIa samples implanted with B or non-dopant ions are used. (ii) The determination of the charge state of H or Hydefects complex as a function of diamond type.For that, annealing under bias is applied to deuterated diamond layers.We show that the presence of implantation defects retards the deuterium diffusion in a B-implantation doped diamond, demonstrating that D strongly interacts with defects, thus inhibiting diffusion.The new-formed complexes deteriorate the electrical properties of the diamonds and are very stable up to high temperatures.We confirm that, as expected, in highly B-doped CVD diamond layers, H diffuses as a positive ion.In lightly B-doped homoepitaxial layers, however, D is incorporated in complexes which seem to be negatively charged. � 2003 Elsevier Science B.V. All rights reserved.

Hydrogen diffusion is investigated in boron-doped diamond from the redistribution profiles under thermal annealing of an initial step-like profile of (B,H) pairs located in a shallow region below the surface. For boron concentrations in the range 2×1019–1×1020 cm−3, the profiles are Gaussian-like and effective diffusion coefficients can be calculated. From the diffusion activation energy, we deduce a (B,H) pair dissociation energy of 2.5 eV. For lower boron concentrations, the redistribution of hydrogen is inhibited by the presence of deep traps for hydrogen which might be associated with structural defects.

Raman scattering and infrared absorption characteristics of B-doped CVD diamond have been studied as a function of the temperature. First order Raman measurements show that the energy and the width of the Raman line depend on the acceptor concentration and, in particular for N A > 10 2 0 cm - 3 , the peak becomes asymmetric. This is due to a Fano resonance interaction, already reported in literature for samples with similar boron concentrations. The dependence of the Raman energy on temperature is reported; it is shown that the shift to lower energy due to anharmonic processes can be described by the Klemens model. Raman data have been compared to infrared absorption results previously obtained. The Fano resonance is also observed in infrared spectra at 1332 cm - 1 for samples with lower boron concentrations. The comparison of these features shows that two different processes take place.

c ´´ Abstract The incorporation of hydrogen in n-type diamond has been investigated through its non-intentional introduction during the growth and through post-growth diffusion experiments. In the first case, (111) n-type diamond homoepitaxial films doped with phosphorus have been grown by microwave plasma chemical vapor deposition from a CH qD mixture. The phosphorus 42 concentrations were in the range 1.3=10 -3=10 cm . The concentration of deuterium incorporated is usually 100 times 18 19 y3

Simultaneous etching of NID, lightly boron-doped, phosphorus-doped homoepitaxial CVD films and Ib HPHT crystal was achieved at RT in a home-made reactor producing O2 ECR plasma which was homogeneous on approximately 200 cm−2. Etching rates varying from 60 (at −30 V) to 40 or 120 nm/min (at −140 V) are obtained with n- or p-type-doped samples, respectively. These etching rates are higher than those with O2 RF plasma, and those with previous inhomogeneous O2 ECR plasma with samples at 100 °C.

b ¨¨ Abstract The n-type doping of diamond by sulfur and phosphorus has been investigated. Diamond thin films were grown epitaxially on (111) oriented synthetic type Ib crystals with phosphine added in the reactant gas (wPxywCxs100-1500 ppm). Each grown sample was characterized by FTIR absorption and conductivity vs. temperature measurements. The infrared signature of neutral substitutional phosphorus appeared as two peaks located at 523 and 562 meV. Activation energy of the conductivity was approximately 490-550 meV above 400 K. All characterizations performed so far suggest a successful n-type doping by phosphorus. Sulfur-doped diamond thin films were grown on (100) oriented synthetic Ib crystals with H S (wSxywCxs500-5000 2 ppm) added in the gas phase. Secondary electron microscopy, AFM and Raman scattering indicate a high quality homoepitaxy of the diamond film. The addition of H S induces a light green-gray or gray color of the doped film. The films are highly resistive 2 after growth and oxidation of the surface, as usual undoped diamond. However, after light-illumination the electrical and photoelectrical properties change drastically. The results are interpreted in term of compensated semiconductor, taking into account contamination by boron atoms. 2002 Elsevier Science B.V. All rights reserved.

MicroRaman signals excited at 457.8 nm have been obtained from some areas of heavily boron doped polycrystalline diamond films which have been used for electrochemical reactions. We could identify sp3 CH, CH2, CH3, all with narrow full width at half maximum. From comparisons to IR absorption from the bulk of undoped films and from the (111) and (100) surfaces of IIa crystal, and to Raman signals from the bulk of undoped polycrystalline films, we ascribed our micro Raman signals to CHx from the film surface. The sp3 CH2 and CH3 components appear more stable than the sp3 CH under CW laser exposure. This implies chemical bonding of H with C atoms of the film surface for all the sp3 CHx sites. This difference with the CHx at the surface of IIa crystals might originate from the heavy boron-doping of our films.

A long-term decay of the photocurrent under red light has been observed and analysed in polycrystalline CVD diamond films. The kinetics of this photocurrent decay is non-exponential and can rather be described by a combination of several exponential functions or by a stretched-exponential function. This relaxation is only observed if the samples are preliminary exposed to band-to-band UV light excitation during a few minutes and it is perfectly reproducible. This long-term relaxation of the below-gap photocurrent following UV exposure is not observed on a homo-epitaxial crystalline CVD layer, where the photocurrent remains almost constant. Therefore, it is related to the disorder in the CVD polycrystalline diamond films and to the broad distribution of localised gap states, which are mainly created by the grain boundaries. The results are discussed in terms of defect influence in a range of diamonds in relation with their nature and synthesis process.

BOLD (Blind to the Optical Light Detectors) is an international initiative dedicated to the development of novel imaging detectors for UV solar observations. It relies on the diamond and nitride materials that have lately undergone key advances. The investigation is proposed in view of Solar Orbiter UV instruments, for which the expected properties of the new sensors—visible blindness and radiation hardness—will be highly beneficial. Solar Orbiter is a selected Flexi mission of the European Space Agency (ESA). Despite various improvements over the last few decades, the present UV detectors exhibit limitations inherent to their actual technology. Yet the utmost spatial resolution, temporal cadence, sensitivity, and photometric accuracy will be decisive for the forthcoming space solar missions. The advent of imagers made of a large bandgap semiconductor would surmount many weaknesses, thus opening up new prospects and making the instruments cheaper. As for the ESA Solar Orbiter, the aspiration for wide bandgap semiconductor-based UV detectors is still more sensible, for the spacecraft will approach the Sun where the heat and the radiation fluxes are high. We depict motivations and present activities and programme to achieve revolutionary flight cameras within the Solar Orbiter schedule.

Point contact methods using metallic needles are widely applied for electrical measurements on the diamond semiconductor surfaces because of the difficulties of alloyed ohmic contact preparation. Contradictions and discussions in the literature concerning the resistance values and the shape of I–V characteristics made necessary a detailed study of the point contact measurements. In this work two- and four-point methods were applied to HPHT bulk crystals and MPCVD monocrystalline epitaxial layers in order to evaluate the applicability of these methods, to estimate the current conductivity character of such metal tip–diamond junctions, and to measure the electrical resistance of these crystals. Some samples underwent various treatments: annealing in vacuum; hydrogenation in molecular hydrogen; deuteration in RF and MW plasmas. Conductivity character of the contacts was determined and the applicability of point contacts was demonstrated. In contrast to some earlier results, only linear I–V characteristics were found. Conducting superficial layer connected with the presence of hydrogen was not observed. After the microwave deuterium plasma treatment, just the contrary, a highly resistive superficial layer posed obstacles before the measurements.

A set of type IIa diamond crystals was processed by cold implantation and rapid annealing at 1050°C ex situ annealing at 1400°C and investigated by ESR measurement. The ESR spectra of CIRA and post-annealed samples show an isotropic line at g =2.003, a set of anisotropic hyperfine lines, and a pair of isotropic hyperfine lines centred at g =2.003 with Δ H =28 G. The intensities of each signal increase with the implantation dose. After the second annealing step the intensities of all signal was reduced, excepted for the centre with Δ H =28 G which increases. This signal was ascribed to a new centre related to phosphorus, probably neutral substitutional phosphorus.

Hydrogen-acceptor interactions are investigated in boron-doped diamond through deuterium diffusion experiments followed by SIMS measurements and through infrared absorption spectroscopy. From deuterium diffusion, we show that BD interactions can be properly demonstrated in low compensation B-doped homoepitaxial layers. However, the presence of defects in such layers strongly affects this interaction. The degree of passivation of boron acceptors by deuterium depends on the diffusion temperature. At 550°C or below, the B and D concentrations exactly match giving rise to a complete disappearance of the absorption bands related to the electronic transitions of neutral boron acceptors. Under thermal annealing above 500°C, (B,D) pairs dissociate and neutral boron acceptors recover. At deuterium diffusion temperatures of 700°C, the B passivation is absent.

Drastic differences in diffusion of H (deuterium) in diamond, B-doped by ion implantation and during homo-epitaxial film growth, and its influence on electrical properties are found by SIMS depth profiling, and by electrical (Hall effect) measurements. Type IIa natural diamond, B-doped by ion implantation and high quality homo-epitaxial B-doped diamond films were subjected to D plasma treatment under similar conditions. The results of SIMS measurements clearly show a huge difference in D diffusion profile for these two samples. While the sample doped during growth was totally deuterated, the implanted one showed only minor D penetration. Electrical measurements indicated that while the homo-epitaxial samples became insulating or showed strong decrease in their free hole concentration following deuteration, the identical treatment to the B-ion implanted sample caused only slight changes in electrical properties. The electrical properties and their dependence on annealing are correlated with the deuterium diffusion into diamond. A possible mechanism of (B, H) and (defect, H) pair formation is suggested as a possible explanation of the observed differences.

Diamond based pixel detectors are a promising radiation-hard technology for use at the LHC. We present first results on a CMS diamond pixel sensor. With a threshold setting of 2000 electrons, an average pixel efficiency of 78% was obtained for normally incident minimum ionizing particles.

TiN (4.5 nm)/AlN (3, 6, 22 nm) superlattices deposited by DC magnetron sputtering on MgO(001) at a temperature of 850°C exhibit Raman signals. They indicate N and Ti vacancies (as in thick TiN) in TiN1−x layers (x=3±2%). x is higher for the sample with 3-nm thick AlN layers, which is ascribed to N diffusion from AlN (standing close to the TiN interfaces) to TiN. In comparison to Raman peaks of thick AlN, there are split signals of wurzite AlN phase, and a signal from another phase, which might be defective rocksalt AlN standing close to the TiN interfaces. The Raman signals clearly show interactions between AlN and TiN layers.

As the boron incorporation level and the wavelength of the exciting laser were varied, we observed systematic modifications of the Raman spectra of homoepitaxial diamond films. A pronounced change in the lineshape of the zone-center optical Raman peak as well as a wide and structured signal at lower wavenumbers appeared simultaneously when the boron incorporation was increased above an abrupt threshold around 3×10 20 cm −1 . This threshold was found to depend on the excitation laser wavelength. Possible origins for the wide peaks at 500 and 1225 cm −1 are also discussed.

Investigation of deep levels in the depletion zone of boron-doped homoepitaxial diamond films is achieved from analysis of the transient responses of Schottky junctions. The active layer consists of a homoepitaxial film grown by microwave plasma decomposition of a very small percentage of B2H6 mixed with CH4 in hydrogen on synthetic Ib diamond substrates. Rectifying contacts are implemented with either aluminium, gold or erbium after suitable pre- and post-treatments. Reverse-current transients due to the thermal emission of holes from deep-level traps into the valence band are recorded and analysed with a Fourier transform deep-level transient spectroscopy (Fourier DLTS) procedure as a function of temperature up to 520°C. At each temperature, a thermal emission time constant is extracted. Arrhenius diagrams are deduced. A deep level at 1.40±0.07 eV above the valence band is detected in samples that have been submitted to a 800°C annealing in ultrahigh vacuum. Another deep level at 1.16±0.03 eV above the valence band exists only if an oxygen radio-frequency plasma treatment is applied to the sample before the Schottky contact deposition. Thermal capture cross-sections are also deduced.

The diffusion and out-diffusion properties of hydrogen have been investigated in homoepitaxial layers of CVD boron-doped diamond which have been exposed to a deuterium microwave plasma. The diffusion experiments show that the onset of (B, H) pair dissociation occurs at 550°C. The hydrogen diffusion activation energy is 1.4 eV. Hydrogen out-diffuses at 880°C and the diamond surface barrier limits the out-diffusion process. In r.f. plasma exposed diamond epilayers, the hydrogen out-diffusion spectra are composed of a peak at 720°C related to the subsurface hydrogen accumulation layer and another one at 840°C attributed to the hydrogen adsorbed at the surface.

The Raman spectra and voltammograms in 0.1 M KCl, 0.1 M KNO 3 and 0.1 M KCl+0.1 M KNO 3 solutions of polycrystalline diamond electrodes vary systematically versus their boron content in the gas phase (200 to 14 000 ppm). Both exhibit the same threshold (2000 ppm, about 1.2×10 20 B cm −3 ) corresponding to the appearance of a low-wavenumber continuum in Raman spectra and to a factor of 10 3 jump in the electrochemical current. In 0.1 M KNO 3 solution, the reduction of nitrates from −0.6 to about −2 V cathodic potential occurs with low hydrogen reduction. The correlation between the electronic and electrochemical properties of these electrodes is discussed.

The room temperature concentration and mobility of electrons introduced by Si-doped cubic GaN films have been derived from their Raman spectra. These films were grown by MBE on cubic SiC thin films deposited by CVD on Si. The Si-doped films has a mobility lower (in the 50 to 210 cm 2 V/s range) than (1650 cm 2 V/ s) the undoped films, attributed to the significant increase upon doping of the hexagonal parasitic volume fraction in the films.

Micro-Raman spectra of cubic GaN films deposited by MBE on cubic SiC were studied versus the thickness of the underlying SiC film and the deposition rate of the cubic GaN. The residual hexagonal content is found to vary from 0.085 to 3%. The quality of cubic GaN assessed by Raman decreased as the roughness of the (3C) SiC template increased, and the wave number of the TO mode of the cubic phase increased between two plateau values of 553 and 560 cm −1 as the hexagonal content rose from 0.7 to 1.6%. On the basis of these results, we propose that the cubic GaN is stress-free below 0.7% of hexagonal content, and under an increasing compressive stress as the parasitic phase concentration increases.

The effect of the preparation conditions on p and n doping, the characteristics of the Schottky diodes, and the MESFET and MISFET are shown. The main applications of undoped and doped polycrystalline and homoepitaxial films (high temperature electronic, particule and UV solar blind detectors and electrodes for various electrochemical reactions) are described in connection with the characteristics of the devices and of the films.

Undoped polycrystalline diamond presents two thermoluminescent (TL) peaks at 480 and 560 K which may potentially be used for ionising radiation dosimetry. In order to increase the TL response sensitivity, CVD diamond samples doped with various boron concentrations have been elaborated. The aim of this work is to investigate the TL properties of these samples in relation with the boron concentration. For concentrations lower than 15 ppm (3×10 18 cm −3 ), the intensity of the 480 and 560 K TL peaks are effectively the most important, but for concentration values higher than 15 ppm, the TL signal decreases. Simultaneously, a new peak appears at 340 K. TL mechanisms related to these peaks are discussed.

The diffusion properties of hydrogen have been investigated in homoepitaxial layers of CVD boron doped diamond as a function of the diffusion temperature, the boron dopant concentration and the nature of the hydrogen source (rf or microwave plasma). Preliminary hydrogen effusion experiments on these hydrogenated samples are also reported. For both kinds of plasma we show that, below diffusion temperatures of 500 °C, the hydrogen diffusion is limited by trapping on boron acceptors. The onset of dissociation of B, H pairs occurs at 550 °C which implies a significantly higher stability of these pairs in diamond compared to silicon. However, a higher hydrogen diffusion activation energy is found in the microwave plasma exposed samples compared with the rf plasma exposed samples together with the absence of the subsurface hydrogen accumulation layer which is observed after rf plasma. Hydrogen effusion experiments show that in the rf plasma exposed samples the main effusion peak at 720 °C is attributed to the subsurface hydrogen accumulation layer. Another effusion peak at 850 °C is ascribed to the desorption of hydrogen adsorbed at the surface.

All AlN films deposited from 300 to 700°C on silica, Si(100) and Si(111) substrates exhibit (00.2) and (10.1) preferential orientations. We obtain the highest degree of preferential alignment of the (0001) planes of AlN on silica substrates reported to date for a deposition temperature of 350°C. In this ‘low’ temperature range, the multiple of random density values (mrd-values) have a low dependence on the nature and orientation of the substrates. At 700°C, we obtain a mrd-value of 165 on Si(111) with additionally a significant in plane orientation. As T increases in this ‘mean’ temperature range (>350°C), crystalline substrates, then the fit of the symmetry of the substrate surface with that of the growing film gives increasing mrd-values.

A large range ([B] from 5×1016 to 8×1020 cm−3) of boron concentration has been obtained for homoepitaxial diamond films. From the variation of the conductivity versus temperature between 300 and 1000 K, a simpler method is used to derive the activation energy(ies) Ea and the compensation ratio than from the variation of the hole concentration and mobility with temperature. For [B]

Thermally stimulated currents (TSC) and thermoluminescence (TL) have been studied in polycrystalline diamond films of different qualities in order to gain information about the deep levels present within the bandgap of this material. The TL has been studied between 300 and 670 K after UV light illumination, and the TSC between 300 and 600 K after various excitations (UV light, from a tungsten ]amp, X-rays). TL and TSC peaks are observed at 470 and 560 K, and depend on the quality of the diamond and on the illumination conditions. At low temperature three TSC peaks appear at 245, 283 and 312 K after illumination with a tungsten lamp. A spectral analysis of the 470 K luminescence and electron emission measurement shows that the defect associated with this signal is an acceptor, and the hole released is trapped on a level 2.6 eV deep. Complementary ESR measurements show that paramagnetic nitrogen centers are not involved in the peak observed at 560 K.

Recent progress on developing diamond-based sensors for vertex detection at high luminosity hadron colliders is described. Measurements of the performance of diamond sensors after irradiation to fluences of up to 5/spl times/10/sup 15/ hadrons/cm/sup 2/ are shown. These indicate that diamond sensors will operate at distances as close as 5 cm from the interaction point at the Large Hadron Collider (LHC) for many years at full luminosity without significant degradation in performance. Measurements of the quality of the signals from diamond sensors as well as spatial uniformity are presented. Test beam results on measurements of diamond-based microstrip and pixels devices are described.

The influence of the addition of high concentrations of diborane in the source gas on the growth of diamond films by chemical vapour deposition is investigated. For polycrystalline films grown on silicon, a decrease in the deposition rate is observed for boron concentration higher than B/C=6000 ppm, and a spurious amorphous carbon phase appears above B/C=10 000 ppm. For homoepitaxial growth on type Ib diamond, the deposition rate is nearly constant up to B/C=4000 ppm. With a higher boron concentration the films are polycrystalline. From the comparison of these two growth conditions shows we ascribed the decrease in the deposition rate, the appearance of a spurious phase and the loss of epitaxy to a modification of the plasma chemistry.